<PRE>
[Federal Register: November 14, 2000 (Volume 65, Number 220)]
[Rules and Regulations]               
[<strong>Page</strong> <strong>68461</strong>-<strong>68510</strong>]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr14no00-18]                         
 
[[pp. <strong>68461</strong>-<strong>68510</strong>]] Ergonomics Program

[[Continued from <strong>page</strong> 68460]]

[[<strong>Page</strong> <strong>68461</strong>]]

wrist bending or other stressful postures.

Epidemiological Evidence

    NIOSH reviewed 30 epidemiological studies that addressed workplace 
risk factors and CTS. Exposed workers in theses studies were usually 
engaged in job activities involving forceful and repetitive hand/finger 
or wrist movements and therefore were concurrently subjected to a 
combination of physical factors. These studies are summarized in Table 
V-5. Thirteen studies used physical examination or electrophysical 
indicators to diagnose CTS as well as direct observation or measurement 
of exposure to risk factors during job activities. The remaining 
studies either relied on symptom questionnaires to determine health 
outcomes or self reports and job title descriptions to evaluate 
exposures. CTS was solely determined by the presence of numbness, pain 
or tingling in the fingers enervated by the median nerve, and a 
positive Tinel's or Phalen's test (symptoms triggered upon wrist 
flexion and palpation) in about half the studies. Nerve conduction (NC) 
tests were not used in defining cases in these studies. In the other 
half of the studies, abnormal median nerve conduction was required in 
addition to symptomatology to diagnose CTS. Since normal NC was often 
defined and measured differently in various laboratories, CTS case 
definition is unlikely to be uniform across studies. Several 
investigations quantitatively estimated force, either from EMG 
measurements or based on weights of tools or other handled parts, and 
recorded job task observations. Repetitive hand/wrist movements were 
sometimes quantitatively measured and categorized based on task 
frequency, quantity of work performed in a specified time, or ratio of 
work time to recovery time.
    Of the 13 studies (eleven cross-sectional and two case control) 
that relied on both objective determination of exposure and medical 
diagnosis of CTS, 10 reported finding statistically significant 
associations between CTS and exposure to biomechanical risk factors. 
The reported ORs ranged from 1.1 to 21.3. Some cross-sectional studies 
provided evidence of an exposure-response relationship with respect to 
CTS and exposure to force and repetition. Silverstein et al.studied 652 
workers in 39 jobs from 7 different plants (Silverstein et al.1987, Ex. 
26-34). Jobs were grouped into high and low repetitiveness and force 
categories based on cycle time and EMG measurements, respectively. The 
OR for CTS (defined by physical tests/symptoms) in highly repetitive 
jobs compared to low repetitive jobs, irrespective of force, was 5.5 
(p0.05) in a multiple logistic model that included age, gender, plant 
site and years on the job. The corresponding OR for high-force jobs, 
irrespective of repetitiveness, was 2.9 (p>0.05) but the OR for 
combined exposures to high repetition and force was 15.5 (p0.05).

                                      Table V-5.--Summary of Epidemiology Studies Examining Carpal Tunnel Syndrome
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                     Risk measure (95%
               Study                    Job type studied       Physical factors         Exposure basis           Diagnosis                CI)\1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bovenzi (1991) Ex. 26-1433.........  Forestry.............  V                       Measurement..........  Physical exam........  OR=21*
                                                                                                                                  (NR)
Roquelaure (1997) Ex. 38-396.......  Manufacturing........  F/R/P                   Measurement..........  Physical exam+NC.....  OR=9.0*
                                                                                                                                  (2.4-33.4)
Silverstein (1987) Ex. 26-34.......  Manufacturing........  V/F/R/P                 Measurement..........  Physical exam........  OR=1.8-15.5*
                                                                                                                                  (1.7-142)
Chatterjee (1992) Ex. 26-942.......  Rock drilling........  V                       Measurement..........  Physical exam+NC.....  OR=10.9*
                                                                                                                                  (1.0-524)
Osorio (1994) Ex. 26-807...........  Supermarket..........  F/R/P?                  Observation..........  Physical exam+NC.....  OR=6.7-8.3*
                                                                                                                                  (2.6-26.4)
Barnhart (1991) Ex. 26-1216........  Ski manufacture......  F?/R/P                  Measurement..........  Physical exam+NC.....  OR=1.9-40*
                                                                                                                                  (1.0-15.8)
Frost (1998) Ex. 38-198............  Slaughter house......  F/R/P                   Measurements.........  Physical exam+NC.....  OR=4.2*
                                                                                                                                  (1.8-10.1)
Bovenzi (1994) Ex. 26-774..........  Stone drilling.......  V                       Measurement..........  Physical exam........  OR=e.4*
                                                                                                                                  (1.4-8.3)
Baron (1991) Ex. 26-697............  Grocery checking.....  F/R/P                   Measurement..........  Physical exam........  OR=3.7
                                                                                                                                  (0.7-16.7)
Moore (1994) Ex. 26-1364...........  Meat processing......  F/R/P                   Measurement..........  Physical exam+NC.....  OR=2.8
                                                                                                                                  (0.2-36.7)
Chiang (1990) Ex. 26-1118..........  Frozen Food Packing..  F?/R/P?                 Measurement..........  Physical exam+NC.....  OR=1.9-11.7*
                                                                                                                                  (2.9-46.6)
Chiang (1993) Ex. 26-1117..........  Fish processing......  F/R/P?                  Cycle time, EMG......  Physical exam........  OR=1.1-1.8*
                                                                                                                                  (1.1-2.9)
Stetson (1993) Ex. 26-1221.........  General industry.....  F/R/P                   Checklist............  NC only..............  NR*
Latko (1999) Ex. 38-123............  Manufacturing........  F/R/P?                  Measurement..........  Physical exam+NC.....  OR=2.3-3.1
                                                                                                                                  (0.9-10.9)
Armstrong (1979) Ex. 26-348........  Sewing machine use...  F/R/P                   EMG, flexion.........  Physical exam........  OR=1.1-2.0*
                                                                                                                                  (1.6-2.5)
Nathan (1988) Ex. 26-990...........  Multiple industries..  F/R/P                   Observation..........  NC only..............  PRR=1.0-2.0*
                                                                                                                                  (1.1-3.4)
Nathan (1992) Ex. 26-989...........  Multiple industries..  F/R/P                   Observation..........  NC, symptoms.........  PRR=1.0-1.5
                                                                                                                                  (1.0-2.2)
Canon (1981) Ex. 26-1212...........  Aircraft plant.......  V/R                     Hand tool measurement  Workers' comp........  OR=2.1-7.0*
                                                                                                                                  (3.0-17)
English (1995) Ex. 26-848..........  CTS case/control.....  F/R/P                   Questionnaire........  Physical exam........  OR=0.4-1.8*
                                                                                                                                  (1.2-2.8)

[[<strong>Page</strong> 68462]]

Feldman (1987) Ex. 26-1210.........  Electronics plant....  F?/R/P                  Cycle time flexion...  Questionnaire........  OR=2.3*
                                                                                                                                  (1.4-4.5)
Koskimies (1990) Ex. 26-973........  Forestry.............  V                       Job title............  Physical exam+NC.....  NR*
McCormack (1990) Ex. 26-1334.......  Textile..............  F/R/P?                  Job title............  Physical exam........  OR=0.4-0.9
                                                                                                                                  (0.3-2.9)
Morgenstern (1991) Ex. 26-1493.....  Grocery cashiers.....  F?/R/P                  Job title............  Questionnaire........  OR=1.9
                                                                                                                                  (0.9-3.8)
Punnett (1985) Ex. 26-995..........  Garment..............  F?/R/P?                 Job title............  Physical exam........  OR=2.7*
                                                                                                                                  (1.2-7.6)
Schottland (1991) Ex. 26-1001......  Poultry processing...  F/R/P                   Job title............  NC only..............  OR=1.9-2.9*
                                                                                                                                  (1.1-7.9)
Weislander (1989) Ex. 26-1027......  CTS case/control.....  V/F/R/P?                Questionnaire........  Physical exam+NC.....  OR=1.8-3.3*
                                                                                                                                  (1.6-6.8)
Liss (1995) Ex. 26-55..............  Dental hygienist.....  F?/R/P                  Questionnaire........  Questionnaire........  OR=3.7*
                                                                                                                                  (1.1-11.9)
DeKrom (1990) Ex. 500-41-28........  CTS case/control.....  F/R?/P                  Questionnaire........  Physical exam+NC.....  OR=5.4-8.7*
                                                                                                                                  (3.1-24.1)
Tanaka (1997) Ex. 26-1185..........  Household survey.....  V/P                     Questionnaire........  Questionnaire........  OR=1.8-5.9*
                                                                                                                                  (3.4-10.2)
Farkkila (1988) Ex. 26-947.........  Chair saw use........  V                       Questionnaire........  Physical exam+NC.....  NR*
SHARP (1993) Ex. 500-41-116........  Poultry processing...  F/R                     Measurement..........  Questionnaire........  NR*
                                                                                                                                  (p 0.0004)
Rosecrance (1994) Ex. 38-203.......  Newspaper work.......  F/P/R/ (pinch)          Questionnaire........  Physical exam........  NR*
Rossignol (1997) Ex. 500-205-24....  Manual labor.........  F/R?/P?                 Questionnaire........  Surgery for CTS......  OR=4.1*
                                                                                                                                  (1.5-3.2)
LeClerc (1998) Ex. 500-41-85.......  Assembly line........  R/P?                    Questionnaire........  Physical exam+NC.....  OR=3.1-6.6*
Atroshi (1999) Ex. 38-181..........  General Population...  F/P/R/V                 Questionnaire........  Physical exam+NC.....  OR=1.0-3.0*
                                                                                                                                  (1.4-6.8)
Gorsche (1999) Ex. 500-121-23......  Meat packing.........  V                       Questionnaire........  Physical exam........  NR
Katz (1998) Ex. 38-393.............  CTS case control.....  F/R/P                   Questionnaire........  Physical exam........  NR
Kerns (2000) Ex. 500-71-34.........  Pork processing......  F/R/P                   Job title............  NC only..............  NR
--------------------------------------------------------------------------------------------------------------------------------------------------------
 F=forceful exertions; R=repetitive motion; P=awkward posture; V=vibration; ?=presence of risk factor unclear.
 NCV=nerve conduction; IR=incidence rate; OR=odds ratio; PRR=prevalence rate ratio; NR=not reported.
 *=p0.05.
\1\ 95% confidence interval expressed for the upper end of the risk measure range.

    Chiang et al.studied 207 workers from 8 fish processing factories 
in Taiwan (Chiang et al.1993, Ex. 26-1117). Jobs were divided into 
three groups based on level of repetitiveness and force using cycle 
times (upper arm movements, not just wrist) and EMG of the forearm 
flexor muscles. There was a statistically significant trend in 
prevalence of CTS (defined by physical tests/symptoms) with exposure 
from low force/repetition, high force or high repetition, and high 
force/repetition. Force alone, but not repetitiveness, significantly 
predicted CTS (OR=1.8; 95% CI 1.1-2.9).
    Several other epidemiological investigations found physical risk 
factors to be significantly associated with prevalence of CTS. In 
another Chiang et al.study of 207 workers from 2 frozen food processing 
plants, job tasks were grouped by low and high repetitiveness based on 
wrist movement cycle time (Chiang et al.1990, Ex. 26-1118). Statistical 
modeling that included gender, age, and cold temperatures resulted in 
an OR of 1.9 (p0.05) for CTS (defined by physical tests/symptoms/NC 
studies). This study stressed the association between CTS and 
repetitive movements, although some forceful hand/wrist exertion 
probably existed in the study group.
    Stetson et al.studied median NC on 103 automotive workers with 
symptoms consistent with CTS compared with 137 asymptomatic automotive 
workers and an unexposed group of 105 administrative and professional 
workers (Stetson et al.1993, Ex. 26-1221). Repetitiveness was evaluated 
by cycle times, hand/wrist grip forces were estimated based on weights 
of handled tools and parts, and wrist deviation was judged from 
videotape analysis. Both symptomatic and asymptomatic workers had 
significantly lower median sensory amplitudes and significantly longer 
distal latency times than the referent group. The same NC trends were 
found between automotive workers in jobs requiring grip force greater 
than 6 pounds compared to those requiring less than 6 pounds. This grip 
force variable probably combines forceful exertion with wrist 
deviation. It was not possible to adequately compare repetitive and 
non-repetitive work since this risk factor was present in almost the 
entire study group.
    Barnhardt et al.found ski manufacturing workers with highly 
repetitive job tasks had a statistically elevated OR of 4.0 (95% CI 
1.0-15.8) for CTS (defined by physical tests/NC studies) compared to 
those workers engaged in non-repetitive tasks (Barnhardt et al.1991, 
Ex. 26-1216). Exposure was evaluated by observational analysis and 
included repetitive jobs with sustained flexion, extension, or ulnar 
deviation of the wrists by 45 degrees. The participation rate for this 
study was lower (less than 70 percent) than most of the other 
investigations. Armstrong and Chaffin reported that CTS (defined by 
physical tests/symptoms) was significantly associated (OR=2.0; 95% CI 
1.6-2.5) with pinch force exertion (combination of force and deviated 
wrist posture) in female sewing machine operators (Armstrong and 
Chaffin 1979, Ex. 26-348). Because of the case-control study design, it 
is not clear whether deviated postures contributed to the development 
of CTS or whether the CTS symptoms

[[<strong>Page</strong> 68463]]

led to the use of abnormal postures during work.
    Four of the studies addressed CTS and manual work involving 
vibrating power tools. A case control study by Chatterjee et al.found a 
significant difference (OR=10.9; 95% CI 1.0-524) in the prevalence of 
CTS cases (defined by NC studies/symptoms) in rock drillers compared 
with controls (Chatterjee et al.1982, Ex. 26-942). The rock drillers 
were exposed to vibration frequencies between 31.5 and 62 Hertz. The 
highest relative risks (OR=21.3; p0.002) for CTS (defined by physical 
tests/symptoms) were found in forestry workers using chain saws 
compared to maintenance workers who did not use power tools (Bovenzi et 
al.1991, Ex. 26-1433). Differences in ambient temperatures (potential 
confounder) between outdoor (chain saw operators) and indoor work 
(maintenance workers) may have contributed to the results. Koskimies et 
al.reported significant correlations between reductions in NC 
velocities in the median and ulnar nerves and number of years of 
vibration exposure in forestry workers who used chain saws greater than 
500 hours in the previous 3 years (Koskimies et al.1990, Ex. 26-973). 
The prevalence of CTS (defined by physical tests/symptoms) in these 
workers was 20 percent. In another study, Bovenzi et al.reported an OR 
of 3.4 (95% CI 1.4-8.3) for CTS (defined by NC studies/symptoms) among 
stone quarry drillers/carvers exposed to hand-transmitted vibration 
when compared to polishers who performed manual operations and were not 
exposed to vibration (Bovenzi et al., 1994, 26-774). In these four 
studies, flexor tendons and the median nerve of the hand were probably 
subjected to a considerable degree of forceful exertion as well as 
mechanical injury during use of these power tools. Vibration can also 
cause direct damage to the digital arteries leading to sensory loss and 
numbness.
    There were three studies that did not find statistically 
significant association between CTS and exposure to physical risk 
factors, even though each reported substantially raised ORs. Moore and 
Garg found an OR of 2.8 (95% CI 0.2-36.7) for CTS (defined by NC 
studies/symptoms) among pork processing workers in hazardous jobs 
compared to safe jobs (Moore and Garg 1994, Ex. 26-1033). Jobs were 
categorized based on videotape analysis for estimates of force, 
repetitition and awkward postures. The possible presence of a healthy 
worker effect (most workers were laid off in the year prior to the 
study) and the short latency period (8-32 months) limits confidence in 
the relative risk estimate.
    An OR of 6.7 (95% CI 0.8-52.9) for CTS (defined by NC studies/
symptoms) was reported in a study of supermarket workers rated for high 
versus low exposure to repetitive and forceful wrist motions as judged 
by an ergonomist and industrial hygienist (Osorio et al.1994, Ex. 26-
807). However, the entire study consisted of only 56 workers grouped 
into 3 categories for analysis limiting the power of the study to find 
a statistically significant association. Baron et. al. (Ex. 26-697) 
also studied CTS (defined by physical tests/symptoms) in 124 grocery 
store checkers and reported an OR of 3.7 (95% CI 0.7-16.7) compared to 
157 non-checkers. Physical examinations were not done on all workers 
and the relative risk measure was based on responses to a standardized 
questionnaire. The exposure level for checkers was characterized as 
having low peak force and a medium level of repetition; therefore, the 
intensity of exposure to physical risk factors was less than that among 
workers examined in other studies.
    Almost all studies controlled for the obvious confounders of age, 
gender, and predisposing medical conditions by selection of an 
appropriate referent population, stratification, or use of a multiple 
logistic regression model. Many of the cross-sectional studies either 
excluded workers with pre-existing CTS prior to employment or excluded 
recently hired workers from the study. Therefore, it is unlikely that 
the reported associations between CTS and exposure to biomechanical 
risk factors reflected preferential employment of those with CTS (i.e., 
the requirements for entry into the cohort made it likely that exposure 
preceded the onset of CTS).
    NIOSH (1997, Ex. 27-1) concluded that there was epidemiological 
evidence of a positive association between CTS and highly repetitive 
work, either alone or in combination with other risk factors. They also 
found evidence of positive associations between forceful work and work 
involving hand/wrist vibration and CTS. However, NIOSH concluded there 
was insufficient evidence of an association between CTS and exposure to 
extreme postures alone because of individual variability in work 
methods and difficulties in measuring postural characteristics. NIOSH 
did recognize that there was strong evidence that exposure to a 
combination of physical risk factors along with non-neutral wrist 
postures was related to the onset of CTS.
    A large number of studies that addressed physical work factors and 
CTS were submitted into the OSHA docket following publication of the 
proposal; those that OSHA found to be of adequate study design are 
included in Table V-5 (Frost et al.1998, Ex. 38-198; Roquelaure et 
al.1997, Ex. 500-41-111; Latko et al.1999, Ex. 38-123; Rossignol et 
al.1997, Ex. 502-420; Leclerc et al.1998, Ex. 500-41-85; Atroshi et 
al.1999, Ex. 38-181; Gorsche et al.1999, Ex. 500-121-23; Kearns et 
al.2000, Ex. 500-71-34; Katz et al.1998, Ex. 38-393). All but three of 
these studies (Ex. 500-121-23; Ex. 500-71-34; Ex. 38-393) found 
significantly increased prevalence of CTS among workers exposed to 
physical risk factors. The three studies that did not find a 
statistically significant association did not rely on independent 
assessment or observation of exposure to physical work factors, but 
instead used job titles or self-reported survey information to infer 
exposure. One of these studies, Gorsche et al.(Ex. 500-121-23), found 
an increased prevalence and incidence of CTS in a cross-sectional and 
longitudinal study of meat packers but it was not statistically 
significant. Kearns et al.(Ex. 500-71-34), who ascertained cases only 
by nerve conduction studies and did not rely on symptoms or clinical 
evaluation to diagnose CTS, also failed to find a statistically 
significant association. Katz et al.(Ex. 38-393) studied factors 
associated with long-term disability rather than the development of 
CTS.
    In contrast, three studies that did measure or observe exposures 
and used a combination of symptoms, physical tests, and nerve 
conduction velocity measurements to diagnose CTS found strong 
associations with exposure to repetition and/or force (Exs. 38-198, 
500-41-111, 38-123). Another study, the SHARP study (Ex. 500-41-116) of 
poultry processing workers summarized in the hand/wrist tendinitis 
section above, found that the number of forceful exertions per hour was 
significantly predictive of CTS (p=0.004).
    Many studies of CTS contained in the rulemaking docket are not 
included in Table V-5 either because it was questionable whether 
exposure to physical risk factors occurred or because the study did not 
address the relationship between physical risk factors and CTS (Nathan 
and Keniston 1993, Ex. 351-14; Stallings et al.1997, Ex 351-20; 
Franzblau et al.1994, Ex. 38-175; Nordstrom et al.1988, Ex. 500-25-9; 
Zetterberg and Ofverholm 1999, Ex. 500-121-78). Other studies were not 
included on OSHA's summary table because they used a flawed study 
design or a flawed statistical analysis to examine the relationship 
between exposure to biomechanical risk factors and CTS (Malchaive et 
al.1996, Ex. 500-

[[<strong>Page</strong> 68464]]

66-5; Homan et al.1999, Ex. 38-172; Olafsdotti et al. 2000, Ex 38-288.
    One of the above studies is among several papers published by Dr. 
Peter Nathan and colleagues, which were based on two group of workers 
whom they have followed prospectively (Ex. 26-990; Ex. 26-988; Ex. 26-
989; Ex. 26-1294; Ex. 26-517; Ex. 38-437; Ex. 38-13; Ex. 351-14). 
Because of the importance of these studies to the ergonomics 
rulemaking, they are addressed in detail here. In one of the earlier 
studies (Nathan et al.1988, Ex. 26-990), nerve conduction was assessed 
on 471 randomly chosen individuals from four industries (steel mill, 
meat/food packaging, electronics, and plastics manufacturing). The 
group was divided into the following exposure categories:
    <bullet> Group 1, very low force, low repetition;
    <bullet> Group 2, low force, very high repetition;
    <bullet> Group 3, moderate force, moderate repetition;
    <bullet> Group 4, high force, moderate repetition; and
    <bullet> Group 5, high force, high repetition.

No significant difference in median nerve sensory latency values was 
found between Group 1 and Group 2, which differed primarily by the 
amount of repetition exposure. There was a statistically significantly 
higher number of subjects with median nerve slowing in Group 5 compared 
to Group 1, but not when compared to Groups 2, 3, or 4. When individual 
hands were used to base calculations rather than number of individuals, 
only Group 3 showed a significantly higher prevalence of median nerve 
conduction slowing. When prevalence ratios were calculated, Groups 3, 
4, and 5 had significantly higher PRs compared to Group 1.
    This same group of workers was followed up for five years in a 1992 
study (Ex. 26-988) and eleven years in a 1998 study (Ex. 38-13). The 
study used hands, rather than individuals, as the basis for analysis. 
The authors stated that they found no significant difference in the 
prevalence of median nerve slowing among any of the exposure groups. 
The authors claimed to have confirmed this finding in a second combined 
cohort of Japanese and American industrial workers (Ex. 38-437) as well 
as validated their exposure categories (Ex. 26-1294). They went on to 
show that slowing of nerve conduction was significantly associated with 
obesity (Ex. 26-989), body mass index (Ex. 26-517), wrist depth/width 
and a number of other non-occupational risk factors (Ex. 351-14).
    However, their research has a number of flaws in the study design, 
analysis and interpretation of the results, which call their 
conclusions into doubt. Chief among these is the failure to adequately 
justify and validate their grouping and rank order of occupational hand 
use. This provides multiple opportunities for exposure 
misclassification and will tend to underestimate the association of 
exposure with health outcome. This aspect of the study has been 
criticized by several experts (Ex. 26-1010; Ex. 26-952; Tr. 1000). 
Despite this potential for misclassification, there was a significant 
increase in prevalence between the lowest (Group I) and higher exposure 
groups combined (Groups III, IV, and V) in the cross-sectional study 
(Ex. 26-990). Others have also concluded that, methodological 
shortcomings aside, the articles by Nathan et al.demonstrate a positive 
exposure-response relationship between ``occupational hand activity'' 
and slowed conduction of the median nerve (Tr. 1519-1522; Tr. 9862). 
Others have testified that alternative exposure grouping of the data 
resulting in less exposure misclassification would result in a clear 
exposure-response relationship between job group and median nerve 
latency (Punnett testimony, Ex. 37-2; Gerr testimony, 27-2). Some who 
testified at OSHA's informal hearing have also stated that Dr. Nathan's 
articles use statistical presentation and analysis methods that obscure 
the evidence, and that not enough data are presented for the reader to 
independently evaluate whether the authors' conclusions are justified 
(Tr. 1521; Tr. 7850.). Low participation rates, unusual and 
inconsistent case definition, and inappropriate statistical analysis 
may also have limited the ability to detect increases in CTS prevalence 
over time in these studies with respect to work-related biomechanical 
factors. For example, the authors reported in the baseline study that 
they randomly selected the study participants (Ex. 26-990). However, 
they did not report the proportion of those who were selected and 
invited that actually participated. Since the 471 subjects represented 
only 26 percent of the total workforce of the participating companies, 
the representativeness of the sample is unknown, the ability to 
generalize from the data is highly limited, and the potential for 
selection bias is substantial. There is no comparative information on 
participants and non-participants with respect to demographics, 
occupational history or exposure, or medical history. The lack of 
clarifying information is particularly problematic because the 
direction of the selection bias could be either toward or away from the 
null value. This problem affects not only the 1988 baseline study but 
all future follow-up studies of the same cohort. Because of these 
criticisms, OSHA finds that the Nathan studies do not convincingly 
demonstrate a lack of association between workplace exposure to 
biomechanical risk factors and CTS.
    In his written testimony, Dr. Peter Nathan calls into question the 
case definition for CTS relied upon by OSHA in their evaluation of the 
epidemiological studies (Ex. 32-241-3-13). He testifies that ``there is 
general agreement among experts that classic symptoms associated with 
positive electrodiagnostic findings for the median nerve are necessary 
for a diagnosis of CTS'' but that ``there is no general agreement that 
symptoms, in the presence of negative electrodiagnostic findings is 
equivalent to CTS.'' (Id., pg 4). Dr. Nathan then goes on to criticize 
OSHA and NIOSH, in their 1997 review, for accepting studies that use 
CTS case definitions without electrodiagnostic confirmation. He argues 
that longitudinal studies are the only study design of value for 
determining causation and concludes ``if one required electrodiagnostic 
studies for a valid case definition of CTS, and a longitudinal design 
for establishing temporal relationships, then only one [his own] of the 
31 studies analyzed by NIOSH would have met standard criteria for 
establishing causation.'' (Id., pg 11).
    OSHA accepts that specific symptoms determined during clinical exam 
in combination with objective evidence of median nerve dysfunction 
through electrodiagnostic tests is the most definitive case definition 
for CTS at the present time. This has been supported by expert 
testimony not only from Dr. Nathan but Dr. Frederick Gerr (Ex. 37-2) 
and Dr. Gary Franklin (Tr. 13363). OSHA also does not dispute lack of 
agreement among experts on CTS diagnosis when symptoms exist in the 
presence of normal median nerve conduction. However, the relevant issue 
is whether clinical symptoms and signs in the absence of 
electrodiagnostic testing are an invalid CTS case ascertainment for the 
purposes of evaluating epidemiological evidence to determine if work-
related physical factors are associated with the disorder. NIOSH 
addressed the issue in its 1997 review and cited studies that found 
satisfactory correlations between CTS diagnosed by nerve conduction and 
the disorder diagnosed by symptom questionnaire and physical 
examination (Ex. 26-1501; Ex. 26-439). It was also reported that 
clinical examination for CTS diagnosis without the benefit of

[[<strong>Page</strong> 68465]]

nerve conduction studies has a sensitivity of 84 percent and a 
specificity of 76 percent (Ex. 26-1208). This indicates that without 
the aid of electrodiagnostics, one would make a CTS diagnosis when the 
disorder is not present (false positive) in about one in four subjects. 
On the other hand, clinical exam is expected to miss a diagnosis (false 
negative) when CTS is present about one in six subjects. While this 
degree of sensitivity and specificity may not be acceptable when making 
treatment decisions, such as surgery, OSHA does not believe it 
introduces substantial bias for purposes of evaluating epidemiological 
evidence.
    OSHA does not agree with Dr. Nathan's assertion that only 
longitudinal studies are relevant in evaluating causation. Longitudinal 
prospective cohort studies are indeed the strongest epidemiological 
study design, especially for establishing temporal relationships. 
However, they often require extended periods of time, are more costly, 
and are not as numerous other study designs. Other types of 
epidemiology, such as cross-sectional and case-control studies, add 
evidence of causality in terms strength and consistency of association 
and exposure-response.
    OSHA has examined the epidemiological data base and finds that even 
if one restricts the evidence to studies that used abnormal median 
nerve conduction to establish CTS case ascertainment, there is 
reasonable evidence of association between repeated, forceful exertions 
of the hand and CTS. There were eleven studies either reviewed by NIOSH 
in their 1997 review or submitted to the OSHA docket during the 
rulemaking process that found statistically significant associations 
between combinations of force, repetitive motion, awkward posture, and 
segmental vibration and CTS defined by electrodiagnostic criteria (Ex. 
38-396; 26-942; 38-198; 26-1118; 26-1221; 23-1001; 26-1027; 500-41-28; 
500-41-85; 38-181; 26-973). The entire body of epidemiological studies 
described in the preceding paragraphs is also supported by impressive 
biomechanical and psychophysical data, discussed in the following 
subsection, that shows sustained force on the flexor tendons along with 
flexion/extension of the wrist increases carpal tunnel pressure and 
reduces exertion and perceptions of discomfort. In his written 
testimony (Ex. 37-2), Dr. Fredric Gerr discussed his evaluation of the 
epidemiological studies that used abnormal nerve conduction to diagnose 
CTS and made the following statement in his oral testimony at the 
hearing:

    However, when significant positive associations between work and 
carpal tunnel syndrome are observed repeatedly, in study after 
study, by investigator after investigator, in country after country 
and at many different times, we must ask ourselves why. In my 
opinion, after reading these studies and considering all the 
possible reasons why so many studies show this relationship, the 
most reasonable, plausible, and likely explanation is that work 
really did cause the carpal tunnel syndrome observed in these 
studies. (Tr. 1525)

Biomechanical and Psychophysical Evidence

    Several clinical and cadaver studies confirm that fingertip force, 
wrist flexion/extension, repetitive tasks and combinations of the above 
are able to raise carpal tunnel pressure (CTP) in a dose-dependant 
manner. Mean CTP was raised from 5 mm Hg in a neutral wrist position to 
approximately 100 mm Hg at 60 degree wrist extension and 80 mm Hg at 60 
degree flexion in a population of CTS patients and controls (Weiss et. 
al. 1995, Ex. 26-236). CTP has been shown to significantly increase 
with increasing finger tip force (Rempel et. al. 1997, Ex. 26-889) and 
with clenching a fist or holding an object in a power grip (Seradge et. 
al. 1995, Ex. 26-325). There was a two- to three-fold increase in CTP 
when performing a repetitive task involving change in wrist posture 20 
times per minute for 5 minutes (Rempel et. al. 1994, Ex. 26-1151). The 
elevated CTPs found in these human biomechanical studies are within the 
range of neuronal pressures shown to impair blood flow, axonal 
transport, and nerve conduction in experimental animals.
    Psychophysical data support the biomechanical findings. They show 
that maximum acceptable weight (MAW) and torque (MAT) decrease and 
perceived exertion and discomfort increase with the frequency and 
duration of repetitive wrist motions. The psychophysical method was 
used to determine the preferred weights for one-handed horizontal 
transfer tasks (e.g. hand/wrist motion used to move an object across a 
supermarket scanner). Frequency and duration of the transfer movement 
significantly decreased MAW in an exposure-dependent manner and 
increased perceived exertion over an eight-hour session (Krawczyk et. 
al. 1992, Ex. 26-974). In another study, MAT was reduced over the 
course of a seven-hour trial of repeated flexion and extension of the 
wrist (Snook et. al. 1995, Ex. 26-212). The magnitude of MAT reduction 
correlated with the frequency of the task and perceived discomfort 
increased with increasing repetition.

Conclusion

    The 1997 NIOSH report concluded the following with regard to the 
relationship between work-related physical risk factors and CTS:

    Based on the epidemiologic studies reviewed, especially those 
with a quantitative evaluation of the risk factors, the evidence is 
clear that exposure to a combination of the job factors studied 
(repetition, force, posture, etc.) increases the risk of CTS. This 
is consistent with the evidence in the biomedical, physiological, 
and psychosocial literature (Ex. 26-1).

OSHA also finds convincing evidence that jobs involving repetitive and 
forceful movements of the hand and wrist are linked to CTS. The 
epidemiological findings are supported by clinical, biomechanical, and 
psychophysical studies showing that repetitive tasks involving flexion/
extension of the wrist and force to the flexor tendons result in 
substantial increases in CTP, reductions in measured exertion, and 
perceptions of discomfort. This evidence is clearly consistent with the 
pathophysiology of CTS in which elevated CTP can lead to compression of 
the median nerve resulting in the clinical signs and symptoms 
characteristic of this MSD. OSHA finds that the epidemiological and 
biomechanical literature convincingly demonstrates a causal 
relationship between forceful and repetitive exertions to the hand, 
especially in combination with a flexed wrist, and an increased risk of 
carpal tunnel syndrome. Forceful and repetitive exertion includes 
vibration from the use of hand-held power tools.

Hand-Arm Vibration Syndrome

    Hand-arm vibration syndrome (HAVS) refers to a collection of signs 
and symptoms that occurs when vibration from a tool is transferred to a 
worker's hand or arm. The symptoms include numbness, blanching of the 
fingers, pain in response to cold exposure, and reduction in grip 
strength. These manifestations are similar to Raynaud's phenomenon 
triggered by cold temperatures. HAVS symptoms are believed to be the 
result of both neurological and circulatory disturbances, probably 
occurring independently and by unrelated mechanisms. Vibration may 
directly injure (as opposed to indirect damage from compression as in 
CTS) peripheral nerve endings and neuroreceptors causing numbness, 
tingling and pain in the fingers. Histopathology of persons suffering 
from HAVS indicate that

[[<strong>Page</strong> 68466]]

vibration may also directly damage endothelial cells of the digital 
arteries resulting in a lack of response to certain vasodilators and 
thickening of the vessel walls. These physiological changes can cause 
vascular constriction and ischemia of the surrounding musculoskeletal 
and neural tissue. The clinical outcome is blanching of the fingers 
(``white finger''), loss of feeling, muscle weakness, and weakened grip 
strength.

Epidemiological Evidence

    NIOSH reviewed 20 post-1988 epidemiological studies that addressed 
workplace risk factors and HAVS. Table V-6 summarizes some key aspects 
of these investigations, such as the occupations examined, the 
biomechanical risk factors they were exposed to, whether exposures were 
directly observed or measured during the study, and whether the health 
outcomes were verified by trained medical personnel during physical 
examination. Previous investigations were reviewed as part of the 1989 
NIOSH criteria document on exposure to HAV (Ex. 26-392). In its 1997 
evaluation, NIOSH featured four cross-sectional studies (Bovenzi et 
al.1988, Ex. 26-1500; 1994, Ex. 26-1239; 1995, Ex. 26-354; Nilsson et 
al.1989, Ex. 26-1148) and one prospective study (Koskimies et al.1992, 
Ex. 26-1490), which met most of NIOSH's criteria for high quality. 
These investigations determined HAVS based on medical exam and did not 
strictly rely on self-reported questionnaires. Standard and relatively 
uniform diagnostic criteria were used in defining HAVS cases. This 
generally included episodes of cold-provoked, well-demarcated blanching 
of the fingers, occurrence of vibration white finger attacks after 
employment and following use of power tools, and abnormal digital 
artery response to cold provocation. All studies used the Stockholm 
Taylor-Palmear scale to grade and stage symptoms. The five 
investigations included vibration measurements of exposure on tools 
used by the study subjects combined with information on exposure time 
obtained by direct interview.
    The four cross-sectional studies found statistically significant 
positive relationship between exposure to vibration and prevalence of 
HAVS. The strength of this association was high with reported ORs 
ranging from 6 to 85. The one prospective study showed significant 
decreases in HAVS prevalence with decreasing exposure to vibration over 
time. All five investigations contributed evidence of exposure-response 
relationships between HAVS and vibration acceleration or duration of 
exposure. One study also documented a relationship between exposure and 
symptom severity.

                                        Table V-6.--Summary of Epidemiology Studies Examining Hand-Arm Vibration
--------------------------------------------------------------------------------------------------------------------------------------------------------
               Study                    Job type studied     Physical Factors       Exposure basis           Diagnosis          Risk measure  (95% CI)<SUP>1</SUP>
--------------------------------------------------------------------------------------------------------------------------------------------------------
Nilsson (1989) Ex. 26-1148.........  Pulp mill machining..  V                   Tool acceleration....  Physical exam........  OR=14-85 *
                                                                                                                              (15-486)
Bovenzi (1995) Ex. 26-354..........  Forestry.............  V                   Chain saw              Cold provocation.....  OR=6.2-32 *
                                                                                 acceleration.                                (11-93)
Bovenzi (1994) Ex. 26-1239.........  Stone drilling.......  V                   Tool acceleration....  Physical exam........  OR=9.3 *
                                                                                                                              (4.9-17.8)
Bovenzi (1988) Ex. 26-1500.........  Stone cutting........  V                   Tool acceleration....  Physical exam........  OR=6.1 *
                                                                                                                              (2.0-19.6)
Brubaker (1987) Ex. 26-762.........  Forestry.............  V                   Chain saw              Symptoms ischemia....  NR
                                                                                 acceleration.
Koskimies (1992) Ex. 26-1490.......  Forestry.............  V                   Chain saw              Physical exam........  NR
                                                                                 acceleration.
Brubaker (1983) Ex. 26-763.........  Forestry.............  V                   Questionnaire........  Symptoms ischemia....  NR
Dimberg (1991) Ex. 26-1395.........  Aircraft machining...  V                   Questionnaire........  Questionnaire........  NR
Krivekas (1994) Cited in Ex. 26-1..  Forestry.............  V                   Questionnaire........  Pyhsical exam........  OR=3.4-6.5 *
                                                                                                                              (2.4-17.5)
Letz (1992) Ex. 26-384.............  Ship-yard............  V                   Tool acceleration....  Questionnaire........  OR=5.0-40.6 *
                                                                                                                              (11-176)
McKenna (1993) Ex. 26-745..........  Machine riveting.....  V                   Questionnaire........  Cold provocation.....  OR=24 *
                                                                                                                              (3.1-510)
Mirbod (1992) Ex. 26-1492..........  Forestry.............  V                   Chain saw              Physical exam........  NR
                                                                                 acceleration.
Mirbod (1997) Ex. 500-121-49.......  Motorcyclists........  V                   Handlebar              Questionnarie........  NR *
                                                                                 acceleration.
Mirbod (1999) Ex. 500-121-48.......  Metal grinding.......  V                   Job title............  Physical tests.......  NR *
Mirbod (1994) Ex. 26-1491..........  Multiple industries..  V                   Tool acceleration....  Questionnarie........  OR=3.8 *
                                                                                                                              (2.1-6.8)
Musson (1989) Ex. 26-743...........  Power tool use.......  V                   Tool acceleration....  Questionnaire........  NR
Nagata (1993) Ex. 26-1494..........  Chain saw operation..  V                   Job title............  Physical exam........  OR=7.1 *
                                                                                                                              (2.5-19.9)
Saito (1987) Ex. 26-1440...........  Chain saw operation..  V                   job title............  Cold provocation.....  NR
Palmer (1998) Ex. 500-121-56.......  Pavement breaking....  V                   estimated tool         Physical exam cold     OR=2.2-2.6*
                                                                                 acceleration.          test.                 (1.4-4.8)
Palmer (2000) Ex. 500-121-57.......  Multiple industries..  V                   Questionnaire........  Questionnaire........  PRR=1.5-2.2*
                                                                                                                              (1.9-2.4)
Lindsell (1999) Ex. 500-205-13.....  Dockyard work........  V                   Job title............  Cold provocations....  NR *
McGeoh (2000) Ex. 500-41-96........  Welding..............  V                   Questionnaire........  Questionnaire........  NR *
Shinev (1992) Ex. 26-836...........  Polishing............  V                   Tool acceleration....  Physical exam........  NR

[[<strong>Page</strong> 68467]]

Starck (1990) Ex. 26-1510..........  Machining............  V                   Tool acceleration....  Questionnaire........  NR
Virokannas (1995) Ex. 26-891.......  Railway..............  V                   Questionnaire........  Questionnaire........  NR
Miyashita (1992) Ex. 26-1223.......  Construction.........  V                   Questionnaire........  Questionnaire........  OR=0.5
                                                                                                                              (0.1-11.8)
--------------------------------------------------------------------------------------------------------------------------------------------------------
 V=vibration; OR=odds ratio; NR=not reported.
<SUP>*</SUP> =p0.05.
<SUP>1</SUP> 95% confidence interval expressed for the upper end of the risk measure range.

    Bovenzi et al.found a significantly greater prevalence of HAVS in a 
group of 222 active forestry workers engaged in chain saw work as 
compared to randomly chosen shipyard workers unexposed to hand 
vibration (Bovenzi et al.1995, Ex. 26-354). The reported OR was 11.8 
(95% CI 4.5-31.1) for all forestry workers and 6.3 (95% CI 2.3-17.1) 
for workers only using ``anti-vibration'' saws. The study found a 
nearly linear dose-response between HAVS prevalence and both vibration 
acceleration and years of exposure. Vibration exposure was determined 
from questionnaire reports on frequency of chain saw work and direct 
measurement of vibration produced by 30 different saws.
    In two earlier studies, Bovenzi et al.examined HAVS in stone quarry 
drillers and carvers exposed to vibration from hand-held power tools 
along with an unexposed referent group. The first investigation found a 
statistically significant HAVS prevalence (OR=6.1; 95% CI 2.0-19.6) in 
75 drillers/cutters compared to unexposed mill workers (Bovenzi et 
al.1988, Ex. 26-1500). There was a significant association between the 
level of vibration acceleration and severity of symptoms. In a much 
larger study of 570 quarry drillers/carvers and 258 polishers/machine 
operators not using power tools, an OR of 9.3 (95% CI 4.9-17.8) was 
reported (Bovenzi et al.1994, Ex. 26-1239). HAVS prevalence showed a 
significant increasing trend with estimates of lifetime vibration 
exposure.
    In the Nilsson study, HAVS was examined in 89 platers and 61 office 
workers from a pulp mill machine manufacturing plant (Nilsson et 
al.1989, Ex. 26-1148). Prevalence of HAVS (OR=85; 95% CI 15-486) was 
much greater for platers with current exposure to vibration than 
unexposed office workers. There was a clear dose-response between HAVS 
and years of exposure.
    Koskimies et al.investigated HAVS in a group of 124 forestry 
workers from 1972 to 1990 using a series of ten cross-sectional studies 
over time (Koskimies et al.1992, Ex. 26-1490). Their analysis showed a 
monotonic decrease in prevalence from 40 percent in 1972 to 6 percent 
in 1990. In a subcohort of 57 workers followed prospectively, HAVS 
cases decreased from 35 percent in 1975 to 6 percent in 1986. Over the 
same time period, modifications in chain saws used by the workers 
resulted in a reduction vibration acceleration from 14 m/s<SUP>2</SUP> 
to 2 m/s<SUP>2</SUP>. While it is likely that the decline in HAVS is 
due to changes in the vibration acceleration, exposures and outcomes 
were never linked for individual workers.
    The 1989 NIOSH criteria document (Ex. 26-392) provides some 
epidemiological evidence for an exposure-response relationship and 
temporal association between HAVS and vibration exposure. NIOSH 
analyzed HAV acceleration levels and prevalence of HAV-related vascular 
symptoms from 23 cross-sectional studies and found the two variables 
linearly correlated (R=0.67; p0.01). Many of these earlier studies 
determined latency between vibration exposure and onset of HAVS 
symptoms providing some evidence of a temporal relationship. 
Unfortunately these data may be subject to recall bias since the mean 
latency was about six years and onset of symptomatology was often self-
reported.
    Most studies accounted for potential age-related effects by 
stratification of the analysis or through the use of multiple logistic 
regression. These studies also controlled for non-occupational 
disorders that involve symptoms similar to HAVS, such as idiopathic 
Raynaud's phenomena, peripheral neuropathy, alcohol-related illness, 
etc. According to NIOSH (1997, Ex. 26-1), it does not appear that these 
potential confounders account for the fairly strong and consistent 
association between HAVS and vibration.
    Four studies that address vibration and HAVS were submitted into 
the OSHA docket following publication of the proposal (Mirbod et 
al.1999, Ex 500-121-48; Mirbod et al.1997; Ex 500-121-49; Ex 500-205-
21; Palmer et al.1998, Ex 500-121-56; McGeoch and Gilmour 2000, Ex. 
500-42-96; These are summarized in Table V-6. Studies that either 
measured tool acceleration or based HAVS on a combination of symptoms 
and medical tests found a significant association between segmental 
vibration exposure and this MSD (Ex. 500-121-49; Ex. 500-121-56 Ex. 
500-121-48).

Conclusion

    The 1997 NIOSH report concluded the following with regard to the 
relationship between work-related physical risk factors and HAVS:

    The 20 epidemiological studies show strong evidence of a 
positive association between high level exposure to hand-arm 
vibration and vascular symptoms of hand-arm vibration syndrome 
(HAVS). These studies are of workers with high levels of exposures 
such as forestry workers, stone cutters or carvers, shipyard 
workers, or platers. These workers were typically exposed to HAV 
acceleration levels of 5 to 36 m/s<SUP>2</SUP> * * * There is 
substantial evidence that as intensity and duration of exposure to 
vibrating tools increase, the risk of developing HAVS increases. 
[Ex. 27-1, Emphasis in original]

    OSHA agrees with the NIOSH statements that intensity and duration 
of exposure to vibrating tools is linked to the risk of developing 
HAVS. Most of the epidemiological studies show a strong and consistent 
association between high-level exposure to HAV and HAVS symptomatology. 
The data indicate there are strong exposure-response relationships 
between the magnitude and duration of exposure and HAVS prevalence and 
severity. Some studies indicate temporal correlation between the 
chronic use of vibrating power tools and the onset of the disorder. A 
causal association between vibration and HAVS is consistent with 
clinical evidence showing that vibration damages nerve tissue and blood 
vessels in the fingers leading to symptoms characteristic of this MSD. 
Therefore, OSHA concludes that workers exposed to segmental vibration 
exposure, such as from long-term use of hand held power tools, are

[[<strong>Page</strong> 68468]]

at increased risk of developing hand-arm vibration syndrome.

Hypothenar Hammer Syndrome

    Hypothenar hammer syndrome (HHS) is a collection of vascular and 
neurological signs and symptoms that have been related to repeated 
trauma to the hand. HHS is associated with striking or pushing hard 
objects with the hypothenar region of the hand using the hook of the 
hamate bone as an anvil. At this location, the palmar blood vessels of 
the ulnar artery and the sensory branch of the ulnar nerve lie 
virtually unprotected near the surface of the skin and become trapped 
between ``the hammer'' (i.e. the hard object) and ``the anvil'' (i.e. 
the hamate bone). As a result, the blood vessels and nerves are 
especially vulnerable to injury by external mechanical stress. The 
repeated blunt trauma can lead to ulnar artery spasm, aneurysm 
formation, and/or thrombosis. These lesions cause arterial occlusion, 
vascular insufficiency, and post-traumatic ischemia of the surrounding 
tissue. The damage to neural tissue and reduced blood flow to the 
fingers are responsible for the most frequently reported symptoms of 
pain, numbness, cold feeling, discoloration and stiffness of the 
affected digits. A diagnosis can be made based on symptoms and a 
physical examination test of the radial and ulnar arterial blood supply 
to the hand, termed the Allen test. This test measures reflow time 
through the arteries following compression. Reflow time is 
substantially delayed in patients that suffer ulnar artery occlusion. 
More recently, arteriography has been used to confirm diagnosis of HHS. 
If elimination of the contact stress fails to resolve symptoms, 
vascular reconstructive surgery is often performed (Ex. 500-41-29).
    There are four case studies of hospital or surgery clinic patients 
with HHS in the OSHA docket that have consistently implicated 
occupational exposure to repeated palmar trauma as a critical risk 
factor (Conn et al.1970 Ex. 26-821; Vayssairet et al.1987 Ex. 500-41-
47; DeMonoco et al.1999 Ex 500-41-39; Ferris et al.2000 Ex. 500-41-33). 
These studies report on 58 patients altogether. In almost every case, 
the individuals suffering from the disorder reported a history of 
repetitive blunt trauma to the hand related to their jobs. Occupations 
such as carpenter, metal worker, machinist, and mechanic were most 
often cited. More infrequently, the HHS patients were engaged in 
hobbies in which the hand was exposed to frequent impact, such as 
karate and wood working. It should be noted that use of the hand as a 
hammer or to repeatedly apply direct impact to a hard object is a 
specialized combination of repetitive motion and mechanical force 
applied directly to a specific anatomical region. Other studies have 
reported HHS in workers repeatedly exposed to high-frequency mechanical 
stress to the palm from occupational use of hand-held vibrating tools 
(Nilsson et al.1989 Ex. 26-1148; Kaji et al.1993 Ex. 500-41-70). Thus, 
HHS is clearly another example of a work-related injury that occurs as 
a result of combined exposure to biomechanical risk factors (e.g. 
repetition, force, vibration) associated with other MSDs of the upper 
extremities.

Epidemiological Evidence

    Besides the case studies mentioned above, there were two cross-
sectional studies in the rulemaking docket that investigated HHS among 
workers (Little and Ferguson 1972 Ex. 500-41-89; Kaji et al.1993 (Ex. 
500-41-70 ). Little and Ferguson examined 79 male vehicle maintenance 
workers from Australia for HHS who self-reported daily use of the hand 
as a hammer and 48 employees in the same shops who did not report 
habitual hand hammering. HHS was identified by both a positive Allen 
and Doppler test. The Doppler test charted blood flow from the radial 
artery and had shown good correlation with ulnar artery occlusion as 
measured by arteriography. The prevalence of HHS was 14 percent (11 out 
of 79) in the exposed workers and 0 percent in the referent population. 
The mean duration of employment (29.9 years) was significantly greater 
(p0.02) in subjects with HHS than in men exposed to repeated trauma 
without the disorder (mean duration of 18.7 years).
    Kaji et al.used arteriography to examine the hands of 330 Japanese 
workers that used vibrating tools in mining, forestry, and several 
other industries. They found a 7.3 percent (24 cases) prevalence of HHS 
among the workers. The injured subjects were predominantly coal miners, 
rock drillers and forestry workers that reportedly used air and jack 
hammers or chain saws. All suffered from HAVS as well as HHS. The mean 
duration of vibration exposure was 19.4 years (range 5 to 30 years). 
There was no unexposed referent group and no direct observation or 
measurements of vibration exposure in the study.

Conclusion

    There is clear evidence that repeated and forceful impact between 
the hypothenar region of the hand and hard objects, such as hand 
hammering while on the job, or frequent exposure to mechanical stress 
from use of hand-held vibrating tools increase the risk of developing 
HHS. The occluded blood vessels that develop in the palmar region of 
the hand as a result of the blunt trauma created by these occupational 
risk factors have been cited in numerous case studies. The 
pathophysiology that links the initial damage with tissue ischemia and 
the characteristic symptoms that define HHS are also well established 
in the medical literature. Although limited in terms of numbers and 
design, the epidemiological findings are consistent with the clinical 
evidence and provide support for a causal association between repeated 
and forceful contact stress to the hand and this disorder. OSHA 
concludes that workers exposed to repeated and forceful impact between 
the hypothenar region of the hand and hard objects, such as hand 
hammering while on the job, or frequent exposure to mechanical stress 
from use of hand-held power tools, are at increased risk of developing 
hypothenar hammer syndrome.

E. Disorders of the Low Back

    Low-back pain has long been associated with the performance of 
heavy physical work (Hales and Bernard 1996, Ex. 26-896; Klein, Jensen, 
and Sanderson 1984, Ex. 26-972; Rowe 1969, Ex. 26-318; 1971, Ex. 26-
319). Studies have demonstrated that back disorder rates vary 
substantially by industry, occupation and by job within given 
industries or facilities (see Bigos et al.1986a, Ex. 26-871; Riihimaki 
et al.1989a, Ex. 26-58; Schibye et al 1995, Ex. 26-1463; Skovron et 
al.1994, Ex. 26-795). Recently, a NIOSH review (Bernard and Fine 1997, 
Ex. 26-1) concluded that several work-related factors are associated 
with low-back disorders. The National Academy of Sciences (NAS 1999, 
Ex. 26-37) also concluded that there is an association between certain 
work factors and low-back disorders. This section summarizes and 
discusses the evidence that physical work-related risk factors 
contribute to the pathogenesis of specific disorders of the back. The 
risk factors are (1) heavy physical work, (2) lifting and forceful 
movement, (3) bending, twisting and awkward posture, (4) static work 
postures, and (5) whole body vibration. Exposure to several factors 
often occurs concurrently in occupational settings and the evidence 
indicates that the risk of injury is greatest when more than one factor 
is present, reinforcing the concept that these MSDs are both multi 
factorial in etiology and that the joint effects of these risk factors 
can be synergistic. The

[[<strong>Page</strong> 68469]]

terms ``back disorder'' or ``back MSDs'' are used to encompass all 
adverse health outcomes related to the back.
    There are several types of evidence that interrelate to support the 
five risk factors stated above as causative factors for MSDs of the 
back. Information on pathophysiology provides evidence that links risk 
factors to the physiological, anatomical, and pathological alterations 
in soft tissues of the back. This speaks to the biologic plausibility 
that work-related risk factors contribute to these injuries. There is 
also a large volume of epidemiological data that provides evidence of 
an association between worker exposure to the identified risk factors 
and the occurrence of MSDs of the back. Finally, there is biomechanical 
and psychophysical laboratory research that provides much corroboration 
and adds to the plausibility and coherence arguments for a causal 
association determination.
    Epidemiologic and laboratory-based research methods have both been 
used to evaluate the significance of various risk factors associated 
with work-related musculoskeletal disorders (MSDs). Epidemiologic 
studies are designed to look for significant associations between 
exposure to ergonomic risk factors and selected health outcomes 
(ranging from medically diagnosed disease entities to subjective 
reports of pain or discomfort) in selected populations of workers. 
NIOSH (Bernard and Fine, 1997, Ex. 26-1) performed a comprehensive 
review of the occupational epidemiology back MSD literature and after 
carefully selecting those highest quality studies, performed an 
assessment of the 42 studies by type of work-related risk factor. This 
evaluation draws from the NIOSH assessment and appends it with 
additional and more recent studies added to the record.
    Although epidemiologic studies provide important insights into 
understanding the causes of MSDs, these studies are sometimes 
criticized due to their inability to precisely measure exposures to 
risk factors and the associated biomechanical and/or physiological 
responses to these exposures. Biomechanical models and laboratory 
studies do not replace epidemiological studies. However, these 
approaches provide important complementary information toward 
understanding the complex process of how exposures to ergonomic risk 
factors result in physiological responses that may ultimately lead to 
work-related injuries and illnesses. Presented here is a summary of 
laboratory studies and biomechanical models of work factors associated 
with increased risk of low-back injuries and disorders.
    Laboratory studies are controlled scientific investigations of how 
humans respond when exposed to specific ergonomic risk factors (e.g., 
forceful exertions, awkward work postures, high repetition, etc.) 
during simulated work activities. Responses include both objective 
biomechanical/physiological measurements, such as the electromyographic 
(EMG) activity of a working muscle, and subjective psychophysical 
measurements, such as ratings of perceived exertion. Most of the 
studies cited were performed in true laboratory settings. A few studies 
were performed in operational workplaces modified as necessary to 
collect data under carefully controlled conditions. Because of ethical 
issues related to the protection and safety of human subjects, 
laboratory studies are designed to keep exposures to risk factors at 
levels below the threshold of injury. As a result, these studies are 
generally incapable of ``proving'' a relationship between exposure and 
injury. Despite this limitation, laboratory studies provide important 
scientific insights as to how the body responds to ergonomic stresses. 
Combined with pathophysiological models of musculoskeletal injury 
mechanisms and epidemiological findings of positive relationships 
between exposure to ergonomic risk factors and musculoskeletal injury, 
laboratory studies are an essential element in understanding the causes 
and prevention of work-related overexertion injuries.
    Biomechanical models simulate and/or predict how the 
musculoskeletal system responds to work factors such as external loads 
placed on the hands, work posture, and movement dynamics. These models 
can be used to estimate musculoskeletal stresses in the absence of a 
human experiment.
    To understand the mechanisms by which work causes or contributes to 
the genesis or expression of low-back pain, it is first necessary to 
comprehend basic low-back anatomy and potential sources of pain. The 
majority of low-back disorders involve soft tissues (muscle and 
ligament) or the three-disc complex (the intervertebral disc and two 
facets). The latter may involve degenerative disc disease, disc 
herniation or osteoarthritic conditions. To understand how the 
performance of work causes lumbar disc disease, a review of lumbar 
anatomy, disc biochemistry, and disc biomechanics is presented here. 
With this foundation, pathogenic models are better appreciated. Several 
references are available for additional information (Bogduk and Twomey 
1991, Ex. 26-720; Chaffin and Andersson 1991, Ex. 26-420; Williams, 
McCulloch, and Young 1990, Ex. 26-1563; Wiesel et al.1996, Ex. 26-
1394). This discussion of the anatomy of the low back region is 
followed by a summary of the occupational epidemiology literature on 
the low back. This section is followed by a discussion of the 
biomechanical and laboratory research literature on stressors on the 
back.
    The epidemiology literature is examined, to the extent possible, by 
grouping by specific work-related stress factor. The biomechanical and 
laboratory section discusses specific stressors separately for soft 
tissue disorders, disc disorders, and arthritis/spondylosis. In the 
conclusion section OSHA makes a determination of causality based on the 
consistency and strength of the epidemiology evidence and the coherence 
with the biomechanical and laboratory evidence. OSHA makes a 
determination of causality on each occupational risk factor examined, 
where possible; however, the final determination of work-related back 
MSDs is based on the totality of the evidence, not on each factor 
separately. OSHA believes that determining causal associations between 
individual work-related risk factors and MSDs is helpful, both in 
making a final determination of causality and in determining ways to 
abate risk. However, in discussing the epidemiology evidence it becomes 
clear that work often involves simultaneous exposure to multiple risk 
factors, even though in any particular situation exposure to one risk 
factor may predominate.

Anatomy of the Low Back

    The lumbar spine is required to redistribute forces related to both 
intrinsic weight bearing and extrinsic load carrying. It is composed of 
five vertebral bodies separated by intervertebral discs acting as shock 
absorbers and stabilizers, as well as the posterior vertebral ring 
composed of pedicles, laminae, spinous and transverse processes, and 
facet joints that enclose and protect the spinal cord and spinal nerve 
roots. The lumbar vertebrae are numbered from the upper (cephalad) or 
first lumbar vertebra (L1) to the lower (caudad) or fifth lumbar 
vertebra (L5). Lumbar vertebrae are larger and wider than those in the 
dorsal and cervical spine, with the fifth vertebra generally the 
largest. This affords a larger surface area for the intervertebral disc 
and for load distribution. Disc anatomy and function will be discussed 
further in this section. At the lower end of the lumbar spine is the 
sacrum, a large, triangular bone

[[<strong>Page</strong> 68470]]

representing the fusion of five sacral vertebrae, and the small coccyx.
    Consistent with the greater vertebral size, the lumbar pedicles are 
shorter and wider than in the dorsal spine. Lumbar facets are posterior 
articular processes where the adjacent vertebrae interface. These 
joints help permit motion and bear some of the compressive load in 
addition to helping maintain stability of the spine against torsion and 
shear. Facet joints are synovial, and they contain nerve innervations 
in the synovial lining.
    Anterior and posterior longitudinal ligaments attach to the 
superior and inferior margins of the lumbar vertebrae, and are 
innervated by pain fibers. The ligamentum flavum is a non-innervated 
structure that runs down the vertebral ring, and may hypertrophy after 
injury. This may become significant when a hypertrophied ligament 
infolds during spinal extension in an individual with disc bulging and 
facet arthropathy, thereby creating relative spinal stenosis. The 
interspinous ligament, also non-innervated, runs down the posterior 
margins of the spinous processes, posterior projections from the 
vertebral ring.
    In adults, the spinal cord terminates as the conus medullaris at 
about the level of the first lumbar vertebra in the upper lumbar spine. 
Branching off from the conus is a bundle of lumbosacral nerve roots 
that resemble a horse's tail, called the cauda equina. These nerve 
roots pass through the lumbar and sacral portions of the spinal canal 
surrounded by the vertebrae, intervertebral discs, pedicles, laminae, 
facet joints, and spinal ligaments and eventually emerge as individual 
nerve roots through the intervertebral foramina. The neural foramen is 
bordered by the transverse processes of adjacent vertebrae, and the 
spinal nerve root takes its name from the adjacent (cephalad) 
vertebrae. The spinal cord is covered by the thecal sac, composed of 
meningeal tissue and cerebrospinal fluid.
    Nerve roots in the lumbosacral spine include ventral (motor) and 
dorsal (sensory) components. Ventral roots contain motor axons sending 
signals to distal areas and control various skeletal muscle motor 
functions. Dorsal roots comprise primarily sensory axons receiving 
signals from distal areas or dermatomes. Thus, symptoms and signs of 
nerve root compression will vary with the location of the compressive 
lesion. As the intrathecal nerve roots reach the intervertebral 
foramen, the root sleeve gradually encloses the nerve more tightly, and 
eventually become extrathecal. Cell bodies for sensory axons are 
located in an extrathecal area of swelling called the dorsal root 
ganglion. These ganglia are encountered in or close to the 
intervertebral foramina. Axons of the nerve roots consist of collagen 
tissue called the endoneurium. This is covered by a thin root sheath 
that separates the endoneurium from a small amount of cerebrospinal 
fluid, and the epineurium and perineurium covering. Blood flow derives 
from segmental arteries that divide into three branches when 
approaching the intervertebral foramen. Nociceptors are present in 
facet synovium and outer layers of annulus (or extension of the 
posterior longitudinal ligament).
    There are several important muscles of the low back. The psoas 
muscles are major spinal flexors that originate at the anterior 
vertebral borders and combine with the iliacus from the crest of the 
pelvic ilium and insert on the pelvis and lesser trochanter of the hip. 
Posteriorly, the erector spinae muscles attach to the spinous processes 
and laminae down to the sacrum to act as major spinal extensors. The 
interspinales muscles run between the five spinous processes of the 
lumbar spine and contribute to extension. Several other coactivating 
muscles assist in spinal stabilization and rotation. The rectus 
abdominis extends from the lower border of the rib cage to the pelvis 
and assist in flexion and maintenance of lordosis. The obliques and 
transversus are coactivators, and contribute to the generation of 
increased intraabdominal pressure, which some feel helps decrease 
compressive loading on the spine. External moments imposed on the 
lumbar spine during lifting are proportional to the weight and distance 
of the load from the spine and the weight and location of the 
individual's body segments. This results in a state of equilibrium 
where the external moments are counteracted by internal moments, 
primarily created by muscle contractions of flexors balancing extensors 
with additional stabilization from co-activators. Ligaments provide 
passive resistance or restorative moment to muscles. It is not clear, 
however, under what lifting conditions the ligaments play a significant 
biomechanical role.

Epidemiology of Work-Related Low Back Disorders

    When discussing causal factors for low-back disorders, outcome 
measures vary and include low-back pain, impairment, and disability. 
Outcome measures may be defined in terms of severity and also whether 
the information was based on self-reports (interview or questionnaire) 
or objective criteria, e.g., lumbar disc pathology.
    Because there are numerous conditions in the low back which may 
cause low back pain, regardless of their relationship to work factors, 
and, in most cases the cause(s) cannot be determined with any degree of 
clinical certainty, the most common form of back disorder is ``non-
specific symptoms,'' which often cannot be diagnosed. Therefore, in its 
review of the epidemiologic evidence for work-relatedness of low-back 
musculoskeletal disorders NIOSH (Bernard 1997; Ex. 26-1) included 
subjectively-defined health outcomes (e.g., ``back pain'') because they 
comprise such a large subset of the total. From a total of 42 studies, 
24 investigations defined the health outcome only by report of symptoms 
on questionnaire or interview, 2 used sick leaves and medical 
disability retirements and 6 used injury/illness reports. The NIOSH 
review of epidemiologic studies of low-back disorders examined the 
following potential risk factors related to physical aspects of the 
workplace: (1) Heavy physical work (HPW, work that has high energy 
demands or requires some measure of physical strength, jobs that impose 
large compressive forces on the spine), (2) lifting and forceful 
movements (LFM), (3) bending and twisting (BT, awkward postures), (4) 
static work postures (SWP), and (5) whole-body vibration (WBV). These 
physical risk factors almost always appear in workplaces in 
combinations with other work-related risk factors, as well as a myriad 
of personal, psychosocial and other factors. However, to the extent 
possible the review seeks to examine the physical factors separately. 
Furthermore, since this ergonomics rule does not contain provisions 
relating to WBV, this last portion of the NIOSH review will be 
substantively omitted from this analysis. Table V-7 contains a listing 
of both the higher quality back studies used in the NIOSH 1997 (Ex. 26-
1) review and additional back studies in the record.

[[<strong>Page</strong> 68471]]

                               Table V-7.--Summary of Epidemiology Studies Examining Musculoskeletal Disorders of the Back
--------------------------------------------------------------------------------------------------------------------------------------------------------
       Study/exhibit number            Job type studied       Physical factors         Exposure basis       Physical exam.     Risk measure (95% CI)\1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Punnett, 1991 Ex. 26-39...........  Auto assembly........  HPW/BT LFM              Observation            Yes...............  OR=2.2-8.1*
                                                                                    measurement.                              (1.4-4.4)
Astrand, 1987 Ex. 26-527..........  Pulp mill............  HPW                     Questionnaire job      Yes...............  OR=2.3*
                                                                                    title.
Bigos, 1991 Ex. 26-1242...........  Aircraft assembly....  HPW                     Observation            No................  NR*
                                                                                    questionnaire.
Burdorf, 1991 Ex. 26-454..........  Concrete fabrication.  HPW/BT LFM              Observation            No................  OR=2.8*
                                                                                    measurement.                              (1.3-6.0)
Clemmer, 1991 Ex. 26-1345.........  Offshore drilling....  HPW                     Questionnaire job      No................  OR=2.2-4.3*
                                                                                    title.
Hildebrandt, 1995 Ex. 26-1516.....  Population based.....  HPW                     Questionnaire job      No................  OR=1.2*
                                                                                    title.                                    (1.33-1.55)
Heliovaara, 1991 Ex. 26-959.......  Population based.....  HPW/LFM                 Questionnaire job      Yes...............  OR=1.9-2.5*
                                                                                    title.                                    (1.4-4.7)
Hildebrandt, 1996 Ex. 26-770......  Steel maintenance....  HPW                     Questionnaire job      No................  NR
                                                                                    title.
Johansson, 1994 Ex. 26-1132.......  Metal workers........  HPW/BT LFM              Questionnaire job      No................  PRR=1.76
                                                                                    title.                                    (1.25-2.47)
Leigh, 1989 Ex. 26-750............  Population based.....  HPW                     Questionnaire job      No................  OR=1.5*
                                                                                    title.                                    (1.1-2.2)
Masset, 1994 Ex. 26-1470..........  Steel workers........  HPW/BT                  Questionnaire job      No................  NR
                                                                                    title.
Partridge, 1968 Ex. 26-1, pg. 6-81  Dock workers.........  HPW                     Questionnaire job      Yes...............  OR=1.2
                                                                                    title.
Riihimaki, 1989 Ex. 26-998........  Concrete workers.....  HPW/BT                  Questionnaire job      No................  OR/1.0-1.5*
                                                                                    title.
Riihimaki, 1994 Ex. 26-1188.......  Heavy equipment        BT                      Questionnaire job      No................  NR
                                     operators.                                     title.
Ryden, 1989 Ex. 26-809............  Hospital employees...  HPW/BT                  Questionnaire job      No................  OR=2.2*
                                                                                    title.                                    (1.25-4.15)
Svensson, 1989 Ex. 26-732.........  Population based.....  HPW/BT LFM              Questionnaire job      No................  OR=1.2*
                                                                                    title.
Videman, 1990 Ex. 26-1023.........  Hospital patients....  HPW/SWP LFM             Questionnaire job      autopsy...........  OR=2.8-24.6*
                                                                                    title.                                    (1.5-409)
Bergenudd, 1988 Ex. 26-1342.......  Population based.....  HPW                     Questionnaire job      No................  OR=1.8*
                                                                                    title.                                    (1.2-2.7)
Burdorf, 1990 Ex. 26-1518.........  Crane operators......  HPW/SWP LFM             Questionnaire job      No................  OR=0.5-4.0
                                                                                    title.                                    (0.8-21.2)
Chaffin, 1973 Ex. 26-876..........  Electronics manufact.  LFM                     Job title............  No................  OR=5.0*
Holmstrom, 1992 Ex. 26-36.........  Manual handling......  LFM/BT SWP              Questionnaire job      Yes...............  OR=1.3* for BT (1.1-1.5)
                                                                                    title.
Huang, 1988 Ex. 26-1204...........  School lunch workers.  LFM                     Observation            No................  NR
                                                                                    measurement.
Kelsey, 1975 Ex. 26-1134..........  Case/control           LFM/SWP                 Questionnaire job      No................  NR
                                     herniated lumbar                               title.
                                     disc.
Kelsey, 1984 Ex. 26-752...........  Case/control           LFM/BT                  Questionnaire job      Yes...............  OR=3.1*
                                     prolapsed lumbar                               title.                                    (1.3-7.5)
                                     disc.
Knibbe, 1996 Ex. 26-766...........  Nurses...............  LFM                     Questionnaire job      No................  OR=1.3
                                                                                    title.
Magora, 1972, 1973 Ex. 26-1513....  8 occupations........  LFM/BT                  Observation            No................  OR=1.0-1.7*
                                                                                    measurement.                              (1.3-2.1)
Liles, 1984 Ex. 26-33.............  Manual handling......  LFM                     Measurement..........  No................  OR=4.5*
                                                                                                                              (1.02-19.9)
Marras, 1995 Ex. 26-14-12.........  Manufacturing workers  LFM/BT/HPW              Observation            No................  OR=10.7*
                                                                                    measurement.                              (4.9-23.6)
Toroptsova, 1995 Ex. 26-1, pg. 6-   Machine builders.....  LFM/BT/SWP              Questionnaire job      Yes...............  OR=1.4*-1.7*
 92.                                                                                title.
Undeutsch, 1982 Ex. 26-731........  Airport baggage        LFM                     Questionnaire job      Yes...............  NR
                                     handlers.                                      title.
Walsh, 1989 Ex. 26-1437...........  Population based.....  LFM/SWP                 Questionnaire job      No................  OR=1.5-2.0*
                                                                                    title.                                    (1.1-3.7)
Skov, 1996 Ex. 26-674.............  Saleworkers..........  SWP                     Questionnaire job      No................  OR=2.5*
                                                                                    title.                                    (1.2-4.9)
Mandel, 1987 Ex. 500-41-92........  Hospital nurses......  LFM                     Questionnaire........  No................  OR=1.4*
Thorbjornsson, 1998 Ex. 500-119-7.  Random selection from  HPW                     Questionnaire........  Yes...............  OR=1.4*
                                     2500 medical exams.                                                                      (1.0-2.0)

[[<strong>Page</strong> 68472]]

Kuh, 1993 Ex. 500-41-80...........  Population based.....  LFM                     Job title............  No................  RR=1.3*
                                                                                                                              (1.0-1.7)
Smedley, 1995 Ex. 500-41-40.......  Hospital nurses......  LFM                     Questionnaire........  No................  OR=1.3-1.8*
                                                                                                                              (1.3-2.5)
Venning, 1987 Ex. 500-41-49.......  Nurses...............  LFM                     Questionnaire job      No................  OR=1.7-4.3*
                                                                                    title.
Xu, 1997 Ex. 500-119-9............  Population based.....  BT/HPW                  Questionnaire........  No................  OR=1.3-1.7*
                                                                                                                              (1.51-1.93)
Stobbe, 1988 Ex. 500-41-45........  Hospital nurses,       LFM                     Questionnaire........  No................  OR=1.0-2.7*
                                     LPNs, attendants.
Park, 1997 Ex. 500-41-104.........  Population based.....  HPW/LFM/BT              Questionnaire........  No................  OR=1.88*
                                                                                                                              (1.64-2.15) for HPW
Latza, 2000 Ex. 500-41-83.........  Population based.....  HPW/BT/SWP/LFM          Questionnaire........  No................  OR=1.77-1.89*
Latza, 2000 Ex. 500-119-6.........  Laying sandstone.....  HPW/LFm                 Questionnaire........  Yes...............  PR=1.8-2.6*
                                                                                                                              (1.1-6.5) for hours/shift
Kerr, in press Ex. 500-39.........  Automotive workers...  LFM/BT                  Measurement..........  No................  OR=1.7-2.0*
                                                                                                                              (1.22-3.59) for
                                                                                                                               biomechanical factors
Krause, 1998 Ex. 500-87-2.........  Transit vehicle        HPW                     Questionnaire records  Yes...............  OR=3.04*
                                     workers.                                                                                 (1.85-5.00)
MacFarlane, 1997 Ex. 500-41-91....  Population based.....  LFM                     Questionnaire........  Yes...............  OR=1.1-2.5*
                                                                                                                              (1.5-4.1)
Waters, 1999 Ex. 500-41-54........  Lifting case/control.  LFM                     Questionnaire          No................  OR=2.45*
                                                                                    measurement.                              (1.29-4.85)
Wang, 1998 Ex. 500-41-52..........  Manual handling......  LFM                     Measurement..........  No................  Significant correlation
                                                                                                                              p0.01
Van Poppel, 1998 Ex. 500-121-71...  Airline baggage        HPW                     Questionnaire........  No................  NR
                                     handlers.
Vingard, 2000 Ex. 500-41-51.......  Population based.....  HPW/LFM/BT              Questionnaire........  No................  RR=1.4-2.9*
                                                                                                                              (1.2-6.8)
Luoma, 1998, (2000) Exs. 500-71-        Not by identifiable risk factor but by     Job title............  Yes...............  OR=2.0-8.1*
 39, (38).                              title--office carpenter machine driver                                                (2.4-21.1)
SHARP, 1993 Ex. 30-7..............  Data entry...........  SWP                     Questionnaire........  No................  NR*
                                                                                                                              (p0.05)
Larese, 1994 Ex. 38-130...........  Hospital nurses......  LFM                     Measurement..........  Yes...............  OR=1.9-2.4*
Myers, 1999 Ex. 500-119-10........  Case/control           HPW/BT/LFM              Questionnaire          No................  OR=1.6-2.0*
                                     municipal workers.                             measurement job                           (1.13-3.67) for BT
                                                                                    title.
--------------------------------------------------------------------------------------------------------------------------------------------------------
HPW=heavy physical work; LFM=lifting or forceful movements;
BT=bending and twisting or other awkward postures; SWP=static work postures
IR=incidence rate; OR=odds ratio; RR=relative risk; NR=not reported; *=p0.05
\1\ 95% confidence limits expressed for the upper end of the risk measure range.

Heavy Physical Work

    The NIOSH summary reviewed the eighteen higher quality studies 
which address the association between HPW and LBP (Ex. 26-1, pgs. 6-4 
to 6-13). Of these eighteen, 14 were cross-sectional, 3 were 
prospective) and one was a case-control (Ryden et al. 1989, Ex. 26-
801). Study populations included individuals working in health care, 
office work, manufacturing and construction, and all with different 
physical work requirements. Despite the fact that the studies assessed 
different groups of workers, defined disorders and assessed exposures 
in many ways, nine of these eighteen found statistically significant 
positive associations. The relative risk estimates for these 
significant associations generally ranged from 1.1 to 4.3, although one 
study of cadavers found a significant OR=12.1 (95% C.I. 1.4--107) for 
the risk of osteophytosis among those in the HPW category. OSHA notes 
that if there were no true associations only one of these eighteen 
studies should have shown a statistically significant result.
    With regard to temporality, this is usually most easily studied 
with a cohort study design. Of these three studies, one had no 
association (Bigos et al. 1991, Ex. 26-1241), while two showed 
statistically significant increases (Clemmer et al. 1991, Ex. 26-1345; 
Bergenudd et al. 1988 Ex. 26-1342). Two cross sectional studies also 
considered temporal relationships by including in the analysis only 
those MSD-free when starting their current jobs, and both showed 
positive associations (Burdorf et al. 1991, Ex. 26-454; Burdorf and 
Zondervan 1990, Ex. 26-1518). Thus, these results are consistent with a 
positive finding for temporality.
    OSHA also notes that the Bureau of Labor Statistics Annual Survey 
of

[[<strong>Page</strong> 68473]]

Injuries and Illnesses as well as other health interview surveys have 
found elevated LBP rates and MSDs in typical HPW associated 
occupations, (female) nursing aides, orderlies and attendants; personal 
care; and air transportation workers (see the risk assessment in 
section VI of this preamble). While survey statistics may not be 
definitive in themselves, they show a pattern of consistency with the 
results from the epidemiology studies discussed above. OSHA notes that 
these types of population-based studies can be less reliable than other 
epidemiology designs due to generally less knowledge about individual 
exposures.
    Since OSHA's Ergonomics proposal was published, several other 
studies on HPW and LBP have been put into the record. Several are 
discussed below:
    The Vingard et al., 2000 (Ex. 500-41-114) population-based case-
referent study suggests that prolonged exposure to many years of heavy 
work and forward bending (cumulative exposure) increases the risk of 
LBP. The Latza et al., 2000 (Ex. 38-424) prospective study, after 
adjusting for trade, found exposure-response relationships for hours 
per shift laying sandstone (PR=1.8, 95% C.I. 0.7--4.7, for 0 to 2 
hours; PR=2.6, 95% C.I. 1.1--6.5, for <gr-thn-eq> 2 hours; trend test 
p=0.03), and stone load (PR=1.8, 95% C.I. 0.4--9.5, for intermediate 
level; PR=4.0, 95% C.I. 0.8--19.8 for high level; trend test p=0.03). 
The Krause et al. 1998 study (Ex. 38-272) found that cable car crews 
performing the heaviest physical labor had a three-fold increased risk 
of spinal injury compared with bus driver (OR=3.04, 95% C.I. 1.85--
5.00). This five year prospective study of 1,871 transit vehicle 
operation also found both physical workload and psychosocial job 
factors independently predict spinal injury in transit vehicle 
operators.
    OSHA has also considered three other studies available since the 
proposal on HPW. Two of these three studies found at least one 
statistically significant association between LBP and HPW while the 
third suffered from methodological problems. Myers et al. (1999, Ex. 
500-119-10) carried out a case-control study of 274 workers with 
symptoms and signs of low back pain from four municipal departments (a 
73% participation rate). The stated purpose was to identify factors, 
both physical work characteristics and psychosocial factors, associated 
with acute low back injury. Two randomly selected controls were chosen, 
one matched according to work tasks, which the authors stated ``could 
be used to examine importance of non-ergonomic factors'' and one 
matched by department. Cases were defined from reports from the city 
Occupational Medicine Clinic, and were those who had been assigned 
restricted work or had lost work time due to back injury. Further 
information was gathered from questionnaire about work history, work 
characteristics, work injuries, back pain, psychosocial behaviors, and 
demographics. Exposure was assessed by questionnaire and measurement; 
the strenuousness of each worker's job classified as light, medium, or 
heavy according to weight capacity, frequency and duration of sitting-
standing-walking. Analyses screened for 2-way, 3-way and 4-way 
interactions. The variables examined included a work movement index, 
which combined twisting, extended reaching, and stooping. Factor 
analysis was used to determine the important psychosocial factors from 
the Job Content Questionnaire. There was no difference in the 
prevalence among the cases and controls regarding physical work demands 
(light, medium, and heavy), nor twisting or extended reach. However, 
because the cases and controls were matched on job department and/or 
job title, the design provided little ability to examine those job 
factors. This would also preclude any conclusions pertaining to the 
relative strength between psychosocial and physical factors. Although 
the authors noted that their ``findings underscore the importance of 
adopting a model that does not focus entirely on physical factors in 
relation to the multifactorial problem of back injury,'' their study 
design did not allow them to focus adequately on the physical factors. 
This study focused on the psychosocial aspects of the acute back pain 
but did not adequately address work factors.
    Park et al. (1997, Ex. 500-41-104) carried out a cross-sectional 
study using data from the National Health Interview Survey Occupational 
Health Supplement, 1988. In this survey, 30,074 randomly selected 
employed persons were asked about back pain occurring every day for a 
week or more in the previous 12 months. The response rate was 87%. 
Causes of back pain were classified into 3 groups: (1) Injury and/or 
repeated activities that occurred at work; (2) injury and/or repeated 
activities that occurred outside work; and (3) other reasons (illness, 
diseases, unknown). Self-reported work activities included repeated 
activities with lifting, pushing, pulling, bending, twisting, or 
reaching. Occupation was coded according to the 1980 classified Index 
of Industries and Occupations of the U.S. Bureau of Census. Confounders 
were controlled for in the regression models. Results found that 17.6% 
of workers reported back pain every day for one or more weeks during a 
12 month period; 26.9% of these reports were attributed to repeated 
activities (RA) at work; 17% to RA and injury, and 8.2% to injury at 
work. The majority of back pain found in blue collar workers (OR=1.38, 
95% C.I. 1.22--1.54), was attributed to work; whereas the majority of 
BP in white-collar workers was not attributed to work conditions. A 
higher proportion of workers with work-related back pain caused by 
injury or RA had pain in the lower back extending to lower body parts, 
had missed work more than 5 days, and had changed jobs than had workers 
with non-work related back pain. Other significant variables were 
``strenuous physical activities at work more than 4 hours per day 
[HPW]'' (OR=1.88, 95% C.I. 1.64--2.15), ``repetitive movements more 
than 4 hours per day'' (OR=2.4, 95% C.I. 2.1--2.77) and current smoking 
(OR=1.57, 95% C.I. 1.39--1.76), BMI greater than 28 kg/m\2\ (OR=1.35, 
95% C.I. 1.2--1.52) and age 35-59 (OR=1.31, 95% C.I. 1.2--1.46). The 
strength of this study is the rigorousness used by the National Center 
for Health Statistics in their study design and analysis. A weakness is 
that it is based on questionnaire data.
    Thorbjornsson et al, (1998, Ex. 500-119-7) used data collected over 
24 years for its cohort study. 252 women and 232 men were randomly 
selected from 2500 for medical examination (a 62% participation rate). 
In 1969 these subjects had a questionnaire-based interview and an 
examination. LBP was defined as pain, aching, or stiffness in the lower 
back in the past 12 months. There was a follow-up a re-examination in 
1993. Exposure assessment was based on a questionnaire from 1969 using 
a dichotomous scale for 11 work factors (e.g., high mental load (hectic 
work, exhaustion at end of day), poor supervisor social support, 
monotonous work, full time work; night or shift work, overtime work, 
high physical load (40 kg for women, 60 kg for men or physical 
exhaustion at end of day), severe vibrations, and non-working 
conditions, using a dichotomous scale. (Insufficient or unsatisfactory 
leisure time, few or unsatisfactory social contacts, additional 
domestic workload). Risk factors for back pain during 1972-1992 
included: for women, unsatisfactory leisure time (OR=1.5, 95% C.I. 
1.1--2.0); for men, 1972-1993: high physical load (OR=1.4, 95% 
C.I.1.0--2.0), vibrations (OR=1.4, 95% C.I. 1.0--2.2), and 
unsatisfactory leisure

[[<strong>Page</strong> 68474]]

time (OR=1.5, 95% C.I. 1.1--2.0). Cumulative incidence ratios for 1972-
1993, adjusted for age, and earlier back pain were 38% for women and 
43% for men.

Lifting and Forceful Movements (LFM)

    The NIOSH summary reviewed the 18 higher quality studies that 
address the association between LFM and LBP (Ex. 26-1, pgs. 6-13 to 6-
21). Of the eighteen studies, 13 were cross-sectional, two were 
prospective, and three were case-control designs. Only the one case-
control study of back pain in auto workers (Punnett et al. 1991, Ex. 
26-39) fulfilled all four of their quality evaluation criteria. Besides 
auto workers, among the study groups which showed increased risks to 
workers with high lifting or manual materials handling (MMH) demands 
were nursing aides, baggage handlers, workers in manufacturing and 
electronics, crane operators, and concrete fabricators, although 
several studies focused more on the actual stresses within the job 
rather than job title. In all 10 of the eighteen studies showed at 
least some statistically significant associations between LFM and LBP, 
with the significant risk estimates generally ranging from 1.2 to 5.2 
(Ex. 26-1, pg. 6-41). For the most part, higher ORs were observed in 
high-exposure populations. The highest risk estimate (OR=10.7) was from 
a group of workers in a cross-sectional study by Marras et al., (1993, 
Ex. 26-170; 1995, Ex. 26-171). The MMH workers with this highest OR had 
the highest combination of exposure measures relating to five specific 
risk factors associated with lifting, twisting, frequency, angle, and 
force, again strongly suggesting synergism among the risk factors. The 
5 studies reviewed for this chapter which showed no association between 
lifting and back disorder used subjective measurements of exposure, had 
poorly described exposure assessment methodology, or showed little 
differentiation within the study group.
    With regard to temporality, both the prospective studies which 
assessed exposures prior to identification of MSDs, had positive 
association. Also, of the four (three cross-sectional and one case-
control) studies which attempted to address temporality, three found 
positive relationships between lifting and LBP. OSHA also notes that of 
the eight studies which examined exposure-response relationships in 
some manner, six found positive associations, including Punnett et al., 
1991, (Ex. 26-39) while two others did not (Ex. 26-1, pg. 6-20).
    Since OSHA's Ergonomics proposal was published, several other 
studies on LFM have been put into the record. Some are more recent, and 
these are discussed first, while several older studies, not part of the 
original review, are also discussed below.
    With respect to the more recent studies, published since 1996, the 
studies of LFM and LBP in a wide variety of industries provide 
substantial additional evidence that repetitive lifting is associated 
with low back disorders.
    There are a limited number of negative studies which provide little 
evidence to weaken the overall conclusion from the much large number of 
positive studies. Other reportedly negative studies of lifting and low 
back disorders have limitations. For example, Feyer, Herbison et al. 
(2000, Ex. 26-1499) conducted a prospective study of low back pain 
among nursing students, but there was no evaluation of the physical 
demands of jobs and there was a 1/3 dropout from the study.
    In addition to the more recent studies, six older studies, not in 
the proposal, also discussed the relationship between LFM and LBP. 
Mandel and Lohman (1987, Ex. 500-41-92) showed an increased risk of 
back pain with lifting more than10 patients per week (OR=1.39, 95% C.I. 
1.05--1.84) in a cross-sectional study in which 428 registered nurses 
in a Midwestern hospital participated (rate was 65%). Fifteen percent 
of the nurses had reported experiencing LBP for the first time during 
the study year, with most episodes occurring in younger workers. 
However, while intensive care unit nurses lifted significantly more 
patients, LBP was not associated with work area. The most significant 
associations were having LBP prior to the study year and having pain in 
another part of the spine. The limitations of this study are its 
participation rate and both its exposure assessment and health outcome 
definition. However, despite these limitations, it provides support for 
patient lifting as a risk factor for LBP in nurses.
    Larese and Fiorto (1994, Ex. 38-130) in a cross-sectional study 
compared 425 general nursing staff from an urban hospital to 198 
oncology nurses (participation rate: 91.4%). LBP cases were based on 
clinical examination or X-ray findings. Exposure measurements included 
the analysis of working conditions, which revealed both groups of 
nurses had to do frequent and heavy lifting, lowering, and pushing-
pulling. Differences were found when analyzing the number of patients 
assisted by the different nursing groups: the staff nurses cared for 
double the number of patients compared to the oncology nurses. 
Calculating crude odds ratios showed that general nurses had an OR=1.9 
(95% C.I. 1.32--2.76) for LBP and an OR=2.4 (95% C.I. 1.35--4.27) for 
back pain sick leave compared to the oncology nurses. The authors used 
the Mantel-Haenzel chi-square statistics to control for age and for 
occupation among the two groups, but multivariate analysis to control 
for both factors simultaneously was not done. The authors concluded 
that ``comparison between the two hospitals suggests factors associated 
with the disorders: work tasks and particularly nurses/patients ratio 
are more important than age and length of exposure.'' The authors did 
not present the data from which they drew these conclusions.
    Stobbe et al. (1988, Ex. 500-41-45) carried out a retrospective 
study of three hospital groups at a major medical center including 143 
licensed practical nurses, 252 nurses aides, and 20 attendants. Two 
groups were identified, one exposed to frequent patient lifting, one 
not. Health outcome was defined as back injuries, including both lost-
time and non-lost-time injuries. Lifting frequency was determined 
through interviews with the nursing director, the head nurse, and 
nursing supervisors. High frequency lifting was defined as an average 
of more than 5 patient lifts per shift. Low frequency lifting (control 
group) was defined as average of less than two patient lifts per shift. 
Nursing personnel with estimated exposures of 3-5 patient lifts per 
shift were excluded. Lifting frequency (OR=2.7, p=0.009), and length of 
employment ( p=0.0085) remained significant in the logistic regression 
model, while occupation did not. The authors used a survivor type 
conditional analysis which assumed that when a person with a back 
injury report resumed work, the future probability of injury was the 
same as if there had been no previous injury. This assumption has not 
been supported in other studies.
    Kuh et al. (1993, Ex. 500-41-80) in their longitudinal study of 
3262 same age Great Britain natives (born the first week, 1946), looked 
at risk factors for LBP, mainly the association with stature and 
height, but also lifting. The study population had been followed every 
2 years in childhood, and every 5 years as adults. Participation rate 
for this study was only 60.8%. Exposure was assessed using job title 
and occupational histories. A matrix assigned jobs to three levels of 
lifting--low, intermediate and high. The interaction of height and 
occupational lifting as a risk factor for LBP was investigated for men. 
The onset

[[<strong>Page</strong> 68475]]

of back pain symptoms was significantly more common in men whose jobs 
were likely to involve heavy lifting (RR=1.3, 95% C.I. 1.0--1.7). The 
main occupations of heavy lifting associated with LBP were farming and 
construction. There was discussion of reporting bias, recall bias, lack 
of direct information about lifting at work. The weakness of this study 
is using ``job title'' as surrogate for exposure, but a bias here is 
likely to mask true associations.
    Smedley et al. (1995, Ex. 500-41-40) conducted a cross-sectional 
survey of 2,405 nurses using a self-administered questionnaire to 
investigate the risk factors associated with low back pain. The 
response rate was sixty-nine percent. Among those who responded to the 
survey, 1616 were women. Due to the low number of male respondents, 
this study focused on female workers. Low back pain was defined as pain 
lasting for longer than a day in an area between the twelfth rib and 
the gluteal folds (indicated on a chart). Questions about non-
musculoskeletal symptoms, included in the questionnaire, were designed 
to investigate whether psychological factors that influence reporting 
of other symptoms also affect reporting of LBP. After adjustment for 
age, height and non-musculoskeletal symptoms, significant associations 
were found for: frequency of manually moving patients around on the 
bed; manually transferring patients between bed and chair; and manually 
lifting patients from the floor.

----------------------------------------------------------------------------------------------------------------
          Frequency                OR         95% C.I.                      Factors controlled
----------------------------------------------------------------------------------------------------------------
                                       Manual Movement of Patients on Bed
----------------------------------------------------------------------------------------------------------------
5-9 moves...................          1.5  1.1-2.2        Age/height.
5-9 moves...................          1.6  1.1-2.3        Age/height/non-musculoskeletal symptoms.
10+ moves...................          1.7  1.2-2.3        Age/height.
10+ moves...................          1.7  1.2-2.4        Age/height/non-musculoskeletal symptoms.
----------------------------------------------------------------------------------------------------------------
                                Manual transfer of patients between bed and chair
----------------------------------------------------------------------------------------------------------------
5-9 moves...................          1.7  1.2-2.3        Age/height.
5-9 moves...................          1.8  1.3-2.5        Age/height/non-musculoskeletal symptoms.
10+ moves...................          1.5  1.1-2.1        Age/height.
10+ moves...................          1.5  1.1-2.1        Age/height/non-musculoskeletal symptoms.
----------------------------------------------------------------------------------------------------------------

    Evaluation of the task of manually lifting patients from the floor 
resulted in similar significantly elevated risks regardless of whether 
age and height alone or all three factors, i.e., age, height, non-
musculoskeletal symptoms, were controlled for (OR=1.3, 95% C.I.1.0--
1.6). In this study, nurses who often report non-musculoskeletal 
symptoms, such as low mood or stress, were significantly more likely to 
report low back pain. For example, frequent low mood was strongly 
associated with subsequent back pain (OR=3.2, 95% C.I.. 2.2--4.8). 
Specific manual handling tasks were associated with an increased risk 
of back pain while no such association was found in this study among 
nurses using mechanized patient transfer (with hoists).
    A study of personal and job-related factors that may affect the 
incidence of back injuries among 5,649 nurses was conducted by Venning 
et al. (1987, Ex. 500-41-49). A ``back complaint'' was defined as any 
work-related injury or complaint of discomfort in the back and reported 
through an employee health office. Nurses were surveyed by 
questionnaire and then observed for a 12-month study period. As annual 
injury rate of 4.9% was observed. Four factors were found to be highly 
statistically significant (p0.01) predictors of back injury. Risk 
estimates for all four factors (service area, lifting, job category, 
and previously reported back injury), remained significantly elevated 
when a forward stepping model of logistic regression was applied. The 
observed adjusted odds ratios were: 4.26 for service areas where 
lifting occurs most often as compared with areas where lifting occurs 
least; 2.19 for daily lifters as compared with light, occasional, and 
nonlifters; 1.77 for nursing aides as compared with registered nurses 
and supervisory personnel; and 1.73 for individuals who have previously 
reported back injury as compared with those who have not reported 
previous injury. No other factors, including age, physical activity, 
availability of lifting aids, height and weight, and instruction in 
back care and lifting procedures, were significantly associated with 
reporting of back injury. The influence of service area is not easily 
explained. The authors chose to define service area as a work activity. 
With an attitudinal measurement, job satisfaction may have also proven 
to be a significant factor. The question would then be one of 
temporality and association between those factors. It is clear, 
however, that service area assignment is a major risk factor. When two 
employees who are similar in job category and history of back injury 
are assigned to different service areas, the risk of back injury is 
dependent on that ward assignment.
    In summary, seven of the eight new studies, and all six of the 
older studies (all of nurses and nursing assistants who did more 
frequent patient lifting), found at least one statistically significant 
association between LFM and LBP. When considered with the 10 studies 
originally reviewed by NIOSH which found statistically significant 
associations, this epidemiology data base provides strong evidence for 
a causal association between LFM and LBP.

Bending and Twisting/Awkward Postures (BT)

    The NIOSH summary reviewed the 12 higher quality studies which 
addressed the association between BT and LBP (Ex. 26-1 pgs. 6-21 to 6-
26). Of the twelve, nine also examined the effects of occupational 
lifting, although for all but the Marras et al., (1993, Ex. 26-170; 
1995, Ex. 26-171) analysis discussed above the presented comparisons 
for LFM and BT are different. As with the analysis for BT above, only 
the Punnett et al., 1991 case-control study fulfilled all four of the 
quality evaluation criteria. Nine studies were cross-sectional, two 
were case-control and one was prospective. Of the twelve studies seven 
reported statistically significant associations, with the significant 
risk estimates generally ranging from 1.2 to 3.5. However, two of these 
ORs were higher; in addition to the previously mentioned OR of 10.7 in 
the Marras et al. (Exs. 26-170, 26-171) study, Punnett et al., 1991, 
(Ex. 26-39) using a multivariate analysis that adjusted for covariates, 
found a statistically

[[<strong>Page</strong> 68476]]

significant OR=8.09 (95% C.I. 1.4-44) for time in a non-neutral 
position for auto workers. Several studies suggested that both lifting 
and awkward postures were important co-contributors to risk of low back 
disorder.
    With regard to temporality and exposure-response, three studies--
one prospective, one case-control, and one cross-sectional--attempted 
designs and analysis to investigate temporality. Only the case-control 
study of Punnett et al., 1991 (Ex. 26-39) found a strong association 
between exposure to awkward postures and back pain. The Riihimaki et 
al., 1994 (Ex. 26-1188) prospective study comparing heavy equipment 
operators with office workers found a three year prevalence ratio for 
LBP of 1.4 (95% C.I. 1.0-1.9) (Ex. 26-1, 6-86). For exposure-response 
relationships between posture and low back disorder, five of the six 
studies which attempted such an analysis found significant 
relationships between some incremental index of LBP and exposures 
relating to awkward postures.
    Since OSHA's Ergonomics proposal was published, three other recent 
studies on BT and LBP have been put into the record. These are 
discussed below:
    With respect to the two most recent studies, both Latza et al., 
2000, (Ex. 38-424) and Vingard et al., 2000 (Ex. 502-410) have been 
discussed above, in both the HPW and LFM sections. The Latza et al. 
study, in a logistic regression analysis controlling for several 
covariables, found that risk factors for LBP included working in a bent 
position, for men, with an OR =1.89 (95% C.I. 1.03-3.46). This OR was 
greater than those, computed in the same regression analysis, for 
carrying heavy loads, OR=1.47 (95% C.I. 0.97-2.24), and heavy physical 
work OR=1.77 (95% C.I.1.06-2.93). For the Vingard et al. study, there 
were statistically significant associations for both men and women when 
related to both heavy and cumulative exposures. When the combined 
physical exposures of ``heavily exposed to forward bending'' and 
``manual handling over the last ten years'' were added to current 
exposures, the estimated RRs in men was 2.8 (95% C.I. 1.1-7.5) and in 
women 2.9 (95% C.I. 1.2-6.8). Multiple logistic analyses adjusting for 
a wide range of variables including age, social support at work and 
outside work, low back pain earlier, and negative life events, did not 
identify many physical or psychosocial factors as significant 
predictors. However, for ``forward bending greater than one hour'' the 
RR in men was 1.8 (95% C.I. 1.1-3.1), and in women 1.2 (95% CI 0.7-
1.8).
    The third recent study, Xu et al., (1997, Ex. 500-119-9), examined 
bending and twisting, as well as physically hard work in the Danish 
population in a cross-sectional survey conducted in 1990. A random 
sample of 5,185 workers with similar sex, age, and occupational 
distributions as in the Danish population was selected, with a response 
rate of 89.3%. The health outcome was defined as symptoms of back pain 
in the past 12 months, assessed by structured interview, and included 
conditions of pain, ache, discomfort localized in the lower back, 
regardless of intensity and severity. Occupational exposure information 
included duration of daily exposure, vibrations affecting the whole 
body, physically hard work, frequently twisting or bending, sitting 
down, standing up, walking a lot, working with hands raised, 
concentration demands, repetition, and lifting heavy loads. The 
psychosocial factor ``concentration demands'' was also included in the 
model. Confounders controlled for included gender, age group, 
educational level, and duration of employment. There was a significant 
dose-response trend towards the greater prevalence of LBP with a 
greater proportion of the day exposed to the risk factors, for two 
physical factors--physically hard work (OR=1.28, 95% C.I. 1.08-1.52), 
and frequent twisting or bending (OR=1.71, 95% C.I. 1.51-1.93). 
Concentration demands and standing up were also significantly 
positively associated with the occurrence of low back pain. The results 
indicate that the associations of risk factors with LBP were stronger 
among those required to work for 37 or more hours/wk. The authors 
addressed issues of recall and participation bias.
    In summary, the statistically significant associations of BT and 
LBP seen in seven of the 12 NIOSH reviewed studies and in all three of 
the more recent studies, provide by strong evidence that the 
associations observed are real.

Recent Epidemiology Reviews of Work-Related Low Back Disorders

    Since the NIOSH 1997 review, there have been three published 
reviews which bear on the epidemiology of the work-related risk factors 
for back pain discussed above. The first is the NAS report, discussed 
elsewhere in this Health Effects section, which reviews and affirms the 
appropriateness of the methodology and the conclusions of the NIOSH 
1997 review (Exs. 26-37). The other two are recently published reviews 
relating specifically to risk factors, especially physical stress 
factors, for back pain. One of these reviews also examines psychosocial 
factors (Ex. 500-71-24). These are discussed below.
    The Burdorf and Sorock (1997, Ex. 500-71-24) review assessed the 
epidemiologic evidence of occupational risk factors for back disorders. 
They included only those published studies that clearly described 
exposure measures, had quantitative estimates of risk for work-related 
factors, and did not have evidence of a serious methodological problem. 
In all they included thirty-five articles, which they assessed for 
associations with physical factors at work, psychosocial factors at 
work, and individual factors. Of the 19 cited studies reporting on 
associations between back disorders and lifting or carrying of loads 
(LFM), sixteen were positive. The risk estimates ranged from 1.12 to 
3.07, with attributable fractions estimated between 11% and 54%. Nine 
out of ten studies reported positive associations with frequent bending 
or twisting of the trunk (BT), three of which reported exposure-
response relationships. Seven studies examined heavy physical load 
(HPW); six of these demonstrated increased risks of 1.54 to 2.58; 
however the one large longitudinal study did not demonstrate an 
association between physical load and the incidence of back injury 
claims during the study period (Ex. 26-1242). For static work postures 
(SWP), seven studies were considered and three of these had positive 
associations, The authors found some evidence of an association between 
the psychosocial factors of job dissatisfaction and low job decision 
latitude and back pain, but the evidence was not consistent across 
different studies and study designs. The review found that age, smoking 
habit, and education may be important confounders, while the individual 
characteristics of gender, height, weight, exercise or sport, and 
marital status were consistently not associated with back disorders. 
The finding that exercise or sport, the one physical individual 
characteristic examined, was not associated with back disorders 
provides supporting evidence that the physical work-related risk factor 
findings are real and are not confounded by leisure time physical 
factors.
    In making their causality determination, Burdorf and Sorock 
acknowledged that the majority of cross-sectional design studies in the 
data base precluded a firm determination of the temporal and 
specificity criteria of the Hill criteria; they also expressed some 
concern that ``the state of the art does not allow unequivocal 
conclusions about the contribution of specific work-related risk 
factors to the incidence of

[[<strong>Page</strong> 68477]]

back disorders.'' (Ex. 500-71-24, pg. 253). Nevertheless, they 
concluded that:

    Despite these methodological concerns, the available literature 
has presented persuasive evidence for several risk factors for work-
related back disorders. Various studies with clear differences in 
design, methodology, and populations have consistently produced 
comparable findings for MMH, frequent BT, heavy physical load and 
WBV. With regard to MMH, sufficient biomechanical and physiological 
evidence is available to support the biological plausibility of 
lifting as a risk factor for back disorders. The results on lifting 
do not distinguish between the effect of infrequent lifting of heavy 
loads and frequent lifting of light loads. The studies among nurses 
indicate that a single lift of a patient is associated with an 
increased risk of back pain or back disability [cite to Exs. 500-41-
92, 500-41-70, and 500-41-49]. This finding is consistent with 
biomechanical evaluations that predict high compression forces on 
the lower back during patient lifting [cite to Ex. 38-141]. Frequent 
BT of the trunk was consistently related to back disorders in 
various studies. In one case-referent study with detailed exposure 
assessment, a clear dose-response relationship was shown [cite to 
Ex. 26-39]. The findings for heavy physical load demonstrate that 
this is an important work-related risk factor. Several community-
based studies have presented dose-response gradients [cite to Exs. 
29-959, and others]. The strength of the gradients is difficult to 
assess since self reports have been applied to rank exposure to 
physical load on ordinal scales. A second problem is that this 
particular risk factor probably includes MMH and frequent BT. Hence, 
in epidemiologic surveys, heavy physical load might be a surrogate 
measure for other risk factors rather than a separate risk factor 
(Ex. 500-71-24, pg. 253).

Finally the review concludes:

    This review concludes that there is a clear relationship between 
back disorders and physical load, that is, between back disorders 
and MMH, frequent BT, HPW, and WBV. * * * the evidence presented 
indicates that preventive measure reducing the exposure to these 
risk factors will decrease the occurrence of back disorders.

    Hoogendoorn et al. (1999, Ex. 500-71-32) conducted systematic 
reviews of the literature for physical load as risk factors for back 
pain. A rating system was used to assess the evidence based on 
methodological quality and consistency of the findings; under this 
scheme cross-sectional studies were excluded based on the authors' 
quality criteria. The review of studies addressing physical load 
examined 28 cohort and 3 case-referent studies. For physical load, the 
review found that strong evidence exists for work-related MMH, BT, and 
whole-body vibration as risk factors for back pain. Moderate evidence 
exists for patient handling (LFM) and HPW, and no evidence was found 
for standing, walking, sitting, sports, and total leisure time physical 
activity.
    OSHA finds that the consistency of findings in the NIOSH 1997 (Ex. 
26-1) and the two other recent reviews, all using different study 
selection and evaluation criteria, provides confirmation of OSHA's 
emphasis on NIOSH's methodology and conclusions for work-related causes 
of back pain. The assessment on physical load factors was insensitive 
to slight changes in the assessment of findings and the methodological 
quality of the studies. Burdorf and Sorock (Ex. 500-71-24), in their 
review, also commented that comparable findings were consistently found 
for heavy physical work, lifting, twisting and bending, and whole body 
vibration at work in various studies with clear differences in design, 
methodology, and populations.

Dr. Tapio Videman's Testimony on Twin Back Studies

    Dr. Tapio Videman, DrMedSci, University of Helsinki, testified that 
a weakness with the OSHA proposal was that in the studies OSHA 
examined, the role of genetic factors was not taken into account in 
studies estimating the effect of work-related stress factors (Tr. 
16996). To make this point, Dr. Videman presented a slide in his 
testimony (Tr. 16997) that referred to a published paper he had co-
authored on the determinants of lumbar disc degeneration in a 
retrospective cohort study (Ex. 26-71). The study design attempted to 
control for the role of genetics by comparing disc degeneration scores 
between identical twins with different exposure factors thought to be 
associated with back pain. Among the factors examined in the paper were 
occupational workload, leisure time physical activities, measures of 
aerobic exercise and other sports participation, occupational driving, 
and smoking.
    The study consisted of 115 pairs of identical twins selected from 
the Finnish Twin cohort, who were among the most discordant pairs in 
terms of the exposure factors mentioned above. The objective was to 
study whether differences in exposure factors correlated with the disc 
degeneration scores, controlling for genetic factors. Both 
observational and digital summary scores for disc degeneration, based 
on an MRI examination, were obtained for both the upper and lower back 
regions. Occupational and leisure physical activity responses were 
derived via personal interviews.
    An important feature of the study design is that of the 115 pairs 
of twins only 23 pairs were discordant for heavy work before the age of 
20. Also, based on a job scale rating of 1 to 4 to aggregate every job 
title and associated task descriptions during a subject's lifetime work 
history, the mean absolute job scale difference in these 115 twin pairs 
was 0.9. For mean hours working in bending/twisting positions the 
absolute mean difference within the 115 pairs was 1.6 hours. This means 
that this study had little statistical power to show differences among 
physical work factors, after adjusting for genetic factors, since only 
discordant pair results factor into an individual matched analysis.
    The authors examined the associations between the several exposure 
factors and disc degeneration scores using both univariate and 
multivariate analyses, and both observational and digital summary 
scores for disc degeneration for both upper and lower bask disc 
degeneration scores. In the univariate analyses, which apparently did 
not factor in the twins matched pair design, only the heavier physical 
work job code score and mean total occupational lifting per day were 
significantly adversely associated with disc degeneration score, and 
then only for the high back discs. Most other increased physical 
activity and smoking scores were also associated with increased disc 
degeneration scores, but the associations were not statistically 
significant. Increased mean time sitting at work was associated with 
less disc degeneration for both high and low back, but only the high 
back scores showed statistical significance.
    To attempt to control for the genetic effect, the authors also used 
multiple regression methods in an attempt to explain the observation 
summary disc scores. Their results found that, for the upper back, only 
the mean job code and age were jointly statistically significant, with 
no other specific environmental or behavioral factors contributing 
significantly. For the lower back, heavy leisure time physical loading 
was the only specific environmental factor of statistical importance; 
this one variable explained 2% of the variance in the multiple 
regression model.
    In an attempt to consider the amount contributed by the genetic 
component in the study design, the authors inserted 114 co-twin 
(indicator) variables in the model and recalculated the estimates. They 
found that together, these 114 variables, ``those of familial 
aggregation, reflecting primary genetic and shared early environmental 
influences * * * explained nearly 75% of the variability in disc 
degeneration score in the upper region and nearly 50% in the lower 
lumbar region (id., pg. 2608). The

[[<strong>Page</strong> 68478]]

authors concluded, as did Dr. Videman in his testimony, that these 
``findings suggest that disc degeneration may be explained primarily by 
genetic and early environmental influences and unidentified factors. * 
* * If disc degenerative changes are associated with symptomatic 
conditions, these studies findings suggest a need to rethink future 
research and prevention strategies in this area.'' (id., pgs. 2610-
2611).
    Dr. Videman and associates made similar findings on the importance 
of genetic factors in disc degeneration in a study comparing 20 pairs 
of twins with discordant smoking status (Ex. 32-241-3-89; Tr. 16994-
16995). Using the same type of multivariate methodology, with one 
variable for smoking and 18 variables for co-twin status, they 
concluded, ``Whereas smoking status and age explained 0 to 15% of the 
variability on the various degenerative findings in the discs, 26% to 
72% of the variability was explained with the addition of a variable[s] 
representing co-twin status. These findings are compatible with a 
marked genetic influence and warrant further investigation.'' (Ex. 32-
241-3-89).
    In his testimony at the hearings, Dr. Videman emphasized the 
relative importance of genetic factors over physical work factors, 
``(W)e could conclude that, from a blood sample, I can predict MRI 
[disc] changes better than having a lifetime work history about another 
interview.'' (Tr. 16998).
    OSHA has considered Dr. Videman's testimony and publications and 
disagrees with his conclusions about the relative importance of 
physical work factors and genetics in the prediction of MRI disc 
changes. Although the agency agrees that the discordant identical twin 
study design is useful to control for genetic and early environmental 
factors, other factors in the design are at least as important. As was 
seen in the first study discussed above (Ex. 26-71), in a matched 
control study the amount of discordance in the exposure variables 
within the twin pairs will determine the power of the study to detect 
an effect. For example, with little discordance in exposure variables 
and few discordant pairs, the study has little ability to detect a true 
effect. In fact OSHA believes that in such a situation degenerative 
disc summary scores between twins should be very similar. To carry this 
example further in that first study, which involved the 115 twin pairs 
with little co-twin difference in the exposure variables, it is not 
surprising that adding 114 co-twin variables to the analysis, it is 
absolutely no wonder that in total these 114 variables will explain 
most of the variation in the multiple regression model. OSHA concludes 
that Dr. Videman's conclusion on the importance of genetic factors in 
his studies is a function of his analysis and his study design. This 
type of matched-control study is designed to control for genetic 
effects, not to study them.
    OSHA also notes that in Dr. Videman's smoking study with 20 twin 
matched-pairs and a mean discordance between siblings of 32 pack years, 
``a very huge difference'' (Tr. 16994), the disc degeneration 
difference was statistically significant at all of the measured disc 
levels. Controlling for genetic traits was undoubtedly important, as 
suggested by the statistical significance of the 18 covariables (Ex. 
32-241-3-89, pg. 1666).
    In the hearings, Dr. Videman was questioned by Ms. Seminario about 
a study he co-authored that concluded, ``environmental factors 
[including physical work factors] account for more than 80 percent of 
the [etiology] of sciatica and more than 90 percent in the case of 
patients admitted to the hospital.'' (Tr. 17054, see also Dr. Videman's 
response to a similar question by Ms. Butterfield, Tr. 17128). Although 
Dr. Videman acknowledged the correctness of this statement, he appeared 
to contradict these findings by explaining that ``all the data from 
that study was based on questionnaire data, so the reliability of the 
diagnosis is unclear.'' (Tr. 17129). OSHA notes, however, that in the 
actual paper the authors note that ``the cumulative age-specific 
incidences of sciatica [were] based on both the questionnaire and the 
hospital discharge records,'' and that the results are in ``accord with 
the results of a previous Finnish study.'' (Ex. 502-227, pg. 397). 
Furthermore, the authors noted that the hospital discharge diagnoses 
are given by doctors based on the WHO manual of the International 
Statistical Classification of Diseases (id., 394). The authors also 
cited studies on the reliability of the nationwide hospital discharge 
registry (id., 394).
    Thus, because that Dr. Videman's conclusions about the relative 
importance of genetics and physical work factors in back disorders were 
based on the questionable methodology used in the two twin studies 
discussed above, and because Dr. Videman's testimony on another study 
which contradicted those conclusions was not supportable, OSHA is 
unable to give much weight to Dr. Videman's testimony on this issue.

The Bigos et al., 1991 Back Study

    Bigos et al.published several papers on a study (see, e.g., Exs. 
500-121-8, 38-280, 26-1241) that assesses the role of work perceptions 
and psychosocial factors in predicting the report of back pain 
disability. The study group was a cohort of aircraft assembly workers 
at the Boeing Company in Everett, Washington who volunteered to 
participate. This longitudinal study ultimately analyzed 1326 out of a 
cohort of 4027 aircraft assembly workers (33% of the original solicited 
population) for the final models.
    The health outcome studied was ``back pain disability lasting 
longer than 3 months,'' and the authors used three notification 
systems--reporting to the company medical department, filing an 
incident report, or filing an industrial insurance claim. The study did 
not investigate the actual presence of back symptoms or specific back 
disorders. At the beginning of the study, subjects answered a series of 
questionnaires which addressed demographics, psychosocial factors, and 
cardiovascular risks, as well as a take-home questionnaire including 
the 566 question Minnesota Multiphasic Personality Inventory (MMPI), 
the Health Locus of Control Questionnaire, and a modified Work 
Adaptation, Partnership, Growth, Affection, and Resolve (APGAR) survey 
(modified from the Family APGAR survey). Other information included 
previous medical history, previous back discomfort or problem, back 
injury claims in the previous 10 years, and work perceptions. Subjects 
were also given a physical examination to assess physical attributes 
including anthropometry, lifting strength, aerobic capacity, and 
sagittal flexibility. A back examination including reflexes, girths, 
sciatic tension, and posture was performed. Thus, each subject provided 
individual responses to questions concerning these physical and 
psychosocial factors.
    In contrast to the above factors, which were collected for each 
worker individually, workplace exposure assessment was limited to all 
jobs that employed more than 19 workers and was not performed on 
individual workers. These jobs were analyzed for tasks that were heavy 
and tiring tasks in terms of maximum loads on the spine, based on some 
unspecified biomechanical mathematic model. Any worker in a job with 
fewer than 19 people did not get physically measured; also, the authors 
did not measure workers' cumulative loads. As with the psychosocial 
factors, workplace

[[<strong>Page</strong> 68479]]

exposure was also measured only at initial recruitment.
    Subjects were followed for slightly more than four years, during 
which 279 subjects reported back problems. After analyzing the data to 
determine which factors could best predict these reports, the authors 
concluded:

    Other than a history of current or recent back problem, the 
factors found to be most predictive of subsequent reports in a 
multivariate model were work perceptions and certain psychological 
responses. * * * Subjects who stated that they ``hardly ever'' 
enjoyed their job tasks were 2.5 times more likely to report a back 
injury (p=0.0001) than subjects who ``almost always'' enjoyed their 
job tasks. These findings emphasize the importance of adopting a 
broader approach to the multifaceted problem of back complaints in 
industry, and help explain why past prevention efforts focusing on 
purely physical factors have been unsuccessful.

    OSHA notes that one major problem with the interpretation by other 
researchers of these results in the Boeing studies is that within the 
Boeing studies, ``physical variables'' include only those physical 
attribute variables that deal with anthropometry, back examination 
indices, and physical capabilities (e.g. flexibility, lifting strength, 
aerobic capacity) (Ex. 38-280, Table 1, pg. 25). It is under the 
``nonphysical variables'' that the authors included workplace factors--
duration of employment, job classification code, and measured peak 
spinal loading--as well as psychological and psychosocial factors. 
Other researchers include workplace factors (e.g., measured peak spinal 
loading and physical workload) as physical variables. Thus, when Bigos 
et al.conclude in their study that none of the physical variables was 
important in predicting back pain reports (back disability > 3 
months)--they are not referring to the same types of work-related 
physical risk factors--lifting/forceful movements, bending/twisting and 
awkward postures, heavy physical work, or static work postures--that 
OSHA refers to in its standard. Bigos et al.did not directly address 
these factors in their study.
    OSHA also notes that the overall participation rate for this study 
was low, which makes representativeness an issue, especially for the 
25% of the group that initially chose not to participate. The 
longitudinal study ultimately analyzed 1326 out of a cohort of 4027 
aircraft assembly workers (33% of original solicited population) for 
the final models. In an attempt to determine whether the voluntary 
aspect of the study would create a bias, the authors compared the 
reported injury rates for those who returned incomplete data (n=1451) 
on their modified APGAR and MMPI packets, with the 1,569 subjects who 
did complete the forms. The difference in injury report rates was not 
statistically significant, which suggests that this final study group 
may be representative of the total.
    OSHA also notes that no individual exposure measurements were 
carried out, although extensive individual psychosocial and 
psychological measurements were done. Workplace exposure assessment was 
limited to jobs that employed more than 19 workers, and there was no 
accounting for individual inter- or intra-variability. Because the 
exposure data represented the ``exposure'' of a group of workers rather 
than the measured exposure of individual workers, the authors would not 
be able to determine the contribution of physical factors to the 
observed outcome in as robust a fashion as they would the contributions 
of medical history, psychological surveys, physical exam, or job 
satisfaction survey, which were all recorded as individual exposure 
data. The authors did not report nor provide information on the 
analysis of the exposure data. There was no report on the data 
collected on biomechanical loads of the spine. They also did not report 
nor provide information on the data collected on the workers' perceived 
physical exertion in their jobs.
    Dr. Bigos, in his testimony to OSHA during the hearings, stated 
that the Schultz model (the only biomechanical model related directly 
to human intradiscal measurements) was applied to the evaluation of 
mechanical stress on the Boeing subjects, and it found no significant 
relationship between mechanical stress on the subjects and the report 
of back problems or disability (Tr. 6725-6727). OSHA is addressing back 
pain in its final standard, and intradiscal measurement changes, 
obtained from the Schultz model, are not directly relevant to the 
existence of back pain or back disability.
    OSHA also notes that this study did not address heavy lifting, or 
even jobs at the moderate or high end of HPW exposure. Bigos et 
al.report, ``the study was done in a diverse, highly sophisticated 
manufacturing industry where job tasks do not tend to be extremely 
stressful for the back.'' (Ex. 500-121-8, pg.5). As Bigos et al.(1991, 
Ex. 26-41) state, ``our study may not be representative of workers with 
extremely physically demanding jobs, where virtually no one remains 
active until retirement age.''
    OSHA also has concerns about the interpretation of the results of 
the ``Work'' Adaptation, Partnership, Growth, Affection, and Resolve 
(APGAR) survey score. The authors added two additional untested items 
to the family APGAR: (1) ``I enjoy the tasks involved in my job,'' and 
(2) ``please check the column that indicates how well you get along 
with your closest immediate supervisor.'' (Ex. 26-1242, pg. 2). Results 
found the strongest statistically significant relationship between back 
disability and statement (1) ``I enjoy the tasks involved in my job.'' 
(id., pg. 3). However, this single initial response from a single point 
in time, rather than from more reliable repeated measures over time, 
was used to explain the outcome over a four-year period.
    OSHA also has some concerns about a potential bias due to subjects 
who were excluded from strength testing if current back symptoms were 
present at the time of testing, or had caused them to miss work in the 
previous six months. This strongly influences the ability to draw from 
the study conclusions that are related to this variable, i.e., 
eliminating the back pain subjects from the study population creates a 
healthy worker effect, which would bias results toward the null.
    For the final predictive model, involving 33% of the original 
solicited population, the percentage of the overall variability 
explained by the model was 2.2% for job satisfaction, 1.9 for 
psychological factors, 1.2% for physical examination factors, and 3.3% 
for medical history; the sum of these individual components was 8.6%; 
7% combined (Ex. 38-280, pg.29). This means that 93% of the variability 
was unexplained by this model for predicting industrial back pain 
reports (back disability > 3 months).
    In sum, with the qualifications discussed above, OSHA acknowledges 
the importance of the Bigos et al.prospective study on the role of 
psychosocial factors in reports of back injuries. OSHA used this study 
in its weight of evidence determination for HPW as a risk factor for 
LBP, and found no association. However, OSHA concludes that physical 
risk factors were not as well determined in this study as were the 
psychosocial risk factors, making their relative contributions 
difficult to assess. Furthermore, the lack of truly HPW, according to 
the authors, among these workers would further limit the ability to 
study this physical risk factor. Thus, OSHA concludes that although 
this study found a significant relationship between psychosocial 
factors and LBP, this study lacked the ability to concurrently study 
the relative contribution of the physical work-

[[<strong>Page</strong> 68480]]

related risk factors of interest to OSHA. In Section G5 OSHA provides 
additional discussion of both the Bigos et al.study and psychosocial 
risk factors.

Biomechanical Factors and Laboratory Experiments

    For a distilled summary of the literature describing laboratory 
experiments and biomechanical models of risk factors associated with 
low back pain in table format, see Table II-1 in the health effects 
appendices to the proposed rule (Ex. 27-1).
    There is some debate as to the exact etiology of low-back pain, and 
some authorities suggest that it is possible to make a precise 
diagnosis in perhaps only 20% of patients presenting with acute low-
back pain (Frymoyer 1988, Ex. 26-118; Nachemson 1976, Ex. 26-1147; 
White and Gordon 1982, Ex. 26-1160). Proposed etiologies for low-back 
pain that have been advanced include the roles of nerve compression, 
tissue ischemia, sensitization of nerve endings, inflammatory 
mediators, spinal instability, and other postulates (Frymoyer 1988, Ex. 
26-118; Nachemson 1992, Ex. 26-490). The majority of cases of work-
related low-back pain are attributed to mechanical causes, such as 
muscle and ligament strains and sprains and disc herniations. 
Degenerative disc or facet disease, spinal stenosis, spondylolisthesis 
and compression fractures have also been attributed, at least in part, 
to work. Additionally, back disorder is multifactorial in origin and 
may be associated with both occupational and nonwork-related factors 
and characteristics (Bernard 1997; Ex. 26-1).
    One additional difficulty in evaluating the etiology of low-back 
pain is that roughly 50% to 60% of patients reporting an episode of 
work-related low-back pain note an insidious onset of pain rather than 
a single, point-in-time event with immediate low-back pain (Bergquist-
Ullman and Larsson 1977, Ex. 26-933). This study also found that cases 
with an insidious onset experienced prolonged recovery. Part of the 
explanation for this may lie in the absence of nociceptors in the disc 
itself and the facet joints (except for the synovial lining) (Pope et 
al.1991, Ex. 502-502). These load-bearing structures may, therefore, 
become injured without immediate recognition (e.g., sudden pain), and 
the eventual manifestation of low-back pain may only occur after a 
series of point-in-time events have sufficiently injured these spinal 
structures to the point where nociceptors become irritated (e.g., in 
the outer one-third annulus or facet synovium).

Specific Low-Back Disorders

    Low-back pain symptoms are caused by a variety of injuries and 
disorders. Although the underlying cause of back pain cannot be 
determined definitively in up to 90% of patients, work-related cases 
are believed to result from the following mechanisms: muscle or 
ligamentous (soft tissue) injury; herniation of the intervertebral disc 
with irritation of adjacent nerve roots; and degenerative changes 
(arthritis/spondylosis) in the intervertebral discs (Deyo, Rainville, 
and Kent 1992, Ex. 26-365). Evidence for work-relatedness for low-back 
disorders of these three sources of etiology is summarized below.

Soft Tissue/Mechanical Low-Back Disorders

    As noted earlier, the exact etiology of low-back pain is unknown in 
many cases, and therefore, there is a lack of universal agreement on 
the contribution of muscle and ligament sprains and strains to work-
related low-back disorders. In part, the difficulty in diagnosis 
relates to the inability to easily palpate deep low-back muscles, the 
lack of imaging information on low-back muscle disorders, and the 
absence of surgical pathologic specimens to evaluate.
    However, in addition to an understanding of muscle anatomy, 
consideration of muscle function (static and dynamic loading), and 
repair mechanisms contribute to understanding the role of muscle and 
ligament sprains and strains in work-related low-back disorders.

Static Loading

    In evaluating the pathogenesis of soft-tissue low-back disorders, 
there are considerations related to static and dynamic work activities. 
Simple maintenance of posture requires balancing of counteracting 
mechanical forces about the spine. Static loading affects muscle and 
connective tissue. During static trunk flexion, low-back extensor 
muscles must progressively increase their activity to maintain trunk 
flexion (Schultz et al.1982, Ex. 26-581).
    Using myoelectric measurements, Andersson et al.(1974, Ex. 26-346) 
ascertained that activity of the erector spinae progressively decreased 
as the angle of the back rest advanced from 10 degrees of forward 
inclination to backward inclination. This results from a partial 
reduction of the lumbar spine load imposed by the upper body as the 
load is transmitted to the back rest (Andersson and Marras 1996, Ex. 
26-412; Chaffin and Andersson 1991, Ex. 26-420). In addition, during 
unsupported sitting, the lumbar spine flattens, and the use of lumbar 
supports and back rests can reduce the loss of normal lordosis 
(Andersson et al.1979, Ex. 26-1553).
    Using a back rest inclination of 110 degrees and a 4 cm lumbar 
support, the authors were able to demonstrate that lumbar posture could 
be similar to normal standing posture. Maintenance of adequate seated 
posture has further implications for the intervertebral disc, with 
lower intervertebral disc pressures noted during supported sitting as 
opposed to unsupported sitting (Andersson et al.1974, Ex. 26-346). 
Inadequate seating can contribute to the development of low-back pain. 
Individuals who sit in chairs that are too high and have their feet 
unsupported experience elevated pressure on the back of their thighs 
(Akerblom 1969, Ex. 26-522; Bush 1969, Ex. 26-455; Schoberth 1962, as 
cited in Chaffin and Andersson 1991, Ex. 26-420). Burandt and Grandlean 
(1963, Ex. 26-1569) observed the tendency of subjects in high seat pans 
to slide forward in their seats to support their feet, negating the 
benefit of a back rest.

Dynamic Loading

    Dynamic loading of the lumbar spine has other implications for 
muscle and ligament. Stresses induced in the low back during manual 
materials handling relate to the load weight and the characteristics of 
the lift. As a result of their anatomic positions, large spinal 
movements are created from relatively small degrees of muscle 
shortening. Unfortunately, this results in the generation of relatively 
large muscle and joint forces, with potential for tissue overloading 
and injury. This could be particularly important during excessive or 
rapid movement (Andersson and Marras 1996, Ex. 26-412), or at the point 
of muscle fatigue.
    A study by Hukins et al.(1990, Ex. 26-143) revealed that greater 
forces are exerted on ligaments as the speed of motion increases. In 
addition, elastic limits of the ligaments and disc may be exceeded 
(Adams and Dolan 1981, Ex. 26-1348). Bush-Joseph et al.(1988, Ex. 26-
939) evaluated the effect of the speed of lifting on the external load 
moment. Subjects were asked to lift at slow, medium, and high speeds. 
There was a direct linear correlation between increasing speed of 
lifting and increased peak moment. Furthermore, a study by Marras and 
Mirka (1992, Ex. 26-982) revealed that muscles must generate a higher 
percentage of electromyographic (EMG) maximal activity to maintain a

[[<strong>Page</strong> 68481]]

constant muscle force as the speed of trunk velocity increases with 
bending.
    Both lifting frequency and load weight affect back muscle work 
capacity, in part related to fatigue. Using EMG assessments, Kim and 
Chung (1995, Ex. 26-858) observed that lifting at 10% of maximum 
voluntary isometric strength (MVIS) at a rate of 6 times a minute was 
more fatiguing than lifting at 20% MVIS at a rate of 3 times per 
minute.
    Frequent loading of the lumbar spine with moderate to heavy weights 
can also cause general physical fatigue with elevation in heart rate 
and energy expenditure. Uncoordinated muscle activation that could 
result from local and systemic fatigue could then place other tissues 
at increased risk with continued lifting (Garg 1986, Ex. 26-121).

Postural Issues

    Additional postural factors during lifting significantly affect 
muscle function and risk of injury. Skeletal muscle is more likely to 
rupture during eccentric contraction (Friden and Lieber 1994, Ex. 26-
546), a factor involved in many manual materials-handling tasks. In 
addition, muscle length affects the amount of force that muscle can 
generate, with maximal force produced when muscles are at their resting 
lengths (Andersson and Marras 1996, Ex. 26-412; Chaffin and Andersson 
1991, Ex. 26-420). Therefore, lifting in positions where skeletal 
muscles are elongated or shortened can increase the risk of injury to 
these tissues.
    Using EMG evaluation of muscle function during lateral flexion of 
the lumbar spine, Andersson, Ortengren, and Herberts (1977, Ex. 26-
1570) demonstrated increased activity on the side contralateral to 
bending. Other researchers have determined that asymmetric loading in 
lateral flexion and axial rotation causes high levels of antagonistic 
activity in abdominal and back extensors. This is associated with 
increased myoelectric activity on the side of spine contralateral to 
the load, although there is still significant activity on the 
ipsilateral side (Astrand 1987, Ex. 26-527; Kelsey 1975, Ex. 26-1134; 
Magora 1970, Ex. 26-297; Merriam et al.1983, Ex. 26-299). Andersson 
(1977, Ex. 26-449) noted that increased intervertebral disc pressure 
and intraabdominal pressure occurs when the trunk is loaded in lateral 
flexion and axial rotation, with rotation being the greater factor.

Muscle Velocity and Acceleration

    Marras (Ex. 26-1412) has indicated that several trunk muscle 
characteristics and demands associated with dynamic lifting may better 
assess the risk of developing a low-back disorder from manual materials 
handling. The authors analyzed 400 lifting jobs in 48 industries using 
a triaxial goniometer (Lumbar Motion Monitor or LMM) that was worn by 
working subjects. A combination of five trunk motion and workplace 
factors was able to reasonably predict jobs posing high risk for low-
back disorders (Marras et al.1995, Ex. 26-1412). These factors include 
the lift frequency, load moment, trunk sagittal range of motion, trunk 
lateral velocity and trunk twist acceleration (Marras et al.1995, Ex. 
26-1412). A recent NIOSH Health Hazard Evaluation provided additional 
verification that the LMM has predictive capacity equal to the NIOSH 
Lifting Equation in job analysis (NIOSH 1993, Ex. 26-521), with perhaps 
greater ease of administration.
    Recently, Marras et al.(1990, Ex. 26-1523; 1993, Ex. 26-170; 1995, 
Ex. 26-171) studied the trunk angular motion characteristics of normal 
and chronic low-back pain subjects. Used in a clinical setting, the LMM 
appears to have good ability to accurately distinguish between normal 
individuals and those with chronic low-back pain or structural disease. 
The authors used anatomic and pain categories previously selected by 
the Quebec Task Force Study on Spinal Disorders (1987, Ex. 26-494). 
Normative trunk motion values for age and gender were derived in a 
study of 339 males and females from ages 20 to 70 years who had never 
experienced significant low-back pain. While wearing the LMM, subjects 
performed trunk flexion and extension in five symmetric and asymmetric 
motion planes (0 degrees, 15 degrees and 30 degrees right and left) 
while trunk angular position, velocity, and acceleration were recorded 
with the LMM. In a repeatability study, 20 healthy normal subjects who 
had never experienced a low-back disorder were tested with the LMM once 
a week for 5 weeks. No statistically significant differences were 
observed among the trunk motion characteristics between the five weekly 
test sessions using multivariate analysis of variance. Correlation 
coefficients were computed to select reliable trunk motion variables to 
be used in the next phase of the study. Correlations varied as a 
function of the angle of asymmetry and measured variables, with motion 
characteristics in the zero plane demonstrating correlation 
coefficients of 0.88 to 0.96 (number of conditions performed, twisting 
range of motion, sagittal range of motion at 0 degrees, sagittal 
extension velocity at 0 degrees, sagittal extension acceleration at 0 
degrees, continuous velocity, continuous acceleration, lateral right 
range of motion at 0 degrees).
    In the next phase, the eight highly reliable trunk motion 
characteristics evaluated in the healthy subjects were compared with 
measurements in subjects with chronic low-back pain (96 males and 75 
females) who were recruited for study from secondary and tertiary 
referral practices. These individuals had been symptomatic for at least 
7 weeks and had been sufficiently studied, including with appropriate 
imaging studies, to permit accurate Quebec classification. Dynamic 
trunk motion characteristics were normalized for age and sex, and using 
quantitative discriminant analysis, the 510 subjects were correctly 
classified in 94% of cases as being either healthy or having chronic 
low-back pain(stage-one analysis).
    In a stage-two analysis, nine variables (the eight previously 
mentioned and continuous position) correctly classified 80% of subjects 
into one of eleven groups (normal, low-back pain alone, low-back pain 
with proximal or distal radiation, disc herniation with high or low 
pain scores, spondylolisthesis, spinal stenosis, postoperative, 
nonorganic components, other) via modified classification using 
splines. It was also noted that trunk range-of-motion parameters 
commonly used to quantify impairment had poor ability to discriminate 
normal vs. chronic low-back pain, nor was it useful in classification. 
Furthermore, a characteristic pattern of recovery from low-back pain 
was noted, with normalization occurring first in range of motion 
followed by velocity and later acceleration of dynamic trunk motion. It 
was opined that the LMM's ability to quantify unloaded free-dynamic 
motion and account for the co-activation of additional structures 
(e.g., internal and external obliques, lattissimus dorsi) affecting 
erector spinae function was in part responsible for its enhanced 
discriminating ability compared to alternate imaging techniques.

Disc Disorders/Disorders of the Three-Joint Complex (Disc and Two 
Facets) and the Nerve Root

    The three-joint complex refers to the intervertebral disc and two 
facet joints. This complex permits the spine to absorb compression and 
resist torsion and shear, while permitting translation and rotation of 
the spine. Epidemiologic evidence suggests that work exposures 
involving heavy lifting or manual materials handling are associated 
with

[[<strong>Page</strong> 68482]]

low-back disorders, including disc disorders (Bernard and Fine 1997, 
Ex. 26-1).
    Excessive or repeated spinal loading and inadequate rest periods to 
permit repair mechanisms to function may be associated with 
biomechanical stresses that damage intervertebral disc cartilage 
endplates. This may then disturb metabolic transport, hastening the 
development of degenerative disc disease and disc herniation with 
secondary nerve root compression or inflammation.
    Rowe (1971, Ex. 26-319) opined that up to 70% to 80% of recurring, 
chronic low-back pain will eventually be diagnosed as discogenic. 
Discogenic pain can include clear and consistent symptoms and signs 
expected with lumbar disc herniation and specific nerve root pathology, 
as well as chronic low-back pain associated with increased pressure in 
the intervertebral disc or degenerative disc disease. In patients with 
lumbar disc herniations, approximately 90% to 95% occur at the lower 
three intervertebral disc spaces (lumbar \3/4\ disc or lumbar 4th nerve 
root, lumbar \4/5\ disc or lumbar 5th nerve root, lumbosacral L5/Sl or 
sacral 1st nerve root) (Deyo, Rainville, and Kent 1992, Ex. 26-365). 
Increased compressive and torsional forces transmitted to the lower 
levels of the lumbar spine probably account for this observation. Peak 
incidence of lumbar disc herniation occurs in adults during the working 
years from ages 30 to 55 (Spangfort 1972, Ex. 26-502). The onset of 
symptoms may be acute, subacute, or chronic, and the relationship to a 
single lifting incident may not always be obvious (Berquist-Ullman and 
Larsson 1977, Ex. 26-933). Symptoms and physical findings depend on the 
location of the disc herniation and the degree of nerve compression.
    An understanding of disc biochemistry and biomechanics assists in 
the understanding of the pathogenesis of work-related lumbar disc 
disorders. For ethical reasons the majority of observations on spinal 
tolerance have been derived from cadaver spines. However, in vitro and 
in vivo comparisons appear to validate these conclusions. There is a 
wide biologic variation in human disc and end plate tolerances 
(Brinckmann et al., 1988, Ex. 26-1318) related to age, gender, 
genetics, prior injuries, and other factors. The maximum axial 
compressive force tolerated by the human cadaver lumbar spine has been 
measured by Brinckmann et al., 1988 (Ex. 26-1318) to range from 2.1 to 
8.8 kN (210 to 880 kg), with 30% fracturing at forces below 4 kN and 
63% fracturing below 6 kN. Adams and Hutton (1982, Ex. 26-1379) studied 
cadaver discs from male subjects aged 22 to 46 years. The authors 
determined that most specimens could withstand an average of 10 kN on 
single loading prior to failure, usually at the end plate. In contrast, 
Bartelink (1957, Ex. 26-349) noted that discs were fractured from 
forces ranging between 1.6 and 6.7 kN, with a mean of 3.1 kN. The wide 
inter-individual variation in tissue tolerance makes it difficult to 
assign a single value of compressive force against which to engineer 
jobs to prevent lumbar disc.
    When mechanical failure occurs, it is generally through the 
cartilage endplates (Adams and Hutton 1982, Ex. 26-1379; Armstrong 
1985, Ex. 26-1070; Brinckmann el al., 1988, Ex. 26-1318; Erdil, 
Dickerson, and Chaffin 1994, Ex. 26-424) Disc height, spinal position, 
and frequency of bending appear to be risk factors. Creep results in 
loss of disc height, increased contact between load-bearing surfaces of 
the facet joints, diminished capacity to dissipate forces, and 
decreased ability of the spinal column to tolerate loading (Kazarian 
1975, Ex. 26-379). Adams and Hutton (1982, Ex. 26-1379) observed 
maximal single loading tolerances of up to 10 kN; however, when the 
spines were flexed forward, 40% of discs prolapsed at an average of 
only 5.4 kN. Repeated lumbar spine loading can cause tissue fatigue 
with fracture at lower loads than the spine would tolerate for non-
repetitive loading. Adams and Hutton (1985, Ex. 26-1315) determined 
that when repetitive loading was simulated, previously healthy discs 
failed at an average of 3.8 kN.
    These studies support the clinical observation that the 
intervertebral disc is especially vulnerable when loaded in the flexed 
position or when subjected to repetitive loading. This becomes more 
significant when workers with lower tissue tolerance from prior injury, 
degenerative disc disease, or age lift at high rates for prolonged 
periods.
    Armstrong (1985, Ex. 22-877) noted that small microtears most often 
occur in the region of the posterior elements of the annulus fibrosus 
and cartilage end plates. As noted, these are the areas subject to the 
greatest spinal compressive forces (Gracovetsky and Farfan 1986, Ex. 
26-128; Hickey and Hukins 1980, Ex. 26-708; Pope et al.1991, Ex. 26-
1296). With repeated lumbar spinal stresses and/or injuries, 
progressive microfractures in cartilage end plates and annular fibers 
(annulus fibrosus) may develop in the intervertebral discs (initially 
toward the center of vertebral bodies). This causes altered metabolism 
and fluid transfer with different mechanical behavior of the disc.
    Eventually radial tears result in the development of degenerative 
disc disease and/or bulging. As a result of this damage, the capacity 
of the lumbar intervertebral discs to tolerate further compressive 
loads during lifting is altered. When these smaller tears extend and 
form complete annular tears, the nucleous pulposis can protrude (disc 
herniation) (Farfan et al. 1970, Ex. 26-113). Over time, sclerosis of 
cartilage endplates and altered disc loading can facilitate the 
development of facet arthropathy, osteophytic change, stenosis, or 
instability. Disc degeneration in combination with facet arthropathy 
may also lead to foraminal narrowing with resultant nerve compression 
and radicular pain. These observations are consistent with a cumulative 
trauma theory that could account for some types of low-back injuries 
and is supported by the research and opinions of other authorities 
(Erdil, Dickerson, and Chaffin 1994, Ex. 26-424; Pope et al. 1991, Ex. 
502-502; Yong-Hing and Kirkaldy-Willis 1983, Ex. 26-405).
    While many individuals with degenerative disc disease are 
asymptomatic, individuals with greater degrees of degeneration are at 
risk for low-back pain. In one study (Vanharanta et al. 1987, Ex. 26-
225) 90% of subjects with severe disc degeneration experienced pain 
during discography, while only 23% of those without disc degeneration 
reported pain.

Arthritis/Spondylosis

    Several studies have suggested a relationship between lumbar 
degenerative disease and work activities (e.g., heavy work, repetitive 
lifting, and vibration). This association has come from both 
radiographic and pathological evaluations in association with work 
histories. One difficulty in these evaluations is the observation that 
lumbar spine x-ray changes are common, occurring in about 40% of all 
low-back x-rays (Rowe 1983, Ex. 26-699). However, the relationship of 
many x-ray changes with symptoms of low-back pain is unclear (Andersson 
1981, Ex. 26-1480; Himmelstein et al. 1988, Ex. 26-962; Magora and 
Schwartz 1976, Ex. 26-389; Rowe 1963, Ex. 26-317; 1969, Ex. 26-318). 
Videman, Nurminen, and Troup (1990, Ex. 26-1023) noted an increase in 
vertebral osteophytosis in autopsy specimens from workers who performed 
heavy work. Of interest is that the heavier work exposures also were 
observed in association with increased rates of low-back disability.

[[<strong>Page</strong> 68483]]

    Riihimaki et al. (1991, Ex. 26-966) performed a radiographic study 
of the lumbar spine in concrete workers and house painters. Lateral 
lumbar x-rays were obtained in 216 concrete reinforcement workers and 
201 house painters aged 25 to 54 years. Disc space narrowing was noted 
10 years earlier and spondylophytes 5 years earlier in the concrete 
workers. Risk ratios for the univariate effect of occupation on disc 
space narrowing was 1.8, and for spondylophytes it was 1.6. Potential 
cofounders such as age, prior back accidents, body mass index, and 
smoking had minimal effect. The authors concluded that heavy physical 
work with materials handling and postural loading enhances the 
degenerative process of the lumbar spine.
    Wickstrom, Nummi, and Nurminen (1978, Ex. 26-1161) evaluated degree 
of lumbar flexion, presence of pain, and x-ray findings of degenerative 
disc disease in 295 concrete reinforcement workers aged 19 to 64 years. 
These workers commonly perform work involving spinal loading in stooped 
postures. Radiographic evidence of degenerative disc disease was noted 
in two-thirds of the 110 individuals with restricted flexion and in 
one-third of those (n=185) with normal flexion.
    Kirkaldy-Willis (1983, Ex. 26-431) described a pathophysiologic 
spectrum of changes that lead to the development of lumbar spine 
degenerative disease. In the first phase, there are early and mild 
changes in the posterior complex, with facet synovitis, joint effusion, 
capsular stretch, and thickening. Inflamed synovium may become 
entrapped in the joint between the cartilage surfaces and initiate 
cartilage damage. Meanwhile, the intervertebral disc develops some 
circumferential tears in the annulus fibrosus. Tears in the periphery 
have at least some potential to heal because of the proximity to 
vascularity, but these deeper tears lack this ability by virtue of 
their distance from blood flow or metabolic diffusion. As these 
circumferential tears enlarge, they develop into large radial tears. As 
a result, the nucleus pulposus begins to lose proteoglycan and exhibits 
structural changes with grade 1 or 2 degenerative disc disease. Loss of 
water and disc height as well as a decline in annular resistance can 
cause increased compression forces on the facets. Individuals may be 
asymptomatic or have vague low-back pain. However, due to the lack of 
nociceptors in the disc and facet joints (except the synovium), a 
significant degree of degenerative disease may occur before pain 
develops. Lumbar disc herniation may occur at this juncture with 
symptoms and signs or radiculopathy.
    In the next phase, the posterior joint capsule and annulus fibrosus 
develops laxity and instability. The intervertebral disc progresses to 
grade 2 or 3 degenerative disease. It may be possible to detect 
instability on dynamic x-rays. Subperiosteal bone formation, 
calcification of the ligaments, and capsular fibers manifest as 
peripheral osteophytes and traction spurs (Dupuis 1987, Ex. 26-1299) in 
an attempt to stabilize the motion complex (MacNab 1977, Ex. 26-1367). 
If laxity predominates over repair processes, the degenerative 
spondylolisthesis (facet laxity) or retrolisthesis (disc laxity) may 
occur (Dupuis et al. 1985, Ex. 26-108).
    In the final phase, there is fibrosis of the posterior facet 
joints, loss of disc material (grade 3 or 4 degenerative disc disease), 
and progressive osteophyte formation (Wedge 1983, Ex. 26-1035). This 
increases the load-bearing surface of the three-disc complex, although 
it decreases motion and results in increased stiffness. The repair 
process may create narrowing of the central canal (central spinal 
stenosis) from facet arthropathy, disc bulging, and hypertrophy of the 
ligamentum flavum. Lateral stenosis may also result from facet 
arthropathy and osteophyte formation adjacent to the neuroforamina. 
Spinal stenosis is a diagnostic entity that has only recently been 
described. A few patients have congenitally small spinal canals; 
however, most present with this type of acquired spinal stenosis 
secondary to longstanding degenerative disease. Most patients first 
become symptomatic after 50 years of age (Turner et al. 1992, Ex. 26-
1455). By virtue of its long-term degenerative nature, spinal stenosis 
is not often considered a work-related disorder; however, patients with 
spinal stenosis may present with co-existing lumbar disc herniation or 
other degenerative changes that have been exacerbated by work factors.

Conclusions

    OSHA finds convincing evidence from the confluence of many 
investigation on biomechanical models, laboratory research and 
epidemiology studies that work related risk factors including (1) heavy 
physical work, (2) lifting and forceful movements, (3) bending, 
twisting and awkward positions, and (4) static work positions are 
causally linked to low back disorders and pain. Work often involves 
several of these risk factors concurrently and there is evidence that 
the first three of these factors may act together in a synergistic way 
to increase the risk. However, OSHA considers that each factor, by 
itself, can increase the risk of back disorder.

F. Disorders of the Lower Extremities

    Work-related disorders of the lower extremities have not received 
the same scrutiny as those of the upper extremities and back. However, 
existing information from pathophysiology, epidemiological studies, and 
biomechanical investigations implicate physical work factors related to 
repetitive, forceful exertion and awkward posture to these disorders, 
especially osteoarthritis of the knee and hip. As more completely 
described in Health Effects Appendix III.D (Ex. 27-1), osteoarthritis 
is considered a disorder of the movable joints characterized by the 
disintegration of the articular cartilage that covers the end of the 
bones. The articular cartilage and subchondral bone that lies just 
beneath the cartilage provide opposing structures and surfaces that are 
matched in such a way as to allow transmission of joint loads at the 
lowest and most uniform pressures, (Meisel 1984, Ex. 26-1562).
    The arthrosis process is thought to begin with disruption at the 
thin surface overlying the load-bearing cartilage (Meisel, 1984, Ex. 
26-1562). This disruption results in progressive erosion of the 
cartilage layer and a joint surface less able to withstand normal loads 
and forces. Continual loading on the joint then disrupts the process of 
bone/cartilage repair and regeneration, leading to formation of 
marginal bone in the shape of spurs (osteophytes). The degenerative 
process continues until the cartilage has been completely destroyed; 
there is bone-on-bone contact, and the structural integrity of the 
joint is lost. The clinical manifestations are joint stiffening, pain 
and loss of movement (Meisel 1984, Ex. 26-1562).
    It is well recognized that acute trauma can trigger osteoarthritis, 
but there is also evidence that less substantial, but repetitive, 
forces to the joints can lead to microfractures of the articular 
cartilage and subchondral bone. The disruption in structural integrity 
results in the onset of the degenerative changes described above (Radin 
et al., 1994, Ex. 26-578). This process has been observed in animals 
subjected to repetitive impact loading of one or more limbs (Moskowitz, 
1992, Ex. 26-1547). Damage to the joints in these animals involve 
fibrillation and splitting of the cartilage, evidence of chondrocyte 
activity as bone remodeling occurs, progressive erosion of the 
cartilaginous layer, and formation of osteophytes.

[[<strong>Page</strong> 68484]]

    Other MSDs of the lower extremity that may be caused by physical 
work-related factors include bursitis and tarsal tunnel syndrome. Joint 
overuse may lead to bursitis, an inflammation of a fluid-filled sac or 
sac-like cavity that serves to reduce friction in a joint (Ex. 502-
317). Repetitive use of the foot may be related to tarsal tunnel 
syndrome, a nerve entrapment syndrome of the lower extremity analogous 
to carpal tunnel syndrome in the wrists (Day 1996, Ex. 26-615).
    In addition to acute and repetitive trauma, MSDs of the lower 
extremities have been linked with congenital abnormalities, underlying 
genetic or metabolic disorders, and chronic conditions, such as cancer, 
diabetes and collagen-vascular disease (Felson 1994, Ex. 26-544; Meisel 
1984, Ex. 26-1562).

Epidemiological Evidence

    Epidemiological evidence of an association between workplace 
factors and MSDs of the lower extremities was discussed in Health 
Effects Appendix I. A summary of the risk factors is presented in Table 
C-1 (for osteoarthritis of the knee) and Table C-3 (for the hip). 
Several work-related activities, such as squatting and kneeling for 
more than 30 minutes per day, were significantly associated 
(OR<gr-thn-eq>3) with osteoarthritis of the knee in a population-based 
case-control study (Cooper et al., 1994, Ex. 26-460). This study also 
showed that a combination of these activities along with lifting loads 
greater than 25 kg (which places an additional load on the lower 
extremities) resulted in an even stronger association (OR<gr-thn-eq>5) 
with this knee disorder. Other epidemiological studies associated 
occupations such as construction work, farming, firefighting, laundry/
dry cleaning, and manual labor, with knee osteoarthritis (Anderson and 
Felson, 1988, Ex.26-926; Vinguard et al., 1991, Ex. 26-1500).
    Three case-control studies reported positive associations between 
MSDs of the hip and work tasks involving biomechanical factors (Coggon 
et al., 1998, Ex. 26-1285; Croft et al., 1992, Ex. 26-1503; Vinguard et 
al., 1997, Ex. 26-1617). One study found that jobs requiring lifting 
over 25 kg more than ten times in an average week for more than 20 
years raised the odds of developing hip osteoarthritis (Ex. 26-1285). 
Farmers, mail carriers, firefighters, and meat processors were 
occupations reported to be significantly associated with hip 
osteoarthritis in a registry-based cohort study (Ex. 26-400). 
Repetitive kneeling, squatting, and lifting are all activities 
involving the biomechanical risk factors of repetition, forceful 
exertion, and awkward postures of the lower joints. Table V-8 
summarizes some key aspects of these investigations, including: 
Occupations examined; biomechanical risk factors involved; whether or 
not exposures were directly observed during the study, whether the 
health outcomes were verified by medical tests, whether evidence 
provided of an exposure-response or other temporal relationship between 
the risk factor and outcome; and the measure of relative risk used 
along with the results of this measure.
    In addition to the evidence previously reviewed, Table V-8 includes 
five additional studies submitted to the docket that address physical 
work factors and disorders of the lower joints, primarily the knee (Ex. 
500-41-114; Ex. 500-121-44; Ex. 500-41-69; Ex. 502-317; Ex. 500-41-68; 
Ex. 500-121-18. Three of the studies examined the prevalence of knee 
disorders among carpet- and floorlayers who spend a substantial amount 
of time working in knee straining postures. Kivimaki (1992, Ex. 500-41-
78) compared 96 floor- and carpetlayers to 72 painters with regard to 
disorders of the knee. An analysis of videotaped work tasks indicated 
that floor- and carpetlayers assume a kneeling posture in their job 42% 
of their work time, compared to 3% of work time by painters. 
Ultrasonographic examination indicated changes in the prepatellar or 
superficial infrapatellar bursa in 49% of the carpet and floor layers 
compared to 7% of painters. On a symptom questionnaire, the floor- and 
carpetlayers reported a significantly greater prevalence of bursitis in 
front of the knee cap, knee pain in a kneeling posture, sudden and 
intense swelling of the knee, aspirations of the knee, and injections 
to the knee than painters.

                                   Table V-8.--Summary of Epidemiology Studies Examining MSDs of the Lower Extremities
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                               Diagnosis/body                         Risk measure (95%
              Study                 Job type studied   Physical factors    Exposure basis           part          Other attributes          CI)\1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
 Kivimaki (1992) Ex. 500-41-78..  carpet laying;       F/R/P             observation         questionnaire                           NR*
                                   floor laying.                          questionnaire.      ultrasound/knee.
Jensen (1997) Ex. 500-41-69.....  carpet laying;       F/R/P             questionnaire       questionnaire        exposure response  OR=1.5-6.4*
                                   carpentry.                             observation.        radiology/knee.                        (3.2-8.9)
Tanaka (1986) Ex. 502-317.......  floor laying; tile   F/R/P             questionnaire.....  questionnaire knee  exposure response.  PRR=1.1-5.0*
                                   setting.                                                                                          (3.2-7.8)
Sandmark (2000) Ex. 500-41-114..  prosthetic knee      F/R/P             questionnaire.....  surgery/knee......  exposure response.  OR=0.7-3.2*
                                   patients.                                                                                         (2.0-5.2)
Cooper (1994) Ex. 26-460........  general population.  F/R/P             questionnaire.....  questionnaire X-                        OR=0.8-6.9*
                                                                                              ray/knee.                              (1.8-26.4)
Anderson (1988) Ex. 26-926......  general population.  F?/R/P            job title           questionnaire X-                        OR=0.8-3.5*
                                                                          questionnaire.      ray/knee.                              (1.2-10.5)
Vingard (1991) Ex. 26-1400......  various occupations  F/R?/P?           job title.........  hospitalization                         RR=0.6-3.8*
                                                                                              knee or hip.                           (1,2-12.1)
Coggon (1998) Ex. 26-1285.......  patients case/       F/R/P?            questionnaire.....   hip replacement..                      OR=1.0-2.1*
                                   control.                                                                                          (1.1-3.9)
Croft (1992) Ex. 26-1503........  patients case/       F/R?/P?           questionnaire job   joint measurement/                      OR=0.8-2.5
                                   control.                               title.              hip.                                   (1.1-5.7)
Vingard (1997) Ex. 26-1617......  patients case/       F/R/P?            questionnaire.....  hip replacement...                      RR=0.8-2.3*
                                   control.                                                                                          (1.5-3.6)
De Zwart (1997) Ex. 500-121-18..  Various occupations  F/R/P             job title.........  questionnaire       temporal            NR*
                                                                                              lower limbs.        relationship.
--------------------------------------------------------------------------------------------------------------------------------------------------------
F=forceful exertions; R=repetitive motion; P=awkward posture; ?=presence of risk factor unclear;
RR=relative risk; OR=odds ratio; PRR=prevalence rate ratio
*=p0.05

[[<strong>Page</strong> 68485]]

\1\ 95% confidence interval expressed for the upper end of the risk measure range.

    Jensen et al. (1997, Ex. 500-41-69) conducted a larger cross-
sectional study of knee disorders among current and former floor- and 
carpetlayers (N=133), carpenters (N=506), and compositors (N=327). 
Based on telephone interviews and video recording of work activities, 
the authors determined that floor- and carpetlayers spent 56% of their 
working time in knee-straining postures. Carpenters were reported to 
have spent 25% of their working time in such postures, while 
compositors did not spend any working time in knee-straining positions.
    Response to a questionnaire revealed that carpenters experienced a 
significantly increased frequency of knee complaints within the last 12 
months (OR=3.8, 95% CI: 2.7-5.5), within the last seven days (OR=3.6, 
95% CI: 2.3-5.8), and for more than 30 days over the preceding 12 
months (OR=2.5, 95% CI: 1.6-3.9) when compared to compositors. Floor- 
and carpetlayers, the highest exposed group, also reported a 
significantly increased frequency of knee complaints within the last 12 
months (OR=6.4, 95% CI: 4.0-10.1), within the last seven days (OR=5.7, 
95% CI: 3.3-10.1), and for more than 30 days over the preceding 12 
months (OR=5.3, 95% CI: 3.1-8.9) when compared to compositors; the odds 
ratios reported for floor- and carpetlayers were uniformly higher than 
those reported for carpenters. Age, weight, body mass index, smoking, 
and sports activities were reported to have had no significant effect 
on the incidence of knee complaints. Among 50 floor- and carpetlayers, 
51 carpenters, and 49 compositors who had radiological examinations of 
their knees, an increased prevalence of osteoarthritis was found in 
floor- and carpetlayers (14%) when compared to carpenters (8%) and 
compositors (6%).
    A third cross-sectional study involving floorlayers by Tanaka et 
al. (1986, Ex. 502-317), and also reported by Thun et al. (1987, Ex. 
26-60), examined the relationship between work activities involving 
strain on the knees and the development of knee disorders. Floorlayers 
(N=112) and tilesetters (N=42) who reported frequent kneeling in a 
survey questionnaire were compared to a group millwrights, bricklayers, 
and decorators (N=243) who did not commonly kneel.
    The floorlayers reported more frequent bursitis of the knee (20% 
vs. 6%) and more needle aspirations of knee fluid (32% vs. 6%) than the 
millwrights and bricklayers. Tilesetters also reported bursitis (11%) 
and knee aspirations (31%) in excess of those reported by millwrights 
and bricklayers.
    In this study questionnaire responses were compared to responses 
given by a representative sample of white males to standardized 
questions about symptoms of knee disease. When compared to sample, 
floorlayers, tilesetters, and millwright and bricklayers all reported a 
higher age-adjusted prevalence for each of the seven symptoms than the 
sample. This result suggests that the relative risk of knee disorders 
in the highly exposed groups may be understated when millwrights and 
bricklayers are the reference group since they may, themselves, be at 
increased risk relative to the general population.
    Physical examination that included radiological tests of a subset 
of the workers was performed to validate the questionnaire. The 
questionnaire was reported to show low sensitivity (38-44%), but 
moderate specificity (82-89%), for both bursitis and arthritis.
    Other studies examined the relationship between lower limb MSDs and 
physical work factors in more diverse occupational settings. Using a 
case-control study design, Sandmark et al. (2000, Ex. 500-41-114) 
compared individuals who had received prosthetic knee replacements due 
to osteoarthritis to control subjects to examine the relationship 
between lifetime physical load from work and the risk of knee 
osteoarthritis. A total of 625 individuals who had received prosthetic 
knee replacements due to osteoarthritis, and who were between the ages 
of 55 and 70 at the time of surgery were compared to 548 age- and 
gender-matched individuals randomly selected from the population of the 
same geographical area who had not reported osteoarthritis or other 
dysfunction of the knee.
    Through telephone interview and written questionnaire, the subjects 
provided information on workloads from occupational and non-
occupational activities, personal characteristics, and general health 
status. The duration and frequency of activities (e.g., kneeling, 
sitting, number of stairs climbed) were computed for each individual. 
Subjects were then divided into three exposure groups: No or low 
exposure comprising the lower quartile; medium exposure comprising the 
middle two quartiles; and high exposure consisting of the top quartile.
    Analysis of the data revealed that, among men, lifting at work 
(OR=3.0, 95% CI: 1.6-5.5), squatting or knee bending (OR=2.9, 95% CI: 
1.7-4.9), kneeling (OR=2.1, 95% CI: 1.4-3.3), and jumping (OR=2.7, 95% 
CI: 1.7-4.1) were significantly associated with osteoarthritis of the 
knee. Individuals who had spent ten or more years in an occupation 
considered to involve high physical load on the knee were also more 
likely to undergo knee replacement due to osteoarthritis than those who 
had not worked in such occupations (men, OR: 2.5, 95% CI 1.7-3.6; 
women, OR: 2.5, 95% CI: 1.6-3.9). The analysis controlled for 
confounders such as age, body mass index, smoking, and sports 
activities.
    The findings of Sandmark et al. (Ex. 500-41-114), Jensen et al. 
(Ex. 500-41-69) and Tanaka et al. (Ex. 502-317) indicate an exposure--
response relationship between the frequency of work involving strain to 
the knees and osteoarthritis, bursitis and other signs of injury to 
this joint.
    In a longitudinal survey study, de Zwart et al. (1997) (Ex. 500-
121-18) investigated changes in musculoskeletal complaints among 
workers performing mentally demanding work (N=4686) and heavy physical 
work (N=7324). Job demands were determined by occupational title. 
Mentally demanding work was described as sedentary, while heavy 
physical work involved tasks such as lifting heavy objects, handling 
heavy tools, and stooping in combination with standing or walking. The 
subject groups were stratified by age (20-9, 30-9, 40-9, 50-9 years 
old). The occurrence of musculoskeletal complaints were compared 
between two surveys having a mean interval of approximately four years. 
No physical examination or examination of medical records was 
performed.
    The incidence of musculoskeletal complaints of the lower limbs on 
the second survey was higher among those who had not reported 
complaints on the first survey for all age groups. However, the 
incidence was only statistically significant for the youngest three age 
groups. The authors concluded that younger and middle-aged employees 
develop musculoskeletal complaints as a result of exposure to heavy 
physical work, and that a healthy worker effect served to mask this 
effect for the oldest age group. Because of its prospective design, 
this investigation provides a temporal link between MSDs of the lower 
extremities and heavy physical work.
    Lemasters et al. (1998) (Ex. 500-121-44) examined the prevalence 
and risk factors for work-related MSDs among carpenters. (N=522) who 
completed a

[[<strong>Page</strong> 68486]]

questionnaire on musculoskeletal symptoms, work history, and 
psycholsocial factors. The symptom questions assessed if they 
experienced pain, numbness, or tingling in a particular body region.
    Generally, as duration of employment increased, the prevalence of 
symptoms increased. An adjusted logistic regression analysis showed 
that duration of employment in carpentry for at least 20 years was 
significantly associated with work-related MSDs of the knees (OR: 3.5, 
95% CI: 1.3-9.2). Carpenters who indicated they felt exhausted at the 
end of day experienced significant increases of work-related MSDs of 
the knees (OR: 1.8, 95% CI: 1.1-3.1). Having minimal influence over 
their work schedule was also reported to be a risk factor for work-
related MSDs of the knees (OR: 2.3, 95% CI:1.2-4.1).
    A subset of the subject group received a physical examination 
including examination of the knees. The authors concluded that reported 
disorders, including those of the knee, were significantly associated 
with positive findings upon physical examination.
    An examination of the reliability of questionnaire responses was 
performed by Booth-Jones et al. (1998) (Ex. 500-121-9). Ten percent of 
the subjects examined by Lemasters et al. (1998) (Ex. 500-121-44) were 
subsequently randomly selected and administered the original 
questionnaire for a second time. All positive responses were 
categorized as ``yes'' answers and all other responses were categorized 
as ``no'' responses. Comparison of the results of the first and second 
administrations of the test indicated that the responses were largely 
consistent, with overall agreement reported to be 85.6%. This result 
provides a strong indication that the questionnaire responses examined 
by Lemasters et al. (1998, Ex. 500-121-9) are a reliable representation 
of the recollections of the subjects examined.
    A significant concern when evaluating studies in which exposure 
measurements and health outcome are based on self-reports is the 
possibility of recall bias. Among the studies pertaining to the lower 
extremities that are described here, those of Sandmark et al. (Ex. 500-
41-114), Jensen et al. (Ex. 500-41-69), Tanaka et al. (Ex. 502-317), 
and Lemasters et al. (Ex. 500-121-44) each depend to a greater or 
lesser extent upon the accuracy of self-reported exposures to ergonomic 
risk factors. Such self-reports have been criticized as being 
unreliable (Exs. 30-276, 500-118). Evidence submitted to the docket 
regarding the studies discussed above, while not eliminating concerns 
about the reliability of self-reports, generally support their 
accuracy.
    The validity of self-reporting as a means of measuring knee-
straining work postures was examined by Jensen et al. 2000, Ex. 500-41-
68). Self-reports were compared to timed video recordings for 39 
carpenters and 33 floorlayers. The carpenters and floorlayers were 
videotaped while working and, then immediately afterwards were 
requested to estimate the amount of time spent in knee-straining 
postures. A close association was reported between the observed and 
self-reported durations (Spearman's correlation coefficient: 0.88). 
While this report provides evidence that immediate self-reports are 
largely accurate, recall bias associated with self-reports of 
historical work activities remains a concern.

Biomechanical Evidence

    Bhattacharya et al. (1985, Ex. 502-270) examined the biomechanical 
forces associated with different working postures involved in carpet 
installation when using a knee kicker. The knee kicker is a device 
consisting of a plate with a set of teeth in one end that grips the 
carpet while an installer kicks the padded end with a knee to stretch 
the carpet. A job analysis indicated that carpet installers spend 
approximately 75% of their time in a kneeling position, and use the 
knee kicker an average of 141 times per hour. Postures were reported to 
require near-maximum knee flexion. Knee-flexion angles at impact 
averaged about 58 deg., while normal daily activities involve less 
flexion (e.g., sitting, 87 deg.; tying shoe laces, 74 deg.; walking 
upstairs, 97 deg.). Workers performing the heaviest of the knee kicks 
produced peak impact forces averaging over 3000 newtons, equivalent to 
approximately four times their body weight. The authors suggested that 
the biomechanical demands of installing carpet may be responsible for 
the high incidence of knee disorders among these workers.

Conclusion

    OSHA concludes that strong evidence is available showing that 
steoarthritis of the knee and other MSDs of the lower extremities can 
result from exposure to the combined physical work-related factors of 
repetition, force, and awkward posture. This evidence comes from the 
consistently positive associations in epidemiological studies of 
carpet- and floorlayers who spend considerable amounts of time in knee-
straining postures. Biomechanical evidence indicates knee flexion and 
impact forces can be substantial during installation of carpet. Other 
occupational activities that involve excessive squatting, kneeling, and 
climbing stairs have also been shown to be associated with 
osteoarthritis of the knee and hip. Some studies indicate an exposure--
response or temporal relationship between physical risk factor and 
health outcome. Therefore, it is biologically plaucible that repetitive 
impact loading on the joints is consistent with the degenerative 
pathophysiology of osteoarthritis. OSHA concludes that the evidence 
reviewed in this section demonstrates that workers who perform job 
tasks requiring repeated forceful flexion of the knee or other joints 
of the lower extremities are at increased risk of serious 
musculoskeletal impairment such as osteoarthritis.

G. OSHA's Response to Health Effects Issues Raised in the Rulemaking

1. Comments on OSHA's Use of the NIOSH (1997) and NAS (1999) Reviews
    Several commenters (Ex. 30-1722; Ex. 500-109; Ex. 32-368-1; Ex. 32-
241-4; Ex. 500-197) criticized OSHA's reliance on the 1997 NIOSH review 
(Ex. 26-1) and the 1999 NAS report (Ex. 26-37) of the evidence for 
work-related MSDs. First, the commenters considered the methodology 
used by NIOSH to evaluate the epidemiological evidence that work-
related factors were associated with MSDs to be seriously flawed. 
Second, they accused OSHA of ignoring obvious limitations of the NIOSH 
review and then misrepresenting its conclusions. Finally, the 
commenters claimed that the NAS workshop report did not support the 
OSHA position with regard to biomechanical risk factors and MSDs. A 
more detailed description of each assertion will follow along with 
OSHA's response.
    The criticisms of the NIOSH methodology were aimed at nearly every 
level of evaluation. It was said that NIOSH exercised a ``publication 
bias in favor of positive studies'' in its study selection (Ex. 500-
197, pg. I-146). It was said that the NIOSH criteria used to assess 
study quality ``emphasize[d] biased and unreliable methodology at the 
expense of sound scientific approaches.'' (Ex. 32-241-4, pg. 109). It 
was said that there was ``no indication of any systematic method for 
assigning weight,'' (Id. pg. 109), and that the weighting could not be 
``replicated and, therefore fails to satisfy one of the most basic 
tenets of scientific inquiry.'' (Ex. 23-109, pg. 23). It was said that 
NIOSH ``failed to adequately consider other confounding factors in 
their analysis'' (Ex. 32-368-1, pg. 40). Finally, it was said that 
NIOSH was ``forced to draw its conclusions from a larger body of

[[<strong>Page</strong> 68487]]

literature that included studies meeting only some, or even none of 
these criteria.'' (Ex. 500-197, pg. I-148). One commenter summed up the 
NIOSH evaluation process as follows:

    The report did not conform to the generally accepted scientific 
methods for critical analysis. It did not use a weight of the 
evidence approach. For example, there is no explanation of how 
studies which met NIOSH's criteria standards were regarded 
differently than studies which did not. In essence, NIOSH put the 
2000 studies into a black box, and out popped 600. Then the 600 went 
into another black box, and out popped the conclusions (Ex. 32-368-
1, pg. 36-37).

    OSHA strongly disagrees that the approach used by NIOSH to evaluate 
the epidemiological studies was flawed or that the conclusions in the 
1997 review are weakly supported by the evidence. In the first chapter 
of its report, NIOSH describes, in detail, where it retrieved 
information on epidemiological studies, how studies were selected for 
more detailed review, the procedure used to analyze the overall 
strength of work-relatedness, the six criteria (strength of 
association, consistency, temporality, exposure-response, coherence, 
and role of confounders) employed to evaluate the evidence of 
causality, and the four categories to classify the evidence. The 600 
studies reviewed by NIOSH [out of more than 2,000 identified in initial 
database searches] were published or accepted for publication in the 
scientific literature or government reports that had undergone peer 
review and were widely available. These had to meet some minimum 
requirement in terms of defined study groups, measurable health 
outcomes, identifiable exposures related to physical factors, and 
adequate study design. The NIOSH selection strategy was a common 
screening approach that has been successfully employed by OSHA and many 
other groups. There was no bias toward the selection of positive 
studies; rather NIOSH selected those only studies that met the above 
criteria. OSHA believes that the NIOSH selection process captured the 
best epidemiological studies available at the time on which to evaluate 
the evidence for a causal association between work-related risk factors 
and MSDs.
    NIOSH analyzed the reviewed studies in terms of well-accepted 
epidemiological principles, such as participation rate, blinded study 
design, exposure method, and case definition and gave greater weight in 
its evaluation process to those that minimized selection and 
observation bias and confirmed the existence of exposure and health 
outcome by qualified experts. NIOSH applied the highly-regarded 
Bradford Hill criteria (see six criteria above) for judging the 
evidence for causation in classifying work-relatedness. These criteria 
were not applied to any single investigation but to the entire database 
of studies as a whole. NIOSH judged there was evidence of work-
relatedness between biomechanical factors and MSDs when there existed 
convincing evidence from several studies for a causal relationship 
using the epidemiologic criteria, and for which chance, bias, and 
confounding factors were not the likely explanation. OSHA believes that 
NIOSH clearly did not use a ``flawed'' methodology and their evaluation 
process represents a systematic weight of evidence approach that relies 
on an unbiased set of sound and reliable scientific principles.
    NIOSH concluded there was evidence that MSDs of the neck, shoulder, 
upper extremities, and back that have been subjected to epidemiological 
investigation were associated with at least some biomechanical factors 
or combination of factors. In several instances, the evidence was 
judged to be strong. For most MSDs, there were situations in which the 
epidemiological evidence was judged insufficient for certain 
biomechanical factors in isolation (e.g. CTS and extreme posture; 
epicondylitis and repetitive motion). However, these factors were 
usually found to be associated with the MSD when present in combination 
with other biomechanical factors (e.g. strong evidence of posture/force 
combination and CTS; strong evidence of repetition/force and 
epicondylitis). For several MSDs, OSHA found that the strength and 
consistency of the associations between biomechanical factors and MSDs 
was even stronger, if the evaluation was restricted to studies where 
exposure was directly observed or measured and the health outcome was 
confirmed by physical exam or medical tests (see Health Effects Section 
V). It is important to note that the NIOSH analysis focused primarily 
on the epidemiological evidence. OSHA believes these conclusions were 
reasonable and based on the selected evaluation criteria.
    Since the evaluation process involved expert judgment, weighting of 
individual studies cannot be precisely ``replicated'' in the same way 
as a scientific measurement, however, substantial evidence in the 
rulemaking record supports NIOSH's conclusions. There were a number of 
written submissions and oral testimony from scientific experts 
supporting the position that sufficient evidence exists that 
biomechanical factors can increase the risk of MSDs (e.g., Exs. 30-
3805, 32-57, Tr. 9819, 16317, 17358, 17687). Some notable testimony on 
the epidemiological evidence from distinguished experts were as 
follows:

    There is a significant body of epidemiological and case study 
literature that indicate that a high rate of work-related MSDs, 
carpal tunnel syndrome, bursitis, tendinitis, and epicondylitis are 
significantly higher in jobs that involve repetitive motions, 
localized stress, awkward positions, vibrations, and forceful 
exertions.

Dr. Robert McCunney (Tr. 17566-67)

    OSHA's conclusion that there is an epidemiological evidence of 
an association between many work factors and certain MSDs is 
consistent with the literature that I've read and my clinical 
experience as an occupational medicine physician treating thousands 
of patients with MSDs over the past 20 years.

Dr. Michael Erdil (Tr. 1112)

    We have, first of all, lots of epidemiological studies that show 
physical factors are involved in MSDs. We have actually no 
epidemiological study that shows, that proves there is no physical 
factor involved.

Dr. Niklas Krause (Tr. 1367)

    Some commenters thought that OSHA misrepresented the findings from 
the NIOSH review in order to support its own conclusions that exposure 
to work-related biomechanical factors increase the risk of serious 
musculoskeletal impairment. It was claimed that OSHA had seriously 
overstated the NIOSH conclusions as ``having established causation'' 
(Ex. 32-241-4, pg. 98) between biomechanical factors and MSDs 
regardless of the length and intensity of exposure, instead of the true 
NIOSH goal of drawing conclusions about the evidence of an association 
between risk factor and health outcome under conditions of prolonged 
exposure. Commenters argued that OSHA ignored the restricted scope of 
the NIOSH analysis that was limited to ``certain objectively defined 
MSDs'' and ``examined only certain very specific stressors of highly 
repetitive and forceful work, lifting and forceful movements, awkward 
and prolonged sustained postures and exposure to vibration.'' (Ex. 500-
109, pg. 24). On the other hand, it was claimed that OSHA used the 
NIOSH findings to ``support causal inferences for all other MSDs * * * 
which include not only those MSDs studied by NIOSH but also 
DeQuervain's disease, trigger finger, Raynaud's syndrome and tarsal 
tunnel syndrome'' and ``attempts to broaden the NIOSH exposure 
associations to include not only the factors that NIOSH studied, but 
also a wide range of other so-called ergonomic risk factors including 
among others, contact stress and cold temperatures.'' (Ex. 30-1722, pg. 
43).

[[<strong>Page</strong> 68488]]

    OSHA does not agree that the findings of the 1997 NIOSH review have 
been misrepresented in any way. The Agency has not stated that the 
epidemiological evidence established that MSDs are caused by exposure 
to work-related biomechanical factors. Epidemiological studies rarely, 
if ever, prove causation. They are designed to identify associations 
between two study variables. Depending on the strength and consistency 
of the associations and whether the association shows aspects of 
temporality and exposure-response, epidemiological data can provide 
evidence of a causal relationship. OSHA has stated that there is 
convincing scientific evidence that biomechanical factors, usually in 
combination, increase the risk of several specific MSDs. These 
conclusions are often based, not on epidemiological studies alone, but 
also on the pathophysiology of the disorder and biomechanical and 
psychophysical research that are able to link ergonomic risk factors to 
biomechanical and subjective measurements under a more controlled set 
of simulated work conditions.
    In general, the conclusions drawn by OSHA based on the entire body 
of scientific evidence track closely with those of NIOSH. OSHA does not 
stretch the NIOSH findings ``far beyond the breaking point'' to support 
causal inferences of the existence of vast numbers of MSDs that are not 
examined by the epidemiological studies (Ex. 30-1722, pg. 44). For 
example, DeQuervain's disease and trigger finger are forms of hand 
tendinitis specifically examined in epidemiological studies (Ex. 26-48; 
Ex. 26-53; Ex. 26-897) relied on by NIOSH to conclude evidence of an 
association between repetition, force, and awkward posture and hand/
wrist tendinitis. In fact, NIOSH states in its review that 
``DeQuervain's disease and other tenosynovitis of the hand, wrist, and 
forearm have been associated for decades with repetitive and forceful 
hand activities as one of the possible causal factors.'' (Ex. 26-1, pg. 
5b-8).
    The other two MSDs cited as not being supported by NIOSH findings 
are Raynaud's phenomenon and tarsal tunnel syndrome (TTS). Raynaud's 
phenomenon refers to blanching of one or several fingers and is a 
characteristic sign of vascular damage that occurs in Hand-Arm 
Vibration Syndrome (HAVS) due to segmental vibration (Ex. 502-18). 
NIOSH concluded that there was strong evidence of a positive 
association between segmental vibration and the vascular symptoms of 
HAVS. TTS is an MSD of the foot and, therefore, was not addressed in 
the NIOSH review. However, it is a nerve impingement disorder analogous 
to CTS in the wrist. Like the carpal tunnel, the tarsal tunnel is a 
relatively ``tight'' compartment filled with flexor tendons and the 
tibial nerve that may be susceptible to compression in response to 
increases in intra-tarsal pressure as a result of repeated flexion/
extension of the ankle.
    In the Final Rule, OSHA does not broaden the set of biomechanical 
risk factors associated with MSDs beyond the four (force, repetition, 
posture, and vibration) supported by the 1997 NIOSH review (contact 
stress, which is covered by the standard, is a particular combination 
of force and repetition). Although OSHA believes that evidence exists 
that cold temperatures can aggravate some MSDs, this environmental 
factor principally operates to modify exposure to some of the 
biomechanical factors listed above and is not regarded as a primary 
risk factor. OSHA included contact stress in the final rule's Basic 
Screening Tool because there is reasonable evidence that repeated 
impact, such as hand hammering, increases the risk of the MSD known as 
hypothenar hammer syndrome (see Part D of the Health Effects section). 
In addition, repetitive knee hammering has been shown to be associated 
with a high risk of bursitis (``carpet layers knee'') (see Part F of 
Health Effects section). The final rule makes clear that it is 
prolonged and regular exposure to a combination of biomechanical work 
factors that presents the greatest potential hazard.
    It should also be noted that workplace intervention is not required 
by the ergonomic standard unless there is an MSD incident that the 
employer has determined to be work-related and there is evidence of 
exposure to the biomechanical risk factors defined by the OSHA basic 
screening tool. This action trigger serves to limit the number of 
stressors and disorders that require action under the OSHA rule.
    For the above reasons, OSHA finds that its conclusions with regard 
to work-related biomechanical factors and risk of MSDs do not 
misrepresent, but are entirely consistent with, the findings in the 
1997 NIOSH review. This view was confirmed by written testimony from 
the Director of NIOSH, Linda Rosenstock:

    OSHA builds on the evidence of the association between workplace 
risk factors and the development of MSDs provided in the 1997 NIOSH 
review and strengthens the evidence with the supporting data 
provided by laboratory and psychophysical studies * * * NIOSH 
concurs with OSHA's conclusion from the discussion of the evidence 
from the epidemiological studies. OSHA concludes that ``In sum, 
although not all of the epidemiological studies reviewed demonstrate 
significant associations, the overwhelming majority justify a 
conclusion that the risk factors noted in this section, with effects 
adjusted by the four modifying factors, cause or exacerbate work-
related MSDs.'' Thus the data justify the conclusion that these 
factors cause or exacerbate work-related MSDs (Ex. 32-450-1, pg. 7-
8)

    The commenters also claimed that OSHA misrepresented the findings 
of the NAS workshop and that the conclusions in their 1999 report 
``simply do not support OSHA's broad conclusions linking physical work-
related factors to musculoskeletal complaints.'' (Ex. 32-241-4, pg. 
117). They allege numerous inadequacies of the workshop, such as the 
fact that the participants included ``only a few scientists who 
seriously questioned OSHA's ergonomic hypothesis'' (Ex. 32-368-1, pg. 
33). Despite this, the workshop participants supposedly seriously 
questioned the NIOSH study and, unlike OSHA, ``admitted that the 
evidence of a link between MSDs and physical risk factors at the 
workplace is inconclusive at best,'' (Ex. 32-241-1, pg. 118). This led 
one NAS panelist, Dr. Howard Sandler, to state ``that the NIOSH 
approach to their review of the evidence was sufficiently flawed to 
make the conclusions questionable.'' (Ex. 32-241-4, p. 112). Presumably 
the NAS report ``actually undermines OSHA's decision to limit its 
analysis to physical, work-related factors'' since it cites 
``individual, organizational, and social factors * * * which are 
possible influences on physiological pathways that lead from soft 
tissue to impairment and disability.'' (Ex. 32-241-4, p. 118 ). The 
argument for the OSHA misrepresentation of the NAS report is summarized 
as follows:

    In sum, the [NAS] Steering Committee advised against doing 
exactly what OSHA does in its analysis--focusing exclusively on 
physical work-related factors: ``Non-biomechanical factors must 
[emphasis added] be considered if understanding of the relationship 
between biomechanical work factors and MSDs is to expand and inform 
in the design of workplace interventions to reduce or prevent such 
disorders.'' (Ex. 32-241-4, p.120).

    OSHA does not believe the NAS report seriously questions findings 
of the NIOSH review or undermines the OSHA position on the evidence 
that exposure to biomechanical factors increases the risk of MSDs. 
Regarding the epidemiological evidence, the NAS Steering Committee 
Report states:

    Restricting our focus to those studies involving the highest 
levels of exposure to biomechanical stressor of the upper

[[<strong>Page</strong> 68489]]

extremity, neck, and back and those with the sharpest contrast in 
exposure among the study groups, the positive relationship between 
the occurrence of musculoskeletal disorders and the conduct of work 
is clear. The relevant studies have not precisely determined the 
causal mechanical factors involved nor the full clinical spectrum of 
the reported MSDs (which are often lumped together nonspecifically 
as MSDs of a body region); nonetheless, those associations 
identified by the NIOSH review as having strong evidence are well 
supported by competent research on heavily exposed populations (Ex. 
26-37, pg 15-16).
    There is compelling evidence from numerous studies that as the 
amount of biomechanical stress is reduced, the prevalence of 
musculoskeletal disorders at the affected body region is likewise 
reduced. This evidence provides further support for the relationship 
between these work activities and the occurrence of musculoskeletal 
disorders (Ex. 26-37. p 16).

    OSHA believes these NAS conclusions are not ``inconclusive at 
best'' but as the commenters claims, instead clearly support those 
associations between work-related biomechanical factors and MSDs 
identified in the NIOSH review where evidence is strong, namely 
combinations of forceful exertions, repetitive motions, awkward 
postures, vibration and heavy lifting. The above biomechanical 
exposures are the same ones that the OSHA standard seeks to reduce.
    The NAS Steering Committee did point out some limitations to the 
epidemiological evidence, particularly that ``it was difficult to make 
strong causal inferences on the basis of evidence from any individual 
study.'' (Ex. 26-37, p. 15; emphasis added). They acknowledged that 
``the occurrence of MSDs among populations exposed to low levels of 
biomechanical stressors was less definite. * * * In case of low levels 
of biomechanical stress, the possible contribution of other factors to 
MSDs is important to consider.'' (Ex. 26-37, p. 16). OSHA agrees with 
these statements and has not ignored the contribution of individual, 
organizational, and psychosocial factors in the etiology of MSDs. The 
Health Effects section of the rule emphasizes the multifactorial nature 
of MSDs. Substantial evidence in the rulemaking record, however, 
demonstrates that biomechanical risk factor show strong associations 
with elevated MSD risk when other non-work-related factors are 
controlled for. Thus, OSHA does not believe that the existence of other 
risk factors should prevent actions that reduce exposures to those 
work-related biomechanical stressors.
    OSHA agrees that the majority of the NAS participants supported the 
ergonomic hypothesis that OSHA is espousing. This is not because the 
NAS selection process excluded those with other views, as implied by 
the commenters. The NAS prides itself on and is regarded world-wide as 
an organization that renders impartial and unbiased expert judgment on 
scientific issues. The reason for the NAS participants' support is 
simply that most ergonomic experts around the world agree there is 
clear evidence that biomechanical work factors increase the risk of 
MSDs.
    OSHA is aware that one member of the six person panel addressing 
physical factors and epidemiology, Dr. Howard Sandler, was critical of 
NIOSH's methodology and findings. OSHA does not agree with Dr. 
Sandler's statements, and neither did the majority of the other panel 
members. In the NAS workshop summary, the consensus of the panel was 
that NIOSH had not overlooked any important body of epidemiological 
evidence. The panelists generally agreed that the NIOSH analysis 
resulted in the review on of high quality studies. With the exception 
of Dr. Sandler, the panelists unanimously agreed that a reassessment of 
the epidemiological literature would not alter the conclusions drawn by 
NIOSH regarding the work-relatedness of MSDs.
    Finally, it is important to note that in evaluating all the 
evidence, not just the epidemiology, the NAS Steering Committee made 
the following conclusions:

    Thus, while there are many points about which we would like to 
know more, there is little to shake our confidence in the thrust of 
our conclusions, which draw on converging results from many 
disciplines, using many methods:
    <bullet> There is a higher incidence of reported pain, injury, 
loss of work, and disability among individuals who are employed in 
occupations where there is a high exposure to physical loading than 
for those employed in occupations with lower level of exposure.
    <bullet> There is a strong biological plausibility between the 
incidence of MSDs and the causative exposure factors in high 
exposure occupational settings.
    <bullet> Research clearly demonstrates that specific 
interventions can reduce the reported rate of MSDs for workers who 
perform high risk tasks. No single intervention is universally 
effective. Successful interventions require attention to individual, 
organizational, and job characteristics, tailoring the corrective 
actions to those characteristics (Ex. 26-37)

    OSHA believes the above NAS conclusions support, not undermine, the 
premise that there is convincing evidence that exposure to work-related 
physical factors increases the risk of MSDs. There is a higher 
incidence of MSDs in exposed individuals; there is strong biological 
plausibility that relates these disorders to biomechanical risk 
factors; and interventions that reduce exposure to those factors have 
been demonstrated to reduce the incidence of the MSDs.
    In summary, the methodology used by NIOSH to arrive at its findings 
that there is evidence of an association between a number of work-
related physical risk factors and MSDs of the neck, upper extremity, 
and back is not a flawed ``black box,'' but a scientifically sound 
approach based on well-accepted epidemiological principles. By NIOSH's 
own testimony, OSHA's conclusions regarding biomechanical factors and 
the risk of MSDs in the workplace reinforce and do not misrepresent the 
1997 NIOSH findings. Finally, the conclusions in the 1999 NAS report 
are supportive of both the NIOSH analysis and the OSHA position. In 
addition, to the NIOSH and NAS, the European Agency for Safety and 
Health at Work (Ex. 500-71-28) and Washington State (Ex. 500-71-93) 
have evaluated the scientific evidence and also reached similar 
conclusions regarding the evidence linking work-related biomechanical 
factors with the development of MSDs.
2. Issues Relating to Causal Inference in Epidemiology
    Several commenters to the Proposal argued that OSHA had failed to 
show causality between exposure to workplace factors and MSDs; one 
group of comments emphasized that the types of studies used by NIOSH 
and OSHA to evaluate causality of the various MSD risk factors were 
inadequate for that purpose because of the studies design (see, e.g., 
Ex. 32-241-4, pg 86-91). Specific comments were:

    Only repeated longitudinal prospective studies can establish 
causation; OSHA relies instead on methodologies prone to error and 
bias. * * * Cross-sectional studies, upon which OSHA heavily relies, 
are incapable of providing evidence of cause and effect, because 
correlation does not establish causation (Id. pg. 86). Case-control 
studies are highly prone to bias. Prospective cohort studies are the 
best method of studying etiology, * * * retrospective studies [are 
prone to] the hazards of * * * ``recall bias.'' (Id. pg. 87). * * * 
In the case of musculoskeletal pain, which OSHA [has] linked to 
``awkward postures'' and other biomechanical exposures, recall bias 
[in any retrospective design] can be extreme. * * * Cross-sectional 
studies are necessarily retrospective and prone to recall bias. (Id. 
pg. 87). [Cross-sectional studies] are useful for observing patterns 
and correlations, but can only generate hypotheses. A review seeking 
evidence of causation must exclude all cross-

[[<strong>Page</strong> 68490]]

sectional studies, because their methodology is inadequate to test a 
hypothesis. (Id. pg. 88)

With respect to case-control study designs, the comments continued:

    [C]ase-control studies generally measure exposure to various 
hypothesized risk factors retrospectively, and consequently are 
prone to a number of biases, particularly in the recall of exposure 
to suspected risk factors. * * * Case-control studies are most 
suitable for examining rare diseases * * * Musculoskeletal 
complaints are hardly `` rare,'' of course, making OSHA's reliance 
on retrospective studies particularly unwarranted and puzzling (Id. 
pg. 89).

With respect to combining studies for a total weight-of-evidence 
assessment, critics were somewhat divided. Some noted that:

    [In order to do a proper assessment] only prospective cohort 
studies reliably establish etiology, that is, valid scientific 
evidence of cause and effect. (Id. pg. 89). * * * Adequate science, 
however, requires more than mere association. It demands clinically 
accepted, rigorously controlled studies. (Ex. 32-241-3-1, pg.3),

while others, including Dr. Stanley Bigos, felt that case-control 
studies could also be used:

    To infer causal relationships, one would look for consistent 
findings in a number of case-control and prospective cohort studies, 
as well as other supporting scientific information. Bradford Hill 
published an influential set of guidelines for causal inference. 
(Ex. 32-241-3-4, pg. 9).

    However, another commenter cautioned about drawing conclusions for 
a group of studies:

    It should be noted that weaknesses of individual studies cannot 
be overcome by synthesizing a large number of studies with different 
weaknesses that suggest the same conclusion. (Ex. 32-241-4, pg. 89).

    Still another commenter, Dr. Lloyd Fisher, noted a methodology 
using a statistical approach for combining studies. This methodology is 
termed meta-analysis:

    The process for properly formally synthesizing information from 
multiple studies of the same thing is described in a textbook I 
coauthored. Requirements for a valid meta-analysis include that (1) 
all studies in the area be considered, without ``publication bias'' 
based on treatment effect indicated in the studies; (2) a careful 
assessment of study quality should be performed; and (3) study 
results should reflect a homogeneity of results. This was not 
attempted where possible in the material that I reviewed.
    Perhaps the most notable example of meta-analysis discussed by 
OSHA is [the NIOSH report]. However, it is not clear that the NIOSH 
report satisfies any of the three conditions. Some relevant studies 
(such as the Boeing back-injury study) are not included. The quality 
of the studies is not directly assessed to any great degree. (Ex. 
32-241-3-7, pg. 3).

    OSHA has carefully considered these comments on the criteria and 
methodology for selecting and combining studies for a weight-of-
evidence approach to evaluating causality and has concluded that OSHA's 
approach and the approach used in the NIOSH report (Ex. 26-1) are 
scientifically sound. First, with respect to the NIOSH methodology, 
OSHA notes that NIOSH did prioritize studies by type of design and did 
discuss each design's inherent capabilities, weaknesses, and potential 
biases (Ex. 26-1, App. A). NIOSH also included in its criteria for 
evaluating the weight of a study the study's population, health 
outcome, and exposure: ``the greatest qualitative weight was given to 
studies that had objective exposure assessments, high participation 
rates, physical examinations, and blinded assessment of health and 
exposure status.'' (Ex. 26-1, pg. 1-9 and 1-10).
    NIOSH then evaluated the data base of studies using guidelines to 
assess causal inference made famous by Bradford Hill (Ex. 26-726). 
These consisted of (1) strength of association; (2) consistency of 
association; (3) specificity of association; (4) temporality; (5) 
exposure-response relationship; and (6) coherence of evidence (a 
combination of consistency with other information and biological 
plausibility). These guidelines are endorsed in the Reference Manual On 
Scientific Evidence (Federal Judicial Center, 2000) that assists 
federal judges in interpreting scientific reasoning as it pertains to 
litigation and is held up by Gibson, Dunn & Crutcher as an 
authoritative source. The Manual states the following about the 
application of the Hill criteria:

    There is no formula or algorithm that can be used to assess 
whether a causal inference is appropriate based on these guidelines. 
One or more factors may be absent even when a true causal 
relationship exists. Similarly, the existence of some factors does 
not ensure that a causal relationship exists. Drawing causal 
inferences after finding an association and considering these 
factors requires judgment and searching analysis, based on biology, 
of why a factor or factors may be absent despite a causal 
relationship and vice versa. While the drawing of causal inferences 
is informed by scientific expertise, it is not a determination that 
is made using scientific methodology. (pg. 375)

NIOSH witness Dr. Larry Fine stated in his testimony:

    Again, it's always hard to talk in generalizations, but in a 
situation where you have evidence of a biologically plausible 
explanation for the relationship between exposure and disease, where 
you had a body of cross-sectional studies that had accurate exposure 
assessment and accurate health outcomes; in that setting, we believe 
that you may well infer causality, particularly if you see, in 
studies with a wide range of exposure, a dose-response relationship 
(Tr. 2095).

    Second, OSHA has considered the NAS review of the NIOSH criteria 
for study inclusion and weighting (Ex. 26-37). In the NAS review seven 
epidemiologists specializing in ergonomics were asked about the NIOSH 
assessment's selection and weighting of studies. Each provided 
individual comments (Id., pgs. 152-174). In general they concurred with 
the NIOSH approach. Dr. Frederick Gerr, Associate Professor, Rollins 
School of Public Health, Emory University, thought that NIOSH had 
included all important epidemiological evidence in its review (Id., pg. 
159), an opinion shared by Dr. Laura Punnett, Professor, University of 
Massachusetts, Lowell (Id., pg. 162), Dr. Alfred Franzblau, Associate 
Professor of Occupational Medicine, University of Michigan School of 
Public Health (Id., pg. 155), and Dr. David Wegman, Professor, 
University of Massachusetts Lowell (Id., pg. 172). With respect to the 
four criteria NIOSH chose to use to further qualitatively weight each 
study, some of the NAS participants found that these ``criteria for 
identifying studies of relatively greater methodological rigor are 
reasonable and appropriate'' (Id., pg. 159), and ``that the studies 
most heavily relied on by NIOSH in its assessment of workplace factors 
and MSDs are of good quality.'' (Id., pg. 156); and ``[t]he quality of 
the studies that were most heavily weighted was generally quite high 
because they met the multiple criteria set out by NIOSH for weighting. 
(Id., pg. 172). One panelist, however, Dr. Howard Sandler (in a study 
co-authored with non-panelist Dr. Richard Blume), thought that this 
weighting method was neither fully explained nor tested and validated. 
(Id., pg.168). Dr. Sandler was scheduled to appear at the OSHA hearing 
as an expert for Keller/Heckman but never did so.
    Because of the NIOSH assessment's use of cross-sectional studies, 
the comments of Dr. Alfred Franzblau in discussing NIOSH's weighting of 
cross-sectional studies should be noted:

    What some researchers have done is to perform cross-sectional 
studies among workers (and jobs) that are known to have been stable 
for some minimum period of time (e.g., six months or one year). This 
type of cross-sectional design overcomes some of the shortcomings of 
cross-sectional studies relative to prospective studies, and serves 
to greatly strengthen the confidence one can

[[<strong>Page</strong> 68491]]

have in the conclusion. Many of the studies that were most heavily 
weighted in the NIOSH assessment fall into this category (Ex. 26-37, 
pg. 156).

Dr. David Wegman provided the following summary comments:

    There is no ``correct'' way to carry out a literature review 
particularly with as large a scope as the one undertaken by NIOSH. 
The authors of the NIOSH report are to be commended for developing a 
methodology that is reasonable, understandable, clearly presented, 
open and conservative. It is hard to imagine a more effective way to 
summarize this literature (Ex. 26-37, pg. 173).

    Third, several witnesses and commenters on OSHA's ergonomics 
proposal also addressed the use of multiple types of epidemiological 
studies to determine causality. Dr. John Frank, Professor of Public 
Health Sciences, University of Toronto, stated in his testimony:

    The best design cannot be read from a cookbook which 
automatically requires there to be a rank ordering of study design 
qualities for all circumstances. Prospective studies can actually 
make some mistakes that are overcome in well designed case-control 
studies (Tr. 1472).

    Dr. Laura Punnett, Professor, University of Massachusetts Lowell, 
in support of the conclusions of the NIOSH report pointed out that:

    Almost all of the studies considered in the review have been 
published in the peer-reviewed scientific literature, meaning that 
they had already been through the standard scientific quality 
control process prior to their publication and review by NIOSH. (Tr. 
864).

    In a statement that contradicts the view of several witnesses 
stating that medicine must rely on randomized clinical trials (RCT) for 
determining causality (e.g., see Ex. 32-241-3-4, pg. 7-10), Dr. Niklas 
Krause, of the Public Health Institute, discussed the necessity of 
doing a careful evaluation of all the evidence:

    So there are design problems in any study. And there is no gold 
standard, not even the randomized control trial is the gold standard 
as some people say. Epidemiologists say it. It is not the gold 
standard. You have to use all the available evidence. It is a 
careful evaluation of all the methodological features from 
measurement to control group to the timing and going through 
criteria that are important for causation as laid down by Hill and 
others. There is a discussion among us, you know, [about] which are 
the most important ones. But I think we all agree * * * we have 
established temporality in another way than doing a longitudinal 
study. And it can be established. We have repeated that. Then, all 
study designs are equally important. (Tr. 1476). * * * If you 
disregard all the cross-sectional studies for causal inference, you 
would not have medicine. (Tr. 1411).

    When questioned about the cross-sectional design's inability to 
establish temporality, a key factor for determining causality, Dr. 
Krause further stated that in his studies this was not the case:

    To give you an example, in our cross-sectional studies of the 
bus drivers, we measured the years of occupational driving. These 
years clearly occurred before they said to us I have back pain now. 
I have no doubt that these risk factors are [temporal], in a 
[temporal] relationship or coming before the back pain. And so this 
study qualifies for causal inference as a cross sectional study. I 
would not disregard this. (Tr. 1411).

    The AFL-CIO post-hearing comments provide their analysis of the 
OSHA record with respect to the evidence for causality (Ex. 500-218). 
In discussing the types of studies that can be used to determine 
causality, they stated:

    The record evidence clearly establishes that cross-sectional and 
case-control studies have been and can be used to identify causal 
relationships between exposures to risk factors and adverse health 
outcomes. In fact, the record demonstrates that cross-sectional and 
case-control studies have been used with great success to infer 
causal relationships addressing some of our nation's most important 
public health issues, such as smoking and lung disease, which have 
led to life-saving intervention measures in the absence of 
prospective studies. The record also does contain prospective 
epidemiological studies which have confirmed findings from cross-
sectional and case-control studies that exposure to biomechanical/
physical factors in the workplace cause MSDs among exposed workers.

(Id., pg. 30)

    In summary, with respect to the selection, use, and weighting of 
studies of multiple designs to make a determination of the causality 
between work-related stress factors and MSDs, OSHA concludes that the 
NIOSH approach is sound.
    With respect to Dr. Fisher's comment that a formal methodology for 
combining study results to derive a weighted estimate of effect is a 
meta-analysis and that NIOSH did not perform a proper meta-analysis, 
OSHA agrees that NIOSH's analysis was not that of a formal meta-
analysis. However, neither Dr. Fisher nor anyone else has provided a 
formal meta-analysis of the epidemiological literature to the record. 
Furthermore, OSHA notes that a necessary criteria for combining studies 
in a successful meta-analysis is that only studies measuring similar 
factors and estimating very similar effects should be analyzed 
together. OSHA's review of the database has determined that comparisons 
both between and within occupations with higher versus lower risk 
factors can be made in the various studies in a basic weight-of-
evidence approach. However, a rigorous meta-analytic approach for a 
combined risk estimate is much more problematic because of the many 
factors being studied and the different response measures.
    In addressing NIOSH's reliance on a qualitative evaluation of the 
epidemiology rather than a formal meta-analysis, Dr. David Wegman, 
Professor, University of Massachusetts Lowell, stated in his review for 
the NAS:

    Meta-analysis is not appropriate when the question under study 
is as broad as the one NIOSH addressed. In my judgement [another 
writer] * * * provides the answer which, in his words is: ``I 
question whether quantitative methods can ever be as thoroughgoing, 
probing and informative as qualitative methods'' [Ex. 26-37].

The NAS Panel's Steering Committee concluded, with respect to the 
findings of the seven epidemiology experts on the NAS panel about 
combining studies for an overall risk estimate:

    Methods used for the assessment of exposures and health outcomes 
vary [among studies], rendering the task of merging and combining 
evidence more challenging than in some other areas of risk 
assessment. But this variability does provide the benefit of 
multiple perspective on a common set of problems [Ex. 26-37].

    In summary, OSHA finds no support for Dr. Fisher's comment that 
NIOSH erred by not performing a proper meta-analysis. Neither Dr. 
Fisher nor anyone else has provided any specific evidence to support 
his contention that a meta-analysis approach would be appropriate in 
this case. Instead, OSHA concurs with the National Academy of Science's 
conclusion that a formal meta-analysis would not be the best 
methodology in this case.
    Gibson, Dunn & Crutcher also claimed that OSHA did not properly 
evaluate the epidemiological evidence according to the Reference Manual 
On Scientific Evidence (Ex. 500-197). Gibson, Dunn & Crutcher cited the 
following alleged weakness: that OSHA characterized the epidemiological 
evidence as proving cause while the Manual makes clear that 
epidemiological studies address association not causation, and that 
OSHA relied on studies of ``employee's recollection of the details of 
past job duties * * * and measures such as job titles coupled with the 
assumption that job duties were consistent across all job titles.'' 
(Id., pg. I-55). The Manual criticizes studies that rely on the memory 
of subjects and states a preference for measurement of exposure. The 
Manual says that the

[[<strong>Page</strong> 68492]]

outcome or health effect being studied must be clearly defined, yet 
OSHA relied on ``studies that examine subjective memories regarding an 
individual's experience with or personal tolerance for pain.'' (Id., 
pg. I-56). While NIOSH found that many studies ``did not take into 
account [confounding] factors beyond job duties and produced odds or 
risk ratios that were not statistically significant'' (Id., pg. I-57), 
OSHA ``just picked the ones that purport to show results favoring its 
hypothesis'' and ``routinely relied on studies reporting associations 
or odds ratios well below 9-10 and indeed often below 2.'' (Id., pg. I-
59). According to Gibson, Dunn & Crutcher, the Manual ``indicates that 
where risk ratios are significantly below nine or ten there is a 
probability that unmeasured factors are the true causes of the effect 
or disease being studied.'' (Id., pg. I-58).
    Gibson, Dunn & Crutcher mischaracterized the nature of the 
epidemiological studies on which OSHA relied, the criteria used by OSHA 
to evaluate those studies, and the conclusions OSHA drew from those 
studies. They also misconstrue a key section of the Manual. OSHA did 
not simply rely on epidemiological studies in which exposures were 
assumed but never measured and in which the health outcome was simply 
self-reported memories of pain. For each MSD, OSHA relied primarily on 
a subset of studies in which exposure to work-related biomechanical 
factors was directly observed or measured and for which the health 
outcome was clearly defined by a combination of symptoms and physical 
exam. This meets the Manual's preference for objective and uniform 
exposure measures and case definition. It is also compatible with the 
1997 NIOSH analysis, which quite properly give the greatest weight to 
studies that involved objective exposure assessments and physical 
examinations in their evaluation of the evidence (Ex. 26-1, pg. 1-10).
    For example, in the case of epicondylitis and other elbow MSDs, 
thirteen epidemiological studies based case definition on physical 
examination and worker exposure determined by observational analysis 
(see Table V-3). In these studies, the diagnosis of epicondylitis was 
consistent and required both pain on palpation of the epicondylar area 
and pain at the elbow with resisted movement of the wrist. Exposures 
relied on videotaped analysis of job tasks to group exposed and 
unexposed workers, sometimes with quantitative estimates of cycle times 
(for repetition), static loading on the forearm (for force), and wrist 
posture. Nine of the thirteen studies found statistically significant 
associations between epicondylitis and exposure to work-related 
physical factors (see, e.g., Exs. 26-907; 500-41-131; 26-53; 26-1117; 
26-1364; 26-1433; 500-41-116; 26-945; 26-1473). Six of the studies 
reported odds ratios or other risk measures of five or greater (Exs. 
26-907; 500-41-111; 26-43; 26-1117; 26-1364; 26-1433). One study found 
that the rate of repetitive exertions is highly predictive (p=0.002) of 
epicondylitis (Ex. 500-41-116). Two studies reported odds ratios 
greater than ten (Exs. 26-907; 500-41-111). This is a much different 
pattern of risk ratios than that presented by Gibson, Dunn & Crutcher, 
which claims that odds ratios are well below 9-10 and often around 2.
    The Manual does not state risk ratios below 10 may indicate that 
confounding factors are responsible for the association, as implied by 
Gibson, Dunn & Crutcher. The Manual states ``a relative risk of 10 * * 
* is so high that it is extremely difficult to imagine any bias or 
confounding factor that might account for it.'' (pg. 376). The Manual 
goes on to say that ``although lower relative risks can (emphasis 
added) reflect causality, the epidemiologist will scrutinize such 
associations more closely because there is a greater chance that they 
are the result of uncontrolled confounding or bias.'' (Pg 377).
    The Manual also discusses the Hill criteria previously cited. OSHA 
has evaluated the epidemiological evidence against these criteria. As 
mentioned above, the large number of studies reporting significant 
associations and risk ratios above five speaks to the strength of the 
association and the replicatibility of the findings for MSDs of the 
elbow. As further explained in the Health Effects section, there was 
one prospective cohort study of meat cutters that provided evidence of 
a temporal relationship between repetitive, forceful exertions of the 
forearm/elbow and epicondylitis (Ex. 26-53). In addition, several 
cross-sectional studies indicated an exposure-response relationship 
between the intensity or duration of repetitive exertions and the 
prevalence of MSDs (Exs. 500-41-116; 500-41-111; 26-1117; 26-697; 26-
1473). Two studies reported ORs between 1 and 3 that were not 
statistically significant, probably because the workers were exposed to 
relatively low force directed at the forearm (Exs. 26-56; 26-697). 
Another study that did not find an association may have misclassified 
exposure, according to NIOSH (Ex. 26-1211). As a group, OSHA found that 
the studies relied on generally controlled for important confounders 
and bias, although not every individual study did so. Pathology 
information that epicondylitis is caused by microrupture of the tendons 
resulting from overuse of the forearm muscles, and the well-established 
connection between epicondylitis and racquet sports (i.e., tennis 
elbow) establish the biological plausibility of the relationship.
    The evidence briefly described above led OSHA to conclude that 
workers that perform job tasks requiring repeated forceful movements, 
especially flexion, pronation, or supination with the arm extended, are 
at increased risk of substantial and serious musculoskeletal impairment 
to the elbow. In its analysis of the epidemiological literature, NIOSH 
also concluded there was strong evidence for a relationship between 
exposure to a combination of work-related physical factors and 
epicondylitis (Ex. 26-1, pg 4-1 to 4-48). It should be noted that these 
OSHA and NIOSH conclusions do not, in fact, speak of causation as 
purported by Gibson, Dunn & Crutcher; both OSHA's and NIOSH's 
conclusions are careful to conform to the language of the Manual.
    In Section V on health effects, OSHA evaluates the epidemiological 
evidence for MSDs of the upper extremity, shoulder, neck, back, and 
lower extremity, be focusing primarily on the most reliable studies. 
This usually means studies where exposures to physical work factors are 
directly observed or measured, not assumed based on job title, and the 
MSDs have been confirmed by a combination of symptoms, physical exam, 
and medical tests as appropriate. In addition to the evidence for 
epicondylitis cited above:
    <bullet> Thirteen studies examined neck and neck/shoulder MSDs 
using physical exam and direct observation of exposure. All but one 
found significant associations between biomechanical risk factors and 
health outcome. At least three studies reported odds ratios greater 
than five (see Table V-1).
    <bullet> Seventeen studies examined shoulder MSDs (mostly 
tendinitis) using physical exam and direct observation of exposure. All 
but one found significant associations between biomechanical risk 
factors and health outcome. At least six studies reported odds ratios 
greater than five (see Table V-2).
    <bullet> Seven studies examined hand/wrist tendinitis using 
physical exam and direct observation of exposure. All but one found 
significant associations between biomechanical risk factors and health 
outcome. At least four studies reported odds ratios greater than five 
(Table V-4).
    <bullet> Seventeen studies examined carpal tunnel syndrome using 
physical exam

[[<strong>Page</strong> 68493]]

and/or nerve conduction and direct observation of exposure. Thirteen 
found significant associations between biomechanical risk factors and 
health outcome. At least five studies reported odds ratios greater than 
five.
    <bullet> Six studies examined hand/arm vibration syndrome using 
physical exam and vibration measurements. Four found significant 
associations between vibration and health outcome; all of which 
reported odds ratios greater than five.

    OSHA has carefully evaluated the collective data base of studies 
for each MSD category using the criteria for causality cited in the 
Manual (pg. 374-378). OSHA used the epidemiological data, biomechanical 
research studies, and information addressing biological plausibility to 
draw its overall conclusions with regard to the evidence that the work-
related biomechanical factors were responsible for the observed 
increase in the risk of health impairment. OSHA finds this evidence 
compelling and points to the need to take action to provide workers 
with necessary protection. OSHA does not believe that it is appropriate 
to wait for ``proof of causation'' since scientific evidence cannot 
ever establish causation beyond any doubt. As Sir Bradford Hill wrote 
over 35 years ago:

    All scientific work is incomplete--whether it is observational 
or experimental. All scientific work is liable to be upset or 
modified by advancing knowledge. That does not confer upon us a 
freedom to ignore the knowledge we already have or to postpone the 
action that it appears to demand at a give time (Ex. 26-726).
3. Evidence for Exposure Response Relationships
    Several submissions, such as those submitted by the U.S. Chamber of 
Commerce and experts testifying on behalf of United Parcel Service 
(Exs. 30-1722, 32-241-3-19, 32-241-3-13, 30-4184, 30-1552), claimed 
that there is no epidemiologic evidence of exposure-response (or 
``dose-response'') relationships between MSDs and the physical 
ergonomic stressors addressed by the OSHA standard. In their joint 
written testimony on the proposed rule, Kellie Truppa and Dr. Michael 
Vender, for example, stated:

    While it may seem very intuitive that decreasing reported 
ergonomic stressors would decrease disorders, there is no scientific 
study that has demonstrated a decrease in the incidence of true 
disease directly attributable to actual ergonomic changes. Unlike 
other risk factors to health (e.g.--smoking) there is no concept of 
threshold exposure or dose-response in relating ergonomic risk 
exposure to the development of disease. Therefore, there can be no 
predictability or guarantee of any benefit with reduction of 
ergonomic exposures * * * (Ex. 32-241-3-19).

    In the preamble to the proposed rule, OSHA presented results of 
several studies that evaluated exposure-response trends; since 
publication of the proposal, OSHA has identified many more studies that 
provide evidence that, as the level (intensity, frequency or duration) 
of exposure increases, so does the risk of MSDs. OSHA summarizes this 
evidence in this section of the preamble. Based on these studies, OSHA 
finds that there is substantial evidence for a positive relationship 
between duration and intensity of exposure to biomechanical risk 
factors and the risk of developing MSDs, and that this evidence 
strengthens the causal relationship between exposure and risk.
    One of the key criteria for demonstrating a causal relationship is 
evidence that the prevalence or incidence of a health outcome increases 
with an increase in the level of exposure to a hazardous condition. In 
occupational epidemiological studies, an exposure-response relationship 
is demonstrated when there is a statistical association between the 
prevalence or incidence of the health outcome in at least three groups 
of workers each with a varying degree of exposure (e.g., no exposure, 
low exposure, high exposure). When exposure response relationships are 
based on groups of workers, the exposure variable is represented as an 
ordinal variable. Alternatively, statistical analysis can be performed 
on data for individual members of study cohorts to derive statistical 
functions that reflect the exposure-response relationship; in this 
case, the exposure variable is represented as a continuous variable. 
For this section, studies were included if the risk between 
musculoskeletal disorders and exposure to one or more biomechanical 
risk factors were examined using either of these two approaches. In the 
studies compiled here, the most common presentations of exposure 
response relationships are when the prevalence, incidence, odds ratio, 
or risk ratio for an MSD increases from one exposure category to the 
next. Typically these are accompanied by confidence intervals or a test 
of linear trend, as measures of statistical stability. In other 
studies, the exposure-response relationship may be expressed in the 
form of a statistically significant linear regression coefficient, or 
(partial) correlation coefficient, showing that, as exposure increases 
so does the prevalence or risk.
    An exposure-response relationship, when present, is considered to 
strengthen the evidence of a causal relationship because it is believed 
to be a characteristic of cause-effect situations, in general, absent 
evidence to the contrary. In addition, it is thought that it would be 
more difficult for many or most forms of bias or confounding to produce 
an artifactual exposure-response relationship than to bias a simple 
association such as an odds ratio. However, it is not a sine qua non, 
in that an epidemiologic study can provide valuable information even if 
both exposure and outcome are represented only as dichotomous variables 
(i.e., exposed versus unexposed), nor does it make unnecessary 
consideration of methodologic issues that must be addressed when 
evaluating a given study. Furthermore, the lack of an exposure-response 
relationship is not necessarily evidence against a causal effect.
    The studies cited in this section utilized a wide range of exposure 
measures, including worker self-reports, observation, and direct 
measurement. As several authors have noted, even though exposure units 
and scaling vary, there is an overall consistency between self-reports 
and other, presumably more objective, measures in these studies (e.g., 
Booth-Jones et al., 1998: Ex. 500-121-9; Jensen et al., 2000: Ex. 500-
41-68; Neumann et al., 1999: Ex. 38-85; Pope et al., 1998: Ex. 500-71-
67). This suggests that worker perception provides a useful guide to 
the identification of jobs involving high exposures to physical risk 
factors, and that, in general, the jobs that will be identified as 
potentially hazardous by workers' own evaluations will generally 
correspond to those that would be identified as potentially hazardous 
by other measures. The results of studies that have examined exposure-
response relationships are summarized in Tables V-9 through V-13, and 
are summarized briefly below.

Work Pace and Repetition

    There is substantial evidence of an exposure-response relationship 
for MSDs of the neck and shoulders. For example, in a case-control 
study of the general population in Sweden, the odds of neck/shoulder 
disorders increased markedly with work pace levels from slow to medium 
to rushed, as well as with hours per day of performing repetitive 
precision movements at work (Ekberg et al., 1994: Ex. 26-1238 ). 
Ohlsson et al.found positive associations with both the number of items 
handled per hour in repetitive assembly work and the number of years 
employed in such work, especially among younger employees (Ohlsson et

[[<strong>Page</strong> 68494]]

al., 1989: Ex. 26-1290 ). Johansson et al. studied blue- and white-
collar manufacturing employees separately and reported exposure-
response relationships with monotonous movements at work in each group 
(Johansson et al., 1994: Ex. 26-1331).

     Table V-9.--Evidence of Exposure-Response Relationships for Musculoskeletal Disorders With Exposure to
                                             Repetitive Manual Work
----------------------------------------------------------------------------------------------------------------
   Measure of repetitiveness     Health outcome/body
            (unit)                 region  affected             Measure of effect                Reference
----------------------------------------------------------------------------------------------------------------
                                                Neck and Shoulder
----------------------------------------------------------------------------------------------------------------
Years sewing machine operator   Neck/Shoulder........  Odds Ratio [unadj]                  Andersen et al.(1993:
 (4 categories).                                       0 (control:  1.0                     Ex. 26-1451).
                                                       0-7:  2.3 (0.5-11.0)
                                                       8-15:  6.8 (1.6-28.5)
                                                       >15:  16.7 (4.1-67.5)
Years sewing machine operator   Chronic neck pain....  Odds Ratio [adj]                    Andersen et al.(1993:
 (4 categories).                                       0 (control):  1.0                    Ex. 26-1502).
                                                       0-7:  1.9 (1.3-2.9)
                                                       8-15:  3.8 (2.3-6.4)
                                                       >15:  5.0 (2.9-8.7)
Years sewing machine operator   Chronic should pain..  Odds Ratio [adj]                    Andersen et al.(1993:
 (4 categories).                                       0 (control):  1.0                    Ex. 26-1502).
                                                       0-7:  1.4 (0.9-2.4)
                                                       8-15:  3.9 (2.3-6.5)
                                                       >15:  10.3 (5.9-17.9)
Years sewing machine operator   Chronic neck and/or    Odds Ratio [adj]                    Andersen et al.(1993:
 (4 categories).                 shoulder pain.        0 (control):  1.0                    Ex. 26-1502).
                                                       0-7:  1.8 (1.2-2.6)
                                                       8-15:  4.3 (2.6-6.9)
                                                       >15:  8.0 (4.7-13.8)
Data entry at video display     Neck (cervical         Odds Ratio [adj]                    Bergqvist et
 unit (hours/week).              diagnoses).           5-20 hr/wk:  1.2 (0.4-4.3)           al.(1995: Ex. 26-
                                                       <gr-thn-eq>20 hr/wk:  1.7 (0.7-      1195, 500-165-25).
                                                        4.3)
Data entry at video display     Neck/shoulder........  Odds Ratio [adj]                    Bergqvist et
 unit.                                                 Data entry:  1.4 (0.7-2.9)           al.(1995: Ex. 26-
                                                       Data entry plus limited rest         1195, 500-165-25).
                                                        breaks:  4.8 (1.3-18.1)
Typing speed..................  Neck.................  Prevalence [unadj] (test of         Burt et al.(1990: Ex.
                                                        trend):                             26-698).
                                                       Slow:  10%
                                                       Moderate:  14%
                                                       Fast:  25% (p0.001)
Percentage of time typing.....  Neck.................  Odds Ratio [adj]                    Burt et al.(1990: Ex.
                                                       20:  1.0                             26-698).
                                                       20-39:  2.0 (1.0-7.7)
                                                       40-59:  2.6 (1.4-5.0)
                                                       60-79:  2.2 (1.0-4.7)
                                                       80-100:  2.8 (1.4-5.4)
Typing speed..................  Shoulder.............  Odds Ratio [adj]                    Burt et al.(1990: Ex.
                                                       Slow:  1.0                           26-698).
                                                       Moderate:  2.6(1.1-5.9)
                                                       Fast:  4.1 (1.8-9.4))
Percentage of time typing.....  Shoulder.............  Prevalence [unadj] (test of         Burt et al.(1990: Ex.
                                                        trend):                             26-698).
                                                       0-19:  6%
                                                       20-39:  10%
                                                       40-59:  13%
                                                       60-79:  11%
                                                       80-100:  15% (p=.10)
Repetitive precision movements  Neck/Shoulder........  Odds Ratio [adj]                    Ekberg et al.(1994:
 (hours/day) (3 categories).                           Low:  1.0                            Ex. 26-1238).
                                                       Medium:  3.8 (0.7-20)
                                                       High:  15.6 (2.2-113)
Work pace (3 categories)......  Neck/Shoulder........  Odds Ratio [adj]                    Ekberg et al.(1994:
                                                       Low:  1.0                            Ex. 26-1238)
                                                       Medium:  7.6 (1.6-36)
                                                       Rushed:  10.7 (2.2-52)
Hour per day of video display   Neck, shoulder, upper  Odds Ratio [unadj] per hour 1.4     Faucett et al.(1994:
 terminal (VDT) use.             back (``upper          (1.0-2.0)                           Ex. 38-256)
                                 torso'').
Monotonous working movements    Neck (in white collar  Partial correlation coefficient     Johansson et
 (duration of repetitive         workers).              [adj] 0.38 (p < 0.05)               al.(1994: Ex. 26-
 movements, static stress and                                                               1331)
 sitting).
Monotonous working movements    Shoulder (in white     Partial correlation coefficient     Johansson et
 (duration of repetitive         collar workers).       [adj] 0.32 (p < 0.05)               al.(1994: Ex. 26-
 movements, static stress and                                                               1331)
 sitting).

[[<strong>Page</strong> 68495]]

Monotonous working movements    Shoulder (in blue      Partial correlation coefficient     Johansson et
 (duration of precision          collar workers).       [adj] 0.15 (p < 0.05)               al.(1994: Ex. 26-
 movements, repetitive                                                                      1331)
 movements, and static and
 stress).
Years employed in repetitive    Neck.................  Increasing odds (graphical          Ohlsson et al.(1989:
 assembly work.                                         presentation only)                  Ex. 25-1290)
                                Shoulder.............  Increasing odds (p=0.03); below 35  .....................
                                                        years of age, p=0.01
Work pace (items/hour) (4       Shoulder.............  Odds Ratio [adj]                    Ohlsson et al. (1989:
 categories).                                          < 100:  1.0                          Ex. 26-1290)
                                                       100-199:  est 8.0 (p=0.0006)
                                                       200-700:  est 9.0 (p=0.0006)
                                                       > 700:  est 2.0 (p-value not
                                                        given)
Hours per day of VDT use (4     Neck.................  Prevalence [unadj] (test of         Rossignol et
 categories).                                           trend):                             al.(1987: Ex. 26-
                                                       0 hr:  7%                            804)
                                                       0.5-3 hr:  7%
                                                       4-6 hr:  12%
                                                       <gr-thn-eq>7 hr:  19% (p0.00001)
                                                       Odds Ratio [adj]
                                                       0 hr:  1.0
                                                       0.5-3 hr:  1.8 (0.5-6.8)
                                                       4-6 hr:  4.0 (1.1-14.8)
                                                       <gr-thn-eq>7 hr:  4.6 (1.7-13.2)
Hours per day of VDT use (4     Shoulder.............  Prevalence [unadj] (test of         Rossignol et
 categories).                                           trend):                             al.(1987: Ex. 26-
                                                       0 hr:  6%                            804)
                                                       0.5-3 hr:  5%
                                                       4-6 hr:  10%
                                                       <gr-thn-eq>7 hr:  16% (p=<
                                                        0.00001)
                                                       Odds Ratio [adj]
                                                       0 hr:  1.0
                                                       0.5-3 hr:  2.5 (0.7-10.8)
                                                       4-6 hr:  4.0 (1.0-16.9)
                                                       <gr-thn-eq>7 hr:  4.8 (1.6-17.2)
Sewing machine operation        Neck.................  Odds Ratio [unadj]                  Schibye et al.(1995:
 (years of employment).                                < 8 yrs:  1.0                        Ex. 26-1463)
                                                       8-14 yrs:  1.1 (0.4-2.6)
                                                       <gr-thn-eq>15 yrs:  2.1 (0.8-5.6
----------------------------------------------------------------------------------------------------------------
                                Shoulder.............  < 8 yrs:  1.0                       15 yrs:  4.3 (1.5-
                                                       8-14 yrs:  1.3 (0.5-3.4)             12.5)
                                                       <gr-thn-eq>
----------------------------------------------------------------------------------------------------------------
                                                  Arm and Elbow
----------------------------------------------------------------------------------------------------------------
Data entry at video display     Arm/hand.............  Odds Ratio [unadj]                  Bergqvist et
 unit (hours/week).                                    5-20 hr/wk:  1.6 (0.6-4.5)           al.(1995: Exs. 26-
                                                       <gr-thn-eq> 20 hr/wk:  1.8 (0.8-     1195, 500-165-25)
                                                        3.9)
Percentage of time typing.....  Elbow/forearm........  Odds Ratio [adj]                    Burt et al.(1990: Ex.
                                                       20-39%:  1.2 (0.6-22.5)              26-698)
                                                       40-59%:  1.7 (0.8-3.5)
                                                       60-79%:  1.9 (0.9-4.3)
                                                       80-100%:  2.8 (1.4-5.7)
Typing speed..................  Elbow/forearm........  Prevalence [unadj] (test of         Burt et al.(1990: Ex.
                                                        trend):                             26-698)
                                                       Slow:  7%
                                                       Moderate:  11%
                                                       Fast:  13% (p=0.02)
Hours per day of VDT use......  Arm..................  Prevelance [unadj] (test of         Rossignol et
                                                        trend):                             al.(1987: Ex. 26-
                                                       0 hr:  4%                            804)
                                                       0.5-3 hr:  2%
                                                       4-6 hr:  4%
                                                       <gr-thn-eq>7 hr:  7% (p=0.01)
----------------------------------------------------------------------------------------------------------------

[[<strong>Page</strong> 68496]]

                                                 Hand and Wrist
----------------------------------------------------------------------------------------------------------------
Typing at video display unit    Hand/wrist...........  Odds Ratio [adj]                    Bernard et al.(1994:
 (hours/day).                                          0-2 hr:  1.0                         Ex. 500-165-21)
                                                       2-4 hr:  1.3 (0.6-1.8)
                                                       4-6 hr:  1.3 (0.8-2.2)
                                                       6-<gr-thn-eq>8 hr:  2.1 (1.3-3.6)
                                                       <gr-thn-eq>8 hr:  3.3 (1.2-8.9)
Typing speed..................  Hand/wrist...........  Odds Ratio [adj]                    Burt et al.(1990: Ex.
                                                       Slow:  0.9 (0.3-2.3)                 26-698)
                                                       Moderate:  1.3 (0.6-3.1)
                                                       Fast:  2.5 (1.0-5.6)
Percentage of time typing.....  Hand/wrist...........  Prevalence [unadj] (test of         Burt et al.(1990: Ex.
                                                        trend):                             26-698)
                                                       0-19:  13%
                                                       20-39:  23%
                                                       40-59:  27%
                                                       60-79:  30%
                                                       80-100:  24% (p0.01)
Hours per day of video display  Hand and arm.........  Odds Ratio [unadj] per hour         Faucett et al.(1994:
 terminal (VDT) use.                                   1.5 (1.1-2.0)                        Ex. 38-256)
Repetition rating (1 unit on 0-                        Odds Ratio [adj]:                   Latko et al.(1999:
 10 scale).                                                                                 Ex. 38-171)
                                Dominant wrist/hand/   1.17  (1.06-1.29)
                                 fingers.
                                Tendinitis (distal     1.23  (1.04-1.46)
                                 upper extremity).
                                Carpal tunnel          1.16  (1.00-1.34)
                                 syndrome.
Cycle length (seconds), in      Carpal tunnel          Odds Ratio [adj]                    Leclerc et al.(1998:
 work performed 4-8 hours per    syndrome.             <gr-thn-eq>1 min:  1.0               Ex. 500-205-11)
 day.                                                  30-59 s:  1.03 (0.56-1.89)
                                                       10-29 s:  1.33 (0.75-2.37)
                                                       10 s:  1.90 (1.04-3.48)
Years employed in repetitive    Hand.................  Increasing odds (p=0.002)           Ohlsson et
 assembly work.                                                                             al.(1989:Ex. 26-
                                                                                            1290)
Repetitive wrist motions        Carpal tunnel          Odds Ratio [unadj]                  Wieslander et
 (years of exposure).            syndrome.             1 yr:  1.0                           al.(1989: Ex. 26-
                                                       1-20 yrs:  2.3 (0.7-7.9)             1027)
                                                       >20 yrs:  9.6 (2.8-33.0)
----------------------------------------------------------------------------------------------------------------
                                              Multiple Body Regions
----------------------------------------------------------------------------------------------------------------
Piece-rate wage system (years   Musculo- skeletal      Odds Ratio [adj]                    Brisson et al.(1989:
 of employment).                 diseases.             0-4 yrs:  1.0                        Ex. 26-937)
                                                       5-9 yrs:  4.3 (0.5-35.9)
                                                       10-14 yrs:  10.0(1.0-79.3)
                                                       15-19 yrs.  8.0 (0.8-76.8)
                                                       <gr-thn-eq>20 yrs: 11.4 (0.9-
                                                        137.1)
Hours per week of video         Upper extremity and    Mean hours per week [unadj]         Knave et al.(1985:
 display terminal use.           back.                 30 in cases, 27 in non-cases         Ex. 26-753)
                                                        (p0.05)
Percentage of recovery time     Upper extremity......  Linear regression coefficient       Moore et al.(1994:
 per work cycle.                                        [unadj]:                            Ex. 26-1033)
                                                       Ln(% recovery): 0.6 (r<SUP>2</SUP>=0.49,
                                                        p0.001)
Hours per day at keyboard.....  Hand, wrist, forearm   Prevalence [unadj] (test of         Oxenburgh (1987: Ex.
                                 and/or elbow.          trend):                             26-1367)
                                                       3 hr:  21%
                                                       4 hr:  24%
                                                       6 hr:  45%
                                                       6 hr:  50%
                                                       >6  hr:  86%(p0.00001)
Keyboarding speed.............  Upper extremity......  Prevalence [unadj] (test of         Polanyi et al.(1997):
                                                        trend):                             Ex. 500-41-106)
                                                       40 wpm:  17%
                                                       40-60 wp,:  22%
                                                       >60 wpm:  29% (p=0.025)
Daily time keyboarding (hours   Upper extremity......  Means (test of difference)          Polanyi et al.(1997:
 per day).                                              [unadj]:                            Ex. 500-41-106)
                                                       Cases 3.9 hours/day, controls 3.2
                                                        hours/day
                                                       (p0.001)
----------------------------------------------------------------------------------------------------------------
Note: adj = adjusted for other covariate(s)
unadj = not adjusted for other covariates

[[<strong>Page</strong> 68497]]

Table V-10.--Evidence of Exposure-Response Relationships for Musculoskeletal Disorders With Exposure to Forceful
                                                 Manual Exertion
----------------------------------------------------------------------------------------------------------------
                                 Health outcome/body
Measure of manual force (unit)     region affected              Measure of effect                Reference
----------------------------------------------------------------------------------------------------------------
                                                Neck and Shoulder
----------------------------------------------------------------------------------------------------------------
Grocery checking: hours per     Shoulder.............  Odds Ration [unadj]                 Baron et al.(1991:
 week of checking work.                                20:  1                               Ex. 26-697)
                                                       20-25:  1
                                                       >25:  3.6 (p0.05)
Forearm rotation while          Shoulder.............  Odds Ration [adj] per unit:         Hughes et al.(1997:
 exerting very high forces                                                                  Ex. 26-907)
 (Frequency of exposure *
 Years of exposure).
                                Interview............  92 (7.3-<plus-minus>)
                                Examination..........  46 (3.8-550)
Light materials handling        Shoulder (in white     Partial correlation coefficient     Johansson et
 [factor formed from frequency   collar workers).       [adj] 0.18 (p  0.05)                al.(1994: Ex. 26-
 and duration of materials                                                                  1331)
 handling 0.5-1 kg and 1-5 kg].
Years of carpentry work (10,    Shoulder.............  Odds Ration [adj]                   Lemasters et
 10 to 20, 20+ years).                                 10-20 yr:  2.3 (1.0-5.4)             al.(1998: Ex. 500-
                                                       20+ yr:  3.2 (1.1-8.9)               121-44)
Load lifted (cumulative         Shoulder: acromio-     Odds Ratio [adj] (per category)     Stenlund et al.(1992:
 exposure, in 3 categories: 0-   clavicular            Right side:  1.55 (1.03-2.34)        Ex. 26-733)
 709; 710-25,999; and >25,999    osteoarthritis.       Left side:  2.55 (1.50-4.35)
 kg).
Load lifted (cumulative         Shoulder tendinitis..  Odds Ratio [adj] (per category)     Stenlund et al.(1993:
 exposure, in 3 categories: 0-                         Right side:  1.02 (0.59-1.76)        Ex. 502-462
 709; 710-25,999; and >25,999                          Left side:  1.81 (0.95-3.44)
 kg).
----------------------------------------------------------------------------------------------------------------
                                                  Arm and Elbow
----------------------------------------------------------------------------------------------------------------
Grocery checking: hours per     Elbow................  Elbows Odds Ratio [unadj]           Baron et al.(1991:
 week of checking work.                                20:  1                               Ex. 26-697)
                                                       20-25:  1.4
                                                       >25:  2.8 (p0.05)
Forearm rotation while          Elbow/forearm:.......  Odds Ratio [adj] per unit:          Huges et al.(1997:
 exerting very high forces      Interview............  4 (0.2-4)                            Ex. 26-907)
 (Frequency of exposure *       Examination..........  37.0 (3.0-470)
 Years of exposure).
Strenuous exertions (years of   Epicondylitis........  Odds Ratio [adj]                    Ritz (1995: Ex. 26-
 high exposure).                                       0 yr:  1.0                           1473)
                                                       1-14 yr:  1.8(0.6-5.9)
                                                       15-38 yr:  3.3 (0.9-12.5)
----------------------------------------------------------------------------------------------------------------
                                                 Hand and Wrist
----------------------------------------------------------------------------------------------------------------
Hand forces (finger flexor      Carpal tunnel          Average force (test of difference   Armstrong et
 muscles on electromyography).   syndrome.              in means):                          al.(1979: Ex. 500-41-
                                                       Cases:  4.3 " 3.5 kp                 8)
                                                       Noncases:  3.8 " 3.2 kp (p0.05)
Grocery checking (years of      Hand/wrist...........  Odds Ratio [adj]                    Baron et al.(1991:
 exposure).                                            0-5:  1                              Ex. 26-697)
                                                       5-10:  2
                                                       10+:  6 (p0.05)
Grocery checking (years of      Carpal tunnel          Odds Ratio [adj]                    Baron et al.(1991:
 exposure).                      syndrome.             0-5:  1                              Ex. 26-697)
                                                       5-10:  4
                                                       10+:  15 (p0.05)
Grocery checking (hours per     Carpal tunnel          Odds Ratio [adj]                    Baron et al.(1991:
 week of exposure).              syndrome.             20:  1                               Ex. 26-697)
                                                       20-25:  2.3
                                                       >25:  4.8 (p0.05)
Forearm rotation while          Hand/wrist:..........  Odds Ratio [adj] per unit           Hughes et al.(1997:
 exerting very high forces      Interview............  17.0 (2.9-106)                       Ex. 26-907)
 (Frequency of exposure *       Examination..........  9.3 (1.0-90)
 Years of exposure).
Years of carpentry work (10,    Hand and wrist.......  Odds Ratio [adj]                    Lemasters et
 10 to 20, 20+ years).                                 10-lt;20 yr:  2.4(1.1-5.3)           al.(1998: Ex. 500-
                                                       20+yr:  3.1(1.1-8.4)                 121-44)
Biomechanical index from        Carpal tunnel          Linear regression [unadj]           Loslever et al.(1993:
 direct measurements of force    syndrome.             Flexion  0.017(r=0.62)               Ex. 26-161)
 and posture.                                          Extension:  0.035(r=0.26)

[[<strong>Page</strong> 68498]]

Mean relative finger flexor     Wrist................  Linear regression coefficient       Malchaire et
 force (by EMG)/45-90 minute                            [adj]:                              al.(1996: Ex. 26-
 work sampling period.                                 Mean relative deviation angle        1473)
                                                        (p0.05)
                                                       Mean relative EMG signal (p0.05)
                                                       Seniority (years employed) (p0.05)
Manual force (as % MVC, in 5    Upper extremity......  Linear regression [unadj]:          Moore et al.(1994:
 categories).                                          Ln (Force:  2.0 (r\2\=0.49,          Ex. 26-1033)
                                                        p0.001)
Forceful wrist motions (3       Carpal tunnel          Prevalence [unadj] (test of trend)  Osorio et al.(1994:
 categories: low, medium,        syndrome By history.  Low:  0%                             Ex. 26-807)
 high).                                                Medium:  10%
                                                       High:  63% (p=0.00006)
                                By nerve conduction    Low:  0%                            .....................
                                 velocity.             Medium:  7%
                                                       High:  33% (p=0.02)
Forceful wrist motions (years   Carpal tunnel          Linear regression [adj], p0.05      Osorio et al.(1994:
 exposed).                       syndrome.              for:                                Ex. 26-807)
                                                       Right median nerve conduction
                                                        velocity
Grip >6 lb. per hand (3         Hand/wrist...........  Prevalence [unadj] (test of trend)  Stetson et al.(1993:
 categories of frequency).                             None:  41%                           Ex. 26-1221)
                                                       Some:  40%
                                                       Frequent:  65% (p=0.30)
High load on wrist (years of    Carpal tunnel          Odds Ratio [unadj]                  Wieslander et
 exposure).                      syndrome.             1 yr:  1.0                           al.(1989: Ex. 26-
                                                       1-20 yr:  2.1 (0.8-5.2)              1027)
                                                       >20 yr:  6.6 (1.4-14.7)
----------------------------------------------------------------------------------------------------------------
                                                      Back
----------------------------------------------------------------------------------------------------------------
Frequency of lifting per shift  Low back.............  Prevalence [unadj]                  Arad et al.(1986: Ex.
                                                       0/shift:  29%                        500-41-7)
                                                       1-5/shift:  33%
                                                       6-10/shift:  49%
                                                       11-20/shift:  55%
                                                       >20/shift:  54%
Frequency of lifting >11.3 kg   Prolapsed lumbar disc  Odds Ratio [adj] (test of trend):   Kelsey et al.(1984:
 (times per day).                                      0:  1.0                              Ex. 500-41-73)
                                                       5:  1.6 (0.4-6.1)
                                                       5-25:  2.7 (0.8-9.2)
                                                       >25:  4.9 (0.5-47.6) (p=0.02)
Frequency of lifting >11.3 kg   Prolapsed lumbar disc  Odds Ratio [adj] (test of trend):   Kelsey et al.(1984:
 (times per day).                                      0:  1.0                              Ex. 500-41-73)
                                                       5:  1.2 (0.7-2.0)
                                                       5-25:  1.3 (0.7-2.5)
                                                       >25:  3.5 (1.5-8.5) (p=0.01)
Frequency of carrying 11.3 kg   Prolapsed lumbar disc  Odds Ratio [adj] (test of trend):   Kelsey et al.(1984:
 (times per day).                                      0:  1.0                              Ex. 500-41-73)
                                                       5:  1.0 (0.6-1.9)
                                                       5-25:  2.1 (1.0-4.3)
                                                       >25:  2.7 (1.2-5.8) (p=0.004)
Lifting 11.3 kg while twisting  Prolapsed lumbar disc  Odds Ratio [adj] (test of trend):   Kelsey et al.(1984:
                                                       Never or rare:  1.0                  Ex. 500-41-73)
                                                       Moderate:  2.5 (0.9-6.8)
                                                       Often:  3.1 (1.3-7.5) (p=0.002)
Load on spine (12 continuous    Low back.............  Odds Ratio [adj] for inter-         Kerr et al.(2000: Ex.
 biomechanical variables: peak                          quartile spreads:                   500-41-74)
 and daily integraetd load).                           Peak lumbar shear (N):  1.7 (1.0-
                                                        2.9)
                                                       Cumulative lumbar disc compression
                                                        (N s/shift):  2.0 (1.2-3.6)
                                                       Peak hand force (N):  1.9 (1.2-
                                                        3.1)
Index of stone load             Low back.............  Odds Ratio [adj]:                   Latza et al.(2000:
 (weight*hours/day).                                   None:  1.0                           Ex. 500-19-6)
                                                       Intermediate:  1.8 (0.3-9.3)
                                                       High:  4.0 (0.8-19.8)

[[<strong>Page</strong> 68499]]

Lifting demands index (``Job    Back.................  Injury incidence rate, disabling    Liles et al.(1984:
 Severity Index'').                                     injury incidence, and severity      Exs. 26-33, 500-41-
                                                        rate increased with JSI             88)
                                                        (graphical presentations)
Dynamic trunk motions (31       Low back.............  Odds Ratio [adj] for combined       Marras et al.(1993:
 continuous biomechanical.                              weighted means of 5 variables:      Ex. 500-41-94)
                                                       10.7 (4.9-23.6)
Load on spine (12 continuous    Low back.............  Higher load in cases vs controls,   Norman et al.(1998:
 biomechanical variables: peak                          by each variable (all p-values      Ex. 38-84)
 and daily integrated load).                            0.04). Odds ratios [adj] computed
                                                        both for full observed ranges of
                                                        exposure and more conservatively
                                                        for inter-quartile spreads:
                                                       Peak shear (N) 1.5 (1.0-2.4)
                                                       Peak trunk velocity (deg/sec) 1.6
                                                        (1.1-2.5)
                                                       Integrated moment (MN m s) 1.4
                                                        (1.0-2.0)
                                                       Usual hand force (N) 1.7 (1.2-2.6)
Transfer a patient on canvas    Low back.............  Odds Ratio [adj]                    Smedley et al.(1995:
 and poles (frequency/average                          0:  1.0                              Ex. 500-41-40)
 working shift).                                       1-4:  1.0 (0.8-1.3)
                                                       <gr-thn-eq>5:  1.3 (0.8-2.1)
Manually transfer patient       Low back.............  Odds Ratio [adj]                    Smedley et al.(1995:
 between bed and chair                                 0:  1.0                              Ex. 500-41-40)
 (frequency/shift).                                    1-4:  1.4 (1.1-1.9)
                                                       5-9:  1.8 (1.3-2.5)
                                                       <gr-thn-eq>10:  1.5 (1.1-2.1)
Manually move patient around    Low back.............  Odds Ratio [adj]                    Smedley et al.(1995:
 on bed (frequency/shift).                             0:  1.0                              Ex. 500-41-40)
                                                       1-4:  1.2 (0.8-1.7)
                                                       5-9:  1.6 (1.1-2.3)
                                                       <gr-thn-eq>10:  1.7 (1.2-2.4)
Manually transfer patient       Low back.............  Odds Ratio [adj]                    Smedley et al.(1997:
 between bed and chair                                 0:  1.0                              Ex. 500-205-25)
 (frequency/shift).                                    1-4:  1.3 (0.9-1.7)
                                                       5-9:  1.6 (1.1-2.3)
                                                       <gr-thn-eq>10:  1.6 (1.1-2.3)
Transfer patient between bed    Low back.............  Odds Ratio [adj]                    Smedley et al.(1997:
 and chair with hoist                                  0:  1.0                              Ex. 500-205-25)
 (frequency/shift).                                    1-4:  1.5 (1.0-2.0)
                                                       <gr-thn-eq>5:  1.6 (0.8-3.0)
Manually move patient around    Low back.............  Odds Ratio [adj]                    Smedley et al.(1997:
 on bed (frequency/shift).                             0:  1.0                              Ex. 500-205-25)
                                                       1-4:  1.3 (0.8-1.9)
                                                       5-9:  1.5 (1.0-2.3)
                                                       10:  1.7 (1.1-2.5)
Lift patient in or out of bath  Low back.............  Odds Ratio [adj]                    Smedley et al.(1997:
 with hoist (frequency/shift).                         0:  1.0                              Ex. 500-205-25)
                                                       1-4:  1.4 (1.0-1.9)
                                                       5:  2.1 (1.2-3.6)
Frequent vs. infrequent         Back.................  Length of time at work without      Stobbe et al.(1988:
 lifting in patient care.                               back injury longer for those with   Ex. 500-41-45)
                                                        infrequent lifting demands (p0.01
                                                        in survival analysis)
Lifting frequency (4            Back.................  Odds Ratio [adj]                    Venning et al.(1987:
 categories of hospital                                Area IV:  1.0                        Ex. 500-41-49)
 service area, from 1, lifting                         Area III:  1.26 (p>0.05)
 most, to IV, lifting least).                          Area II:  1.73 (p>0.05)
                                                       Area I:  4.26 (p0.01)

[[<strong>Page</strong> 68500]]

NIOSH Lifting Equation Lifting  Low back (severity     Mean severity (standard             Wang et al.1998
 Index (LI) (4 categories).      rating, range 0-5).    deviation):                         (1998: Ex. 500-41-
                                                       LI:1:  0.18 (0.15)                   52)
                                                       1<ls-thn-eq>LI <ls-thn-eq>3:  3.57
                                                        (0.86)
                                                       LI>3:  4.07 (0.73)
                                                       RWL*=0:  3.86 (0.75)
                                                       ANOVA (<greek-a>=0.05)
                                                       *Recommended Weight Limit
NIOSH Lifting Equation Lifting  Low back.............  Odds Ratio [unadj]                  Waters et al.(1999:
 Index (LI).                                           0:  1.0                              Ex. 500-121-76)
                                                       0LI <ls-thn-eq>1:  1.1 (0.2-5.3)
                                                       1LI <ls-thn-eq>2:  1.5 (0.6-3.8)
                                                       2LI <ls-thn-eq>3:  2.5 (1.3-4.9)
                                                       LI <gr-thn-eq>3:  1.6 (0.7-4.0)
Strenuous physical activity at  Back.................  Odds Ratio [unadj]                  Wild (Ex. 26-1104; 26-
 work (hours per day).                                 0-2 hr: 1.0                          1107)
                                                       2-4 hr: 4.2
                                                       4-6 hr: 6.4
                                                       6-8 hr: 5.6
                                                       <gr-thn-eq>8 hr:  6.8
                                                       Odds Ratio [adj] per hour of
                                                        strenuous work: 1.14
                                                       (1.11-1.17)
Physically hard work..........  Low back.............  Odds Ratio [unadj] (test of         Xu et al.(1997: Ex.
                                                        trend):                             500-71-53)
                                                       No or seldom:  1.0
                                                       \1/4\ of the time:  1.3
                                                       \1/2\ of the time  2.3
                                                       \3/4\ of the time:  2.2
                                                       All of the time:  2.5 (p0.001)
----------------------------------------------------------------------------------------------------------------
                                    Lower Extremity or Multiple Body Regions
----------------------------------------------------------------------------------------------------------------
Strength demand of job (3       Knee (radiographic     Odds Ratio [adj]                    Anderson et al.(1988:
 categories: none, some, much).  osteoarthritis).      Men, ages 55-64:  1.9 (0.9-4.0)      Ex. 26-926)
                                                       Women, ages 55-64:  3.1 (1.0-9.4)
Kneeling, squatting or stair-   Knee osteoarthritis..  Odds Ratio [adj]                    Cooper et al.(1994:
 climbing, with and without                            Neither kneeling nor lifting:  1.0   Ex. 500-41-27)
 heavy lifting.                                        Kneeling/squatting:  2.5 (1.1-5.5)
                                                       Kneeling and lifting:  5.4 (1.4-
                                                        21.0)
Maximum compressive force       ``Overexertion         Incidence rate (per 200,000         Herrin et al.(1986:
 (lb.) on L5/S1 lumbar disc.     incidents'' by         hours):                             Ex. 26-961)
                                 clinic visit.         1000 lb:  65
                                                       1000-1500 lb:  150
                                                       >1500 lb:  208
Index of physically strenuous   Overall MSD            Linear regression coefficient       Leino et al.(1995:
 load.                           morbidity:  .          [adj]:                              Ex. 32-241-3-54)
                                Symptoms.............  0.127  (p=0.002)
                                Findings.............  0.091  (p=0.026)
Years of carpentry work (10,    Knee.................  Odds Ratio [adj]                    Lemasters et
 10 to 20, 20+ years).                                 10-20 yr:  1.9 (0.9-4.1)             al.(1998: Ex. 500-
                                                       <gr-thn-eq>20 yr:  3.5 (1.3-9.2)     121-44)
Lifting at work (kilograms per  Knee.................  Odds Ratio [adj]                    Sandmark et al.(2000:
 day).                          Men:.................  Medium:  2.5 (1.5-4.4)               Ex. 500-41-114)
                                Women:...............  High:  3.0 (1.6-5.5)
                                                       Medium:  1.2 (0.7-1.9)
                                                       High:  1.7 (1.0-2.9)
----------------------------------------------------------------------------------------------------------------

[[<strong>Page</strong> 68501]]

Table V-11.--Evidence of Exposure-Response Relationships for Musculoskeletal Disorders of the Neck and Shoulders
                                      With Exposure to Non-Neutral Posture
----------------------------------------------------------------------------------------------------------------
                                 Health outcome/body
      Measure of posture           region affected              Measure of effect                Reference
----------------------------------------------------------------------------------------------------------------
                                                Neck and Shoulder
----------------------------------------------------------------------------------------------------------------
Height of video display unit    Neck/shoulder........  Linear regression coefficient       Bergqvist et
 keyboard relative to elbow                             [unadj] 0.18 (-0.03, 0.40)          al.(1995: Ex. 500-
 height (centimeters).                                                                      165-24)
Duration of shoulder flexion    Shoulder/neck........  Ratio for cases vs. controls:       Bjelle et al.(1981:
 or abduction >60 degrees                              Right:  2.0 (p 0.005)                Ex. 26-1519)
 (hours/day).                                          Left:  2.4 (p 0.025)
Frequency of shoulder flexion   Shoulder/neck........  Ratio for cases vs. controls:       Bjelle et al.(1981:
 or abduction >60 degrees                              Right:  2.0 (p 0.001)                Ex. 26-1519)
 (times/day).                                          Left:  2.2 (p 0.005)
Arms lifted (hours per day, 3   Neck/shoulder........  Odds Ratio [adj]                    Ekberg et al.(1994:
 categories).                                          Low:  1.0                            Ex. 26-1238)
                                                       Medium:  2.4 (0.8-7.1)
                                                       High:  4.8 (1.3-18)
Elbow flexed >1 time/minute     Shoulder.............  Odds Ratio [adj]                    English et al.(1995:
 (per hour/day).                                       1.10  (0.98-1.23)                    Ex. 26-848)
Head rotation.................  Neck, shoulder, upper  R-squared [adj]                     Faucett et al.(1994:
                                 back (``upper         Pain:  0.11 (p0.01)                  Ex. 38-256)
                                 torso'').             Stiffness:  0.18 (p0.01)
Keyboard height relative to     Neck, shoulder, upper  R-squared [adj]                     Faucett et al.(1994:
 elbow.                          back (``upper         Pain:  0.05 (p0.05)                  Ex. 38-256)
                                 torso'').             Stiffness:  0.06 (p0.05)
Years of exposure to            Shoulder impingement   Increasing prevalence ratio [adj]   Frost et al.(1999:
 repetitive shoulder flexion     syndrome.              with cumulative exposure non-       Ex. 38-97)
 (angle <gr-thn-eq>30 degrees,                          linear trend, p=0.002 for
 600 times/hour) with high                              quadratic term
 forces.
Hands above shoulder level      Neck/shoulder pain     Prevalence Ratio [adj]              Holmstrom et al
 (hours per day).                with impairment.      1 Hr.  1.1 (0.8-1.5)                 (1992: Ex. 500-41-
                                                       1-4 hr.  1.5 (1.2-1.9)               64)
                                                       >4 hr.  2.0 (1.4-2.7)
Stooping (hours per day)......  Neck/shoulder pain     Prevalence Ratio [adj]              Holmstrom et al
                                 with impairment.      1 Hr.  1.0 (0.8-1.3)                 (1992: Ex. 500-41-
                                                       1-4 hr.  1.4 (1.1-1.8)               64)
                                                       >4 hr.  1.5 (1.1-2.1)
Bent work postures              Neck (in white collar  Partial correlation coefficient     Johansson et
 [factor=duration of precision   workers).              [adj]                               al.(1994: Ex. 26-
 movements and head bent                               0.20  (p0.05)                        1331)
 foward; frequency and
 duration of trunk forward
 flexion (20 deg.-60 deg.)].
Twisted work postures           Neck (in white collar  Partial correlation coefficient     Johansson et
 [factor=duration of trunk       workers).              [adj]                               al.(1994: Ex. 26-
 rotation (>45 deg.) and head                          0.23  (p0.05)                        1331)
 rotation (>45 deg.)].
Extreme work postures           Shoulder (in blue      Partial correlation coefficient     Johansson et
 [factor=frequency and           collar workers).       [adj]                               al.(1994: Ex. 26-
 duration of trunk forward                             0.14  (p0.05)                        1331)
 flexion (>60 deg.); frequency
 of trunk forward flexion (20
 deg.-60 deg.); and duration
 of head rotation (>45 deg.),
 trunk rotation (>45 deg.),
 and work with hands above
 shoulders].
Twisted work postures           Shoulder (in white     Partial correlation coefficient     Johansson et
 [factor=duration of trunk       collar workers).       [adj]                               al.(1994: Ex. 26-
 rotation (>45 deg.) and head                          0.16  (p0.05)                        1331)
 rotation (>45 deg.)].
Percentage of work cycle with   Cervicobrachial (neck  Odds Ratio [adj]                    Jonsson et al.(1988:
 shoulder elevated.              to hand).             1.04  (p0.05)                        Ex. 26-969)
Neck flexion (percentage of     Neck.................  Regression coefficient p-value      Kilbom et al.(1986:
 work cycle).                                           [adj]                               Ex. 500-41-75)
                                                       p0.01
Shoulder elevated (percentage                          Regression coefficient p-value      Kilbom et al.(1986:
 of work cycle).                                        [adj]                               Ex. 500-41-75)
                                Neck.................  p0.05                               .....................
                                Shoulder.............  p0.05                               .....................
Neck flexion (movements per     Neck/shoulder........  Ratio of median for cases vs.       Ohlsson et al.(1995:
 hour).                                                 controls [unadj]                    Ex. 26-868)
                                                       Total movements: 1.3 (p=0.008)
                                                       Flexions <gr-thn-eq>30 deg.: 1.3
                                                        (p=0.02)

[[<strong>Page</strong> 68502]]

Frequency of shoulder flexion   Neck/shoulder........  Median elevation >30 deg. (% of     Ohlsson et al.(1995:
 or abduction.                                          time) [unadj]:                      Ex. 26-868)
                                                       Cases=16, controls=9 (p=0.05)
                                                       Median elevation >30 deg.
                                                        (movements per hour) [unadj]:
                                                       Cases=60, controls=9 (p=0.004)
                                                       Median abduction <gr-thn-eq>60
                                                        deg. (% of time) [unadj]:
                                                       Cases=1, controls=0 (p=0.04)
                                                       Median elevation <gr-thn-eq>60
                                                        deg. (movements per hour)
                                                        [unadj]:
                                                       Cases=47, controls=0 (p=0.04)
Shoulder flexion or abduction   Left shoulder........  Odds Ratio [unadj] (test of trend)  Punnett et al.(2000:
 >90 degrees (duration, as      Right shoulder.......  >0%-10%:  2.5                        Ex. 500-41-109
 percentage of work cycle).     Either shoulder......  <gr-thn-eq>10%:  5.1 (p=0.0001)
                                                       >0%-10%:  1.7
                                                       <gr-thn-eq>10%:  2.8 (p=0.002)
                                                       Ratio of mean duration in cases
                                                        vs. controls [unadj]: 2.6
                                                        (p=0.003)
                                                       Odds Ratio (95% CI) per 10%
                                                        increment [adj]:  1.4 (1.1-1.8)
Twisted or bent postures (4     Neck/shoulder........  Odds Ratio [adj]                    Tola et al.(1988: Ex
 categories).                                          Little:  1.0                         26-1018)
                                                       Moderate:  1.2 (1.0-1.5)
                                                       Rather much:  1.6 (1.4-1.9)
                                                       Very much:  1.8 (1.5-2.2)
Twisting of trunk (hours/day)   Neck.................  Odds Ratio [adj]:                   Viikari-Juntura et
 (4 categories).                                       Not at all:  1.0                     al.(2000: Ex. 500-41-
                                                       Little:  1.3 (0.7-2.4)               50)
                                                       Moderately:  1.9 (1.1-3.5)
                                                       Much:  2.3 (1.2-4.3)
Working with hand above         Neck.................  Odds Ratio [adj]:                   Viikari-Juntura et
 shoulder level (hours/day) (3                         0.5  1.0                             al.(2000: Ex. 500-41-
 categories).                                          0.5-1:  1.2 (1.0-1.3)                50)
                                                       >1:  1.4 (1.3-1.6)
Twisting or bending of trunk    Neck.................  Odds Ratio [unadj]:                 Viikari-Juntura et
 at work (3 categories).                               Very or rather little:  1.0          al.(1994: Ex. 26-
                                                       Moderate:  1.7 (0.9-9-3.2)           873)
                                                       Rather or very much:  1.9 (1.2-
                                                        3.2)
----------------------------------------------------------------------------------------------------------------
                                                 Hand and Wrist
----------------------------------------------------------------------------------------------------------------
Wrist bending or twisting (per  Carpal tunnel          Odds Ratio [unadj]                  Blanc at al. (1996);
 2 hours/day).                   syndrome.             1.5 (1.2-1.7)                        Ex. 26-42 500-41-16)
Wrist flexion (hours/week)      Carpal tunnel          Odds Ratio [unadj]                  De Krom et al.(1990:
 (hours truncated at 40).        syndrome.             0:  1.0                              Ex. 26-102)
                                                       1-7:  1.5 (1.3-1.9)
                                                       8-19:  3.0 (1.8-4.9)
                                                       20-40:  8.7 (3.1-24.1)
Wrist extension (hours/week)    Carpal tunnel          Odds Ratio [unadj]                  De Krom et al.(1990:
 (hours truncated at 40).        syndrome.             0:  1.0                              Ex. 26-102)
                                                       1-7:  1.4 (1.0-1.9)
                                                       8-19:  2.3 (1.0-5.2)
                                                       20-40:  5.4 (1.1-27.4)
Shoulder rotation with arm                             Odds Ratio [adj]                    English et al.(1995:
 elevated, >1 time/minute (per                                                              Ex. 26-848)
 hour/day).
                                Wrist/forearm........  1.6 (1.2-2.3)
                                Carpal tunnel          1.8 (1.2-2.8)                       .....................
                                 syndrome.
Shoulder rotation with elbow    Finger...............  Odds Ratio [adj]                    English et al.(1995:
 flexed, >1 time/minute (per                           5.1 (2.0-12.8)                       Ex. 26-848)
 hour/day).
Wrist flexion or extension      Thumb................  Odds Ratio [adj]                    English et al.(1995:
 (per 20 repetitions/min).                             1.4 (1.1-1.8)                        Ex. 26-848)
Ulnar abduction (degrees of     Forearm..............  Increasing percentage of operators  Hunting et al.(1981:
 ``typical'' work posture).                             w/medical findings vs. angle of     Ex. 26-1276)
                                                        ulnar abudction (graphical
                                                        presentation only)

[[<strong>Page</strong> 68503]]

Relative angle of wrist ulnar   Wrist................  Linear regression coefficient       Malchaire et
 or radial deviation/45-90                              [adj]:                              al.(1996: Ex. 26-
 minute work sampling period.                          Mean relative deviation angle        1473)
                                                        (p0.05)
                                                       Mean relative EMG signal (p0.05)
                                                       Seniority (years employed) (p0.05)
Wrist bending or twisting       Carpal tunnel          Odds Ratio [adj]                    Nordstrom et
 (mean hours/day) (5             syndrome.             0:  1.0                              al.(1997: Ex. 26-
 categories).                                          0.25-1.75:  1.34(0.64-2.80)          900)
                                                       2-3:  1.23(0.60-2.53)
                                                       3.5-6:  2.33 (1.24-4.36)
                                                       7-16:  2.47 (1.38-4.43) quadratic
                                                        dose-response effect in
                                                        alternative model, p=0.03
Wrist deviation (3 categories   Hand/wrist...........  Prevalence [unadj] (test of trend)  Stetson et al.(1993:
 of frequency).                                        None:  35%                           Ex. 26-1221)
                                                       Some:  43%
                                                       Frequent:  45% (p=0.43)
----------------------------------------------------------------------------------------------------------------
                                                      Back
----------------------------------------------------------------------------------------------------------------
Postural load (index of         Low back pain........  Odds Ratio [adj] (test for trend)   Bovenzi et al.(1994:
 frequency and/or duration of                                                               Ex. 26-774)
 4 postures, in 4 categories).
                                Lifetime.............  Mild:  1.0
                                                       Moderate:  1.3(0.8-2.4)
                                                       Hard:  1.7(1.0-3.0)
                                                       Very hard:  3.6(2.0-6.5) (p=0.001)
                                12 month pervalence:.  Moderate:  1.8 (1.1-3.2)
                                                       Hard:  2.2(1.3-3.8)
                                                       Very hard:  4.6 (2.6-8.0)
                                                        (p=0.0001)
Hands above should level        Low back (severe pain  Prevalence Ratio [adj]:             Holmstrom et
 (hours per day).                with impairment).     1 hr:  1.1 0.8-1.5)                  al.(1992: Ex. 500-41-
                                                       1-4:  1.5 (1.2-2.0)                  65)
                                                       >4 hr:  1.6 (1.0-2.6)
Stopping (hours per day)......  Low back (severe pain  Prevalence Ratio [adj]:             Holmstrom et
                                 with impairment).     1 hr:  1.3 (0.9-1.8)                 al.(1992: Ex. 500-41-
                                                       1-4 hr:  1.9 (1.4-2.6)               65)
                                                       >4 hr:  2.6 (1.7-3.8)
Kneeling (hours per day)......  Low back (severe pain  Prevalence Ratio [adj]:             Holmstrom et
                                 with impairment).     1 hr:  2.4 (1.7-3.3)                 al.(1992: Ex. 500-41-
                                                       1-4 hr:  2.6 (1.9-3.5)               65)
                                                       >4 hr:  3.5 (2.4-4.9)
Extreme work postures [factor   Low back (in blue      Partial correlation coefficient     Johansson et
 formed from frequency and       collar workers).       [adj] 0.16 (p0.05)                  al.(1994: Ex. 26-
 duration of trunk forward                                                                  1331)
 flexionn (>60 deg.);
 frequency of trunk forward
 flexion (20 deg.-60 deg.);
 and duration of head rotation
 (>45 deg.), trunk rotation
 (>45 deg.), and work with
 hands above shoulders].
Monotonuous working movements   Low back (in white     Partial correlation coefficient     Johansson et
 [factor formed from duration    collar workers.        [adj] 0.22 (p0.05)                  al.(1994: Ex. 26-
 of repetitive movements,                                                                   1331)
 static stress, and sitting].
Driving (hours/week)..........  Low back.............  Odds Ratio [adj] for prevalence:    Pietri et al.(1992:
                                                       10:  1.0                             Ex. 29-309)
                                                       10-14:  1.5 (1.0-2.4)
                                                       15-19:  1.2 (0.8-1.9)
                                                       20-24:  2.0 (1.3-3.1)
                                                       <gr-thn-eq> 25  2.1 (1.3-3.4)

[[<strong>Page</strong> 68504]]

Driving (hours/week)..........  Low back.............  Odds Ratio [adj] for 1 year         Pietri et al.(1992:
                                                        cumulative incidence:               Ex. 38-309)
                                                       10:  1.0
                                                       10-14:  4.0 (1.1-14.3)
                                                       15-19:  4.8 (1.4.8-16.4)
                                                       20-24:  3.3 (0.9-12.0)
                                                       <gr-thn-eq> 25  3.7 (0.9-14.0)
Percentage of work cycle in     Low back.............  Odds Ratio [unadj] (test of trend)  Punnett et al.(1991:
 trunk flexion (3 categories).                         Mild flexion:                        Ex. 26-1289)
                                                       0%:  1.0
                                                       1-10%:  4.2
                                                       <gr-thn-eq>10%:  6.1 (p=0.014)
                                                       Severe flexion:
                                                       0%:  1.0
                                                       0-10%:  4.4
                                                       <gr-thn-eq>10%:  8.9 (p=0.003)
Percentage of work cycle in     Back.................  Odds Ratio [adj]                    Punnett et al.(1991:
 non-neutral trunk posture                             8.09  (1.5-44.0)                     Ex. 26-1289)
 (mild flexion, severe
 flexion, twist or lateral
 bend).
Twisted or bent postures (4     Low back.............  Odds Ratio [adj]                    Riihimaki et al.
 categories).                                          Rather or very little:  1.0          (1989: Ex. 26-58)
                                                       Moderate:  1.3 (1.0-1.7)
                                                       Rather much:  1.5 (1.2-1.9)
                                                       Very much:  1.5 (1.2-1.9)
Forward bending (minutes per    Low back.............  Odds Ratio [adj]:                   Vingard et al.(2000:
 day).                                                 Men                                  Ex. 500-41-51)
                                                       1-59 min:  1.6 (1.1-2.5)
                                                       <gr-thn-eq>60 min:  1.8 (1.1-3.1)
                                                       Women
                                                       1-59 min:  1.1 (0.8-1.6)
                                                       <gr-thn-eq>60 min:  1.2 (0.7-1.8)
Repeated bending, twisting,     Back.................  Odds Ratio [unadj]                  Wild (Ex. 26-1106; 26-
 and reaching at work (hours                           0 hr:  1.0                           1107)
 per day.                                              >0-2 hr:  5.8
                                                       2+-4 hr:  8.4
                                                       4+-6 hr:  10.4
                                                       6+ hr:  14.1
                                                       Odds Ratio [adj] per hour of
                                                        repeated bending, twisting and
                                                        reaching:  1.09 (1.06, 1.13)
Frequent twisting or bending..  Low back.............  Odds Ratio [unadj] (test of         Xu et al.(1997: Ex.
                                                        trend):                             500-71-53)
                                                       No or seldom:  1.0
                                                       1/4 of the time:  1.8
                                                       1/2 of the time:  1.9
                                                       3/4 of the time:  2.0
                                                       All of the time:  2.0 (p0.001)
----------------------------------------------------------------------------------------------------------------
                                                 Lower Extremity
----------------------------------------------------------------------------------------------------------------
Knee-bending demand of job (3   Knee: radiographic     Odds Ratio [adj]                    Anderson et al.(1988:
 categories: none, some, much).  osteoarthritis.       Men, ages 55-64:  2.5 (1.2-5.0)      Ex. 26-926)
                                                       Women, ages 55-64:  3.5 (1.2-10.5)
Kneeling and/or squatting       Knee.................  Odds Ratio [unadj]                  Kirkeskov Jensen et
 (Floor- and carpetlayers 56%,                         Compositors:  1.0                    al.[Jensen,
 carpenters 25%, compositors                           Carpenters:  3.9 (2.7-5.5)           1977#1975]
 0% of working time).                                  Floor- and carpetlayers:  6.4 (4.0-
                                                        10.1)
Standing (hours per day)......  Knee.................  Odds Ratio [adj]                    Sandmark et al.(2000:
                                                                                            Ex. 500-41-114)
                                Men..................  Medium:  1.5 (0.9-2.4)              .....................
                                                       High:  1.7 (1.0-2.9)
                                Women................  Medium:  1.2 (0.7-1.9)              .....................
                                                       High:  1.6 (1.0-2.8)
Squatting or knee bending       Knee.................  Odds Ratio [adj]                    Sandmark et al.(2000:
 (number per day).                                                                          Ex. 500-41-114)
                                Men..................  Medium:  1.3 (0.8-2.2)              .....................
                                                       High:  2.9 (1.7-4.9)

[[<strong>Page</strong> 68505]]

Kneeling (minutes per day)....  Knee.................  Odds Ratio [adj]                    Sandmark et al.(2000:
                                                                                            Ex. 500-41-114)
                                Men..................  Medium:  1.4 (0.9-2.2)              .....................
                                                       High:  2.1 (1.4-3.3)
Jumping (number per day)......  Knee.................  Odds Radio [adj]                    Snadmark et al.(2000:
                                                                                            Ex. 500-41-114)
                                Men..................  Medium:  (0.9-2.4)                  .....................
                                                       High:  2.7 )1.7-4.1)
Jumping (number)..............  Hip..................  Odds Ratio [adj]                    Vingard et al.(1977:
                                                                                            Ex. 26-1617)
                                                                                           Medium:  1.0 (0.5-
                                                                                            2.0)
                                                                                           High:  2.1 (1.1-4.2)
Stairs climbed (flights)......  Hip..................  Odds Ratio [adj]                    Vingard et al.(1997:
                                                       Medium:  1.3 (0.8-2.0)               Ex. 26-1616)
                                                       High:  2.1 (1.2-3.6)
----------------------------------------------------------------------------------------------------------------

Table V-12.--Evidence of Exposure-Response Relationship for Musculoskeletal Disorders With Exposure to Segmental
                                       Vibration, by Body Region Affected.
----------------------------------------------------------------------------------------------------------------
 Measure of vibration exposure   Health outcome/body
            (unit)                 region affected              Measure of effect                Reference
----------------------------------------------------------------------------------------------------------------
Vibration exposure (energy      Upper extremity......  Odds Ratio [adj]                    Bovenzi et al.(1991:
 equivalent frequency-weighted                         7.5 m/sec \2\  2.7                   Ex. 500-41-18)
 acceleration) for 4 hours/day.                        >7.5 m/sec \2\  14.1 (p0.005)
Daily vibration exposure        Upper extremity......  Odds Ratio [adj] per unit           Bovenzi et al.(1991:
 (energy equivalent frequency-                         1.29 (p0.5)                          Ex. 500-41-18)
 weighted acceleration).
Daily vibration exposure        Upper extremity        Odds Ratio [adj] per unit           Bovenzi et al.(1991:
 (energy equivalent frequency-   muscle-tendon         1.42 (p0.5)                          Ex. 500-41-18)
 weighted acceleration).         syndrome.
Daily vibration exposure        Carpal tunnel          Odds Ratio [adj] per unit           Bovenzi et al.(1991:
 (energy equivalent frequency-   syndrome.             1.73 (p0.5)                          Ex. 500-41-18)
 weighted acceleration).
Lifetime dose (5 categories of  Hand-arm vibration     Odds Ratio [adj] per unit           Bovenzi et al.(1991:
 acceleration \2\ years).        syndrome.             0:  1.0                              Ex. 500-41-17)
                                                       0-19:  4.1 (1.1-16.4)
                                                       19-20:  4.7 (1.3-16.1)
                                                       20-21:  9.4 (3.1-28.4)
                                                       >21:  34.3 (11.9-99.0)
Riveting (years)..............  Wrist................  Odds Ratio [adj] per year           Burdorf et al.(1991:
                                                       1.12 (p0.05)                         Ex. 500-41-21)
Riveting (years)..............  Hand-arm vibration     Odds Ratio [adj] per year           Burdorf et al.(1991:
                                 syndrome.             1.07 (p0.05)                         Ex. 500-41-21)
Power tool usage..............  Forearm-hand (right).  Median values for workstations      Fransson Hall et
                                                        with high vs. low symptom           al.(1996: Ex. 500-41-
                                                        prevalence [unadj]                  56)
                                                       Holding time: 12 sec. vs 6 secs.
                                                        (p0.05)
                                                       Total duration: 21 sec. vs 15
                                                        secs. (p0.05)
Years of exposure to vibration  Vibration-induced      Positive association with duration  Futatsuka et
 (chain saw use).                white finger.          of exposure                         al.(1985: Ex. 26-
                                                       Higher prevalence and earlier        1430)
                                                        onset of symptoms with earlier
                                                        first exposure (higher
                                                        acceleration levels) (all data
                                                        presented graphically)

[[<strong>Page</strong> 68506]]

Cumulative hours of exposure    Median and ulnar       Correlation coefficient [unadj]     Koskimies et
 to vibration.                   motor and sensory     R median motor NCV: 0.274 (p=0.01)   al.[Koskimies, 1990
                                 nerve function.       L median motor NCV: 0.123 (p>0.05)   #1983]
                                                       R ulnar motor NCV: 0.259 (p=0.05)
                                                       L ulnar motor NCV: 0.389 (p>0.001)
                                                       R median distal latency: 0.172
                                                        (p=0.05)
                                                       L median distal latency: 0.214
Cumulative exposure to          Hand-arm vibration     Odds Ratio [adj] per common log     Letz et al.(1992: Ex.
 vibration (log hours).          syndrome:.             unit                                26-384)
                                Vascular.............  2.9 (1.7-5.0)                       .....................
                                Sensorineural........  1.8 (1.2-2.9)                       .....................
Tool use (years)..............  Hand-arm vibration     Odds ratio [adj] per year           McGeoch et al.(2000:
                                 syndrome (Stockholm                                        Ex. 500-41-96)
                                 workshop scales):.
                                Neurological stage     1.09 (p0.05)                        .....................
                                 <gr-thn-eq> 1.
                                Vascular stage <gr-    1.10 (p0.05)                        .....................
                                 thn-eq> 1.
Years of exposure to vibration  Hand-arm vibration     Odds ratio [adj] per year           Nilsson et al. (1989:
                                 syndrome.             1.11 (1.05-1.17)                     Ex. 26-1148)
Years of exposure to vibration  Median nerve latency   Odds ratio [adj] per year           Nilsson et al.(1994:
                                 at carpal tunnel.     Right:  1.12 (1.02-1.23)             Ex. 26-1190)
                                                       Left:  1.09 (1.00-1.20)
Cumulative vibration exposure   Shoulder:              Odds Ratio [adj] (per category)     Stenlund et al.(1992:
 (3 categories: 0-8999; 9000-    osteoarthritis of     Right side:  1.3 (0.9-1.8)           Ex. 26-733)
 255,199; and >255,199 energy-   the                   Left side:  1.8 (1.2-2.6)
 weighted hours).                acromioclavicular
                                 joint.
Cumulative vibration exposure   Shoulder tendinitis..  Odds Ratio [adj] (per category)     Stenlund et al.(1993:
 (3 categories: 0-8999; 9000-                          Right side:  1.7 (1.1-2.6)           Ex. 502-462)
 255,199; and >255,199 energy-                         Left side:  1.8 (1.1-3.1)
 weighted hours).
----------------------------------------------------------------------------------------------------------------

      Table V-13.--Evidence of Exposure-Response Relationship for MSDs With Combination of Exposures (e.g.,
                  Repetition, Force and Posture), by Type of Exposure and Body Region Affected.
----------------------------------------------------------------------------------------------------------------
                                 Health outcome/body
       Exposure factors            region affected              Measure of effect                Reference
----------------------------------------------------------------------------------------------------------------
Index of physical stress at     Neck.................  Odds Ratio [adj]                    Makela et al.(1991:
 work (sum of 6 items).                                Age 30-64 years:  1.26 (1.18-1.33)   Ex. 26-980)
                                                       Age <gr-thn-eq> 65 years:  1.12
                                                        (1.00-1.26)
Index of mechanical workload    Elbow: epicondylitis.  Odds ratio [adj]:                   Ono et al.(1998: Ex.
 (sum of 6 items).                                     Model 2:  1.5 (1.0-2.3)              500-66-4)
                                                       Model 3:  1.7 (1.2-2.6)
Repetition; force (4            Hand/wrist:            Prevalence Rate Ratio [unadj]       Armstrong et
 categories: LF = low force;     tendinitis.           LF LR:  1.0                          al.(1987: Ex. 26-48)
 LR = low repetition; HF =                             HF LR:  4.8 (0.6-39.7)
 high force; HR = high                                 LF HR:  5.5 (0.7-46.3)
 repetition.                                           HF HR:  17.0 (2.3-126.2)
Work at video display unit,     Arm/hand.............  Odds Ratio [adj]                    Bergqvist et
 with and without specific job                         Data entry:  1.5 (0.7-3.4)           al.(1995: Ex. 26-
 features.                                             Data entry plus keyboard too low:    1195 500-165-25)
                                                        2.8 (0.9-8.6)
                                                       <gr-thn-eq> 20 hr/week:  0.5 (0.2-
                                                        1.4)
                                                       <gr-thn-eq> 20 hr/week plus
                                                        limited rest breaks, no lower arm
                                                        support:  4.6 (1.2-17.9)
Work at video display unit,     Arm/hand.............  Odds Ratio [adj]                    Bergqvist et
 with and without specific job                         Limited rest breaks, plus no lower   al.(1995: Ex. 500-
 features.                                              arm support, vs. one or neither:    165-24)
                                                        10.1 (2.4-43.2)

[[<strong>Page</strong> 68507]]

Force and repetition of hand    Hand: Median nerve     Test of positive linear trend:      Nathan et al.(1988:
 activities (5 classes, from     sensory conduction    p  0.01                              Ex. 26-990)
 very light/low to very heavy/   velocity.
 high).
Force and repetition of hand    Hand: Median nerve     Linear regression coefficient       Nathan et al.(1992:
 activities (5 classes, from     sensory conduction     [adj]:                              Ex. 26-988)
 very light/low to very heavy/   velocity.             Class of hand activity: 0.011 (p
 high).                                                 0.05)
Index of physical risk factors  Hand: Radial tunnel    P 0.001, test for trend             Roquelaure et
 (sum of 3 items: force; 1 kg,   syndrome.                                                  al.(1996: Ex. 500-41-
 cycle time  30 sec, static                                                                 111)
 hand work).
Index of physical risk factors  Hand: Carpal tunnel    Odds ratio [adj]                    Roquelaure et
 (sum of 5 occupational items    syndrome.             <ls-thn-eq> 2 factors:  1.0          al.(1997: Ex. 38-
 plus parity <gr-thn-eq> 3).                           3 factors:  5.6 (1.6-24.5)           396)
                                                       4 factors:  93.7 (13.4-93.8)
                                                       <gr-thn-eq> 5 factors:  90.0 (8.0-
                                                        366.5)
Repetition; force (4            Hand/wrist...........  Odds Ratio [adj]                    Silverstein et
 categories: LF = low force;                           LF LR:  1.0                          al.(1986: Ex. 26-
 LR = low repetition; HF =                             HF LR:  5.2                          1404)
 high force; HR = high                                 LF HR:  3.3
 repetition).                                          HF HR:  29.1 (p  0.05)
Repetition; force (4            Hand: Carpal tunnel    Odds Ratio [adj]                    Silverstein et
 categories: LF = low force;     syndrome.             LF LR:  1.0                          al.(1987: Ex. 26-34)
 LR = low repetition; HF =                             HF LR:  1.8
 high force; HR = high                                 LF HR:  2.7
 repetition).                                          HF HR:  15.5 (p  0.001)
Repetitiveness and forceful                            Test of positive linear trend:      Chiang et al.(1993:
 exertions of the upper limbs                                                               Ex. 26-1117)
 (Group I = neither, Group II
 = either, Group III = both).
                                Neck symptoms........  p = 0.04
                                Shoulder symptoms....  p = 0.000
                                Shoulder girdle        p = 0.000
                                 diagnosis.
                                Elbow symptoms.......  p = 0.11
                                Epicondylitis........  p = 0.14
                                Wrist symptoms.......  p = 0.03
                                Hand symptoms........  p = 0.04
                                Carpal tunnel          p = 0.02
                                 syndrome.
Index of ergonomic stressors    Upper extremity        Prevalence ratio [adj]              Punnett (1998: Ex. 26-
 (sum of 9 items, range 0-25).   (neck, shoulder/      0-6:  1.0                            38)
                                 upper arm, elbow/     7-12:  2.0 (1.2-3.4)
                                 forearm, and/or hand/ 13-18:  2.6 (1.6-4.3)
                                 wrist).               19-25:  2.8 (1.6-4.8)
                                Shoulder/upper arm...  0-6:  1.0
                                                       7-12:  2.6 (1.1-6.2)
                                                       13-18:  3.6 (1.6-8.3)
                                                       19-25:  3.3 (1.3-8.3)
                                Wrist/hand...........  0-6:  1.0
                                                       7-12:  1.9 (1.0-3.8)
                                                       13-18:  2.4 (1.3-4.7)
                                                       19-25:  2.3 (1.1-4.7)
Index of occupational physical  Low back.............  Odds Ratio [adj]:                   Heliovaara et
 stress (sum of 5 items, range                         0:  1.0                              al.(1991: Ex. 26-
 0-5).                                                 1:  1.2 (0.9-1.6)                    959)
                                                       2:  1.7 (1.3-2.1)                   Lifting >11.3 kg
                                                       3:  2.1 (1.6-2.7)                    while twisting Low
                                                       4:  3.2 (2.3-4.5)                    back: Prolapsed
                                                       5:  2.5 (1.4-4.7)                    lumbar disc Odds
                                                                                            Ratio [adj]:
                                                                                           Knees bent: 2.7 (0.9-
                                                                                            7.9)
                                                                                           Knees straight: 6.1
                                                                                            (1.3-27.9)
                                                                                           Kelsey et al.(1984:
                                                                                            Ex. 500-41-73)
Lifting > 11.3 kg while         Low back: Prolapsed    Odds Ratio [adj]                    Kelsey et al.(1984:
 twisting.                       lumbar disc.          Knees bent:  2.7 (0.9-7.9)           Ex. 500-41-73)
                                                       Knees straight:  6.1 (1.3-27.9)
Physical exposure index (sum    Low back.............  Odds Ratio [adj]:                   Liira et al.(1996:
 of 3 items, range 0-3.                                0:  1.0                              Ex. 26-748)
                                                       1:  1.41 (1.02-1.94)
                                                       2:  2.45 (1.63-3.68)
                                                       3:  3.18 (1.72-5.81)
Forward bending and manual      Low back.............  Odds Ratio [adj]:                   Vingard et al.(2000:
 materials handling (MMH)                                                                   Ex. 500-41-51)
 (highly exposed now, 5 and 10
 years ago).

[[<strong>Page</strong> 68508]]

                                                       Men
                                                       Forward bending:  1.8 (1.0-3.3)
                                                       MMH:  2.0 (1.0-4.3)
                                                       Bending and MMH:  2.8 (1.1-7.5)
                                                       Women
                                                       Forward bending:  1.5 (0.8-2.6)
                                                       MMH:  1.1 (0.6-2.1)
                                                       Bending and MMH:  2.9 (1.2-6.8)
Kneeling, squatting or stair-   Knee osteoarthritis..  Odds Ratio [adj]:                   Cooper et al.(1994:
 climbing, with and without                            Neither kneeling nor lifting:  1.0   Ex. 500-41-27)
 heavy lifting.                                        Kneeling/squatting:  2.5 (1.1-5.5)
                                                       Kneeling and lifting:  5.4 (1.4-
                                                        21.0)
Kneeling, with (floor layers)   Knee: bursitis.......  Prevalence ratio [adj]:             Thun et al.(1987: Ex.
 and without (tile/terrazzo                            Floor layers:  3.2 (1.9-5.4)         26-60)
 setters) use of knee kicker.                          Tile setters:  1.8 (0.8-3.9)
----------------------------------------------------------------------------------------------------------------

    In a cross-sectional study of newspaper workers, the risk of both 
neck and shoulder disorders increased with typing speed and with 
percentage of time working at the keyboard (Burt et al., 1990: Ex. 26-
698). Similarly, several investigators have shown exposure-response 
relationships for neck and shoulder disorders among video display unit 
operators with the number of hours per day (or week) of VDU work 
(Bergqvist et al., 1995: Exs. 26-1195, 500-165-25; Faucett et al., 
1994: Ex. 38-256; Rossignol et al., 1987: Ex. 26-804).
    Two different studies of sewing machine operators in the garment 
industry have shown increasing prevalence of neck and shoulder 
disorders with cumulative years of exposure to repetitive work 
(Andersen et al., 1993: Ex. 26-1451; Andersen et al., 1993: Ex. 26-
1502; Schibye et al., 1995: Ex. 26-1463). (Note that Andersen 1993a 
(Andersen et al., 1993: Ex. 26-1451) computed both crude and adjusted 
odds ratios, and the latter estimates were higher. However, in the 
adjusted model, each of the potential confounders had little 
association with the risk of neck/shoulder syndromes, so this model was 
deemed overly conservative and statistically inefficient, and the 
unadjusted ORs are shown in the table.) Andersen et al., (Andersen et 
al., 1993: Ex. 26-1502) also computed chi-square tests of trend with 
exposure for specific diagnoses. The following had a positive trend 
with years of exposure: cervicobrachial fibromyalgia (p0.001); rotator 
cuff syndrome (p0.01); and cervical syndrome (p0.001). The probability 
of having no MSD symptoms showed a negative trend with years of 
exposure (p0.001). These findings are compatible with those of Brisson 
et al., (Brisson et al., 1989: Ex. 26-937), who examined long-term 
musculoskeletal disability in general, and specifically that due to 
arthritic and back disorders, including regular pain in the lower back, 
upper back/neck, shoulders, hands/wrists/elbows, or knees/ankles. The 
risk of long-term disability, both overall and for musculoskeletal 
disorders, increased with years of piece-rate garment work.
    Elbow and forearm disorders are typically less prevalent, so there 
are fewer opportunities to evaluate exposure-response relationships 
with adequate statistical power. Nevertheless, several studies of VDU 
operators have shown such associations with speed or daily duration of 
VDU work (Bergqvist et al., 1995: Ex. 26-1195, 500-165-25; Burt et al., 
1990: Ex. 26-698; Rossignol et al., 1987: Ex. 26-804).
    Intensity and duration of VDU work have shown similar exposure-
response relationships with disorders of the hand and wrist region, 
including carpal tunnel syndrome (Bernard et al., 1994: Ex. 500-165-21; 
Burt et al., 1990: Ex. 26-698; Faucett et al., 1994: Ex. 38-256), as 
well as with cases that include both proximal and distal regions of the 
upper extremity (Knave et al., 1985: Ex. 26-753; Oxenburgh, 1987: Ex. 
26-1367; Polanyi et al., 1997: Ex. 500-41-106).
    In the manufacturing sector, there is also evidence that the risk 
of hand and wrist disorders increases with work pace and repetitiveness 
(Latko et al., 1999: Ex. 38-171; Leclerc et al., 1998: Ex. 500-41-85) 
and with cumulative years of exposure to repetitive manual work 
(Ohlsson et al., 1989: Ex. 26-1290; Wieslander et al., 1989: Ex. 26-
1027). Moore et al., (Moore et al., 1994: Ex. 26-1033) showed that the 
risk of reported upper extremity disorders decreased with the 
percentage of recovery time in each work cycle.

Force

    Forceful manual exertions have been characterized by different 
investigators with a variety of metrics, some of them involving the 
combination of at least two of object weight, frequency of handling, 
and duration of exposure. These various approaches have yielded 
evidence of the risk of shoulder disorders increasing with exposure in 
white collar, construction, and manufacturing jobs (Hughes et al., 
1997: Ex. 26-907; Johansson et al., 1994: Ex. 26-1331; Stenlund et al., 
1993: Ex. 502-462), and similar evidence for elbow disorders, even 
though limited by the smaller numbers of cases mentioned above (Hughes 
et al., 1997: Ex. 26-907; Ritz, 1995: Ex. 26-1473).
    Among grocery store workers, grocery checking has been identified 
as a job requiring forceful exertions. In two different studies, the 
risk of shoulder, elbow, and wrist/hand disorders, including CTS, was 
associated with the level of forcefulness required by each employee's 
job, the number of hours of checking work per week, and the cumulative 
number of years of checking (Baron et al., 1991: Ex. 26-697; Osorio et 
al., 1994: Ex. 26-807). Note that Osorio et al. defined three 
categories of exposure, but there were no CTS cases in the low exposure 
group, so in multivariate modeling only the odds ratio for low/medium 
vs. high exposure could be calculated. These dichotomous

[[<strong>Page</strong> 68509]]

estimates, adjusted for age, gender, medical history and alcohol 
consumption, ranged from 6 to 40.
    In other studies of hand and wrist disorders, exposure-response 
relationships have been found for finger flexor forces, measured by 
electromyography, as well as for simpler estimates of force based on 
object weight and on self-report. In particular, these showed trends in 
risk of CTS that are compatible with the experimental evidence, as 
summarized recently by Viikari-Juntura and Silverstein (Viikari-Juntura 
et al., 1999: Ex. 500-121-73).
    There is a particularly large number of studies demonstrating that 
the risk of back disorders, including prolapsed lumbar disc, increases 
with the frequency or duration of manual material handling, with load 
weights, and with other indicators of physically strenuous work 
including but not limited to lifting and carrying tasks. Again, 
exposure has been variously characterized on the basis of observation, 
self-report, and bio-instrumentation measures and/or combined into 
indices. The volume of evidence is extremely impressive and 
demonstrates that such exposure-response relationships have been found 
in nursing and other health care work, in construction, in 
manufacturing, and in the wide range of jobs encountered in the general 
population. For example, Venning et al. (Venning et al., 1987: Ex. 500-
41-49 ) published a prospective study of a closed cohort, which showed 
the predictive value of work area classified a priori in terms of 
lifting demands. Kerr, Norman, and colleagues (Kerr et al., Ex. 500-41-
74 ; Norman et al., 1998: Ex. 38-84 ) compared cases to controls on 12 
continuous biomechanical variables, representing both peak and daily 
integrated load on the spine. There was a higher load in the cases by 
each variable (all p-values  0.04). There was a moderate amount of 
correlation among these variables, so the final regression model was 
reduced to four, with adjustment for demographic and psychosocial 
factors. The odds ratios, computed both for full observed ranges of 
exposure and more conservatively for inter-quartile spreads, showed 
that several dimensions of load on the lumbar spine made independent 
contributions to risk of back disorders.
    It is of particular interest that three different studies (Marras 
et al., 1993: Ex. 500-41-94 ; Wang et al., 1998: Ex. 500-41-52; Waters 
et al., 1999: Ex. 500-121-76) showed such a relationship when lifting 
demands were characterized using the NIOSH lifting index (Waters et 
al., 1993: Ex. 26-521). (It should be noted that Waters et al. (Waters 
et al., 1999: Ex. 500-121-76) also estimated the odds ratios in a 
multivariate logistic regression model that included nine other 
covariates. These estimates so obtained were higher for the category of 
LI=1-2 and otherwise lower than the crude estimates. However, 7 of the 
covariates in the model had little association with LBP, so this model 
was deemed overly conservative and the unadjusted ORs were selected as 
summary measures of the study results.)
    Studies of other, related health outcomes, including knee arthritis 
and ``overexertion incidents'' of any body part, provide compatible 
findings regarding the effects of strenuous work. In addition, Krause 
et al. (Krause et al., 1997: Ex. 26-1281) found that disability 
retirement was increasingly frequent from jobs with heavy physical 
demands and also showed an exposure-response trend with an index of 
repetitive strain that included lifting demands, muscle effort, and 
non-neutral postures. The cases of disability retirement were due to 
any medical condition; however, a large proportion was caused by 
musculoskeletal conditions (see Table 2 of (Krause et al., 1997: Ex. 
26-1281)).

Posture

    Studies of the effect of non-neutral postures also include a wide 
range of exposure measures, including estimated frequency or duration 
of specified postures, as well as tasks that imply specific postural 
demands (e.g., driving as an indicator of highly constrained static 
sitting) and workstation characteristics that directly influence 
posture (e.g., VDU keyboard too high). Since the anatomic segments of 
the body form a kinematic chain, non-neutral postures may affect not 
only the same joint region but also other joints along that chain. For 
example, if the work layout requires the trunk to be twisted while the 
eyes are facing forward, the neck will also be twisted and health 
effects may be found all along the spine. Work with the arms elevated 
may alter wrist posture or impose a biomechanical disadvantage on the 
arm muscles; it will increase the torque exerted by an object held in 
the hands, which in turn increases the compressive forces experienced 
in the lumbar spine (Chaffin et al., 1991: Ex. 26-420).
    There are a very large number of studies showing that neck and 
shoulder disorders exhibit an exposure-response relationship with arm 
and neck postures, especially arm elevation to form an included angle 
of at least 30 deg. flexion or abduction. Both Bergqvist et al. 
(Bergqvist et al., 1995: Ex. 500-165-24 ) and Faucett et al. (Faucett 
et al., 1994: Ex. 38-256 ) showed an increasing risk as the height of 
the VDU keyboard increased relative to seated elbow height. In a case-
control study within a single automobile assembly plant, Punnett and 
colleagues found an increasing risk of shoulder disorders with the 
observed proportion of the work cycle in which the included angle at 
the shoulder was at least 90 degrees (Punnett et al., 2000: Ex. 500-41-
109). This association was not confounded by gender or other 
demographic or medical history factors.
    Viikari-Juntura et al. (Viikari-Juntura et al., 2000: Ex. 500-41-
50) carried out a longitudinal study with four repeated questionnaires 
among 5180 workers in a large forest industry enterprise. The authors 
used a modified Nordic questionnaire (Kuorinka et al., 1987: Ex. 38-
204) for the health outcome of `` radiating neck pain'' and validated 
exposure assessment and psychosocial questionnaires. There was a 
statistically significant dose-response relationship for radiating neck 
pain with the frequency of ``twisting movements of the trunk during a 
work day'' (ORs from 1.0 to 2.3), as well as a dose-response 
relationship for hands above the shoulder. These estimates were 
adjusted for body mass index and high mental stress.
    English et al. conducted a study of patients in the general 
population seeking medical care for upper extremity disorders (English 
et al., 1995: Ex. 26-848 ). Conditions affecting the wrist and hand 
showed exposure-response relationships with several different shoulder 
and wrist postures (Table 3b). The degree of ulnar deviation has been 
reported to be associated with the risk of forearm and wrist disorders 
(Hunting et al., 1981: Ex. 26-1276; Malchaire et al., 1996: Ex. 26-
1473). Several authors have found that the risk of carpal tunnel 
syndrome increases with the number of hours per day or week in which 
the wrist is flexed or extended (Blanc et al., 1996: Exs. 26-42, 500-
41-16; de Krom et al., 1990: Ex. 26-102; Nordstrom et al., 1997: Ex. 
26-900).
    In studies of back disorders, a number of investigators have 
reported exposure-response relationships with trunk forward flexion, 
lateral bending, and rotation. These studies address non-neutral 
postures in both seated and standing work, and they cover a range of 
industries and occupations from tractor driving to construction to 
automobile assembly. Similar data for the U.S. general population were 
obtained from analysis of the National Health Interview Study (Exs. 26-
1106, 26-1107). There is also evidence of

[[<strong>Page</strong> <strong>68510</strong>]]

increasing risk with static sitting, both assessed directly and through 
estimated time or distance driving per week (although the latter may 
also involve exposure to whole-body vibration). In the study by Pietri 
et al. (Pietri et al., 1992: Ex. 38-309), the odds ratios for both 
prevalence and one-year cumulative incidence of low back pain showed 
increases with hours of driving per week in multivariate models 
adjusted for age, gender, comfortable car seat (y/n), carrying loads 
(y/n), standing (y/n), tobacco consumption, and psychosomatic factors.
    With regard to disorders affecting the lower extremity, knee-
bending, kneeling, squatting, jumping from one level to another, and 
stair-climbing are all found in these studies. In a series of Danish 
studies, direct observations showed that the average proportion of time 
that was spent kneeling and/or squatting by workers in three different 
trades (Jensen et al., 1997: Ex. 500-41-69). The prevalence of knee 
disorders among the same three trades increased proportionately to the 
exposure prevalences. Anderson and Felson utilized the U.S. Department 
of Labor Dictionary of Occupational Titles and characterized each 
occupation on the basis of the proportion of job titles within it that 
required knee-bending (0%, up to 50%, more than 50%) (Anderson et al., 
1988: Ex. 26-926). Among subjects aged 55 to 64 years, there was a two 
to three-fold increase in risk of radiographic osteoarthritis with each 
category of knee-bending, adjusted for gender, race, education, and 
body mass index. These odds ratios represent the increase in risk 
across the three categories, i.e., from no to some and from some to 
much knee-bending.

Vibration

    Segmental vibration exposure to the distal upper extremity, 
especially through holding and operating power tools, is another area 
of research where exposure-response relationships have been reported by 
numerous authors. Some studies have shown the association with years of 
exposure, and others combined work history with direct measurements of 
frequency and acceleration to construct biologically informed 
cumulative exposure indices. Most of the evidence concerns neurological 
and circulatory impairment of the hand and wrist. Three different 
investigations reported an odds ratio of about 1.1 for each year of 
occupational exposure to hand-arm vibration, which represents a 
doubling of risk about every 7 years. In addition to those studies 
shown in Table 4a, Nordstrom et al. (Nordstrom et al., 1997: Ex. 26-
900) reported an ``alternative'' multivariate model of CTS in which 
there was a positive quadratic dose-response relationship (p=0.01) for 
use of power tools or machinery. While this variable was not conclusive 
regarding exposure to segmental vibration, it does suggest an exposure-
response trend between segmental vibration and CTS.
    In an historical cohort, Futatsuka et al. (Futatsuka et al., 1985: 
Ex. 26-1430) found a positive association between the prevalence of 
``vibration-induced white finger'' and the duration of exposure to 
vibration (chain saw use). In addition, there was an interaction with 
year of first exposure: higher prevalences and earlier onset of 
symptoms were observed among workers with earlier first exposure, when 
the acceleration levels were higher (all data presented graphically). 
One study team found similar associations for the risk of shoulder 
disorders (Stenlund et al., 1993: Ex. 502-462; Stenlund et al., 1992: 
Ex. 26-733).
    Several statements contained in submissions by the Chamber of 
Commerce and others cited OSHA's statement in the preamble to the 
proposal that it had not constructed ``generalized quantitative 
exposure-response relationships'' for standard-setting (64 Fed. Reg. at 
65927), and that the Agency's reluctance to set permissible exposure 
levels for risk factors provided evidence of a lack of exposure-
response relationship in the epidemiologic literature (e.g., Chamber of 
Commerce, Ex. 30-1722, p. 46 and Ex. 500-188, pp. 10-11; United Parcel 
Service, Ex. 500-197, pp. I-61 to I-62). Such arguments confuse 
exposure-response relationships as evidence of a causal relationship 
with the last stage of quantitative risk assessment, namely computation 
of a permissible exposure level.
    It is critical to distinguish between these points. Exposure-
response relationships have been demonstrated in the epidemiologic 
literature, using a variety of exposure metrics and for a variety of 
health outcomes, and a number of reviewers have cited this evidence in 
concluding that there are causal relationships (eg., Armstrong et al., 
1993: Ex. 26-1110; Bernard, 1997: Ex.26-1; Burdorf et al., 1997: Ex. 
500-121-13; Hagberg et al., 1992: Ex. 8-1; Hales et al., 1996: Ex. 26-
896; Viikari-Juntura et al., 1999: Ex. 500-121-73). At the same time, 
although the indicted exposures and their associations with MSDs are 
qualitatively similar across many studies, the variations in 
measurement approaches results in very limited numbers of studies with 
any single exposure metric. More importantly, there is substantial 
evidence of interactions among physical exposures, so that (for 
example) jobs requiring both repetitive and forceful motions have a 
higher risk than jobs requiring either exposure alone (Armstrong et 
al., 1987: Ex. 26-48; Silverstein et al., 1986: Ex. 26-1404; 
Silverstein et al., 1987: Ex. 26-34). (Numerous examples of other 
additive or multiplicative effects between physical ergonomic exposures 
have been listed in Tables V-9 through V-13). Thus, the exposure-
response curve for each exposure should ideally be described as a 
function of the level of each other exposure that might also be present 
in the same job. This represents an enormous number of combinations of 
exposure, of which only some have been studied epidemiologically to 
date. Given the available exposure-response relationships, plus 
evidence that exposures interact with each other, the decision not to 
attempt quantitative risk assessment calculations at this time is 
readily justifiable. However, this does not at all imply that the 
evidence for exposure-response relationships is insufficient to 
conclude that there is a causal relationship between exposure to risk 
factors and the risk of MSDs.
    Another argument made in the testimony cited above is that if an 
exposure-response relationship existed, it would necessarily be linear 
or monotonic, and that it would necessarily provide an exposure level 
that could be used to differentiate between background risk of MSDs and 
an elevated risk (United Parcel Service, Ex. 500-197, pp. I-62 to I-
67). This assertion is false. An exposure-response relationship need 
not take the form of a straight line through all data points; it may 
conceivably be better described as a logistic curve, or as a step-
function, or as any other of a variety of mathematical functions. As 
one example, the analyses presented by Frost et al. (Frost et al., 
1999: Ex. 38-97) clearly show a non-linear exposure-response trend with 
cumulative exposure to repetitive and loaded shoulder flexion. Two 
among many other illustrations of non-linear, positive exposure-
response relationships can be found in Liles et al., 1984 (Liles et 
al., 1984: Ex. 26-33 500-41-88), where the authors suggested that their 
graphs provided evidence of exposure thresholds, and Moore et al., 1994 
(Moore et al., 1994: Ex. 26-1033), where a log-log transformation 
improved the fit of the model. A non-linear relationship, for example, 
accommodates the likelihood that some physical activity is beneficial 
and that only at more extreme levels do

[[Continued on <strong>page</strong> 68511]]
</PRE>