<PRE>
[Federal Register: November 14, 2000 (Volume 65, Number 220)]
[Rules and Regulations]               
[<strong>Page</strong> <strong>68511</strong>-<strong>68560</strong>]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr14no00-19]                         
 
[[pp. <strong>68511</strong>-<strong>68560</strong>]] Ergonomics Program

[[Continued from <strong>page</strong> 68510]]

[[<strong>Page</strong> <strong>68511</strong>]]

adverse health effects occur, a point advanced by several in their 
testimony to the docket (e.g., United Parcel Service, Ex. 500-197, pp. 
I-68; Vender attachment to UPS post-hearing comments, Ex. 500-118, <strong>page</strong> 
17). Dr. Hadler opined that ``whenever a relationship between exposure 
and effect is not linear (not monotonic), you can be sure there are 
confounders, * * *.'' (Hadler attachment to UPS post-hearing comments, 
Ex. 500-118, <strong>page</strong> 4). He offered no evidence in support of this 
assertion, and in fact there is no requirement in epidemiology that the 
relationship must either be linear or monotonic. OSHA has relied on 
non-linear dose-response relationships in other health standard 
rulemakings (see Formaldehyde, 54 FR46168, Cadmium 57 FR 42101).
    Second, most exposure-response relationships do not indicate a 
single exposure level that unambiguously differentiates risk from no 
risk. This is especially true if exposure is treated as continuous and 
the relationship fits a straight line through the origin, in which case 
each small increment in exposure increases the probability of an 
adverse health outcome and, extrapolated downward, there may be no 
discernable point without excess risk above the zero exposure level. 
Note that in this regard U.P.S. criticized OSHA for the assumption 
that, in fact, UPS had made: ``OSHA has falsely assumed that any 
increment of human muscle usage is harmful, * * *.'' (United Parcel 
Service, Ex. 500-197, pp. I-68).
    On the other hand, when exposures have been categorized and are 
ordinally associated with risk of disease, it can be argued that the 
first exposure level where an elevated risk is observed above baseline 
represents an appropriate point for a permissible exposure level (at 
least until subsequent studies clarify whether there is still excess 
morbidity occurring below that level). This type of approach was taken 
recently by the American Conference of Governmental Industrial 
Hygienists (2000), which used essentially the same epidemiologic 
evidence available to OSHA--with its variety of exposure metrics--to 
determine the proposed new Threshold Limit Value<Register> for 
occupational hand activity level (see Exs. 38-162, DC-387).
    Several authors have called attention to the complexity of the 
process of utilizing exposure-response data for quantitative risk 
assessment in the multi-dimensional domain of physical ergonomics 
(e.g., Armstrong et al., 1993: Ex. 26-1110; Burdorf et al., 1997: Ex. 
500-121-13; Frank et al., 1996: Ex. 502-407; Kilbom, 1999: Ex. 38-406; 
Viikari-Juntura et al., 1999: Ex. 500-121-73). OSHA finds that it is 
reasonable to conclude, as these experts have done, that there is a 
need for continuing study of those relationships and interactions, 
while at the same time, that it is appropriate to implement the 
scientific knowledge in hand in order to reduce the risk of work-
related MSDs.
    In the preamble to the proposed rule (64 FR 65768), OSHA presented 
the results of several studies that provided evidence for positive 
trends between exposure to biomechanical risk factors and the 
prevalence or incidence of MSDs. Three commenters critiqued twelve of 
these studies, claiming a variety of design or methodological flaws in 
the studies, computational errors in the studies, or that OSHA misused 
some of the data (Exs. 30-276, 500-79, 32-241-4). The comments are 
those of Dr. Steven Moore, Professor, Environmental and Occupational 
Health, Texas A&M University (Ex. 30-276), Marathon Ashland Petroleum 
LLC (Ex. 500-79), and Gibson, Dunn & Crutcher (Ex. 32-241-4). Marathon 
Ashland Petroleum LLC includes Dr. Moore's comments as an Appendix. 
Gibson, Dunn & Crutcher summarize the critiques of several experts, 
whose statements are attached to their comment. OSHA responds to all 
these comments below.
    Dr. Moore and Gibson, Dunn & Crutcher criticized the study on risk 
factors for CTS by deKrom et al., (1990, Ex. 500-41-28). They claim 
that the study does not account for psychosocial factors and that it is 
methodologically flawed in relying on self-reported information about 
duration of exposure, rendering the results meaningless. With respect 
to the lack of analysis on psychosocial factors, OSHA acknowledges that 
this case-control study, with cases mostly of hospital outpatients and 
controls from the general population, did not examine or control for 
psychosocial factors. However, OSHA finds nothing in the design and 
analysis of this study that would invalidate the statistically 
significant positive associations among work related physical factors 
and CTS that the study did find. The authors concluded that activities 
with a flexed wrist or with an extended wrist (exposure-related 
increased ORs) were risk factors for CTS. Dr. Moore criticized the 
duration analysis used to estimate exposure-response as a function of 
time, claiming that the survey questionnaire instrument for collecting 
exposure information was unreliable. OSHA responds that with little 
information about the survey questionnaire in the published paper, the 
agency cannot determine the reliability. However, from a description in 
the paper of the blindness with which the survey was administered, OSHA 
believes that such an imperfect exposure measurement instrument would 
yield non-differential exposure misclassification. Such non-
differential misclassification would bias both the ORs and the slope 
toward a finding of no increasing trend. The fact the deKrom et al. 
study found statistically significant ORs for each incremental number 
of weekly hours of activities with extended or flexed wrist separately, 
plus finding a statistically significant exposure-response trend for 
both duration variables, despite the negative bias, provides strong 
evidence that the effect is real. This finding is further strengthened 
by the final analysis of de Krom et al. which used a multiple 
regression model simultaneously containing both duration of ``flex'' 
and ``extended'' wrist activities as variables, with both variables 
found to be statistically significant for duration-of-exposure-response 
trends (Ex. 500-41-28, pg. 1108). The finding of joint statistical 
significance of collinear variables when simultaneously modeled 
increases confidence in the significance of the separate variables.
    OSHA also responds to the criticism that ``in a conclusion that 
would devastate OSHA's attempt to redesign the American office, [deKrom 
et al.] found no significant risk of CTS related to typing.''OSHA notes 
that of the 156 cases of CTS, only 12 cases reported any work-related 
typing at all. In a case-control study such as this with only 12 cases 
exposed to typing, the statistical ability to determine a significant 
result is very small. Either a different study recruitment procedure or 
a much larger sample size would be required. With respect to another 
criticism by Gibson, Dunn & Crutcher on the apparently spurious finding 
of an association of CTS with varicosis in men, the authors reported 
this result of their analysis for the scientific world to contemplate, 
but found it inconsistent with that of other authors (Ex. 32-241-4).
    Dr. Moore also criticizes OSHA's use of the MSD prevalence study by 
Luopajarvi et al., (1979, Ex. 26-56) used as part of the agency's 
determination of causality for hand/wrist tendinitis. Dr. Moore claims 
the study's poor exposure assessment and lack of statistical 
comparisons provide poor support. In response, OSHA notes that the same 
exposure assessment methods were used in the study comparisons between 
the assembly-line packers and the shop assistants, so that the 
differences should be unaffected. OSHA also notes that

[[<strong>Page</strong> 68512]]

these comparison showed that the assembly-line packers had a highly 
statistically significant (p0.001) increased prevalence of (1) 
syndromes found in the neck, shoulders and elbows; and (2) muscle-
tendon syndromes in the hands (p0.001). The most common neck syndrome 
in this study was tension neck and the most common shoulder disorder 
was humeral tendinitis. For hands, Luopajarvi et al. noted the 
prevalence of tenosynovitis/peritendinitis at 53% in the assembly-line 
packers, but only 14% in the shop-assistants (who endured prolonged 
standing, but otherwise physically light work). For the assembly-line 
packers the authors noted especially the repetitive motions at a high 
speed, and fingers and hands constantly used at the pace of the 
machine, up to 25,000 cycles per workday. For these packers the authors 
also noted difficult static muscle work, extreme work positions of the 
hands, and difficult lifting. OSHA believes that this study provides a 
good comparison between similar demographic groups, and that it 
provides good evidence that work-related physical stress factors were 
causing shoulder and upper extremities injuries.
    Dr. Moore also claims that errors in the evaluations of two other 
studies are materially related to the NIOSH's and OSHA's conclusions 
(Ex. 30-276, pg. 2). With respect to the study by Kuorinka and 
Koskinen, he criticizes NIOSH for not specifically mentioning the 
``non-positive'' finding of no evidence of association of with time 
spent in deviated wrist postures per day. OSHA responds that the 
Kuorinka and Koskinen study did not specifically mention peritendinitis 
and tenosynovitis in its analysis, only the total complex of muscle-
tendon syndrome. Their definition of muscle-tendon syndrome used in 
this study came from an accompanying article they coauthored in the 
same journal (see Ex. 26-1218); the definition included syndromes of 
the shoulder and elbow, along with the wrist and hands. Every one of 
the seventeen (out of 93) manual workers with muscle-tendon syndrome 
also had tension neck syndrome, but none was specifically identified as 
having either peritendinitis or tenosynovitis (Ex. 26-639). While Dr. 
Moore is correct that Kuorinka and Koskinen found no correlation 
between the number of signs in the wrist and the deviation load of the 
wrist joint (1979, Ex. 26-639). OSHA finds too few details in the 
analysis for any conclusions with respect to peritendinitis and 
tenosynovitis.
    Dr. Moore also criticizes the NIOSH 1997 (Ex. 26-1) review for its 
failure to include the findings of a second study, Armstrong et al., 
(1987, Ex. 500-41-4) in NIOSH's evaluation on the effect of posture for 
hand/wrist tendinitis. Dr. Moore claims that NIOSH rated the Armstrong 
et al. study as high quality for other physical risk factors (i.e. 
force and repetition, for which the study found highly statistically 
significant associations) but didn't include the study at all in the 
discussion of the effect of posture. Armstrong et al. reported no 
significant associations for differences in posture ``comparing the 
percentage of the time spent in various postures between jobs in which 
there were workers with tendinitis and those in which there were no 
workers with tendinitis'' (Ex. 500-41-4). Dr. Moore claims that this 
omission by NIOSH and OSHA is an error in evaluation and that this 
error ``would likely have a material impact on the conclusion'' (Ex. 
30-276).
    OSHA has considered Dr. Moore's claim about NIOSH's evaluation of 
the Armstrong et al. study and has concluded that while Dr. Moore is 
correct in his claim that Armstrong et al. found no associations with 
the posture variable stated above, there is simply not enough detail in 
the publication to weight that study highly with regard to the posture 
variable. With this study group Armstrong et al. found a highly 
statistically significant odds ratio of 29.4 (p0.001) for high force/
high repetitiveness hand/wrist motion compared with a low force/low 
repetitiveness motion group. These groups appeared well defined and 
well studied with respect to force and repetitiveness, with 652 workers 
divided fairly evenly among the four groups increasing the statistical 
power to detect an effect if one exists. However, no detail is given 
for the posture analysis, only a short paragraph result (Ex. 500-41-4). 
To study this same highly force- and repetitiveness-stressed group for 
the effect of posture differences on hand/wrist tendinitis, (and CTS, 
see Silverstein et al., 1987, Ex. 26-34, and comment in Ex. 32-241-4, 
pg.143) would appear to be quite difficult, considering the proven 
effect of force and repetitiveness as risk factors in this worker 
group. Silverstein et al. (1986) studying essentially the same group, 
discussed postures, stating:

    (W)rist postures required on a job are often determined by the 
height of the work station with respect to the location of the 
worker. * * * to test this hypothesis the job of each worker in a 
job would have to have been videotaped and analyzed. This was not 
done in this investigation. * * * Awkward postures (wrist deviation, 
flexion, hyperextension, and finger pinching) * * * were not 
controlled for in this investigation. (Ex. 26-1404).

    OSHA concludes that NIOSH was correct in not considering the 
Armstrong et al. (Ex. 500-41-4) and Silverstein et al.1986 and 1987, 
(Exs. 26-1404, 26-34) study further for posture with this particular 
study group.
    Gibson, Dunn & Crutcher also criticize OSHA's omission that the 
Armstrong et al., study ``found no significant association between * * 
* vibration and [hand/wrist tendinitis] (Ex.32-241-4, pg. 140). OSHA 
responds that the Armstrong et al., 1987, (Ex. 500-41-4) publication 
provided less information about vibration in the study group than it 
did about posture, and that apparently it was not a well studied factor 
in this group.
    Dr. Moore also criticizes the ``NIOSH and OSHA reviews [for] 
inappropriately generaliz[ing] results of some studies beyond the 
constructs used to measure or categorize MSD risk factor [i.e., force 
and repetitiveness]'' (Ex. 30-276, pg. 2-3), singling out Armstrong et 
al. (Ex. 500-41-4) and Silverstein et al., 1987, (Ex. 26-34). OSHA has 
considered this comment and disagrees with Dr. Moore. Most authors 
define risk factors slightly differently and the NIOSH analysis had to 
categorize the slightly different definitions into categories. OSHA 
believes this categorization does not detract from either the NIOSH 
analysis or the ability to generalize that force and repetitiveness are 
etiologically related to hand/wrist tendinitis. In fact, OSHA believes 
that the different studies' abilities to detect significant 
associations using different definitions actually make the overall 
results more generalizable.
    Gibson, Dunn & Crutcher, also criticize the Silverstein et al., 
1986 study of hand wrist cumulative trauma disorders (CTDs, Ex. 26-
1404, and by implication Exs. 26-34 and 500-41-4) for being 
methodologically flawed, specifically citing recall bias and observer 
bias as leading to an overestimation of the associations between risk 
factors and health effect (Ex. 32-241-4, pg. 142-143). They also cite 
the study's cross-sectional design, the omission of a number of jobs 
from the investigation, and lack of analysis on non-biomechanical 
factors as serious flaws.
    OSHA has considered this criticism of the methodology, but 
disagrees with the characterization that a cross-sectional design 
cannot establish causation. In another section of this preamble, OSHA 
discusses the value of all the studies together in forming a database 
to determine causality. OSHA also notes

[[<strong>Page</strong> 68513]]

the claims of bias in this study, but agrees with the Silverstein et 
al., 1986 study authors who found significant positive and publishable 
associations between hand wrist CTDs and high force-high repetitive 
jobs:

    The findings in this investigation may also have underestimated 
the prevalence of hand wrist CTDs in several ways. Firstly, subject 
selection was limited to active workers. those away from the job 
with CTDs at the time of evaluation (potentially severe cases) would 
not have been available for study. Secondly, the one year seniority 
criteria for subject selection excluded those who might have had 
CTDs and transferred before one year as well as those with CTDs but 
not on the job for at least one year. The finding that hand wrist 
CTDs were negatively associated with age and years on the job 
support the argument of selection/survival bias in the study 
population [which would underestimate the effect] (Ex. 26-1404, pg. 
784).

    Gibson, Dunn & Crutcher criticize the study of shoulder pain in 
shipyard workers (welders and steel plate-workers) by Herberts et al., 
1984, (Ex. 26-51), for methodological flaws, including cross-sectional 
design, and the lack of demographic matching between the exposed and 
control groups. (Ex. 32-241-4, pg. 142). They also criticized OSHA for 
not recognizing what Herberts et al. did, have ``chronic shoulder pain 
is * * * common in people not necessarily active in arduous physical 
work.'' (Ex. 26-51, pg. 167). OSHA responds that the Agency does 
recognize that people other than those in HPW have shoulder pain; that 
recognition allows researchers, OSHA and other analysts to compare the 
prevalence of shoulder pain in workers doing HPW to that in workers not 
so engaged, in order to estimate the contribution from HPW. Herberts et 
al. also did this and concluded that ``Rotator cuff tendinitis 
constitutes a major problem in people with arduous occupations, i.e., 
shipyard welders (PR=18.3%), and steel plate-workers (PR=16.2%).'' By 
contrast, of the 57 clerks in the comparison group only one (1.7%) 
reported this disorder. Of this highly statistically significant 
difference, Herberts et al., note:

    Since the clerks are on an average older than the other two 
groups, there would be a higher likelihood of age-induced tendinitis 
in this [clerks] group. However, the hypothesis is that those with a 
high physical workload have tendinitis to a greater extent than 
normal. (Ex. 26-51).

    Gibson, Dunn & Crutcher also criticize OSHA's use of the Punnett et 
al., 1991 (Ex. 26-39) study of back disorders and nonneutral trunk 
postures in automobile assembly workers. The study is criticized as 
methodologically flawed in that it is a case-control study that does 
not consider non-biomechanical variables (Ex. 32-241-4, pg. 140). 
Gibson, Dunn & Crutcher quote the authors' own cautions of the 
limitations of such a design, which is necessarily retrospective in 
recalling exposures and pre-existing conditions. OSHA acknowledges the 
limitations of such as design. However, OSHA considers the design, 
conduct, and analysis of this study quite persuasive--in terms of 
strength of association, temporality, and exposure-response--in the 
overall determination of causality of BT and LBP; see OSHA's section on 
back disorders in this preamble. The authors in their publication 
conclude:

    Back disorders were associated with mild trunk flexion (OR=4.9 
(p5% C.I. 1.4-17.4), severe trunk flexion (OR=5.7, 95% C.I. 1.6-
20.4), and trunk twist or lateral bend (OR=5.0, 95% C.I. 1.6-21.4). 
the risk increased with exposure to multiple postures and increasing 
duration of exposure. (Ex. 26-39, pg. 337).

    Gibson, Dunn & Crutcher also criticize Dr. Punnett's more recent 
study (1998, Ex. 26-38) of upper extremity disorders in vehicle 
manufacturing, as being methodologically flawed in that it is a cross-
sectional design and does not include an analysis of the relative 
importance of psychosocial factors. OSHA has considered this comment 
and disagrees. Even though this study is cross-sectional, OSHA 
considers it well-conducted and analyzed. Using a primary exposure 
score relating to responses to psychophysical exposure items, Punnett 
found both statistically significant PRs and significant exposure-
response relationships for both (1) shoulder and upper arm disorders 
and (2) wrist and hand disorders. The results were consistent when the 
analyses were done both for the symptom cases and the physical 
examination cases. The authors concluded that ``musculoskeletal 
disorders of the upper extremities were strongly associated with 
exposure to combined ergonomic stressors.'' (Ex. 32-241-4) Gibson, Dunn 
& Crutcher also criticize OSHA's use of the prospective study by Liles 
and Deivanayagam, 1984 (Ex. 26-33) on job severity index (JSI) for the 
evaluation and control of lifting injury of the back. The JSI is a 
function of lifting frequency of task, maximum required weight of lift, 
adjusted capacity of the individual, and total lifting frequency. 
Criticism of the study focuses on a potential bias which Gibson, Dunn & 
Crutcher call a ``nocebo effect'', a bias due to differential reporting 
of pain symptoms by the subjects, knowing that their symptoms are being 
monitored. OSHA responds that such a potential bias is purely 
speculative, and, in any case, does not explain either the increasing 
injury rate, the cumulative disabling injury rate or the cumulative 
severity rates seen with increasing JSI. (Ex. 26-33, pgs. 690-691).
    Gibson, Dunn & Crutcher also criticize the study by Snook et al., 
(1978, Ex. 26-35) on three preventive approaches to low back injury. 
The study is criticized as being methodologically flawed in that it is 
a cross-sectional study which looks solely at biomechanical risk 
factors, and cannot establish causation. However, Gibson, Dunn & 
Crutcher also quote several portions of the article that it wants OSHA 
to recognize: (1) that most cases of industrial back injury have no 
known cause, and recovery occurs before any cause is ever found, (2) 
some workers never suffer from low back pain regardless of their type 
of work, and others seem to get it in spite of what they do; and (3) 
``low back injuries are usually not serious; four out of five workers 
suffering from low back injuries return to the job within three 
weeks.'' (Ex.32-241-4). OSHA responds that this Snook et al., case-
series study of 191 low back injuries is of limited usefulness in 
determining causality, but it does suggest that low back injury is 
associated with excessive manual handling tasks. OSHA also acknowledges 
the general apparent truthfulness of statement (2), by Snook et al., 
but can find no reference for it in the article. Statement (1) of Snook 
et al., references a 1970 published article and a 1971 editorial. There 
is more recent science available. Statement (3) cites one 1966 study as 
its reference.
    Gibson, Dunn & Crutcher also criticize a study by (1992, Ex. 26-36) 
on low back and neck/shoulder pain in construction workers. They claim 
that the study is methodologically flawed in that it is cross-sectional 
in design, limiting its ability to show causality. At the same time 
they criticize OSHA for failing to discuss the study's findings of 
positive associations between LBP and both psychosocial factors and 
age, as well as the finding(s) of no significant association between 
sitting posture and LBP (and severe LBP). OSHA responds that with 
respect to sitting (>4 hours) posture and the Holmstrom et al. (Ex. 26-
36) finding of no significant association with either LBP or severe 
LBP, both NIOSH (Ex. 26-1, pg. 6-47) and OSHA (see Table on back 
studies considered) do consider the finding of this study as ``no 
association'' for SWP and LBP. With respect to specific psychosocial 
factors being significant in this analysis, OSHA concurs. However, the 
discussion of psychosocial factors

[[<strong>Page</strong> 68514]]

by Holmstrom et al. fails to mention whether or not the multiple 
regression model used also found the physical risk factors 
simultaneously statistically significant with these data, which would 
suggest that physical and psychosocial factors are independent risk 
factors (Ex. 26-36, pg. 667).
4. Comments on the Role of Individual and Non-Work Factors
    In their posthearing testimony, Gibson, Dunn and Crutcher assert 
that:

    In developing its unfounded assertion that biomechanical 
workplace factors play a predominant role in the development of 
MSDs, OSHA has also ignored a great number of scientifically valid 
studies establishing that non-work-related factors, such as genetic 
predisposition, age, general health, smoking, social activities, and 
psychosocial factors exert a greater influence than biomechanical 
factors on the development of MSDs (Ex. 500-118).

Other commenters also expressed concern about the role of non-work 
factors in the etiology of MSDs (e.g., Exs. 30-1722, 60-2037, 30-4184, 
30-3077, 30-1352, 30-4130, 30-3922, 30-3114, 30-3354).

    While some commenters tended to lump individual factors along with 
psychosocial factors, these two types of factors are clearly separate 
and distinct. OSHA has separated its discussion of individual factors 
from that of psychosocial factors, and has fully addressed comments on 
psychosocial factors later in this part of the Health Effects section. 
In this section OSHA presents it's response to comments in the record 
on individual factors, sometimes called ``personal'' factors. The 
factors that are discussed in the literature include age, 
susceptibility, either by genetic predisposition or medical conditions, 
and other factors that may be thought of as those that modify the 
capacity of individuals to perform work.
    The above post-hearing comment (Ex. 500-18) makes two claims:
    (1) that OSHA ignored an entire body of literature relevant to this 
rulemaking, and
    (2) that had OSHA not ignored this body of literature, it would 
have come to an opposite conclusion than that reached by OSHA, i.e., 
that these factors ``exert a greater influence'' presumably than 
biomechanical risk factors, on the development of MSDs.
    OSHA, in fact, did not ignore the literature on individual factors. 
On the contrary, OSHA introduced the appendices to the proposed Health 
Effects section with a discussion of ``Individual Factors and 
Epidemiology of Work-Related Musculoskeletal Disorders,'' stating that:

    The multifactorial nature of MSDs requires a discussion of 
individual factors that have been studied to determine their 
association with or influence on the incidence and prevalence of 
work-related MSDs. These factors include age (Guo et al., 1995; 
Biering-Sorensen et al., 1983; English et al., 1995; Ohlsson et al., 
1994); gender (Hales et al., 1994; Johansson, 1994; Chiang et al., 
1993; Armstrong et al., 1987a); anthropometry (Werner et al., 1994; 
Nathan et al., 1993; Heliovaara, 1987); physical activity 
(Holmstrom, Lindell, and Moritz, 1992; Baron et al., 1991; Craig et 
al., 1998); strength (Chaffin and Park, 1973; Chaffin et al., 1977; 
Troup, Martin, and Lloyd, 1981); cigarette smoking (Finkelstein, 
1995; Owen and Damron, 1984; Svensson and Andersson, 1983; Kelsey, 
Golden, and Mundt, 1990; Hildebrandt, 1987); and alcohol, caffeine, 
and vitamins (Nathan et al., 1996, Keiston et al., 1997). In 
addition, psychosocial factors have been associated with upper-
extremity and back disorders (Ex. 27-1, p. I-1).

    OSHA has stated elsewhere that it relied on two major reviews of 
the evidence for work-relatedness of MSDs available at that time, 
NIOSH's ``Musculoskeletal Disorders and Workplace Factors: A Critical 
Review of the Epidemiologic Evidence for Work-Related Musculoskeletal 
Disorders of the Neck, Upper Extremity, and Low Back'' (Bernard, 1997; 
Ex. 26-1) and the National Research Council/National Academy of 
Sciences' ``Workshop on Work-Related Musculoskeletal Injuries: The 
Research Base'' (Ex. 26-37). OSHA believes that it was appropriate to 
place great weight on these two sources, as they are comprehensive 
reviews of recent peer-reviewed scientific literature conducted by 
highly-reputable and independent groups of scientists expert in their 
respective fields.
    To the extent that the studies reviewed by NIOSH considered 
exposure to nonoccupational physical activities, such as 
nonoccupational VDT use, hobbies, second jobs, and household activities 
that might increase risk for MSDs, NIOSH included this information in 
its review, and acknowledges that:

a number of factors can influence a person's response to risk 
factors for MSDs in the workplace and elsewhere. Among these are the 
following: age, gender, smoking, physical activity, strength, 
anthropometry.

    The literature, as reviewed by NIOSH (NIOSH, 1997; Ex. 26-1): on 
each of these individual factors is summarized here:
    Age: The prevalence of MSDs increases as people enter their working 
years. By the age of 35, most people have had their first episode of 
back pain (Guo et al. 1995, Ex. 26-1474; Chaffin 1979, Ex. 26-1489). 
Once in their working years (age 25 to 65), however, the prevalence is 
relatively consistent (Guo et al. 1995, Ex. 26-1274; Biering-Sorenson 
1983, Ex. 26-843). Musculoskeletal impairments are among the most 
prevalent and symptomatic health problems of middle and old age. 
Nonetheless, age groups with the highest rates of compensable back pain 
and strains are the 20-24 age group for men, and the 30-34 age group 
for women.
    NIOSH acknowledges that age-related degenerative disorders may 
result in decreases in musculoskeletal function, and loss of tissue 
strength with age may also increase the probability or severity of soft 
tissue damage. NIOSH also notes that:

    Another problem is that advancing age and increasing number of 
years on the job are usually correlated. Age is a true confounder 
with years of employment, so that these factors must be adjusted for 
when determining relationship with work. Many of the epidemiologic 
studies that looked at populations with a wide age variance have 
controlled for age by statistical methods.

    However,

Several studies found age to be an important factor associated with 
MSDs (Guo et al. 1995; Biering-Sorenson 1983; English et al. 1995; 
Ohlsson et al. 1994; Riihimaki et al. 1989a; Toomingas et al. 1991) 
others have not (Herberts et al, 1981; Punnett et al. 1985). [Ex. 
26-1]

    Riihimaki et al. (1989, Ex. 26-58) found a significant relationship 
between sciatica and age in machine operators, carpenters, and 
sedentary workers. Age was also a strong risk factor for neck and 
shoulder symptoms in these same groups of workers (Riihimaki et al. 
1989, Ex. 26-58).
    When a study does not find a relationship between an increased risk 
for MSDs and aging, lack of an observed relationship may be due to 
``survivor bias.'' If workers who have health problems leave their 
jobs, or change jobs to one with less exposure, the remaining 
population includes only those workers whose health has not been 
adversely affected at their jobs. As an example, in a study of female 
plastics assembly workers, Ohlsson et al. (1989, Ex. 26-1290) reported 
that the degree of increase in the odds of neck and shoulder pain with 
the duration of employment depended on the age of the worker. For the 
younger subjects, the odds increased significantly as the duration of 
employment increased, but for the older ones no statistical change was 
found with length of employment. The older women who had been employed 
for shorter periods of time had more reported symptoms than the

[[<strong>Page</strong> 68515]]

younger ones, while older workers with longer employment times reported 
fewer symptoms than younger workers. Ohlsson et al. (1989, Ex. 26-1290) 
interviewed 76 former assembly workers and found that 26% reported pain 
as the cause of leaving work. This finding supports the likely role of 
a survivor bias in this study, the effect of which is to underestimate 
the true risk of developing MSDs, in this case in the older workers.
    Some studies report observing an increased risk for MSDs with age, 
others do not. Where the effects of age have been controlled for in 
studies, thus eliminating the influence of ``age'' in the equation, the 
physical risk factors discussed here have been consistently shown to be 
associated with the development of MSDs in exposed populations. This 
means that, regardless of whether or not age plays a role in the 
development of a particular MSD in a particular population, the 
influence of physical risk factors is independent.
    Gender Some studies have found a higher prevalence of some MSDs in 
women (Bernard et al. 1994, Ex. 26-842; Hales et al. 1994, Ex. 26-131; 
Johansson 1994, Ex. 26-1331; Chiang et al. 1993, Ex. 26-1117). A male-
to-female ratio of 1:3 was described for carpal tunnel syndrome (CTS) 
in a population study in which occupation was not evaluated (Stevens et 
al. 1988, Ex. 26-1009). However, in the Silverstein et al. (1985, Ex. 
26-1173) study of CTS among industrial workers, no gender difference 
could be seen after controlling for work exposure. Franklin et al. 
(1991, Ex. 26-948) found no gender difference in workers' compensation 
claims for CTS. Burt, Hornung, and Fine (1990, Ex. 26-698) found no 
gender difference in reporting of neck or upper-extremity MSD symptoms 
among newspaper employees using video display terminals (VDTs). Nathan 
et al. (1988, Ex. 26-990; 1992, Ex. 26-988) found no gender differences 
for CTS. In contrast, Hagberg and Wegman (1987, Ex. 26-32) reported 
that neck and shoulder muscular pain is more common among females than 
males, both in the general population and among industrial workers.
    Whether the gender difference seen with some MSDs is due to 
physiological differences or differences in exposure is unclear. One 
laboratory study, Lindman et al. (1991, Ex. 26-976), found that women 
have more type I muscle fibers in the trapezius muscle than men, and 
have hypothesized that myofascial pain originates in these type I 
muscle fibers. Ulin et al. (1993, Ex. 26-223) noted that significant 
gender differences in work posture were related to stature and 
concluded that the lack of workplace accommodation to the range of 
workers' height and reach may, in part, account for the apparent gender 
differences.
    The fact that more women are employed in hand-intensive jobs and 
industries may account for the greater number of reported work-related 
MSDs among women. Bystrom et al. (1995, Ex. 26-897) reported that men 
were more likely to have de Quervain's disease than women; they 
attributed this to more frequent use of hand tools.
    The reporting bias may exist because women may be more likely to 
report pain and seek medical treatment than men (Armstrong et al., 
1993; Hales et al., 1994). Some studies have reported that workplace 
risk factors account for increased prevalence of MSDs among women more 
than personal factors (e.g., Armstrong et al. 1987, Ex. 26-1110; 
McCormack et al. 1990, Ex. 26-1334). In a recent evaluation of Ontario 
workers' compensation claims for repetitive strain injury (RSI), Asbury 
et al. (1995, Ex. 26-250) reported a relative risk (RR) for female to 
male claims ranging from 1.3 to 1.6 across industries. Within five 
different broad occupational categories, females were approximately 2 
to 5 times as likely to have a lost-time RSI claim. No information on 
gender differences in hand-intensive jobs was reported. Many 
researchers have noted that men and women tend to be employed in 
different jobs.
    Smoking. In the Viikari-Juntura et al. (1994, Ex. 26-873) 
prospective study of machine operators, carpenters, and office workers, 
current smoking (OR: 1.9; 95% CI: 1.0-3.5), was among the predictors 
for change from ``no neck trouble'' to ``severe neck trouble.'' In a 
study of Finnish adults aged 30 to 64 (Makela et al. 1991, Ex. 26-980), 
neck pain was found to be significantly associated with current smoking 
(OR: 1.3; 95% CI: 1.0-1.61) when the logistic model was adjusted for 
age and gender. However, when the model included mental and physical 
stress at work, obesity, and parity, then smoking (OR: 1.25; 95% CI: 
0.99-1.57) was no longer statistically significant (Makela et al. 1991, 
Ex. 26-980). With univariate analysis, Holmstrom (1992, Ex. 26-36) 
found a prevalence rate ratio (PRR) of 1.2 (95% CI: 1.1-1.3) for neck/
shoulder trouble in ``current'' smokers vs. people who ``never'' 
smoked. But using multiple logistic regression, when age, individual, 
and employment factors were in the model, only ``never smoked'' 
contributed significantly to neck/shoulder trouble.
    While investigating reasons for higher compensation claims for CTS 
in certain employee groups, Nathan et al. (1996, Ex. 26-882) evaluated 
the effects of tobacco, caffeine, and alcohol on the prevalence of 
median entrapment neuropathy at the wrist, CTS symptoms, and CTS 
confirmed by nerve conduction studies among industrial workers 
(nonclaimants and working patients referred for upper-extremity 
symptoms) who volunteered for the study. Nathan et al. (1996, Ex. 26-
882) stated that greater use of tobacco combined with greater 
consumption of caffeinated beverages and alcohol abuse was associated 
with more median nerve slowing, more specific hand/wrist symptoms, and 
more electrophysiologically confirmed CTS. However, the effects 
explained only a small portion of the total risk.
    Toomingas et al. (1991, Ex. 26-1019) found no associations between 
multiple health outcomes (including tension neck syndrome, rotator cuff 
tendinitis, CTS, or problems in the neck/scapula or shoulder/upper arm) 
and nicotine habits among platers, assemblers, and white collar 
workers. In a case/referent study, Wieslander et al. (1989, Ex. 26-
1027) found that smoking or using snuff was not related to CTS among 
men operated on for CTS.
    Several papers have presented evidence that a positive smoking 
history is associated with low-back pain, sciatica, or intervertebral 
herniated disc (Finkelstein 1995, Ex. 26-369; Frymoyer, Pope, and 
Clements 1983, Ex. 26-950; Svensson et al. 1983, Ex. 26-1158; Kelsey et 
al. 1984, Ex. 26-152); whereas other papers have found a negative 
relationship (Kelsey, Golden, and Mundt 1990, Ex. 26-52; Riihimaki et 
al. 1989, Ex. 26-997). Boshuizen et al. (1993, Ex. 26-81) found a 
relationship between smoking and back pain only in those occupations 
that required physical exertion. In their study, smoking was more 
clearly related to pain in the extremities than to pain in the neck or 
the back. Deyo and Bass (1989, Ex. 26-105) observed that the prevalence 
of back pain increased with the number of pack-years of cigarette 
smoking and with the heaviest smoking level. Heliovaara et al. (1991, 
Ex. 26-959) only observed a relationship in men and women older than 50 
years. Two studies did not find a relationship between sciatica and 
smoking among concrete reinforcement workers and house painters 
(Heliovaara et al. 1991, Ex. 26-959; Riihimaki et al. 1989, Ex. 26-
997).
    Several explanations for the relationship with smoking have been 
postulated. One hypothesis is that back pain is caused by coughing from 
smoking. Coughing increases the abdominal pressure and intradiscal 
pressure and puts strain on the spine. A

[[<strong>Page</strong> 68516]]

few studies have observed this relationship (Deyo and Bass 1989, Ex. 
26-105; Frymoyer et al. 1980, Ex. 26-707; Troup et al. 1987, Ex. 26-
1307). The other mechanisms proposed include nicotine-induced 
diminished blood flow to vulnerable tissues (Frymoyer, Pope, and 
Clements 1983, Ex. 26-950), and smoking-induced diminished mineral 
content of bone causing microfractures (Svensson et al. 1983, Ex. 26-
1158). Similar associations with diminished blood flow to vulnerable 
tissues have been found between smoking and Raynaud's disease.
    Strength. Some epidemiologic support exists for the relationship 
between back injury and a mismatch of physical strength and job tasks. 
Chaffin and Park (1973, Ex. 26-1115) found a sharp increase in back 
injury rates in subjects performing jobs requiring strength that was 
greater than or equal to their isometric strength-test values. The risk 
was 3 times greater in the weaker subjects. In a second longitudinal 
study, Chaffin et al. (1977, Ex. 26-1111) evaluated the risk of back 
injuries and strength and found the risk to be 3 times greater in the 
subjects without lower static strength. Keyserling, Herrin, and Chaffin 
(1980, Ex. 26-970) strength-tested subjects, biomechanically analyzed 
jobs, and assigned subjects to either stressed or non-stressed jobs. 
Following medical records for a year, they found that job matching 
based on strength criteria appeared to be beneficial. In another 
prospective study, Troup, Martin, and Lloyd (1981, Ex. 26-1456) found 
that reduced strength of back flexor muscles was a consistent predictor 
of recurrent or persistent back pain, but this association was not 
found for first-time occurrence of back pain.
    Other studies have not found the same relationship with physical 
strength. Two prospective studies of low-back pain reports (or claims) 
of large populations of blue collar workers (Battie et al. 1989, Ex. 
26-72; Leino, Aro, and Hasan 1987, Ex. 26-1142) failed to demonstrate 
that stronger (defined by isometric lifting strength) workers are at 
lower risk for low-back pain claims or episodes. One study followed 
workers for 10 years after strength testing and the other followed 
workers for a few years. Neither of these studies included precise 
measurement of exposure level for each worker, so the authors could not 
estimate the degree of mismatch between workers' strength and task 
demands. Battie compared workers with back pain with other workers on 
the same job (by isometric strength testing) and did not find that 
workers with back pain were weaker. In two studies of nurses (Videman 
et al. 1989, Ex. 26-1155; Mostardi et al. 1992, Ex. 26-986), lifting 
strength was not a reliable predictor of back pain.
    When examined together, these studies reveal the following: the 
studies that found a significant relationship between strength and back 
pain used more thorough job assessment analysis and focused on manual 
lifting jobs. However, these studies only followed workers for periods 
of 1 year, and whether this same relationship would hold over a much 
longer working period remains unclear. The studies that did not find a 
relationship, although they followed workers for longer periods of 
time, did not include precise measurements of exposure level for each 
worker, so they could not assess the strength capabilities that were 
important in the jobs.
    Anthropometry. Weight, height, body mass index (BMI) (a ratio of 
weight to height squared), and obesity have all been identified in 
studies as potential risk factors for certain MSDs, especially CTS and 
lumbar disc herniation. Obesity seems to play a small but significant 
role in the occurrence of CTS (see Section B.4.a). Anthropometric data 
are conflicting, but in general indicate that there is no strong 
correlation between stature, body weight, body build, and low-back 
pain.
    Few studies examining anthropometric risk factors in relationship 
to CTS have been occupational epidemiologic studies; most have used 
hospital-based populations that may differ substantially from working 
populations. Nathan et al. (1988, Ex. 26-990; 1992, Ex. 26-989; 1994, 
Ex. 26-517) have published several papers about a single industrial 
population and have reported an association between CTS and obesity; 
however, the methods employed in their studies have been questioned in 
a number of subsequent publications (Gerr and Letz 1992, Ex. 26-384; 
Mackinnon et al. 1997, Ex. 26-1309; Stock 1991, Ex. 26-1010; Werner et 
al. 1994, Ex. 26-237). Several investigators have reported that their 
industrial study subjects with CTS were shorter and heavier than the 
general population (Cannon et al. 1981, Ex. 26-1212; Dieck and Kelsey 
1985, Ex. 26-944; Falck and Aarnio 1983, Ex. 26-1122; Nathan et al. 
1992, Ex. 26-989; Werner et al. 1994, Ex. 26-237; Wieslander et al. 
1989, Ex. 26-1027).
    Werner et al. (1994, Ex. 26-237) studied a clinical population 
requiring electrodiagnostic evaluation of the right upper extremity, 
patients classified as obese (BMI > 29) were 2.5 times more likely than 
slender patients (BMI  20) to be diagnosed with CTS. These researchers 
developed a multiple linear-regression CTS model (with the difference 
between median and ulnar sensory latencies as the dependent variable). 
The regression highlighted BMI as the most influential variable, but 
still only accounted for 5% of the variance in the model. In Nathan's 
(1994, Ex. 26-517) logistic model, BMI accounted for 8.6% of the total 
risk; however, this analysis used both hands from each study subject as 
separate observations, although they are not independent of each other. 
Falck and Aarnio (1983, Ex. 26-1122) found no difference in BMI among 
17 butchers with (53%) and without (47%) CTS. Vessey, Villard-
Mackintosh, and Yeates (1990, Ex. 26-229) found that the risk for CTS 
among obese women was double that for slender women.
    Nordstrom et al. (1997, Ex. 26-900), in a study of risk factors for 
CTS in a general population, concluded that BMI is one factor that 
seems to have a causal relation to CTS. These researchers found that 
for each increase of one unit of BMI, about 6 pounds for the average-
sized adult, risk of CTS increases by 8%. Werner et al. (1997, Ex. 26-
718), in a study at five different worksites (four industrial, one 
clerical), concluded that obesity (BMI > 29), industrial work, and age 
were independent risk factors for median mononeuropathies. Their study, 
which did not define specific work-related exposures, showed no 
significant interaction between work activity and obesity. However, the 
authors caution interpretation of the data and urge more investigation. 
It has been suggested that relationship of CTS with BMI involves 
increased fatty tissue within the carpal canal or increased hydrostatic 
pressure throughout the carpal canal in obese persons compared with 
slender persons (Werner 1994, Ex. 26-237).
    Two other anthropometric risk factors, carpal tunnel size and wrist 
size, have been suggested as risk factors for CTS; however, some 
studies have linked both small and large canal areas to CTS (Bleecker 
et al. 1985, Ex. 26-934; Winn and Habes 1990, Ex. 26-1029).
    Schierhout et al. (1995, Ex. 26-403) found that short stature was 
significantly associated with pain in the neck and shoulder but not in 
the forearm, hand and wrist, or back, among workers in 11 factories. 
Height was not a factor for neck, shoulder, or hand and wrist MSDs 
among newspaper employees (Bernard et al. 1994, Ex. 26-842). Kvarnstrom 
(1983, Ex. 26-1201) found no relationship between neck/shoulder MSDs 
and body height in a

[[<strong>Page</strong> 68517]]

Swedish engineering company with more than 11,000 workers.
    Examples exist where biomechanical or physical risk factors have 
been labeled as individual factors. During the hearing for this 
rulemaking, Dr. Niklas Krause mentioned two of these examples, the 
first refers to people in the military who drive tanks, and found that 
tall people have more back pain than short people. A very logical 
explanation for the observation of increased back pain was provided by 
Dr. Krause:

    Well, if you have ever entered a tank, you know that it is not 
constructed for very tall people. There is not much room in there. 
[Tr. 1378]
    And a second example, also provided by Dr. Krause:
    And we have actually found in our bus drivers, too, and we 
measured. We had their height and their weight. We found that an 
ergonomic evaluation of the bus fleet showed that the buses that are 
running in San Francisco were constructed for people--that is what 
the ergonomics Professor Thompson from Sanford found out when he 
looked at them--were constructed for people in the upper 10 percent 
of the North American population.
    You can imagine if you hire small people, Asians and women for 
example, into that work force and put them on this bus that the fit 
is bad. And actually, what we see is that over the years, the 
percentage of small drivers drops on that work force rapidly.
    When they enter, when people take the job, there is about 6 
percent of drivers who are small, defined as * * * the lower half of 
the population. * * * After one to five years, only 2.9 percent of 
these small people are in the workforce. After six to ten years, 
only 1.3 percent. And after eleven to fifteen years, only 0.4 
percent. This is a statistically significant trend. And it clearly 
shows you that people based on their smallness and misfit probably 
had to leave the occupation. [Tr. 1378-1380]

    When used to determine whether a correlation exists between 
stature, body weight, body build and low back pain, anthropometric data 
are conflicting, but in general indicate that there is no strong 
correlation. Obesity seems to play a small but significant role in the 
occurrence of CTS.
    Genetics. Another type of factor that affects an individual's 
capacity is genetic make-up. While the term ``genetic susceptibility'' 
is often heard; in reality both the amount of genetic information 
involved in the response and the variability of possible responses are 
vast and for the most part, not yet understood. The little bit of work 
done in this area was done by Videman, and is covered in a brief 
discussion in the section on the low back.
    A worker's ability to respond to work factors may be modified by 
his or her own capacity. The capacity to perform work varies with 
gender and age, among workers, and for any individual over time. The 
relationship between biomechanical risk factors, both inside and 
outside the workplace, these individual as well as other factors and 
the resulting risk of injury to the worker is complex, but not unique 
to this OSHA standard.
    For each of the ``individual factors'' discussed here, some studies 
report observing an increased risk for MSDs, others do not. What they 
have in common, is their ability to effect the capacity of individuals 
independently from biomechanical risk factors. In other words, in those 
studies where the effects of age, gender, smoking, etc. have been 
controlled for, the physical risk factors discussed here have been 
consistently shown to be associated with the development of MSDs in 
exposed populations. This means that, regardless of whether or not age 
plays a role in the development of a particular MSD in a particular 
population, the influence of biomechanical risk factors is independent 
from other associated factors. Furthermore, it has been demonstrated 
repeatedly, that reducing these biomechanical factors in the workplace 
results in reductions in the incidence of work-related MSDs.
    The AFL/CIO found that the record provides some additional evidence 
that individuals may vary in their susceptibility to developing certain 
work-related MSDs, such as carpal tunnel syndrome, based on individual 
factors including age, body weight and gender (Ex. 26-1, Ex. 26-37, Ex. 
500-71-93). They also found that other evidence in the record indicates 
that for back and neck pain or disorders, for example, no association 
with age, gender, height or weight has been established (Ex. 500-71-24, 
Tr. 1332).

    The AFL/CIO point out that:
    Obviously the underlying principle of ergonomics is to fit the 
job to the worker, and so personal physical characteristics do come 
into play when evaluating certain MSD risk factors. A worker who is 
5'2" may have a much longer reach to an assembly line than her 6'0" 
co-worker. But other than as relevant to evaluating exposure to 
known risk factors, personal characteristics and differences in 
susceptibility are irrelevant to this rulemaking. This regulation, 
and all other OSHA standards, are designed to regulate risks that 
are found in the workplace that may result in the development of an 
adverse outcome (MSDs) in workers who are exposed to risk factors 
which have been demonstrated to cause MSDs. The ergonomics 
regulation is consistent with OSHA's responsibility to regulate 
hazards which are present in the workplace. To shift the focus 
toward personal characteristics, as some industry opponents have 
argued, only clouds this issue by blaming the victims. [Ex. 500-218]
    On this same subject, Dr. Frederick Gerr, Emory University (Tr. 
1525-26):
    Some will argue that personal factors, such as gender and body 
weight, are the cause of these disorders among American workers, 
rather than ergonomics hazards in the workplace. The fact that 
personal characteristics can increase the risk for these disorders 
in no way undermines the evidence that work has been clearly shown 
to increase their risk as well.
    The blame-the-victim approach to these disorders is both 
scientifically and ethically bankrupt. Virtually all occupational 
illnesses, including asthma, cancer, skin disease, peripheral and 
central nervous system disorders, and many others, have causes that 
extend outside of the workplace. This fact does not lessen the added 
burden of disease that occupational exposures produce.

Non-Work Leisure Activities

    The commenters (e.g., Exs. 30-2493, 31-324, 30-3368, 30-605, 30-
3783, Tr. 5073) also raise the issue of the relationship of ``non-
work'' to the development of MSDs. By this, OSHA assumes the reference 
is to those activities such as nonoccupational VDT use, hobbies, second 
jobs, and household activities, activities that may result in 
additional exposure to biomechanical factors similar to that the 
individual is experiencing at the workplace. If this assumption is 
correct, then ``non-work'' may actually refer to exposure to the same 
types of physical/biomechanical factors that may be additive to similar 
workplace exposure.
    And, while it is true that the physical/biomechanical risk factors 
which increase the risk of MSDs at work can also be found outside of 
work and may lead to MSDs (Ex. 500-71-93). However, according to Dr. 
Nicholas Warren from the University of Connecticut (Tr. 1077-78):

    It is very seldom the case that home risk factors are 
encountered with the same intensity or the same duration as they are 
encountered in the workplace.
    On the same subject , the AFL/CIO (Ex. 500-218) notes:
    Opponents of the standard, while arguing that there is no 
evidence that physical factors at work cause MSDs, also 
simultaneously argue that it is non-work leisure physical activities 
which cause MSDs and that an OSHA standard cannot regulate adverse 
health conditions and exposures to risk factors which are partially, 
primarily or exclusively the result of non-work activities (Ex. 32-
241-4).
    For most musculoskeletal disorder cases, ``workplace factors are 
the predominant risk and it is upon these risks, obviously, that the 
OSHA proposed rule focuses (Tr.1079). Other evidence in the record 
confirms that there is little or no impact on the development of 
MSDs related to the back from non-work

[[<strong>Page</strong> 68518]]

participation in sports, exercise, and leisure time physical 
activity (Ex. 500-71-24, Ex. 500-71-32, Ex. 502-510).
    The AFL/CIO also states:
    Thus the record evidence suggests that the non-work exposures to 
risk factors rarely, if ever, occur at the same frequency, duration 
or magnitude as workplace exposures. Even where workers are exposed 
to non-work risk factors off the job, it is important to point out 
that this standard is designed only to decrease exposures to 
biomechanic risk factors occurring at the workplace. An analogy may 
be drawn to the risks of incurring hearing loss from excessive 
exposure to noise. Exposure to noise at levels and durations which 
can cause or contribute to noise-induced hearing loss can and do 
occur both at the workplace as well as in non-work situations. While 
these work and non-work exposures and risks of developing hearing 
loss exist, OSHA's noise standard is confined exclusively to 
addressing excessive noise exposures in the workplace. [Ex. 500-218]
    And from Dr. Nicholas Warren, University of Connecticut (Tr. 
1078-79):
    When I work with an individual with, for instance, carpal tunnel 
syndrome, carrying out forceful, repetitive tasks over most of a 
nominal 40 hour work week and then often into another 10 hours of 
voluntary overtime, it's painful to hear an insurer gleefully inform 
me that this person bowls in a league on Saturday night. It is 
equally painful to hear the worker blame him or herself by saying, 
``That's probably because I knit,'' when, in fact, a clear objective 
assessment of the workplace risk factors reveals that these are much 
more important in the etiology of his or her disease.

    OSHA concludes that, in general, each individual's capacity is 
affected differently by many factors including some of those presented 
here: age, gender, smoking, physical activity, strength, anthropometry, 
genetic factors and activities outside the workplace. This is also true 
in the more specific case of the development of work-related MSDs. 
However, it is important to remember that exposure to biomechanical 
factors in the workplace is independent of those factors that each 
individual brings to the workplace, i.e., when the influence of 
individual factors is controlled for in studies, effects due to 
exposure to biomechanical factors are still observed . It is also true 
that in the vast majority of cases, where exposure to biomechanical 
exposures is high, the effects due to biomechanical exposures are far 
greater than those associated with these types of individual factors.
5. Role of Psychosocial Factors in the Etiology of MSDs
    The role of psychosocial factors in the etiology of MSDs was a 
subject of much debate during the rulemaking. Many participants, in 
particular the Chamber of Commerce (Ex. 500-188), Gibson, Dunn & 
Crutcher (Exs. 32-241-4, 500-197), and several research and medical 
scientists who testified on behalf of UPS (Exs. 32-241-3-2, 32-241-3-3, 
32-241-3-5, 32-241-3-8, 32-241-3-12), criticized the proposed rule for 
its failure to take into account the contribution of psychosocial risk 
factors to MSD causation and exacerbation, believing that psychosocial 
factors play a significantly greater role than do biomechanical risk 
factors in the development of MSDs and the disabilities associated with 
them.
    Much of the scientific literature that addresses the etiology of 
MSDs has examined aspects of the social and psychological environment 
that may have a causal or moderating role in MSD development and 
exacerbation. In this part of the Health Effects section, OSHA first 
discusses what is meant in the literature by the term ``psychosocial 
factors.'' Following this discussion, OSHA summarizes the expert 
testimony of witnesses and rulemaking participants who have evaluated 
the body of psychosocial literature as it relates to the work-related 
risk of MSDs. Finally, OSHA presents its own literature review, 
summarizing specific studies contained in the rulemaking docket that 
have examined and compared the roles of biomechanical and psychosocial 
factors in the etiology of MSDs, and summarizes several literature 
reviews that have been published on this topic.

Definition of Psychosocial Factors

    The study of psychosocial factors as it applies to the study of 
work-related MSDs is surrounded by a measure of confusion because there 
are several very different definitions of ``psychosocial'' used in 
common and in technical parlance. Lack of clarity and consensus in 
defining psychosocial factors was addressed by some researchers at the 
public hearing (Tr. 867-868, 1306, 17443). There are three general 
concepts of psychosocial factors that apply. Most researchers who have 
examined the role of psychosocial factors in the etiology of MSDs have 
emphasized the external aspects of the psychological and social work 
environment that cause the worker to experience ``stress'', a condition 
of chronic or prolonged arousal of the human ``flight or fight'' 
mechanisms that has been linked to a wide variety of negative health 
outcomes, including MSDs. The primary aspects of the psychosocial work 
environment include level of psychological job demands, level of worker 
control over the job process, and level of social support received from 
co-workers, supervisors and the organization. Some researchers focus on 
additional conceptualizations of psychosocial exposures, including job 
security, monotony, and job satisfaction (for example, Krause, 1998, 
Ex. 38-242, Bigos, 1991b Ex. 26-1242). Psychosocial factors reflecting 
these external aspects of the work environment have been the subject of 
investigation in nearly all of the studies and literature reviews 
discussed in this section.
    As is the case with biomechanical risk factors, proposed exposure-
outcome relationships for psychosocial factors are multifactoral, i.e., 
several of these factors may be in play in any given situation, and may 
combine and interact in complex ways that are difficult to study and 
understand (Bongers et al., 1993, Ex. 26-1292, Bernard, 1997, Ex. 26-1 
Warren et al., 2000a, b, Exs. 38-75, 38-73). It is unlikely that these 
psychosocial workplace risk factors occur and act in isolation of 
biomechanical risk factors (Tr. 868-869, 1264, 5942-5943, NIOSH 1997 
(Ex. 26-1), NAS 1999 (Ex. 26-37)).
    A growing body of literature also identifies aspects of 
organizational structure, technology, policy, and culture as potential 
contributors to occupational disease and characterizes them as 
organizational risk factors (Shannon, et al., 1996, Ex. 26-1368, 1997, 
Ex. 26-1369, Warren, 1997, Ex. 38-72, Warren et al., 2000a, Ex. 38-75). 
Organizational risk factors are proposed as the underlying bases of 
work design in the company; through their effect on work organization, 
they determine levels of both psychosocial and biomechanical risk 
factors experienced by employees. It is this common set of roots that 
results in the strong co-variation of psychosocial and biomechanical 
risk factors noted below. The second concept of psychosocial factors 
that has been used in the literature relates to the internal 
characteristics of the worker's psychological makeup that affect how 
he/she appraises, processes and reacts to external biomechanical and 
psychosocial factors, and thus moderates how these external factors are 
experienced internally. There are studies demonstrating that individual 
psychological factors can increase susceptibility to MSD development 
and affect MSD recognition and reporting (Linton, 2000, Ex. 502-413, 
NAS, 1999 Ex. 26-37). Emerging research sugg influence care-seeking and 
disability than initial onset of disease (Linton, 1992, 2000, Ex. 502-
413 ests that internal psychological factors more strongly, Waddell & 
Burton, 2000, Ex. DC-151-A). Some researchers and physicians combine 
internal and external psychological factors in their

[[<strong>Page</strong> 68519]]

definition of psychosocial factors; for example, Dr. Raymond Bellamy, 
an orthopedic surgeon testifying on behalf of UPS et al., included such 
factors as dislike of job, recent poor performance evaluation, 
depression and anxiety, hypochondriasis, and desire for narcotics in 
his description of psychosocial factors (Ex. 32-241-3-3). Dr. Arthur 
Barsky, also testifying on behalf of UPS et al., stated that 
psychosocial factors (his use of the term conflates external factors 
and internal psychological factors) ``exacerbate, perpetuate, and 
maintain these [musculoskeletal] symptoms and amplify the disability 
they engender'' (post-testimony comments, p.1, Ex. 500-118-1). Thus, it 
is not always clear in the literature or in the testimony contained in 
the record when the term ``psychosocial factors'' is being used to 
refer to external psychological or social workplace factors, internal 
psychological makeup of the worker, or both.
    The third concept of psychosocial factors relates to aspects of the 
legal, insurance and medical environment that influence a worker's 
tendency to identify a particular constellation of symptoms as a 
disease. At its most extreme, this definition is used to claim that 
workers make up and fake disease, for ``secondary gain''. A broader 
interpretation is the argument that these aspects of legal and medical 
recognition and possible financial gain may subtly, even unconsciously 
influence a worker's honest identification of symptoms as a disease and 
predisposition to report it.
    Although individual psychological factors or medical/legal factors 
may affect MSD perception and reporting to a degree, it is unlikely 
that they play a major causal role in the etiology of MSDs. This is 
because the increased prevalence and incidence of MSDs seen among 
workers who are highly exposed to biomechanical risk factors cannot be 
adequately explained primarily by psychological factors given the 
present state of the evidence. As the discussion in this Health Effects 
section has demonstrated, the epidemiological, laboratory, 
psychophysical, and intervention literature demonstrating quantifiable 
links between biomechanical exposures and MSD outcomes is overwhelming. 
Many studies have demonstrated substantial differences in MSD incidence 
and prevalence between companies and industry sectors that correlate 
strongly with the presence of physical risk factors (for example, 
Franklin et al., 1991, Ex. 26-948, NAS, 1999, Ex. 26-37, see also the 
Risk Assessment section (Section VI) of this preamble). Thus, it is 
highly unlikely that an individual with psychological tendencies 
towards negative reactions at work or tendencies to seek out care-
givers would preferentially select themselves into physically demanding 
jobs. It is also impossible to imagine how prospects for secondary gain 
would be differentially distributed into occupations or industry 
sectors that involve highly physical work.
    Consequently, this part of the Health Effects section focuses on 
the large number of studies that have simultaneously examined the roles 
of biomechanical risk factors along with psychosocial factors that 
relate to external aspects of the psychological and social work 
environment. These studies generally represent the most recent studies 
of work-related MSDs in the literature.

Discussion of Testimony on the Psychosocial Literature

    Based on these studies, the Chamber of Commerce (Ex. 500-188) and 
Gibson, Dunn & Crutcher representing UPS, Anheuser-Busch, the National 
Coalition on Ergonomics, and others (e.g., Exs. 32-231-4, 500-197, 
32,435, 30-3346, Tr. 3655) were critical of OSHA emphasizing the role 
of biomechanical risk factors over psychosocial factors in its 
scientific literature review. For example, in their post-hearing brief, 
Gibson, Dunn & Crutcher commented that

    The science has shown that where psychosocial factors in 
particular are considered, they generally overwhelm the weak and 
inconsistent associations between biomechanical exposures and the 
reporting of MSDs. Yet the * * *  [A]gency dismissed the validity of 
psychosocial factors in cavalier fashion * * * [Ex. 500-197, p. I-
33]

Similarly, the Chamber of Commerce stated that ``The Agency has 
egregiously ignored each and every one of these indisputably relevant 
factors * * *'' (Ex. 500-188), and explained the necessity for OSHA to 
evaluate the role of psychosocial factors in the workplace:

* * * [D]etermining why individuals feel the need to report and/or 
to seek medical care for such complaints is a complex problem 
involving not only the physical exposures, but psychosocial factors 
such as job satisfaction, ability to control the work environment, 
interpersonal relationships at work, and the like * * * And, in the 
vast majority of studies that have assessed whether biomechanical 
workplace factors and psychosocial factors cause musculoskeletal 
complaints, psychosocial factors are just as significant, or more 
significant than, biomechanical factors. (Ex. 500-188, p. 41)

    In addition, several research and medical scientists testifying on 
behalf of UPS et al. stated in written or oral comment that the 
scientific literature strongly supported that psychosocial factors play 
a dominant role in the etiology of MSDs (Exs. 32-241-3-2,32-241-3-3, 
32-241-3-5, 32-241-3-8, 32-241-3-12). For example,
    Dr. Alf Nachemson concluded a review of the literature by stating 
that

* * * [t]he research indicates that psychosocial factors are not 
simply an overlay but rather an integral part of the pain disability 
process that includes emotional, cognitive and behavioral aspects * 
* * [T]here was strong evidence of the highest level that 
psychosocial variables generally have more impact than biomedical or 
biomechanical factors on pain disability.'' (Ex. 32-241-3-12, p. 13)

    Dr. Norton Hadler stated in written comment that

    Associations between disabling regional musculoskeletal symptoms 
and psychosocial variables overwhelm and explain away any and all 
associations with biomechanical exposures. (Ex.32-241-3-8, p. 18)

    Taking a more moderate interpretation of the literature, Dr. Arthur 
Barsky agreed that MSDs are not entirely a psychosocial problem; 
however, he felt that ignoring them in designing intervention programs 
can make the problem worse (Ex. 500-118-1, p. 1). At the public 
hearing, he explained that

* * * [workers'] symptoms really are better understood as a social 
communication, as a kind of non-verbal way of responding to 
difficulties in the workplace--job dissatisfaction, role conflicts, 
insecurity around the job, a whole variety of psychosocial work 
conditions--and to hear these as a biomedical complaint is to 
totally miss the point * * * What really concerns me, is * * * [that 
complaints of MSD symptoms are] a kind of social communication * * * 
a metaphor for life stress, for psychosocial distress * * * and the 
response that too often is made to a symptom like that, is [an 
inappropriate] referral to orthopedics. Tr. 17043-17044]

Dr. Barsky illustrated his point with an example of a widowed mother of 
two worked two jobs and visited the emergency room of a hospital 
complaining of tired feet [Tr. 17043-17044], and viewed the proposed 
ergonomics standard as an inappropriate response to such an 
``interpersonal communication'' (Tr. 17044).
    Other scientists testifying on behalf of the UPS echoed the 
conclusions reached by Dr. Nachemson in his literature review and Dr. 
Bigos, who referred to

[[<strong>Page</strong> 68520]]

his groups Boeing study (Ex. 26-1241, 26-1242,26-1393) in contending 
that low back pain (LBP) is primarily a psychosocial phenomenon (Exs. 
32-241-3-2, 32-241-3-5). Other commenters also remarked on the 
importance of psychosocial factors in the development of MSDs (e.g., 
Exs. 32-435, 30-3346, 30-3086, 30-536, 30-4046, 30-1070, Tr. 3655).
    Many of OSHA's scientific witnesses disputed these interpretations 
of the psychosocial literature, stating that the literature is not in 
conflict with the causal relationship that has been demonstrated 
between exposure to biomechanical risk factors and development of MSDs, 
and that psychosocial factors had generally less of an influence than 
biomechanical factors in these studies (Tr. 842, 874, 1087, 1206, 1364, 
1537-1540). For example, Dr. Thomas Armstrong testified that

* * * [M]ore than a critical mass of epidemiological literature 
shows that biomechanical factors are important predictors of the 
occurrence of musculoskeletal disorders and the elevated risk of 
harm.
    In studies where we have included both psychosocial and physical 
risk factors, the physical factors come out as the strongest 
predictor. [Tr. 842]

Dr. Laura Punnett testified that ``* * * the impact of physical 
exposures at work is beyond that explained by demographics, medical 
history, psychosocial features of the work environment or other 
factors'' (Tr. 874). Similarly, Dr. Nicholas Warren testified that in 
studies that have measured both biomechanical and psychosocial factors

* * * we almost always find that both contributed. If you control 
for psychosocial risk factors[,] which well-designed studies allow 
you to do, you'll find a strong contribution from biomechanical risk 
factors and that it generally, not in all workplaces, but in most 
workplaces, is a larger effect than that of the psychosocial risk 
factors. [Tr. 1087]

When asked whether he would agree with Gibson, Dunn & Crutcher's 
statement in their pre-hearing submission that ``a majority of medical 
experts who study the causes of MSDs believe most chronic workplace 
pain is caused by psychosocial issues'' (Ex. 32-241-4, p. 36), both Dr. 
Bradley Evanoff and Dr. Fred Gerr disagreed. Dr. Evanoff believed the 
opposite was true, that ``the majority of people studying work-related 
musculoskeletal disorders * * * feel that physical exposures are a very 
strong risk factor'' Tr. 1358). Dr. Gerr stated that he was ``aware of 
absolutely no basis in the medical or scientific literature that 
[would] substantiate that statement'' (Tr. 1538). Both also strongly 
disagreed (Tr. 1538-1539) with Dr. Hadler's statement in his written 
testimony that psychosocial factors ``overwhelm and explain away any 
and all associations with biomechanical factors'' (Ex.32-241-3-8, p. 
18).
    Several other researchers and medical scientists appearing at the 
hearing on their own behalf disagreed with the UPS witnesses 
assessments that psychosocial factors predominate in the etiology of 
MSDs (Tr. 2838, 2840, 7857-7858, 9504, 9880). Dr. George Piligian of 
the Mt. Sinai Center for Occupational and Environmental Medicine, when 
asked whether it was appropriate for OSHA to emphasize the role of 
biomechanical factors in its proposed rule given the evidence on 
psychosocial factors, responded with an analogy:

* * * [Suppose] a person is thirsty and has come from the desert, 
and if you have only half a glass of water to offer that person[.] * 
* * Someone argued and said * * * I don't think we should give this 
person that half a glass of water until it's full * * * I would 
venture to say that the person who is thirsty would probably beg you 
to give them that half a glass of water, then, go back and fill it * 
* * .
    We are doing what we can with the knowledge we have rather than 
using the argument, which I find actually counterintuitive * * * 
that we must have every single thing that we know of in place before 
we proceed. [Tr. 7857-7859]

    Some of OSHA's expert witnesses who are actively engaged in 
research on work-related MSDs testified that an important finding from 
the more recent literature is that biomechanical risk factors have been 
shown to be associated with MSDs independently from psychosocial 
factors (Tr. 1327-1328, 1331-1332, 1335, 1343, 1365, 1412). Dr. Niklas 
Krause, in testifying on his own prospective study of public transit 
operators and low back disorders (Ex. 500-87-2), stated that

    The main result * * * is that both biomechanical and 
psychosocial job factors were independently associated with spinal 
disorders * * * [I]ndependent positive dose response relationships 
were also found for ergonomic problems * * * I conclude from this 
new high quality evidence [referring to the Loisel et al.(Ex. 38-28) 
randomized trial study] and the literature that has been already 
collated by OSHA [in its preamble to the proposed rule and Health 
Effects Appendices (Ex. 27-1) that high-quality epidemiological 
studies confirm that physical work place factors cause MSDs 
independently from individual worker characteristics and 
psychosocial job factors * * * [Tr. 1331-1335].

Dr. John Frank testified that the Kerr et al. case-control study (Ex. 
38-82) in which he participated also found an association between MSDs 
and exposure to biomechanical risk factors independent from 
psychosocial factors. When asked about the significance of that 
finding, Dr. Frank responded

    The importance particularly for the proposed standard or any 
public health efforts to reduce biomechanical hazards at work is 
that[,] * * * acting on biomechanical risk factors will bring risk 
reductions according to our understanding of the multifactorial 
causal process even if we are unable * * * at the present time to 
conclusively act to reduce psychosocial factors * * * [Tr. 1365-
1366]

    Dr. Frank also drew a parallel with successful efforts to control 
cholesterol blood levels to reduce heart disease incidence, despite 
``two dozen or more'' other risk factors that contribute to heart 
disease because high cholesterol levels are independently associated 
with an increased risk of heart disease (Tr. 1365-1366).
    In the preamble to the proposed rule, OSHA's focus on 
identification and control of biomechanical risk factors in the 
workplace was based on two considerations. First, OSHA preliminarily 
concluded that there was substantial evidence of a clearly demonstrated 
causal relationship between exposure to physical risk factors and MSD 
outcomes (64 FR 65926), and that most researchers who studied the 
etiology of MSDs placed emphasis on biomechanical risk factors. Second, 
research into role of psychosocial risk factors in the etiology of MSDs 
was considered to be a less mature field than that addressing the role 
of biomechanical risk factors, characterized by emerging methodology, 
as pointed out by Dr. Martin Cherniak at the hearing (Tr. 1307), and 
sometimes by inconsistent results. Thus, most interventions designed to 
address work-related MSDs focused on biomechanical, rather than 
psychosocial factors.
    The 1997 NIOSH review (Ex. 26-1) on which OSHA relied heavily, 
examined psychosocial risk factors that might contribute directly and 
indirectly to musculoskeletal illness and injury. The review noted that 
the results from the literature were not entirely consistent, and that 
a lack of consensus on standard measurements and procedures might be 
one reason for lack of consistency. Perceptions of intensified 
workload, monotonous work, low job control, low job clarity, and low 
social support were associated with MSDs in some studies. NIOSH found 
that these associations, despite the variance in methods used to assess 
these factors, were significant in the better studies; however, the 
size of

[[<strong>Page</strong> 68521]]

effect was relatively weak compared to that of the biomechanical 
variables.
    In his testimony, Dr. Frank (Tr. 1343-1345, 1397-1398) discussed 
the reasons for this inconsistency, relating it to the field being in 
the embryonic stage of understanding psychosocial effects, and to 
imperfect measurement instruments. He pointed out that the Institute 
for Work and Health study discussed below (Kerr et al., 2000, Ex. 38-
82) did not confirm findings of Bigos et al. (1991a, b, Exs. 26-1241, 
26-1242, 1992, Ex. 26-1393) or Krause (1998, Ex. 500-87-2) that low job 
satisfaction contributed to risk. In contrast, Dr. Frank (Tr. 1344) 
noted that, in newer studies that simultaneously assessed the effect of 
physical and psychosocial factors, biomechanical loads make a 
consistent and generally stronger contribution to MSD outcomes.
    Although psychosocial exposure assessment has grown rapidly in the 
last decade and is characterized by continually improving 
methodological developments, it is still a relatively young field. 
Measurement methodologies are not well standardized; this was addressed 
by Dr. Barbera Silverstein, who testified that there was no consensus 
on the kinds of psychosocial issues that should be studied or how they 
could be assessed ``with the same rigor that has been * * * looked at 
[for] physical load factors'' (Tr. 17444).
    In addition, less is known about the causal relationship between 
psychosocial factors and MSDs. Many studies performed so far have been 
cross sectional, thus making it difficult to evaluate the temporal 
nature of the association (i.e., whether psychosocial factors preceded 
the MSD or whether the presence of a disorder led to negative 
psychosocial outcomes). Dr. Punnett addressed this issue in her 
testimony:

* * * [S]ince psychosocial factors may be perceived and reported 
differently by the worker after the development of musculoskeletal 
disorders, the reported associations are particularly difficult to 
interpret with respect to * * * [etiology].
    The occurrence of a work-related musculoskeletal disorder * * * 
may itself cause psychosocial strain. And that strain may also 
subsequently slow or interfere with the recovery process without 
necessarily having been involved in the initial etiology. In this 
context, we should note that associations with cross-sectional * * * 
[studies] with physical exposures are far less ambiguous. [Tr. 869-
870]

    As a result, associations found between psychosocial exposures and 
MSD outcomes are, relative to biomechanical associations, less 
consistent and generally weaker (NAS, 1999, Ex. 26-37). Further, the 
underlying mechanisms are still not nearly as well understood as those 
developed for biomechanical associations (Tr. 1344-1345, NAS, 1999, Ex. 
26-37). Similarly, understanding and evaluating psychosocial 
interventions is also in its infancy, making it difficult to design 
appropriate interventions.
    None of the studies cited by either proponents or opponents of an 
ergonomics standard can demonstrate that any of the risk factors 
measured, whether biomechanical, psychosocial, personal, or 
demographic, can completely explain an increased prevalence or 
incidence of MSD outcomes. (In other words, the combined contribution 
of all factors to statistical models never comes close to explaining 
100 percent of the variance between exposure groups in the outcome 
measure; there are always other, unmeasured factors involved.) Dr. 
Tapio Videman (Ex. 32-241-3-20), Dr. Arthur Barsky (Ex. 500-118-1) and 
most other researchers agreed that a simple biomechanical model of 
tissue wear and tear is not sufficient by itself to explain disease 
development in humans, which is characterized by complicated 
interactions with external environmental factors and individual 
characteristics. In fact, testimony at the hearing (Tr. 868, 1264, 
5942-5943) made it clear that considering psychosocial and 
biomechanical factors to be separate kinds of exposures is a somewhat 
artificial distinction in that the two classes of stressors are 
strongly linked, both resulting from core aspects of the organization: 
its technology, culture and work organization.
    For example, Dr. Punnett testified that

    There is also a recognized overlap between some characteristics 
of physical and psychosocial work environment.
    A repetitive, monotonous job on a machine paced assembly line 
can be described equally well by the ergonomist as consisting of 
stereotyped repetitive motion patterns with rigid pacing and few 
rest breaks or as having poor psychological job content with few 
opportunities to make decisions, work collaboratively with co-
workers, utilize existing skills or learn new ones.
    And I suggest that the worker performing that job would be hard 
pressed to make a distinction between the physical and the 
psychosocial characteristics of that job. [Tr. 868-869]

Ms. Sue Rahula, an ergonomist technician with United Auto Workers, 
described how biomechanical exposure and the presence of an MSD can 
affect worker morale, which can be reflected in negative psychosocial 
outcomes:

    When you're feeling pain your morale is going to be low, your 
discomfort level is low, your attitude is bad, and you may be one of 
the silent sufferers. * * * When * * * we take our risk factor 
checklist out and we verify that, yes, these postures are awkward 
postures and when you add that along with the forces and the 
exertions that you're using that that's a possibility it sure could 
cause pain. It's no wonder the morale becomes low. And they 
[biomechanical and psychosocial factors] do intertwine. But the pain 
is usually the cause of [low morale], in my opinion, from what I 
see. [Tr. 5942-5943]

These underlying sources of biomechanical and psychosocial exposures 
can themselves be seen as a single exposure category known as 
organizational exposure (Warren, 1997, Ex. 38-72, Warren et al., 2000a, 
b, Exs. 38-75, 38-73, Shannon et al., 1996, 1997, Exs. 26-1368, 26-
1369), which, as Dr. Warren described, recognizes that ``the way work 
is organized will have an effect on the levels of both biomechanical 
and psychosocial work stresses'' (Tr. 1264).

Summary of Primary Literature on Biomechanical and Psychosocial Factors

    OSHA's review of the literature presented below shows that most of 
the best studies available suggest that MSDs are the result of a 
complicated combination of biomechanical and psychosocial factors, with 
the prevalence or incidence of MSDs being generally more strongly 
associated with biomechanical risk factors. Given the present state of 
research into MSD etiology, there can be little doubt that a 
multifactoral model, incorporating both biomechanical and psychosocial 
risk factors, would best explain the differences in MSD prevalence or 
incidence seen among various groups of workers. Nevertheless, from the 
testimony presented above and the review of the literature that 
follows, OSHA concludes that biomechanical risk factors contribute 
independently from psychosocial factors to MSD etiology, that the 
association between the risk of MSDs and exposure to biomechanical risk 
factors has been observed to be generally stronger than for 
psychosocial factors, and that, consequently, it is reasonable to 
design interventions that focus on exposures to biomechanical risk 
factors to reduce the risk of MSDs in exposed workers.
    Because the scientific literature summarized in this section 
addresses the relative strength of association between MSD risk and two 
broad categories of workplace factors, and because of the potential for 
interacting or modifying effects between biomechanical and psychosocial 
factors,

[[<strong>Page</strong> 68522]]

it becomes particularly important to consider certain elements of 
epidemiological study design to ensure that study results are 
appropriately interpreted. These design considerations include the 
following:
    Best study design. Epidemiological studies can be of three general 
designs: cross-sectional, case-control, and prospective (longitudinal) 
cohort. Dr. Stanley Bigos presented a comprehensive review of the 
advantages and disadvantages of each study design (Ex. 32-241-3-4, pps. 
7-9). OSHA also addressed general issues regarding study design and 
causal inference in a previous part of this Health Effects section. All 
researchers agree that prospective studies can most persuasively 
establish causality, with cross-sectional studies presenting the most 
potential problems in this area. In the absence of any other 
information, prospective studies are generally preferable. However, 
several factors may recommend against this design: in particular, the 
high cost of these studies and the dynamic nature of the modern 
workplace, which may change job classifications (and hence workers' 
exposures) over the follow-up period of the study.
    Although cross-sectional studies identify associations and cannot 
by themselves permit a definite attribution of a causal relationship, 
it is still possible to draw inferences when one causal direction 
(i.e., exposure precedes disease) is much more plausible than the 
alternative explanation (i.e., disease precedes exposure). As Dr. Gerr 
noted in his testimony (Tr. 1525) the many cross-sectional studies 
showing an association between carpal tunnel syndrome and physical 
workplace factors strongly indicate that exposure to these workplace 
factors causes disease. This conclusion arises in part because it is 
illogical to postulate that the presence of CTS would cause exposure to 
physical factors (i.e., workers select themselves into physically 
harmful jobs on the basis of disease status). Dr Gerr testified that 
this would be ``like saying cancer causes smoking. It's as wrong as it 
is silly to hear'' (Tr. 1525). However, for psychosocial factors such 
as poor job satisfaction or low supervisory support, it is more 
difficult to logically infer or exclude a temporal relationship between 
a psychosocial factor and an MSD; this was described by Dr. Punnett in 
her testimony (Tr. 869). That is, it cannot be known whether having 
poor job satisfaction preceded development of the MSD or whether the 
presence of the MSD is causing a worker to become less satisfied with 
their job. Thus, in evaluating the causal nature of psychosocial 
factors, the use of a prospective study design that follows groups of 
workers over time becomes particularly important to evaluate the 
temporal relationships between exposure to biomechanical risk factors, 
psychosocial factors, development of MSDs.
    In addition, as was the case with the biomechanical literature 
reviewed in earlier parts of the Health Effects section, determination 
of exposure and health outcome by objective means, such as direct 
observation or measurement of exposure and medical assessment of health 
status, is preferable over sole reliance on worker self-reports because 
objective measures rule out the possibility of reporting bias (e.g., 
the possibility that a worker's disease status might influence the 
self-report of exposure). This design consideration points to another 
difficulty in studying the role of psychosocial factors in that they 
can only be assessed by administering questionnaires or interviews.
    Simultaneous assessment. It is obvious that to accurately assess 
the relative contribution of biomechanical and psychosocial risk 
factors to MSD causation and exacerbation, both classes of exposure 
must be measured.
    Address collinearity. Levels of both biomechanical and psychosocial 
risk factors are in large part the result of the way work is organized, 
the technology and sector of the company, and the organizational 
policies and culture that drive work organization. Thus the two classes 
of stressor are generally highly correlated in a workplace (Tr. 868-
869, 1264, 5942-5943). Concurrent analysis of exposure-outcome 
associations must be very careful to avoid modeling problems that arise 
from collinearity.
    Assess both stressor categories with equal precision. Some studies 
assess both categories of exposure, but assess one with more precision 
or detail than the other. The category characterized in more detail 
presents fewer opportunities for non-differential exposure 
misclassification (which biases results towards a lower effect) and 
will thus show artificially elevated relative associations with 
outcome. Dr. Wells stated that a factor measured with poor precision in 
an epidemiological study will often not appear as a risk factor in 
statistical modeling (Tr. 1355).
    Ensure adequate variance in all measures. Studies that assess both 
categories of exposure, but with little variance between exposure 
groups in one or the other category of exposure will generally not find 
effects associated with that category or measure. Regression analysis 
(a standard modeling method in many studies) cannot assess the 
contribution of an exposure if its magnitude or intensity is 
essentially the same in all study participants.
    Assess both stressor categories at the same individual or group 
level. Studies that assess both categories of exposure, but at 
different levels of analysis (i.e., the level of the individual worker 
versus groups of workers), will generally not find an effect for the 
variables measured at a higher (group) level of aggregation; this was 
addressed by Dr. Frank in his testimony (Tr. 1364-1365). For example, 
the Boeing study (Bigos, et al., 1991a, b, Exs. 26-1241, 26-1242, 1992 
Ex. 26-1393) assessed psychological and emotional variables at the 
individual level and biomechanical variables at the group level. This 
error also reflects violation of the preceding two criteria since 
measurement at the group level reduces both precision in the 
biomechanical exposure measure (compared to measuring exposure at the 
individual level) and variance in biomechanical exposure between 
groups. When one variable is aggregated or represented at the group 
level, as in the Bigos measurement of biomechanical risk, the 
variations in exposure within each group are lost; internal variance 
within each group is reduced to zero.
    The studies summarized below relied on assessment of both 
biomechanical and psychosocial factors in the workplace. Thus, in 
accordance with the second criteria described above, studies were 
excluded if they did not assess one class of stressor or did not 
include both classes in multivariate analysis. Such studies are useless 
for the exploration of combined biomechanical and psychosocial effects.
    The majority of the studies below demonstrate at least equal, and 
often stronger, associations with biomechanical stressors than with 
psychosocial. This fact, combined with the independent effects of both 
stressor classes, as discussed above, is sufficient to support OSHA's 
focus on biomechanical risk factors in the final rule. However, 
relative magnitude of the associations for biomechanical and 
psychosocial risk factors should only be seen as a qualitative 
indicator of relative strength of association with MSD prevalence or 
incidence. Actual quantitative effect sizes may not be comparable 
within or between studies for a number of reasons, including:
    <bullet> Use of different measurement scales;
    <bullet> Use of different analytical strategies to categorize risk 
levels; and

[[<strong>Page</strong> 68523]]

    <bullet> Use of different outcome measures in different studies.
    Table V-14. summarizes the key features of the design of each study 
as well as the range of measures of association for biomechanical and 
psychosocial factors.
    Wickstrom & Pentti 1998 (Ex. 500-121-77). This 2-year prospective 
study of 117 white-collar and 189 blue-collar workers in two metal 
industry facilities assessed both biomechanical and psychosocial 
exposures (4 items each) at baseline, using equivalent levels of 
detail. Back pain was assessed twice in the follow-up period by 
questionnaire, and data on sick leave attributed to back pain and other 
MSDs (doctor diagnosis if over 3 days) was obtained from company 
records. The exposure assessment at baseline plus physician diagnosis 
at follow-up made this design capable of strongly implying causal 
status to both physical and psychosocial risk factors. As predictors of 
self-reported LBP, 3 physical exposures were predictive for both white 
collar (RRs: 2.82-6.19) and blue-collar workers (RRs: 2.49-3.67). Since 
other authors (Marras, 2000, Ex. 500-121-46) have hypothesized that 
psychosocial exposures have less effect if the physical load is high, 
it is interesting that psychosocial stress was predictive of LBP in 
white-collar workers, while none of the 4 psychosocial exposures were 
significantly predictive in blue-collar workers. However, sick leave 
was predicted for blue-collar workers by both biomechanical exposures 
(RRs: 1.72-2.04) and psychosocial (RRs 1.58-1.99). In general, this 
study supports the interpretation that MSDs are caused by both classes 
of risk factor, with biomechanical showing stronger effects.

                                       Table V-14.--Studies Assessing Both Biomechanical and Physical Risk Factors
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                      Number of                                                                                  Results: outcome and
             Reference                 subjects   Study  type   Exposure  measure     Outcome  measure      Study  design               effect
--------------------------------------------------------------------------------------------------------------------------------------------------------
                      Association with Biomechanical Factors Stronger than with Psychosocial Factors (or effect size not reported)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Wickstrom & Pentti (1998)..........          306            3  1..................  1, 2, 3............  all                  LBP & sick leave due to
                                                                                                                               LBP; Physical RR: 1.97-
                                                                                                                               6.19; Psychosocial RR:
                                                                                                                               1.58-1.59.
Bergqvist et al.(1995).............          260            1  2..................  3..................  all                  UE/LBP sympt./MD diag.;
                                                                                                                               Physical OR: 3.1-7.4;
                                                                                                                               Psychosocial OR: 2.1-7.4.
Kerr et al.(2000)..................          381            2  3..................  1..................  all                  Reporting of LBP; Physical
                                                                                                                               OR: 1.7-3.0; Psychosocial
                                                                                                                               OR: 1.6-2.6.
Koehoorn et al.(1999)..............         4020            3  2..................  2..................  a, c                 MSD symptoms & claims;
                                                                                                                               Physical RR: 1.41-4.65;
                                                                                                                               Psychosocial RR: 0.45-
                                                                                                                               2.78.
Krause et al.(1998)................         1449            3  1, 2...............  2..................  b, c                 Spinal injury through WC;
                                                                                                                               Physical OR: 3.04
                                                                                                                               (driving cable car); 0.37
                                                                                                                               (part-time driving: 20-30
                                                                                                                               hrs); Psychosocial OR:
                                                                                                                               1.50-1.56.
Latko et al.(1997, 1999)...........          352            1  2..................  1, 3...............  all                  Symptoms, MD Dx of CTS;
                                                                                                                               Physical OR (high
                                                                                                                               repetition vs. low rep.):
                                                                                                                               2.32-3.23; Psychosocial
                                                                                                                               OR: n.s.
Latza et al.(2000).................          230            3  1..................  1..................  all                  Self-reported LBP;
                                                                                                                               Physical PR: 1.8-4.0;
                                                                                                                               Psychosocial PR: n.s.
Leclerc et al.(1998)...............         1210            1  1..................  3..................  all                  CTS by signs or NCV;
                                                                                                                               Physical OR: 1.90-2.24;
                                                                                                                               Psychosocial OR: 1.59-
                                                                                                                               2.24.
Linton (1990)......................       22,180            3  1..................  1..................  all                  Neck & LBP symptoms
                                                                                                                               Univariate ORs; Physical:
                                                                                                                               0.86-2.95; Psychosocial:
                                                                                                                               1.15-2.60; Combined ORs:
                                                                                                                               2.42-3.65.
Ono et al.(1998)...................          575            1  1..................  3..................  all                  Epicondylitis, MD Dx;
                                                                                                                               Physical OR: 1.7;
                                                                                                                               Psychosocial OR: 1.2.
Videman et al.(1989)...............          199            3  2..................  1..................  b, c                 Incidence of back injury;
                                                                                                                               Low skill OR: 37-156 (if
                                                                                                                               also 3 hrs. strenuous
                                                                                                                               working postures)
Bernard et al.(1992, 1994).........          973            1  1, 2...............  1..................  all                  UE symptoms; Physical OR:
                                                                                                                               1.4-2.5; Psychosocial OR:
                                                                                                                               1.4-1.7.
Faucett & Rempell (1994)...........          150            1  2..................  1..................  all                  UE symptom severity,
                                                                                                                               (effect measured by R \2\
                                                                                                                               change): Physical: 0.11-
                                                                                                                               0.15; Psychosocial: 0.03-
                                                                                                                               .12.
Heliovaara (1987)..................        * 592            3  1 (occ.)...........  3..................  none                 Hospital Admission for
                                                                                                                               disc herniation/sciatica;
                                                                                                                               Occupational RR: 2.2-3.0;
                                                                                                                               Psychic Distress: NR.
Josephson & Vangard, 1998..........          269            2  1..................  1..................  all                  LBP medical visit;
                                                                                                                               Physical OR: 2.3-8.7;
                                                                                                                               Psychosocial OR: n.s.
Svensson & Andersson (1981)........          940         ** 1  1..................  2..................  all                  LBP sickness absence;
                                                                                                                               Heavy Lifting (effect
                                                                                                                               NR); Reduced overtime/
                                                                                                                               monotonous work (effect
                                                                                                                               NR).
Thorbjornsson et al.(2000).........          484            2  1..................  1..................  all                  LBP med. visit or absence;
                                                                                                                               Physical OR: 1.7-2.2;
                                                                                                                               Psychosocial OR: n.s.;
                                                                                                                               Interaction OR: 3.1-3.7.
Vingard et al.(2000)...............         2118            3  1..................  1..................  a, b                 Care-seeking for LBP;
                                                                                                                               Physical RR: 1.8-2.9;
                                                                                                                               Psychosocial RR: 1.5-1.6.
Warren et al.(2000a)...............          845            2  1..................  1..................  all                  NIOSH MSD case def.;
                                                                                                                               Physical OR: 1.89-2.13;
                                                                                                                               Psychosocial OR: 1.56-
                                                                                                                               1.69.
Waters et al.(1999)................          284            1  1, 2...............  1..................  all                  Prevalence of LBP; Lifting
                                                                                                                               Index OR: 1.04-2.20;
                                                                                                                               Satisfaction OR: 4.57-
                                                                                                                               7.65.
Burt et al.(1990)..................          834            1  1..................  1..................  all                  UE Symptoms; Physical OR:
                                                                                                                               2.0-4.1; Dissatisfaction
                                                                                                                               OR: 1.9-2.3.

[[<strong>Page</strong> 68524]]

Lemasters et al.(1998).............          522            1  1..................  3..................  c                    Pain, all body parts, self-
                                                                                                                               report and MD Dx;
                                                                                                                               Physical OR: 2.3-3.5;
                                                                                                                               Psychosocial OR: 1.6-2.9.
Scov et al.(1996)..................         1306            1  1..................  1..................  all                  UE and low back symptoms;
                                                                                                                               Physical OR: 1.64-2.80;
                                                                                                                               Psychosocial OR: 1.43-
                                                                                                                               2.04.
Warren et al.(2000b)...............         7712            1  1..................  1..................  all                  MSD symptoms & pain;
                                                                                                                               Physical <greek-b>: 0.06-
                                                                                                                               0.16; Psychosocial <greek-
                                                                                                                               b>: 0.04-0.12.
Hales et al.(1992, 1994)...........          533            1  1..................  1..................  a, b                 UE MSD symptoms; Physical
                                                                                                                               OR: 1.1-3.8; Psychosocial
                                                                                                                               OR: 1.1-3.5.
Hoekstra et al.(1994)..............          108            1  1..................  1..................  a, b                 MSD symptoms; Physical OR:
                                                                                                                               3.5-5.1; High Control: OR
                                                                                                                               0.6.
Houtman et al.(1994)...............         5865            1  1..................  1..................  b, c                 Complaints: muscle/joint &
                                                                                                                               back; chronic back
                                                                                                                               problems; Physical OR:
                                                                                                                               1.36-1.62; Psychosocial
                                                                                                                               OR: 1.20-1.35.
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                         Association with Psychosocial Factors Stronger than with Biomechanical
--------------------------------------------------------------------------------------------------------------------------------------------------------
Viikari-Juntura & Riihimaki (2000).         5179            3  1..................  1..................  all                  Radiating neck pain;
                                                                                                                               Physical OR: 1.2-2.3;
                                                                                                                               Psychosocial OR: 1.1-6.1.
Waters et al.(1999)................          284            1  1, 2...............  1..................  all                  Prevalence of LBP; Lifting
                                                                                                                               Index OR: 1.04-2.20;
                                                                                                                               Satisfaction OR: 4.57-
                                                                                                                               7.65.
Elberg et al.(1995)................          637            1  1..................  1..................  all                  Neck & shoulder symptoms;
                                                                                                                               Physical OR: 1.2;
                                                                                                                               Psychosocial OR: 1.2-1.3.
Sauter (1984)......................          333            1  1..................  1..................  all                  Somatic complaints;
                                                                                                                               Physical <greek-b>: 0.16-
                                                                                                                               0.21; Psychosocial <greek-
                                                                                                                               b>: 0.19-0.26.
Warren et al.(submitted)...........         7712            1  1..................  1..................  all                  LBP, absenteeism; Physical
                                                                                                                               OR: 1.45-1.88;
                                                                                                                               Psychosocial OR: 1.32-
                                                                                                                               2.27.
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                          Biomechanical Effect Not Significant
--------------------------------------------------------------------------------------------------------------------------------------------------------
Leino & Hanninen (1995)............          902            3  1..................  1, 3...............  b, c                 Back/limb symp. & MD Dx;
                                                                                                                               Physical <greek-b>: n.s.;
                                                                                                                               Psychosocial <greek-b>:
                                                                                                                               .110-.146.
Bigos et al.(1991a)................         3020            3  1, 2...............  2..................  none                 Reporting back injury;
                                                                                                                               Physical RR: n.s.;
                                                                                                                               Psychosocial RR: 1.34-
                                                                                                                               1.70.
Svensson & Andersson (1989)........         1746            1  1..................  1..................  all                  Low back pain; Physical
                                                                                                                               n.s.; effect NR; Fatigue,
                                                                                                                               dissatisfaction, worry;
                                                                                                                               sig., but effect NR.
--------------------------------------------------------------------------------------------------------------------------------------------------------
n.s.: not significant
NR: controlled for factor, but effect not reported
Table only notes statistically significant effects (p0.05)
Key:
  Study Type:
    1--Cross sectional
    2--Case-control/Referent
    3--Cohort/Prospective
  Exposure Measure:
    1--Worker self-report
    2--Observation of job
    3--Instrumentation
  Outcome Measure:
    1--Worker self-report
    2--Observation/record
    3--Clinical findings
  Study Design
    a--Biomechanical and psychosocial factors studies with equal precision
    b--Biomechanical and psychosocial factors assessed at same individual or group level
    c--Adequate variance between groups in all measures
* case 2140 con.
** retro. outcome

    Bergqvist, Wolgast, Nilsson, Voss 1995 (Ex. 26-1195). hese 
investigators found a number of upper extremity diagnoses to be 
consistently associated with standard biomechanical risk factors 
(especially postural stressors, ORs 2.2-4.4, and lack of rest breaks, 
ORs 2.7-7.4); some personal factors (especially age and presence of 
children at home), task flexibility (OR 3.2) and quality of peer 
contacts (ORs 2.1-4.5) had independent associations. Although the study 
was cross-sectional, confidence in study findings is improved by the 
detailed physical examination used to determine outcome and the broad 
array of exposure measures (including individual factors, non-work 
risks, work organizational factors and biomechanical factors). Muscle 
problems in each body location showed a different pattern of personal, 
psychosocial and biomechanical stressor associations.
    Faucett and Rempel 1994 (Ex. 38-67). his study of 150 newspaper 
editorial work found that upper extremity pain and numbness symptoms in 
VDT workers were related primarily to postural variables (R<SUP>2</SUP> 
changes 0.11-

[[<strong>Page</strong> 68525]]

0.15), with smaller additions to model R<SUP>2</SUP>s from 
psychological demands, decision latitude, and employee relationship 
with the supervisor (R<SUP>2</SUP> changes 0.03-0.12). The effects of 
postural variables on upper torso pain and stiffness were greater than 
those for pain and numbness (R<SUP>2</SUP> changes 0.19-0.32), while 
psychosocial effects were reduced (R<SUP>2</SUP> changes 0.01-0.08). 
Interaction terms between keyboard height and psychosocial variables 
added to the model R<SUP>2</SUP>s (R<SUP>2</SUP> changes 0.04-0.15), 
suggesting that the effect of biomechanical variables can be modified 
by psychosocial variables. In this study, biomechanical stressors were 
clearly the dominant factor, but the size of the effect for interaction 
terms may have meaning for the mechanism of psychosocial action as 
being an effect modifier.
    NIOSH Health Hazard Evaluations (Exs. 26-439, 26-842, 26-725). 
Three cross-sectional NIOSH studies, at the L.A. Times (Bernard, 
Sauter, Petersen, Fine, & Hales, 1992, Ex. 500-165-20, 1994, Ex. 26-
439), Newsday (Burt, et al., 1990, Ex. 26-842) and two Social Security 
Administration teleservice centers (Hoekstra et al., 1994, Ex. 26-725) 
found associations of biomechanical risk factors (in particular, 
duration of VDU work) with MSD symptoms, while also finding independent 
associations of these symptoms with several psychosocial factors. 
Another NIOSH HHE at U.S. West Communications (Hales et al. 1992 (Ex. 
26-727), 1994 (Ex. 26-131) did not find associations between symptoms 
and physical workplace characteristics other than use of bifocal 
glasses (OR 3.8), because the standardized workstations presented 
virtually no variance in biomechanical measures. Thus, psychosocial 
factors were dominant in the models, although work pressure (OR 1.1-
1.2), workload surges (OR 1.2) and information processing demands (OR 
1.2) probably represent a combination of physical and psychosocial 
exposures. See Table V-14. for strength of association estimated by 
multivariate logistic regression models in all these studies.
    Kerr, et al.2000 (Ex. 38-82). Researchers at the Institute of Work 
and Health (IWH) have carried out several well-designed studies 
measuring both biomechanical and psychosocial stressor levels in 
detail. These studies demonstrate the independent contributions of 
biomechanical, psychosocial and organizational factors to models 
explaining back injury and accidents (Shannon et al., 1996, 1997, Exs. 
26-1368, 26-1369). The most recent IWH study (Kerr, et al., 2000, Ex. 
38-82), performed in concert with the Ontario Universities Back Pain 
Study (OUBPS) group, is a case-control study reviewed in detail by John 
Frank (Ex. 37-27). Subjects reported levels of physical demands 
(including perceived exertion) as well as psychosocial factors. In 
addition, videotape analysis and biomechanical modeling provided 
quantifiable estimates of actual spinal loading. These biomechanical 
measures acted independently to substantially increase risk of workers 
reporting new cases of LBP, after controlling for individual and 
psychosocial factors. In final models, the biomechanical risk factors 
demonstrated ORs of 1.7-3.0, while psychosocial risks were associated 
with ORs of 1.6-2.6. This study improved on earlier study designs by 
directly measuring forces on back during job performance. The case-
control study also matched controls by actual job, allowing analysis of 
the degree to which job exposures influenced self-reported LBP. 
Compression, peak shear force, peak hand force were associated with 
doubled risk of LBP reporting. These findings are consistent with much 
of the other epidemiological data reviewed in this section. Thus this 
study strengthens confidence in the results of other studies that rely 
on less detailed exposure assessment and/or self-reported exposures and 
outcomes.
    Krause et al.1997 (Ex. 38-267), 1997 (Ex. 38-266), 1998 (Ex. 500-
87-2). Niklas Krause and colleagues, studying a cohort of San Francisco 
drivers, examined relationships between biomechanical and psychosocial 
exposures and neck and shoulder outcomes. The cross-sectional analyses 
(Krause et al., 1997a, Ex. 38-267, 1997b Ex. 38-266) determined that 
both biomechanical and psychosocial job factors were separately and 
simultaneously associated with non-disabling neck and back pain. The 5-
year longitudinal follow-up of this cohort (Krause et al., 1998, Ex. 
500-87-2) found that workers' compensation cases of spinal injury were 
predicted by a combination of biomechanical (measured by hours driving) 
and psychosocial risk factors at baseline. (See Krause testimony, Ex. 
37-15). The physical risk factors addressed by this measure of hours 
spent driving included prolonged sitting, twisting/bending, vibration, 
and use of foot pedal (Krause testimony, Tr. 1376, Ex. 37-15). Although 
all measures were gathered at the same (individual) level, the 
surrogate measure for biomechanical exposure (hours spent driving) was 
a more generalized measure than the psychosocial data and thus subject 
to greater non-differential misclassification and consequent dilution 
of effect in statistical modeling. Psychosocial stressors demonstrated, 
on average, higher ORs than the surrogate physical measure of hours 
spent driving. This is an example of the fourth study design criterion 
discussed above: the factor measured in greater detail has a greater 
likelihood of showing stronger associations in the modeling. The fact 
that a biomechanical effect still emerged in the modeling strongly 
suggests that if physical exposures were measured in the same detail as 
psychosocial exposures, they would have demonstrated a larger effect in 
modeling; however, it cannot be known whether the resulting size of the 
effect for biomechanical factors would have surpassed that for 
psychosocial factors. For cable car operators, biomechanical factors 
were more strongly associated with back cases than were psychosocial 
factors.
    In his written comments, Dr. Nortin Hadler (Ex. 32-241-3-8) 
demonstrated a basic misunderstanding of the research by taking the 
Krause studies to task for showing a biomechanical effect only for 
cable car drivers. The data did show that only cable car drivers' 
injury rate was significantly elevated when compared to diesel bus 
drivers. However, the pooled data for all drivers showed a highly 
significant increase (2.7 times) in injury rate between drivers who 
worked 20-30 hrs per week compared to those who worked 31-40, 
suggesting a significant effect related to biomechanical factors. 
Hours-per-week-driven was the study's surrogate measure for exposure to 
physical risk factors.
    Latko et al.1997 (Ex. 38-122), 1999 (Ex. 38-123). These researchers 
performed a cross-sectional study with some of the most detailed 
exposure assessments to be found in the literature. The study, 
described elsewhere in the testimony (Franzblau, Ex. 37-3, Armstrong, 
Ex. 37-21) measured a wide variety of demographic, personal, and 
exposure variables, including 13 psychosocial parameters. It is 
distinguished by precise measurement of exposure variables and several 
levels of outcome measurement objectivity, ranging from symptom 
reports, through physical findings, to nerve conduction velocity (NCV) 
results. The contribution of the psychosocial variables did not reach 
significance in the final modeling, strongly implying that the effect 
of biomechanical factors predominates in these 3 manufacturing plants 
(testimony

[[<strong>Page</strong> 68526]]

by Armstrong, Ex. 37-3, Franzblau, Ex. 37-21).
    Nortin Hadler (post hearing comments, Ex. 500-118-1, p 7) cited 
this study as evidence for a lack of a significant association between 
repetitive motion and decrements in median NCV. These results were, in 
fact, marginally significant. Moreover, if a more conservative 
definition of CTS was used, (i.e., 0.8ms threshold plus positive hand 
diagram report), the association was significant (Franzblau testimony, 
Ex. 37-21). In addition, Dr. Hadler failed to note either the wide 
range of significant associations found for repetition, symptom reports 
and tendinitis as indicated by physical exam findings, and that these 
associations did demonstrate a positive exposure-response relationship.
    Warren 1997 (Ex. 38-72), Warren et al.2000 (Ex. 38-73). Nicholas 
Warren and colleagues at the University of Massachusettes at Lowell and 
at TNO, the Netherlands, performed analyses on the Dutch Monitor data 
set, collected from a broad sample of companies and industry sectors in 
1993--a cross-sectional study. The data set contained completed 
questionnaires from 7,717 Workers in 528 companies that assessed in 
detail both workplace exposure to biomechanical and psychosocial risk 
factors and a variety of musculoskeletal and stress outcomes, as well 
as reports of extended sick leave. Controlling for gender, education 
and tenure on the job, the multivariate linear analyses found roughly 
equal contributions of both stressor classes to the pain and MSD 
symptom reports, with physical factors having a somewhat larger 
magnitude of effect (standardized regression coefficients of 0.06-0.16) 
than psychosocial (0.04-0.12). Logistic modeling of low back pain and 
absenteeism outcomes found similar results, with biomechanical ORs of 
1.35-1.88 and psychosocial ORs of 1.32-1.64, excluding social support. 
However, low social support did demonstrate the highest OR (2.27) in 
the model explaining low back pain. The study was cross-sectional and 
thus could not definitively evaluate temporal associations. However its 
large size and wide range of companies and sectors allowed precise 
separation of biomechanical and psychosocial exposure-outcome 
associations, without collinearity problems.
    Dr. Alf Nachemson criticized this study (post-hearing comments, Ex. 
500-118-1), confusing it with a completely different study of a 
different database submitted to Spine. The results of this study are 
reported in a doctoral thesis (Warren, 1997, Ex. 38-72) and an article 
submitted to the Scandinavian Journal of Work Environment and Health 
(Warren et al., 2000b, 38-73). Contrary to Dr. Nachemson's 
mischaracterization, the express purpose of this study was to 
simultaneously measure biomechanical and psychosocial MSD risk factors 
at the same level and degree of detail.
    Warren et al.2000 (Ex. 38-75). Warren and colleagues from the 
University of Connecticut Health Center carried out a separate study of 
the Connecticut working population, using a random-digit-dialing study 
design. This cross-sectional study is one of the few to randomly sample 
workers with unreported cases of MSD (using the NHIS definition; Tanaka 
et al.1995 (Ex. 26-59)). Psychosocial and biomechanical variables were 
assessed at equal levels of detail. Logistic regression analysis found 
case status to be associated with a broad mix of psychosocial and 
biomechanical stressors, with biomechanical exposures showing somewhat 
higher odds ratios. Significant psychosocial ORs ranged from 1.56-1.69, 
while biomechanical ORs were between 1.89 and 2.13. Stressors were 
measured at equivalent levels of detail and demonstrated independent 
effects for psychosocial and biomechanical exposures.
    Koehoorn, 1999 (Ex. 500-40). This doctoral thesis used a 
retrospective cohort design to follow 4020 health care workers from an 
acute-care hospital over a 4-year follow-up period, assessing outcomes 
of musculoskeletal symptoms and claims. Results varied by body 
location. In multivariate models explaining upper body symptoms, a 
biomechanical index showed risk ratios of 1.41-1.84, while psychosocial 
variables showed RRs ranging from 0.45-2.78. For lower-body symptoms, 
RRs for biomechanical risk factors ranged from 2.12-4.65; psychosocial 
variables generally did not reach statistical significance. Outcomes of 
compensation claims related to these two body areas showed similar 
ranges of effect. In subcohorts analyzed for departmental sicktime and 
overtime, increased sick time was associated with symptoms and claims, 
but increased overtime was not. The study design assessed detailed 
biomechanical factors by observation, but only by occupational title, 
while psychosocial factors were assessed by individual questionnaire. 
Thus, the relative strength of association may have been underestimated 
for biomechanical stressors. This large, carefully designed cohort 
study provides evidence for a multifactoral model of MSD causation, 
with physical factors being more strongly associated with MSD 
incidence.
    Waters et al.1999 (Ex. 500-41-54). This study was designed to 
provide epidemiologic data linking the NIOSH lifting index (LI, a 
quantitative measure of manual lifting stress calculated with the 
revised NIOSH lifting equation) to prevalence of low back pain. 
Measurements used to calculate the LI were collected on a sample of 
workers over a 2-4 day period by trained observers. Workers also 
completed a self-administered questionnaire that included psychosocial 
items. In multivariate modeling, increasing values of the LI were 
associated with increases in period prevalence of LBP over the last 12 
months, with an exposure-response relationship that reversed at the 
highest LI (>3). The authors noted that this drop in negative outcomes 
in the highest exposure category is seen in other studies and seems to 
indicate a ``healthy worker'' or survivor effect (representing the 
departure of workers with pain or high risk of back injury from highly 
stressful jobs). Psychosocial factors of demands, control and social 
support did not enter significantly into these models, perhaps because 
they were entered as continuous, not categorized, variables. However, a 
four-category measure of decreasing work satisfaction showed a 
significant exposure-response relationship with LBP. This high-quality 
study, which relied on independent measurement of physical job 
characteristics, demonstrated the combined contribution of physical and 
some psychosocial stressors to prevalence of LBP, with physical effects 
predominating in multivariate modeling.
    Leclerc et al. 1998 (Ex. 500-41-85). This cross-sectional study of 
1210 workers in 3 industry sectors incorporated a sophisticated mixture 
of individual measurement of both physical and psychosocial factors, 
combined with group-level assessment of cycle time and autonomy. Given 
the study design principles outlined above, the effects of these group-
level factors may thus be underestimated. With this caveat, the 
research still demonstrated a combined contribution to physician-
diagnosed CTS for cycle times less than 10 seconds (OR 1.90) and 
psychological ``problems'' (OR 1.41). Other physical and psychosocial 
factors dropped out of this model. In a final model incorporating the 
presence of just-in-time production organization at the plant, this 
factor replaced cycle time, with an OR of 2.24. Other physical and 
psychosocial risk factors were associated with marginal significance.

[[<strong>Page</strong> 68527]]

The work organization variable of just-in-time production is probably a 
surrogate for a combination of increased biomechanical and psychosocial 
risk. This study thus demonstrates the combined contribution of both 
types of risk. This study also found that industry sector did not enter 
significantly into the model when both physical and psychosocial risk 
factors were more precisely measured at the individual level.
    Latza et al.2000 (Ex. 38-424). This prospective study of 
construction workers in Hamburg took detailed observational 
measurements of biomechanical stressors associated with a wide variety 
of construction tasks. Of the 571 workers who filled out baseline 
questionnaires, 285 individuals free of LBP were selected; 230 were 
followed up after 3 years. The physical stressors at baseline predicted 
subsequent 1-year prevalence of LBP (PRs: 1.8-4.0), while psychosocial 
stressors did not enter significantly into the models. This is somewhat 
surprising since, although the physical stressors were evaluated in 
detail, they were measured at the job level, while psychosocial factors 
were measured at the individual level. As noted above, this usually 
results in an underestimate of the physical stressor contribution 
relative to psychosocial factors.
    Vingard et al.2000, MUSIC study (Ex. 500-41-51). The Swedish MUSIC 
project has consistently demonstrated combined associations of 
biomechanical and psychosocial stressors with back, neck and shoulder, 
and other disorders. This study assessed prospectively the individual 
and combined effects of physical and psychosocial exposures on 
subjects' seeking care for LBP over a 5-year period. Gender 
stratification reduced significance levels but demonstrated somewhat 
different exposure-outcome associations for males and females. For men, 
forward bending and manual material handling time, when compared to 
levels 5 and 10 years ago, were significantly predictive (RR 1.8 and 
2.0 respectively) with a combined exposure having a RR of 2.8. This 
combined exposure was also significant for females (RR of 2.3). For 
both genders, a combination of physical stressors including metabolic 
stress was also a risk factor. Although included in these multivariate 
models, most psychosocial stressors did not enter significantly 
(exceptions were low work satisfaction and low skill use for males, RRs 
of 1.6 and 1.5, respectively). A subset of the study sample reflecting 
a combination of high physical load and high psychosocial load showed 
much higher RRs, but the sample size was small. Overall, the MUSIC 
study provides well-designed and detailed evidence that physical and 
psychosocial exposure combine in the etiology of LBP, with the physical 
stressors demonstrating stronger effects.
    Houtman et al.1994 (Ex. 26-1230). This paper reported a cross-
sectional analysis of pooled 1977-1986 results from the National Work 
and Living Condition Survey in the Netherlands. The study asked one 
question on work pace, four on intellectual discretion, and one on 
physical load. The items were all assessed at the same level of 
precision (dichotomous, yes/no) and at the same analytical level, but 
the greater detail in intellectual discretion assessment may have 
biased the estimated effects of that particular construct upwards. 
Multivariate logistic regression models were constructed to explain 
variance in 3 musculoskeletal outcomes: back complaints, muscle/joint 
complaints, and chronic back problems. Work pace was consistently 
associated with these outcomes (ORs 1.21-1.29) as was heavy physical 
load (ORs 1.36-1.62). Of the intellectual discretion items, only one, 
monotonous work, was consistently associated with musculoskeletal 
symptoms (ORs 1.29-1.35), but when all four items were combined, the 
scale demonstrated the strongest association of the study with chronic 
back pain (OR 2.10). Thus, in addition to providing more evidence for 
independent association of physical and psychosocial stressors with 
musculoskeletal outcomes, the study supports the hypothesis that 
psychosocial stressors have their strongest effect with duration of 
pain, not its inception.
    Videman et al.1989 (Ex. 26-1155). This study is difficult to 
interpret, but is included because of its relevance to interventions. 
The researchers dichotomized graduating nursing students by skill 
level. Half the students had received traditional lifting training; 
half had received advanced, biomechanically-oriented training. Skill 
assessment was performed through video analysis of standardized tasks, 
not by simple assignment to trained or untrained groups. Nurses were 
also dichotomized by hours/day in strenuous postures (3 hrs/day, >=3 
hrs/day). In addition, the study collected extensive anthropometric, 
strength and psychological measures. Incidence of back injury was 
assessed at a 1-year follow-up. The results seem to confuse training 
level and activity level, but a combination of >3 hours/day of 
strenuous activity and low skill level significantly predicted self-
reported incidence of back injury (ORs of 37 or 156, further stratified 
by high and low abdominal strength, respectively). The authors 
emphasized that ergonomic interventions must be coupled with training 
and describe the training as resulting in biomechanically less 
stressful lifting choices by nurses. They concluded that training is an 
effective intervention and ``the biomechanical and ergonomic components 
of training in patient-handling appear to be inescapable'' (Ex. 26-
1155).
    Thorbjornsson et al. 2000 (Ex. 500-71-49). This retrospective 
nested case control study examined a cohort of 484 subjects from the 
general population, examined first in 1969 and again, 24 years later, 
in 1993. Exposure information was collected retrospectively for the 24-
year period and the 12 months previous to the 1993 interview. Outcomes 
measured were LBP that resulted either in a medical visit or sick leave 
more than 7 days. The study identified a small number of physical 
factors (heavy physical work, sedentary work) and psychosocial factors 
(poor social relations and overtime work) associated with LBP, as well 
as high load outside of work. Most importantly, the research 
demonstrated significant ORs for a wide variety of interaction terms 
between workplace biomechanical and psychosocial risk factors (ORs: 
2.2-3.5). In final modeling incorporating the interaction terms, 
individual psychosocial effects became non-significant, but an 
interaction between poor social relations and overtime work showed an 
OR of 3.1-3.7 for men, depending on LBP onset time. The finding of 
significant interactions between biomechanical and psychosocial factors 
suggests that control of biomechanical risk factors in the workplace 
should reduce not only the effects associated with biomechanical risk 
factors, but the effects of their interaction with psychosocial 
exposures.

Boeing Study. (Bigos et al.1991 (Ex. 26-1241), 1991 (Ex. 26-1242), 1992 
(Ex. 26-1393)).

These studies were discussed earlier in the Health Effects section. In 
addition, several witnesses who appeared at the public hearings (Frank, 
Krause, others, e.g. Exs. 37-27, 37-15) have explored the 
methodological problems with this study, which explain its finding that 
the only significant predictor of back pain reporting found was job 
dissatisfaction. In sum, the study assessed physical factors at the 
group level (although the articles never make clear the exact 
methodology), while assessing psychosocial and psychological variables 
at the individual level. Assessed at the group level, the variance

[[<strong>Page</strong> 68528]]

in predictive physical factors was drastically reduced. For instance, 
Dr. Bigos stated (Bigos et al., 1991b, Ex. 26-1242, testimony, Tr. 
6908) that no-one was required to lift over 20 lbs., and no-one 
actually lifted more than 50. However, the analysis had no way to 
assign actual lifting frequency or compressive forces at the individual 
level. It is difficult to determine whether even the poor 
characterization of physical load approached statistical significance 
because the authors elected simply not to report results that were not 
significantly associated with outcomes (testimony, Tr. 6786). In 
addition to this measurement problem, psychosocial and psychological 
factors were measured with much greater precision. As noted above, 
these assessment differences virtually ensure the primacy of the 
better-measured factors, in this case the psychosocial factors, in 
statistical modeling.
    In addition, the factors entered in the Boeing study models 
explained only an extremely small percentage of variance in the 
outcome; job satisfaction explained 2.2 percent and psychological 
variables explained 1.9 percent. All of the psychological, physical 
exam and medical history variables assessed in the study combine to 
explain only 8.6 percent of the variance (Bigos et al., 1992, Ex. 26-
1393). Thus, 91.4 percent of the variance in reporting of back pain is 
not explained by the combination of poorly measured physical risk 
factors and the more detailed psycho-emotional factors. This suggests 
relatively poor characterization of overall exposure.
    The flaws noted above also pertain to the psychological factor 
assessment in this study. Psychological factors were measured at a much 
finer level of detail than physical factors, which were measured at the 
group level. Overall explanatory power of any of these measures was 
poor. As a minor point, specific to the psychological assessment, the 
study used non-standard and out-of-date instruments (Cherniack 
testimony, Tr. 1150).
    Svensson and Andersson 1989 (Ex. 26-732). This study evaluated the 
association of a number of physical and psychosocial and psychological 
variables with incidence (retrospective) and prevalence of LBP in 
women. Both physical and psychosocial/psychological variables showed 
univariate associations with the outcome, but multivariate analysis 
found associations only with 3 ``psychological'' variables: 
dissatisfaction with the work environment, worry/tension at the end of 
the day, and fatigue. The analysis is not helpful to the separation of 
physical and psychosocial effects for three reasons. First, the study 
only reports the p-value range of the significant associations and does 
not report effect size, thus making it impossible to tell if physical 
exposures were of near significance and to compare relative strength of 
association. Second, it is not at all clear whether variables of 
dissatisfaction and worry/tension represent a psychological exposure or 
an outcome, resulting from an underlying combination of physical and 
psychosocial/psychological workplace factors, or from underlying 
symptoms (see, Linton, 2000, Ex. 26-642). Most importantly, it is 
clearly a mistake to label ``fatigue'' a psychosocial variable. In 
fact, fatigue represents an integrated measure of all stressors, 
physical and psychosocial, encountered by the worker and may well be 
weighted towards the obvious biomechanical stressors. As such, it is 
not surprising that this measure might capture variance from the 
individual physical exposures tested in the study. (Recall how the 
combined index of psychosocial exposures in the Houtman et al.study, 
(1994, Ex. 26-1230) had the highest ORs in the study, while the 
individual items composing the index had much lower ORs.) As 
confirmation, it is interesting to note that these authors' earlier 
research (1983, Ex. 26-1158), which assessed a similar set of exposures 
but did not include the fatigue item, did demonstrate a contribution 
from a physical stressor (high degree of lifting). Thus, this research 
appears to be unable to accurately separate the contribution of 
physical and psychosocial/psychological factors to LBP.
    Leino and Hanninen 1995 (Ex. 38-76). This paper reported the 
results of a prospective study begun in 1973, in 2653 industrial 
workers, including managerial and office positions. Nine hundred two of 
these participants were reexamined after 10 years. Outcomes were self-
reported musculoskeletal symptoms and evaluations by physiotherapists. 
At follow-up, both self-reported symptoms and medical findings were 
predicted by one psychosocial scale (social relations, OR 2.63-3.41) 
and occupational class (OR 2.67-3.73). The only factor that partly 
captures physical load in this model is occupational class. A single, 
4-level measure of physical load was also entered into the equation. 
However, this measure is much less precise than the 6-question scale 
(each item with 5 levels) assessing social relations. This unequal 
precision would bias the results towards the exposures measured with 
greater precision, the psychosocial factors.
    The authors noted that their physical load measure did enter into 
the cross-sectional models at baseline, along with more psychosocial 
exposures (work content, overstrain) and occupation. It was surprising 
to find that physical load (a slightly more precise measure of 
biomechanical exposures than exposure) dropped out of final models 
while occupation class remained. Both physical load and occupation in 
this study represent biomechanical exposures assessed at a much less 
precise level than the psychosocial measures. This study, though 
provocative, cannot provide useful information about the relative 
strength of effect.

Summary of Literature Reviews

    Several reviews have been published that have evaluated the 
literature dealing with work-related MSDs; many of these reviews 
included evaluations of studies that concurrently examined the effects 
from exposure to both biomechanical risk factors and psychosocial risk 
factors. In this section, OSHA summarizes the reviews contained in the 
rulemaking docket.
    Burdorf & Sorock 1997 (Ex. 502-232). These authors reviewed 35 
studies that collected quantitative information on exposures and back 
disorder outcomes. Eight of these studies assessed psychosocial and 
biomechanical risk factors simultaneously. Of these, six found positive 
associations of back disorders with a combination of physical and 
psychosocial exposures and two identified several of the physical 
factors to be significantly associated, while the psychosocial factor 
measured (job dissatisfaction) did not show a significant association.
    The analysis identified lifting or carrying loads, whole-body 
vibration, and frequent bending and twisting to be the biomechanical 
risk factors having consistent associations with work-related back 
disorders. Unlike some other studies (e.g., Leino & Hanninen, 1995, Ex 
38-76), height and weight (as well as gender, exercise and marital 
status) were consistently not associated with back disorders in these 
studies. The review identified low job decision latitude and job 
dissatisfaction as possibly important predictors of MSDs, but the 
evidence was not consistent across studies with different designs. 
Although the majority of these eight studies acknowledged the 
importance of psychosocial factors, the generalization that emerges 
from them is that biomechanical factors were more

[[<strong>Page</strong> 68529]]

consistently associated with back disorders.
    Punnett and Bergqvist 1997 (Ex. 38-13). This review of a large 
international body of literature linking biomechanical and psychosocial 
factors to upper extremity symptoms and findings in computer users 
(classified by neck/shoulder, arm/elbow, and hand/wrist). The authors 
found strong, consistent evidence linking MSD development with 
biomechanical factors (hours/day and cumulative years of exposure, 
intensive or repetitive data entry, and non-neutral postures due to 
poor workstation design), while controlling for work organizational and 
psychosocial factors in 7 of the 72 papers included in the analysis. 
The work organizational factors included in 3 papers (repetitive work, 
work pressure and insufficient rest breaks represent a combination of 
physical and psychosocial risks. In 4 papers, this review found 
suggestive but inconsistent associations (making generalization 
impossible) between MSD symptoms and the psychosocial factors of low 
decision latitude, low social support, job insecurity and job 
dissatisfaction (Bergqvist et al., 1995, Ex. 26-1195, Faucett & 
Rempell, 1994, Ex. 38-67, Kamwendo et al., 1991, Ex. 26-1384, Hoekstra 
et al., 1994, Ex. 26-725). The authors also noted the difficulty of 
using job dissatisfaction as a predictor for MSDs since it could easily 
be either a cause or consequence of an MSD.
    Lagerstrom et al. 1998 (Ex. 38-102). In this review of studies 
relating to low back problems in nursing, 42 articles passed the 
inclusion criteria: 21 cross-sectional, 10 prospective, and 11 
intervention (also prospective). One of the reviewers' quality criteria 
was that the studies include both physical and psychosocial exposure 
information. The authors noted that a problem in many of the studies 
was the assessment of physical stressor information at an aggregate or 
group level, while psychosocial exposures were assessed at the 
individual level. As noted above, this non-comparability would tend to 
underestimate biomechanical effect in relationship to psychosocial 
effect. Still, the authors conclude from their review that 
biomechanical and psychosocial exposures generally combine in their 
associations with or (in prospective studies) effects on back disorder 
outcomes. Looking at well-designed studies with dual exposure 
measurement, the authors report that ``[t]o our knowledge there are no 
studies that show that work organizational or psychosocial factors, as 
such, cause low-back problems.'' They do acknowledge the importance of 
these factors in the ``consequence and maintenance'' of low-back 
related disorders, through differences in pain perception and reporting 
behavior.
    Bongers et al. 1993 (Ex. 26-1292). This article was one of the 
earliest reviews of the evidence for an association between 
psychosocial factors and MSD outcomes. The authors looked at 29 cross-
sectional and 3 longitudinal studies addressing work-related 
psychosocial factors. Of these, 22 measured physical load, and the 
authors of this review did not think that the physical load assessment 
was of a high enough quality to specifically assign relative 
association effects to physical and psychosocial factors. Thus, this 
review is included to demonstrate how far the field has moved since 
1993. Subsequent reviews and studies addressed in this section show 
that research in the intervening 7 years has moved towards more 
accurate characterization of biomechanical and psychosocial loads and 
defining their associations with MSD outcomes.
    National Academy of Sciences, 1999 (Ex. 26-37). The NAS study 
(cited by Armstrong, Exs. 37-21, 37-1, 37-9 and others, Ex. 37-15, 
testimony) was discussed in OSHA's preamble to the proposed rule and is 
described in part B of this Health Effects section. It reviewed a 
number of studies that found strong evidence for biomechanical 
contribution to MSD etiology, controlling for psychosocial factors.
    Linton, 2000 (Ex. 26-642). This paper is a careful literature 
review of studies addressing the association between psychological 
factors and back and neck pain. The author concentrated on individual 
psychological measures (i.e., internal psychological factors) but also 
included some external psychosocial factors. Since many of the studies 
also assessed outcomes of disability and time to return-to-work (RTW), 
the author was able to provide evidence for his suggestion that 
psychological factors may play a greater role in these long-term 
outcomes.
    The findings of this review are strengthened by its assessment of 
only prospective studies. This might allow an interpretation that the 
positive relationship found between various psychological factors and 
the outcomes of pain, disability, RTW time, etc. might represent a 
causal connection. However, there are two important caveats. Dr. Linton 
noted that longitudinal relationships of this sort may still mask 
reverse causal connections. The studies generally cannot determine 
whether some psychological ``predictor'' variables and the outcome 
variables are not both the result of initial or underlying pain. 
Secondly, he noted that the psychological variables identified in the 
37 reviewed studies explain only part of the variance in outcome. Thus, 
the review's results are consistent with the multifactoral model of MSD 
etiology (including biomechanical, psychosocial, psychological and 
personal variables).
    Despite the care with which the studies were selected and analyzed, 
however, the review did not identify the type of biomechanical 
exposures assessed in the studies or the level at which they were 
studied. Instead, it simply noted that 18 studies controlled for 
miscellaneous confounding factors, one of which was ``workplace 
factors''. No indication was given as to the nature of these factors 
and which of these 18 studies addressed ``workplace factors''. Given 
the age of some of the papers, controlling for other factors (instead 
of simultaneously assessing their effect) is understandable, but it 
renders the review useless in contributing to the central debate 
concerning relative contribution of biomechanical and psychosocial 
factors (i.e., both external psychological and social workplace factors 
and internal psychological factors). To further compromise the utility 
of this review, the studies evaluated in this review included several 
that measured physical exposure at the wrong analytical level (e.g., 
Bigos et al., 1991, Exs. 26-1241, 26-1242) or at a reduced level of 
detail (e.g., Leino & Hanninen, 1995, Ex. 38-76, Viikari-Juntura et 
al., 1991, Ex. 26-1219), compared to the psychological factors. This 
review, although a significant contribution to the literature overall, 
provides no useful information concerning relative contribution of 
physical and psychological factors to MSDs.
    Nachemson 1999 (Ex. 32-241-3-31). This article is a comprehensive 
review of the studies purporting to demonstrate that physical workplace 
factors are irrelevant to the development of back pain, injury and 
disability. Instead, the studies implicate personal biology and 
psychological factors, stress and psychosocial factors in the 
workplace, and the monetary incentives of the compensation system. Some 
of these studies have been addressed above (e.g., Bigos, 1991b, Ex. 26-
1242). In general, Dr. Nachemson's claim that these factors contribute 
to low back disorders is credible. Very few of the researchers cited 
above would deny their contribution. What is emphatically not credible 
is the claim that physical factors are thus not implicated.

[[<strong>Page</strong> 68530]]

    There are 3 primary problems with this claim. First, many of the 
studies cited in the article have not assessed the role of physical 
factors at all or have assessed them at levels of analysis or detail 
that make examination of their contribution impossible. The results of 
these errors have been discussed above. These studies overestimate the 
role of non-physical risks and thus cannot address the question or 
relative effects of biomechanical and psychosocial exposures in the 
workplace.
    Second, the basic conceptual gap in the Nachemson review is a 
failure to acknowledge and address the implications and mechanism of 
multifactoral causation. There is a broad literature of well-designed 
studies, both epidemiological and laboratory (reviewed above and in 
earlier parts of the Health Effects section) demonstrating that 
psychosocial and psychological factors can add to the effects of 
physical exposures or even potentiate them (interaction or effect 
modification) (see Linton, 1990, Ex. 26-977, for a clear example). Dr. 
Nachemson's reluctance to consider such effects is represented by his 
citation of the Valfors et al. (1985, Ex. 26-685) examination of LBP. 
This study reported that physical risk factors (poorly characterized by 
a physiotherapist and a physician) were similar in workplaces of 
controls and low back cases, while reporting case/control differences 
in psychosocial work environment (again, poorly characterized). Valfors 
thus attributed the back injuries in the case group to the psychosocial 
factors. The logical fallacy, of course, is to assume that this 
difference removes physical exposures from a causal role. The more 
logical explanation, especially in light of all the evidence for 
multifactoral etiology presented in this section, is that the 
combination of physical exposures and psychosocial exposures presented 
increased risk. A level of physical risk that is acceptable in a 
psychosocially benign work environment can combine with elevated levels 
of psychosocial risk to cause disorders.
    Finally, many of the studies cited in this article confuse cause 
with effect. To continue with Dr. Nachemson's citation, Valfors 
concluded that the measured differences in work satisfaction were the 
cause of the low back pain episodes, when it is just as likely that the 
LBP itself affected patients assessment of their work satisfaction (see 
Linton, 2000, Ex. 26-642).
    These three errors, together or individually, characterize many of 
the studies in the Nachemson article. In sum, this review, while useful 
in collecting a wide variety of studies addressing the complex issues 
of low back pain, disability, and management, does not demonstrate that 
physical workplace factors are not involved in the etiology of LBP. Nor 
does it demonstrate that workplace interventions directed towards 
reduction of biomechanical risk factors would be ineffective. His 
citation of the Daltroy (Daltroy et al., 1997, Ex. 38-57) training 
intervention in the postal service, for example, is not a refutation of 
the central causal role of biomechanical exposures in the etiology of 
back injury. Rather, it is emblematic of the general failure of ``back 
schools'', when introduced in the absence of measures directed towards 
control of physical risk factors. Dr. Nachemson, himself, states in 
this review: ``[I]t is obvious that certain types of lifts and working 
positions should be avoided and this in particular applies to twisted 
lifts.'' Ideally, this review will advance the development of more 
effective intervention techniques that address the combination of risk 
factors presented by Dr. Nachemson.
    Waddell & Burton 2000 (Ex. DC-151-A). This thorough review of 
management protocols for LBP includes evaluation of epidemiological and 
clinical studies addressing etiology of LBP. Because the review and 
recommendations focus primarily on medical management issues, it is not 
surprising that it concentrates on the psychosocial factors involved in 
pain perception, sickness absence, disability and return-to work. Most 
of the studies addressed above acknowledge the importance of 
psychosocial factors in medical management issues, not only for LBP but 
also for other musculoskeletal disorders. The evidence reviewed above 
corresponds with these authors' conclusions that low job satisfaction, 
``unsatisfactory psychosocial aspects of work'' and individual 
psychosocial findings are risk factors for onset of LBP, health care 
use and work loss, but the size of that association is small to modest 
(strong evidence). The authors also noted that physical demands of work 
(manual materials handling, lifting, bending, twisting, and whole body 
vibration) can be associated with onset of LBP, increased LBP reports, 
symptom aggravation, and back ``injury'' (authors'' quotes). However, 
they find that the association ``appears to be'' weaker than those of 
individual, non-occupational and unidentified factors (strong 
evidence).
    The authors make an elementary error in ascribing potential LBP 
causation only to dynamic back activities. Their noting the high 
prevalence of LBP in non-dynamic jobs, and even in the unemployed, is, 
of course, related to the well-established research findings that 
sedentary and constrained postures are also physical risk factors for 
back disorders (Putz-Anderson, 1991, Ex. 26-1255, Hoogendoorn et al., 
1999, Ex. 38-81, Burdorf & Sorock, 1997 Ex. 502-232).
    More importantly, the studies used to provide ``strong evidence'' 
for various conclusions are sometimes categorized as being of high 
quality when, in fact, they violate some of the important 
epidemiological design criteria cited above. In particular, in making a 
case for primarily psychosocial causation, the authors used studies 
that measured biomechanical exposures inadequately (e.g., Bigos et al., 
1991b, Ex. 26-1242, and others reviewed above) or studies that did not 
include both biomechanical and psychosocial factors in statistical 
modeling (Macfarlane et al., 1997, Ex. 500-41-91, Papageorgiou et al., 
1997, Ex. 32-241-3-41). Several reviews are cited that, on closer 
examination, are only modest in their assessment of both psychosocial 
and biomechanical risk contribution, noting the problems with study 
design and, especially, the relatively few studies that assessed both 
exposures adequately and at equal levels of precision (Burdorf & 
Sorock, 1997, Ex. 500-232, Bongers et al., 1993, Ex. 26-1292, Davis & 
Heaney, 2000).

Conclusions

    Based on the rulemaking testimony, scientific studies, and 
literature reviews considered in this section, OSHA concludes that the 
evidence contained in the record supports a combined contribution of 
biomechanical and psychosocial risk factors to the onset, development 
and prolongation of MSDs. Biomechanical contributions to the etiology 
of work-related MSDs have been demonstrated to be more consistent than 
psychosocial factors across different study populations, and most well-
designed studies reported stronger associations between exposure to 
biomechanical risk factors and an increased MSD prevalence or incidence 
than has been observed for psychosocial factors. However, it is not 
possible to determine the relative strength of association between 
biomechanical and psychosocial factors with any precision because of 
differences in measurement techniques used in the various studies to 
assess biomechanical and psychosocial factors, and because of the 
different ways in which psychosocial factors are defined by various 
investigators. Most importantly is the finding by several investigators 
that

[[<strong>Page</strong> 68531]]

biomechanical and psychosocial factors influence MSD risk in 
independent fashon, which suggests that reductions in biomechanical 
exposures absent any change in psychosocial influences should reduce 
the risk of work-related MSDs.
    Findings from published literature reviews of studies that conform 
to the epidemiologic design principles discussed above are consistent 
with the Agency's conclusions. Four reviews (Burdorf, Ex. 502-232, 
Punnett, 38-13, Lagerstrom, Ex. 38-102, NAS, Ex. 26-37) reported that 
biomechanical risk factors generally showed stronger and/or more 
consistent associations with elevated MSD prevalence or incidence than 
did psychosocial factors.
    Three reviews reached an opposite conclusion (Linton, Ex. 26-642, 
Nachemson, Ex. 32-241-3-31, Waddell, DC-151-A); however, these reviews 
relied more heavily on studies where biomechanical factors were not 
evaluated at all, were evaluated in jobs having little variance in 
physical load, or were evaluated at different analytical levels or with 
less precision, or than psychosocial factors. All of these design flaws 
bias results towards increased psychosocial effects in modeling. It is 
on the basis of these reviews and the underlying studies that the 
Chamber of Commerce, Gibson, Dunn & Crutcher, and several of their 
scientific witnesses base their conclusion that psychosocial factors 
outweigh the importance of biomechanical factors in the etiology of 
MSDs. Accordingly, OSHA is not persuaded by these arguments, and finds 
the preponderance of evidence supports a multifactorial model of MSD 
causation involving both biomechanical and psychosocial factors acting 
independently on risk.
    Moreover, testimony and evidence presented above suggests that 
biomechanical and psychosocial risk factors are, to a degree, 
inextricable (Punnett, testimony, Tr. 868, Kerr et al., 2000, Ex. 38-
82). The degree of influence each exerts on MSD risk is in large part 
determined by company characteristics and work organization, and their 
very separation is somewhat artificial. The final rule's focus on 
reducing exposures to biomechanical risk factors reflects the 
intervention strategy that has been emphasized in the literature and 
implemented by many sophisticated companies. Simply less is known about 
how to intervene effectively on psychosocial factors. However, this 
does not mean that biomechanical intervention will have no effect on 
psychosocial factors in the wortkplace. Because of the correlation and 
interactions between biomechanical and psychosocial factors in their 
associations with MSD outcomes, interventions focused towards 
biomechanical stressor reduction are likely to have a positive effect 
on levels of psychosocial stress. The arguments of Bellamy and Vendor, 
above (testimony) are addressed by the reality of this close 
correlation between stressor types.
    The intervention literature demonstrates that the very fact of a 
company's undertaking even a limited program to control biomechanical 
exposures is, de facto, also a psychosocial intervention. If workers 
report MSD symptoms and the company responds with workplace 
alterations, medical intervention, training, and the other program 
elements in the final rule, this response often represents a reduction 
in excessive psychological demands, an increased sense of control, and 
an improvement in the social support structure of the workplace. In 
Sweden, Kvarnstrom (1992, Ex. 38-69) found that changes in the physical 
work characteristics, combined with changes in the psychosocial work 
environment (increased variety, decision-making latitude, and 
individual control over the work situation) in a small department of a 
large, multi-national company greatly reduced the high rate of 
absenteeism and turnover due to musculoskeletal disease. In the United 
States, Smith and Zehel (1992, Ex. 38-70) reported that employee focus 
groups identified the need for physically-oriented engineering changes 
as well as psychosocial changes in a meat-processing plant; the 
combined intervention resulted in decreased physical symptoms for part 
of the work force. Worker participation in problem identification and 
solution development is a central feature of many successful approaches 
to work environment change and is at the core of the proposed rule. For 
example, Pasmore & Friedlander (1982, Ex. 38-71), addressing an 
outbreak of upper extremity disorders in a United States electronic 
assembly facility, designed an intervention in which the employees 
determined the data to be collected and solutions based on these data. 
While this level of employee involvement focused on reducing 
biomechanical risk factors, it also increased employee participation 
and task control and altered role relationships within the 
organization.
    A number of witnesses testified at the hearing that ergonomic 
programs designed to address biomechanicla factors have positive 
effects on psychosocial factors that have been implicated in MSD 
etiology. Dr. Warren explained why this is the case:

    I think what happens hypothetically and in my experience is that 
when you control a biomechanical workpalce factor, you are de facto 
making a small psychosocial intervention in the workplace.
    When * * * somebody says [``]my back hurts[''] and it's followed 
* * * immediately by [``]and nobody cares[''], you know that there's 
a psychological problem in that workpalce. So I think that, yes, * * 
* a control of a biomechanical risk factor with no change in a 
psychosocial environment would reduce the chance of injury, but that 
it would probably also change the psychosocial environment to a 
small degree. [Tr. 1265]

Dr. Rosecrance (Tr. 2319-20) presented a specific example. He noted 
that the biomechanical intervention in his study of the Cedar Rapids 
Gazette resulted not only in reductions of MSDs, but also improvements 
in the company social structure.

    Mr. Dave Alexander believed that the employee participation 
provision of the proposed standard would address psychosocial issues:

* * * the opportunity for worker participation in the form of 
contributing information, suggesting solutions, having a mechanism 
to report problems would, in fact, tie in with the psychosocial 
issues that would be important in the workplace. [Tr. 2713-2714]

Similarly, Dr. Silverstein testified that providing workers with basic 
information on MSDs and employee involvement in the ergonomics program 
increases the decision latitude for workers [Tr. 17445].
    These studies and testimony indicate that the basic precepts of 
management commitment and employee participation contained in the final 
rule, while forming the administrative infrastructure of an ergonomics 
program focused on physical risk abatement, has the potential to have 
positive effects on the psychosocial characteristics of the work 
environment.
6. Final Rule's Consistency With Medical Guidelines
    Several commenters questioned whether the program elements of 
OSHA's final rule were consistent with existing medical practice 
guidelines, primarily with respect to diagnosing and treating low back 
pain, but also diagnosing and treating other MSDs. For example, when 
referring to the Agency for Health Care Policy and Research (AHCPR) low 
back pain guidelines, Gibson, Dunn and Crutcher stated that the review 
of evidence published with the guidelines

contradicts OSHA's ergonomic hypothesis that work causes physical 
injury, contradicts OSHA's view that ``ergonomic'' interventions can 
alleviate workplace pain, and contradicts

[[<strong>Page</strong> 68532]]

OSHA's prescription for rest as a response to back pain. [Ex. 500-
118]

    OSHA disagrees with these commenters. In reviewing the record, OSHA 
finds that the final rule is consistent with the medical literature, 
including the AHCPR guidelines, the American College of Occupational 
and Environmental Medicine (ACOEM) Occupational Medicine Practice 
Guidelines (Ex. 38-234), The Royal College of General Practitioners' 
Clinical Guidelines for the Management of Acute Low Back Pain (Royal 
College guidelines) (Waddell et al. 1999; Ex. 32-241-3-38), the Faculty 
of Occupational Medicine's Occupational Health Guidelines for the 
Management of Low Back Pain at Work (British guidelines) (Ex. 500-118-
2), and other evidence-based medical practice.
    The first assertion, that the AHCPR guidelines ``contradict[ ] 
OSHA's ergonomic hypothesis that work causes physical injury'' is 
incorrect for several reasons. The AHCPR guidelines acknowledge that

* * * several studies have identified an increased incidence of low 
back problems among individuals whose work involves heavy or 
repetitive lifting, exposure to total body vibration (from vehicles 
or industrial machinery), asymmetric postures, and postures 
sustained for long periods of time. [Ex. 32-241-3-93]

The guidelines also recognize that

    Other biomechanical research suggests that certain postures and 
activities increase the mechanical stress on the spine. It is not 
clear whether these mechanical stresses are the cause of low back 
problems. However, once symptoms are present, mechanical stresses 
correlate with worsening of symptoms. Prolonged sitting and postures 
that involve bending and twisting have been shown to increase the 
mechanical stress on the spine according to pressure measurements in 
lumbar intervertebral discs. Heavy lifting also appears to increase 
mechanical stress on the spine, but this stress can be reduced if 
the lifted object is held close to the body rather than at arm's 
length. [Ex. 32-241-3-93]

These conclusions are clearly consistent with the conclusions of the 
Health Effects section of the final rule that biomechanical factors are 
associated with low back pain. It must be recalled that the AHCPR 
guidelines were

* * * intended to provide primary care clinicians with information 
and recommended strategies for the assessment and treatment of acute 
low back problems in adults. [Ex. 32-241-3-93]

They were not intended to provide a comprehensive review of work-
related low back pain, ergonomics or low back pain prevention. There 
are few references to ergonomics, and the guidelines promotes the 
utility of ergonomics in return to work decision making by stating 
that: ``Several ergonomic guidelines on lifting and materials-handling 
tasks are available to help the clinician provide ranges of activity 
alterations at work.'' (Ex. 32-241-3-93)
    Finally, the AHCPR guidelines (Ex. 32-241-3-93) do not suggest that 
patients with acute low back pain immediately return to work involving 
physical factors that may stress the spine. Rather they advise 
appropriate activity modification to assist in the recovery process. 
AHCPR guidelines Activity Recommendations panel findings and 
recommendations state: (1) ``Patients with acute low back problems may 
be more comfortable if they temporarily limit or avoid specific 
activities known to increase mechanical stress on the spine, especially 
prolonged unsupported sitting, heavy lifting, and bending or twisting 
the back while lifting. (Strength of Evidence = D.);'' and (2) 
``Activity recommendations for the employed patient with acute low back 
symptoms need to consider the patient's age and general health, and the 
physical demands of required job tasks. (Strength of Evidence = D.)'' 
As to the duration of activity modification, the AHCPR guidelines 
demonstrate an understanding of the impact that the physical demands of 
work have on recovery and modified activity. The guidelines state that 
``The nature and duration of limitations will depend on the clinical 
status of the patient and the physical requirements of the job.''
    Several other components of the final rule are supported by AHCPR 
recommendations, including the use of job hazard analysis and medical 
management involving communication with the HCP. Pertinent AHCPR 
guidelines statements are as follows: (1) ``In recommending activity 
modifications for patients who work, the clinician may find it helpful 
to obtain from the employer a description of the physical demands of 
required job tasks,'' and (2) ``The panel recommends that clinicians 
help patients establish activity goals, in consultation with their 
employer when applicable.''
    As with the AHCPR guidelines (Ex. 32-241-3-93), the commenters 
cited above did not accurately represent the findings of the Royal 
College guidelines (Ex. 32-241-3-38) and British guidelines (Ex. 500-
118-2) in criticizing OSHA's proposal. They also failed to acknowledge 
evidence and recommendations from these reports that are consistent 
with the final rule.
    The Royal College guidelines (Ex. 32-241-3-38) were developed for 
the purpose of disseminating evidence-based recommendations on the 
management of acute low back pain to clinicians. The Royal College 
guidelines do not purport to relate to, nor were they focused on, the 
same purpose as OSHA's proposal, that is to reduce MSDs and control MSD 
hazards in the workplace. These guidelines do not contain information 
on evidence based conclusions on ergonomics or low back pain 
prevention. Several elements of the proposal are supported by the Royal 
College guidelines (Ex. 32-241-3-38). For example, under Initial 
Assessment Methods, they recommend: ``The patient's age, the duration 
and description of symptoms, the impact of symptoms on activity and 
work, and the response to previous therapy are important in the care of 
back problems.'' Under Information to Patients, the guidelines state: 
``About 10% of patients will have some persisting symptoms a year 
later, but most of them can manage to continue with most normal 
activities. Patients who return to normal activities feel healthier, 
use less analgesics and are less distressed than those who limit their 
activities.'' The Royal College guidelines suggest that most workers 
can manage with most normal activities, but do not suggest that this 
includes extremely physical tasks that cause very significant 
mechanical loading to the lumbar spine and are associated with elevated 
risks of low back pain.
    Similarly, the purpose and findings of the British occupational 
health low back pain guidelines (Ex. 500-118-2) have also been 
misrepresented (e.g., Ex. 32-241-3-20). The British guidelines state: 
``These guidelines represent the main recommendations and evidence 
statements derived from a detailed Evidence Review and developed by a 
multidisciplinary group of practitioners. They concern the clinical 
management of workers affected by non-specific low back pain, including 
advice on placement, rehabilitation and measures for prevention.'' The 
British guidelines further clarify that they were not intended to 
disseminate information regarding workplace health and safety, job 
design, and ergonomics when they state: ``They focus on actions to be 
taken to assist the individual and do not specifically cover legal 
issues, health and safety management, job design and ergonomics.'' 
Again, this is a different focus than the proposal, and conclusions 
should be interpreted in that light. Under evidence review methods, the 
British guidelines state:

    In view of the occupational health focus of the guidelines and 
the present review, the following areas were excluded from the 
review, except where they impact directly on the guideline 
recommendations: chronic

[[<strong>Page</strong> 68533]]

intractable pain, long-term disability and pain management 
programmes; spinal surgery and post-operative states; primary 
ergonomic interventions. [Ex. 32-241-3-93]

    The British guidelines (Ex. 500-118-2) acknowledge the role of work 
in contributing to low back pain in its own preface. In reviewing 
challenges for the review the authors state: ``The need for everyone to 
recognize that work is only one contributor to back pain but that back 
pain whatever its cause can, if poorly managed, have a devastating 
effect on a person's ability to work.'' The review goes on to classify 
evidence based literature recommendations using the following 
classification scenarios:
    ***Strong evidence--provided by generally consistent findings in 
multiple, high quality scientific studies.
    **Moderate evidence--provided by generally consistent findings in 
fewer, smaller or lower quality scientific studies.
    *Limited or contradictory evidence--provided by one scientific 
study or inconsistent findings in multiple scientific studies.
    --No scientific evidence--based on clinical studies, theoretical 
considerations and/or clinical consensus.
    Several British guidelines (Ex. 500-118-2) findings are consistent 
with the final rule. With respect to the relationship of physical work 
factors and work-related low back pain, the guidelines report the 
following evidence based findings: There is strong evidence that

Physical demands of work (manual materials handling, lifting, 
bending, twisting, and whole body vibration) can be associated with 
increased reports of back symptoms, aggravation of symptoms and 
``injuries.'' [Ex. 500-118-2]

These guidelines therefore acknowledge potential for physical work 
factors to precipitate low back pain episodes, and recognize some 
evidence of a cumulative effect of spinal loading. In addition, 
management of work-related low back pain, as noted in the AHCPR low 
back pain guidelines, may reasonably include elements similar to those 
in the OSHA final rule, such as

* * * temporarily limit[ing] or avoid[ing] specific activities known 
to increase mechanical stress on the spine, especially prolonged 
unsupported sitting, heavy lifting, and bending or twisting the back 
while lifting. [Ex. 32-241-3-93]

In summary, the British guidelines (Ex. 500-118-2) state that there is 
moderate evidence that ``From an organisational perspective, the 
temporary provision of lighter or modified duties facilitates return to 
work and reduces time off work.''
    The British guidelines (Ex. 500-118-2) go on to cite other 
conclusions about work and low back pain using evidence based 
literature reviews (Evidence) and consensus opinion (Recommendation). 
In making recommendations on prevention and case management, the 
authors advise the ``need to be directed at both physical and 
psychosocial factors.'' If physical work is not harmful and it does not 
contribute to low back pain, then why would the authors advise 
addressing the physical task factors of work in prevention efforts? 
Similarly, if physical characteristics of work are not significant 
issues for workers who return to work after developing a low back 
disorder, then why do the authors state the following?

    There is a pragmatic argument that individuals at highest risk 
of LBP should not be placed in jobs that impose the greatest 
physical demands. The basic concern is that workers with physically 
(or psychologically) demanding work report rather more low back 
symptoms, have more work-related back ``injuries'' and lose more 
time off work with LBP. Even if physical demands of work may be a 
relatively modest factor in the primary causation of LBP (see 
Background above), people who have LBP (for whatever cause) do have 
more difficulty managing physically demanding work (T3: (Muller et 
al.1999) T2: (Waddell 1998)). It may be argued, therefore, that 
avoiding putting people at highest risk of recurrent LBP and 
sickness absence into more physically demanding work would be in the 
interests of the individual worker, the employer and the total 
societal burden of LBP. [Ex. 500-118-2]

Similarly, the ACOEM guidelines (Ex. 38-234) agree with the observation 
that specific physical work factors are associated with certain work-
related MSDs.
    One of the criticisms raised by a commenter was the limited 
reference to the Cochrane Collaboration Back Review Group in low back 
sections of the Health Effects section of the preamble to the proposed 
rule. However, as a significant contributor to this effort, Dr. 
Nachemson clarified that neither work-related back pain nor ergonomics 
were the focus of these reviews (Tr. 6779).
    Although Dr. Nachemson questioned OSHA's findings of the 
relationship of work to the development of work-related low back 
disorders, he contradicts this in the chapter he authored for the 
International Society for the Study of the Lumbar Spine, entitled 
``Future of Low Back Pain'' (Wiesel et al. 1996, Ex. 26-1620). The 
chapter has a table compiled on the effects of external load on low 
back structures. The table lists extreme loading activity, several 
hours of hard training, extreme body position, as having negative 
influences on muscle, cartilage, and disc.
    Dr. Stanley Bigos admitted that physical work factors could result 
in the development of low back pain in an exchange with one of the 
questioners.

    MS. GWYNN: Doctor, you believe, do you not, that lifting and 
bending while lifting and twisting while lifting can aggravate low 
back pain?
    DR. BIGOS: I believe that it can bring on symptoms in people who 
have had prior back problems. And perhaps, it could bring on 
symptoms of people who haven't, depending upon the condition they 
are in. [Tr. 6916]

    Along other lines, some commenters raised issues with OSHA's 
inclusion of symptoms in the definition of an MSD. Gibson, Dunn and 
Crutcher stated that:

    These sensations that the agency treats as tantamount to 
musculoskeletal injury are ubiquitous in the general population and 
do not warrant interference by the agency. [Ex. 500-118]

    OSHA does not agree with this argument. OSHA is not attempting to 
regulate common symptoms. Rather, OSHA has proposed strategies to 
modify physical workplace factors that are associated with the 
development of MSDs, when the physical factors at work are present in 
frequency, intensity, and/or duration likely to be responsible for 
causing observed MSDs. As required in the final rule, the employer's 
responsibility is that it must evaluate employee reports of MSD signs 
and symptoms to determine whether an MSD incident has occurred. The 
evaluation may include an evaluation by an HCP to determine the nature 
of the condition and assist the employer in evaluating the work-
relatedness of the MSD. Many employers presently act in a very similar 
manner when an employee reports a potential problem. The employer may 
perform an accident or incident investigation, offer temporary modified 
duty, correct the problem, and/or refer the employee to a HCP for 
evaluation.
    Gibson, Dunn, and Crutcher also suggested that paying attention to 
subjective complaints would lead to inaccurate diagnoses. They state 
that:

    One of the challenges presented by MSDs is that, in order to 
diagnose an affliction (in an effort to determine what response is 
required to comply with the proposed standard), an employer or the 
employer's physician must rely principally, if not solely, on 
subjective reports of pain from employees. [Ex. 500-118]

    These assertions are incorrect, and are not consistent with medical 
literature and opinion. A worker's medical history, including 
subjective reports like pain, is a key element that has been

[[<strong>Page</strong> 68534]]

utilized since the beginnings of medicine to help physicians diagnose 
medical conditions. The AHCPR guidelines emphasize the role of the 
medical history when they state:

    A few key questions on the medical history can help ensure that 
a serious underlying condition, such as cancer or spinal infection, 
will not be missed * * * Symptoms of sciatica (leg pain) or 
neurogenic claudication (walking limitations due to leg pain) 
suggest possible neurologic involvement. Pain radiating below the 
knee is more likely to indicate a true radiculopathy than pain 
radiating only to the posterior thigh. A history of persistent 
numbness or weakness in the leg(s) further increases the likelihood 
of neurologic involvement. The articles indicate that cauda equina 
syndrome can be ruled out with a medical history that ascertains the 
absence of bladder dysfunction (usually urinary retention or 
overflow incontinence), saddle anesthesia, and unilateral or 
bilateral leg pain and weakness. [Ex. 32-241-3-93]

The AHCPR guidelines go on to clarify that the examination is used to 
confirm clinical impressions derived from the medical history, 
including pain characteristics:

    The physical examination supplements the information obtained in 
the medical history in seeking an underlying serious condition or 
possible neurologic compromise. [Ex. 32-241-3-93]

The AHCPR low back pain guidelines also indicate that ``The physical 
examination is less useful than the history in searching for underlying 
serious conditions.'' Thus OSHA's approach to the use of employee 
symptoms is similar to the AHCPR rigorous analysis of the literature on 
acute low back pain evaluation and treatment that concluded that 
symptoms and history give important information to diagnose and manage 
adults with acute low back pain.
    Both the Royal College and British guidelines support the role of 
history, including symptoms, in the diagnosis and management of low 
back pain. The British guidelines state:

    The patient's age, the duration and description of symptoms, the 
impact of symptoms on activity and work, and the response to 
previous therapy are important in the care of back problems. (B: 
Moderate research based evidence). [Ex. 500-118-2]

The guidelines confirm AHCPR recommendations by indicating:

    The initial clinical history can identify `red flags' of 
possible serious pathology. Such inquiries are especially important 
in patients over age 55. (B: Moderate research based evidence). [Ex. 
500-118-2]

    OSHA's approach, in particular the acknowledgment of worker 
symptoms, parallels this literature based analysis.
    Further validation of the importance of symptom reporting for low 
back pain comes from the ACOEM guidelines (Harris et al. 1997; Ex. 502-
240). The ACOEM guidelines included peer review by Dr. Stanley Bigos, 
expert witness for UPS and Anheuser-Busch and others. The following 
quotes are excerpted from the guidelines:

    A focused medical history, work history, and physical 
examination are generally sufficient to assess the worker with a 
complaint of an apparently job related disorder. [Ex. 502-240]

In this assessment, certain patient responses and findings raise the 
suspicion of serious underlying medical conditions.

    The patient's description of the mechanism of injury (so far as 
is known), his or her presenting symptoms, the duration of symptoms, 
exacerbating factors, and the history of previous episodes will help 
define the problem. [Ex. 502-240]

In Chapter 14, the ACOEM guidelines state:

    Thorough medical and work histories and a focused physical 
examination are sufficient for the initial assessment of the worker 
with a complaint of potentially work-related low back symptoms. [Ex. 
502-240]

    These statements from clinical medicine practice guidelines provide 
further support for the use of symptoms as a trigger in the final rule. 
The practice guidelines make use of the patient history and reports of 
symptoms and take a consistent approach to the physical examination 
referent to patients with low back pain.
    This approach is consistent with the one medical text brought to 
OSHA's attention. The International Society for the Study of The Lumbar 
Spine publishes a text entitled ``The Lumbar Spine'' (Wiesel, et al. 
1996; Ex. 26-1620). In Chapter 3 on clinical evaluation of low back 
pain by Jeremy Fairbank and Hamilton Hall (History taking and physical 
examination: Identification of syndromes of back pain), the authors 
state:

    Conventional western medical therapy is practiced on the basis 
of a diagnosis that is made from a synthesis of information acquired 
from the patient's history, physical examination, and special 
investigations. Back pain is a common presenting symptom, and its 
diagnosis should be approached in the same manner as that of any 
other symptom. [Ex. 26-1620]

They further state that

    A detailed history obtained from the patient is essential for 
making a diagnosis, assessing disability, and dictating management. 
Time spent listening to the patient is not wasted. Back pain has a 
wide variety of causes, and many of these can be revealed during 
history taking. [Ex. 26-1620]

providing support that

    Objective evidence obtained on physical examination should 
enhance and support the diagnostic hypotheses arising from the 
patient's history. [Ex. 26-1620]

    The authors go on to propose a classification system for low back 
pain (Pynsent-Fairbank-Hall Classification of Extraspinal Pain), which 
is primarily based upon patient symptoms. The acknowledgment of the 
importance of symptoms in this text is of particular interest to OSHA 
due to the fact that two principal expert witnesses who testified on 
behalf of UPS and others that symptoms are not meaningful, Dr. Stanley 
Bigos and Dr. Alf Nachemson, are members of The International Society 
for the Study of The Lumbar Spine, the organization that published the 
above text.
    The classification of low back pain primarily upon patient symptoms 
is similar to the approach used by the Quebec Task Force (1987; Ex. 26-
494). Dr. Nachemson also served as a member of the task force for this 
publication. The Quebec classification included 11 categories, with 1-
4, 8, 9 and 10 based upon symptoms.
    The American Medical Association, in its Guides to the Evaluation 
of Permanent Impairment, 4th edition, (Ex. 38-246) also include 
symptoms in classifying impairment. In particular, Table 72 in that 
publication contains a Diagnosis Related Estimate for Lumbosacral 
Category II: Minor Impairment (5% whole person impairment). The 
guidance used by the AMA for this is ``The clinical history and 
examination findings are compatible with a specific injury or illness. 
The findings include significant intermittent or continuous muscle 
guarding that has been observed and documented by a physician, 
nonuniform loss of range of motion, or nonverifiable radicular 
complaints. There is no objective sign of radiculopathy and no loss of 
structural integrity.'' There is similar guidance for the cervical 
spine.
    Guidelines for diagnosis and treatment of low back pain that have 
been published in the United States include the AHCPR guidelines (Ex. 
32-241-3-93) and the ACOEM guidelines (Ex. 38-234). These will be 
addressed in the discussion on rest and activity to follow in this 
section.
    It must also be recognized that low back pain is not the only 
potentially covered MSD, and other potential MSDs may present as 
symptoms only. For example, it is clear that patients with CTS may have 
symptoms of numbness without any physical findings (Erdil and

[[<strong>Page</strong> 68535]]

Dickerson 1997, Ex. 502-18; Katz et al. 1991, Ex. 38-101; Moore 1992, 
Ex. 26-985). Of significance, commonly utilized physical signs to 
clinically diagnose carpal tunnel syndrome, such as the Tinel's test 
and Phalen's sign, do not have as high a sensitivity or specificity as 
the Hand Diagram (Katz and Stirrat 1990; Ex. 500-121-33), a symptom 
based tool. Clearly, utilizing symptoms to identify possible cases of 
carpal tunnel syndrome and other MSDs is consistent with the knowledge 
based upon reviewing the medical literature.
    Dr. Malcolm Jayson argued that

* * * if a person has pain in the knee, the most effective form of 
treatment is knee exercises. When we rehabilitate back problems we 
prescribe[] exercises with a progressive regime to increase physical 
capacity. There is now overwhelming evidence that exercise is good 
for back problems and damaged joints and rest is harmful. [Ex. 32-
241-3-9]

However, nowhere does OSHA state that all exercise is harmful, nor does 
it support rest as the treatment for MSDs. With regard to work factors 
like repetition, it is important to recognize that biomechanical 
factors that are present in a sufficient intensity, duration, and/or 
frequency to cause or contribute to an MSD are addressed. In these 
circumstances, OSHA recommends modification of exposure to these 
factors. It is clear that, when excessive, repetition and other cited 
work factors can cause MSDs. Several studies were presented in the 
Health Effects Section of the final rule to demonstrate the pathogenic 
mechanisms through which physical work factors can be responsible for 
causing or contributing to certain MSDs identified in the epidemiologic 
review. Unfairly, this statement simplifies physical factors in work 
settings as solely characterized by repetition, without considering the 
frequency, duration, and periodicity of the repetitive activities. In 
addition, it ignores other factors that have potential to cause MSDs in 
the workplace, such as excessive force, awkward posture, contact 
stress, and vibration. Also neglected is the observation that 
combinations of factors like force, posture, etc. with repetition, may 
compound the effect of repetition on musculoskeletal tissues. Finally, 
the statement does not differentiate types of tissue affected and 
whether the tissue is healthy or damaged.
    In the preface to The American Academy of Orthopedic Surgeons' book 
entitled ``Repetitive Motion Disorders of the Upper Extremity'' (Gordon 
et al. 1995; Ex. 26-1399), the editor states:

    There is overwhelming evidence that the number of reported cases 
of repetitive motion disorders is rapidly growing. These disorders 
have become an extremely costly public health issue. Although some 
individuals believe that the underlying issue may be improper 
reporting or false claims of a medical problem, the organizers and 
most of the participants believe that for the vast majority of 
cases, there is an underlying physiologic insult to one or more of 
the various tissues involved.

    The text goes on to cover epidemiologic evidence; pathophysiology 
of biomechanical loads, connective tissue, muscle and nerve. Chapters 
on rehabilitation of the wrist, elbow and shoulder all indicate that 
time limited periods of rest may be indicated for acute MSDs. The book 
is the result of a workshop organized by the National Institute of 
Arthritis and Musculoskeletal and Skin Disease, NIH. Co-sponsors 
included NIOSH, CDC, Orthopedic Research and Education Foundation, the 
National Center for Medical Rehabilitation Research, and others. One 
expert witness Dr. Stanley Bigos, who testified on behalf of one 
industry group organized in opposition to OSHA's proposed standard in 
general, is a member of AAOS.
    In June 1998, Clinical Orthopedics and Related Research (Exs. 26-
1310, 26-1322, 26-1316) covered Cumulative Trauma Disorders of the 
Upper Extremity through a joint sponsorship of the Association of Bone 
and Joint Surgeons, the Academic Orthopedic Society, the Hip Society, 
the Musculoskeletal Tumor Society, and the Knee Society. This text 
again covered sections regarding the effects of physical work factors 
(i.e. repetition) on nerve, muscle, joints, and certain clinical 
conditions.
    Similarly, the National Academy of Sciences, in 1999, (Ex. 26-37) 
published the results of a workshop they sponsored on work-related 
MSDs. While there was some variance in opinions about the contribution 
of physical work factors to MSDs, there was agreement among most that 
physical work factors contribute to MSDs. ``MSDs are multifactorial, 
with work and biomechanical aspects of work being important 
contributors.'' The NAS reviewers also explained the concepts behind 
temporary rest or activity modification for injured tissues.
    Contrary to the view of NAS, Dr. Stanley Bigos provided the 
following comment:

    Contrary to ergonomists' beliefs, usage is a prerequisite to 
health--using the body, even vigorously using the body, is not 
intrinsically harmful. That is why repetitive motion that fatigues 
musculoskeletal tissues is medically prescribed, to the point of 
being the preferred method of treatment even of tissues that have 
sustained traumatic injury or age-related degeneration. Properly 
conditioned; a traumatically injured joint may be restored to full 
function by the protection of muscles stronger than before the 
injury. [Ex. 32-241-3-4]

    Dr. Bigos' statement that ``repetitive motion that fatigues 
musculoskeletal tissues is medically prescribed, to the point of being 
the preferred method of treatment even of tissues that have sustained 
traumatic injury or age-related degeneration,'' while having elements 
of validity, again fails to look at the various work-related MSDs as 
well as the stage and severity of the condition. There is supporting 
literature and consensus, including clinical practice guidelines (e.g. 
ACOEM; Ex. 38-234) that recommend periods of splinting and rest for 
MSDs like acute tendonitis or stenosing tenosynovitis, DeQuervain's 
disease and carpal and cubital tunnel syndromes. A comparison could be 
made to a patient who experiences an acute myocardial infarction with 
muscle damage. In this scenario, rehabilitation often includes 
carefully controlled exercise appropriate to the stage of recovery and 
level of function of the remaining heart muscle. It would not be 
reasonable to presume that a patient one day after a significant 
myocardial would be improved if forced to run a marathon. Neither would 
a worker benefit from intensive and uncontrolled exercise after the 
onset of an acute MSD with significant inflammation, degeneration and 
loss of function.
    The same commenters stated that OSHA's use of the term ``rest'' in 
the proposal implied that OSHA recommends or promotes bed rest for 
workers with MSDs. This statement is incorrect and fails to recognize 
the purpose and application of the standard. This standard is not 
intended as a guideline for the medical treatment of MSDs. Medical 
treatment is left to the licensed health care provider, utilizing sound 
medical judgement, and evidence based literature and clinical practice 
guidelines.
    What OSHA did intend when it used the term ``rest'' was appropriate 
activity modification. The standard supports return to work where there 
are effective controls of biomechanical factors causing or contributing 
to the MSD. The preamble to the proposal stated:

    Although some covered MSDs are at such an advanced state that 
complete removal from the work environment is the appropriate 
treatment, it should usually be the recommendation of last resort. 
Where appropriate, work restrictions that allow the employee to 
continue working (e.g., in an

[[<strong>Page</strong> 68536]]

alternate job, or by modifying certain tasks in the employee's job 
to enable the employee to remain in that job) are preferable during 
the recovery period.

Dr. Stanley Bigos argued that the proposed ergonomics rule was at odds 
with the recommendations of the AHCPR guidelines, in that the proposed 
rule recommended rest, reduced work, and inactivity in response to 
pain, while the AHCPR guidelines recommend increased activity and 
conditioning (Ex. 32-241-4).
    The AHCPR guidelines (Ex. 32-241-3-93) do recommend that adults 
with acute low back pain maintain activity. However, the guidelines do 
not suggest that patients with acute low back pain immediately return 
to work involving physical task factors that may stress the spine. 
Rather they advise appropriate activity modification to assist in the 
recovery process. AHCPR guidelines Activity Recommendations panel 
findings and recommendations state: ``Patients with acute low back 
problems may be more comfortable if they temporarily limit or avoid 
specific activities known to increase mechanical stress on the spine, 
especially prolonged unsupported sitting, heavy lifting, and bending or 
twisting the back while lifting. (Strength of Evidence = D.);'' and, 
``Activity recommendations for the employed patient with acute low back 
symptoms need to consider the patient's age and general health, and the 
physical demands of required job tasks. (Strength of Evidence=D.)''
    The AHCPR guidelines acknowledge that

several studies have identified an increased incidence of low back 
problems among individuals whose work involves heavy or repetitive 
lifting, exposure to total body vibration (from vehicles or 
industrial machinery), asymmetric postures, and postures sustained 
for long periods of time.'' [Ex. 32-241-3-93]

The guidelines also recognized that

    Other biomechanical research suggests that certain postures and 
activities increase the mechanical stress on the spine. It is not 
clear whether these mechanical stresses are the cause of low back 
problems. However, once symptoms are present, mechanical stresses 
correlate with worsening of symptoms. Prolonged sitting and postures 
that involve bending and twisting have been shown to increase the 
mechanical stress on the spine according to pressure measurements in 
lumbar intervertebral discs. Heavy lifting also appears to increase 
mechanical stress on the spine, but this stress can be reduced if 
the lifted object is held close to the body rather than at arm's 
length.'' [Ex. 32-241-3-93]

    As to the duration of activity modification, the AHCPR guidelines 
(Ex. 32-241-3-93) demonstrate an understanding of the impact that the 
physical demands of work have on recovery and modified activity. They 
state that ``The nature and duration of limitations will depend on the 
clinical status of the patient and the physical requirements of the 
job.''
    While the AHCPR guidelines (Ex. 32-241-3-93) did not find evidence 
that bed rest was beneficial for the majority of individuals with acute 
low back pain, the panel did acknowledge that, in some circumstances, 
bed rest may be required for select patients with acute low back pain 
(``The majority of low back patients will not require bed rest. Bed 
rest for 2 to 4 days may be an option for patients with severe initial 
symptoms of primarily leg pain.'')
    Program elements in OSHA's proposal are also consistent with the 
British guidelines, that state that there is moderate evidence that

    From an organisational perspective, the temporary provision of 
lighter or modified duties facilitates return to work and reduces 
time off work. [Ex. 500-118-2]

    Some commenters appeared to confuse the concepts relevant to the 
practice of sports medicine with concepts relevant to the prevention of 
MSDS in workers. For example, Gibson, Dunn & Crutcher state

    Increase in physical activity (compared to past activity level) 
is a guiding principle in musculoskeletal rehabilitation, and has 
been the primary intervention and treatment in many musculoskeletal 
disorders. These treatment protocols include many of the physical 
stresses that OSHA recommends avoiding. [Ex. 500-118]

    This again is an overly simplistic statement, since there are 
differences in the intensity, duration, and/or frequency of guided 
rehabilitation of an injury that is tailored to the individual's type 
of injury, severity of the condition, stage of rehabilitation and the 
individual's conditioning, as opposed to intensity, duration, and/or 
frequency of physical job factors that are based upon delivery of goods 
or services and have no bearing upon individual capabilities or 
injuries. Dr. Tapio Videman, another expert witness for the UPS 
attempted to explain the importance of physical activity as follows:

    Sports medicine--and much of modem mainstream medicine--views 
physical loading as a means of increasing fitness, strength, and 
function, and is part of most related intervention today. Why would 
physical loading be harmful in work but beneficial in leisure time? 
* * * Physical activity can promote physical adaptation to loading, 
and restore and maintain functional capacity. This may explain why 
there is some evidence of the benefits of exercise for spinal 
disorders. [32-241-30-20]

    However, comparisons of workers with young and highly skilled 
athletes is not appropriate. This is pointed out by the ISSLS text on 
the Lumbar Spine (Wiesel et al.1996; Ex. 26-1620). The following quote 
is from the chapter on biomechanics:

    Comparison of athletic exercises with industrial labor is 
complicated because, in the athletic field, (1) one deals with 
young, healthy subjects; (2) there is a selection of individuals for 
the specific tasks; (3) the specific task is always accompanied by 
remedial exercises. In industrial labor, one is dealing with the 
average population. There is almost no selection of the individuals, 
and there are many monotonous tasks that are not interrupted by 
remedial exercise. [Ex. 26-1620]

    Dr. Michael Vender explained his belief that soft tissue has almost 
limitless capacity to recover from injury.

    We cannot explain the natural process of aging and gradual 
deterioration of all body parts by the concept of cumulative trauma. 
The most basic flaw in this logic revolves around the comparison of 
the human body to a piece of metal [as reflected in the 
biomechanical model espoused by ergonomists). [Unlike metal], the 
body, when stressed or even injured, has the ability to heal and 
recover.--When one repeatedly bends a piece of plastic, it becomes 
permanently deformed. When one repeatedly exercises a muscle, it 
becomes stronger and more functional. [Ex. 32-241-3-19]

    This belief is in contrast to the opinion of the NAS workshop 
(1999) (Ex. 26-37) noted above, and fails to recognize concepts of 
muscle disruption, tendon and ligament viscoelastic deformation and 
creep discussed in the Health Effects Preamble.
7. Additional Criticisms of Epidemiological Studies Raised by 
Commenters
    Gibson, Dunn & Crutcher in their post-hearing comments (Ex. 500-
118, Section B, pgs. 65-81) supply critiques of additional ``studies on 
which OSHA relies or may rely in support of the proposed rule.'' (id., 
pg. 65). OSHA's response to these critiques is given below.
    Gibson Dunn & Crutcher criticize the study by Latza et al. (2000, 
Ex. 38-424) that examined occupational risk factors of low back pain 
among construction workers. Among their criticisms, Gibson Dunn & 
Crutcher argue that the authors drew causal inferences from a study 
that is only an exploratory analysis. Further, they claim that the 
researchers were vague in their methods and did not come up with a 
single promising association.
    OSHA disagrees with these criticisms. First, the study as a whole 
cannot be

[[<strong>Page</strong> 68537]]

fairly characterized as an ``exploratory analysis.'' This study is an 
adequately designed longitudinal epidemiological study where 
construction workers who reported no low back pain at baseline were 
followed for three years. The ``exploratory approach'' reported by the 
authors refers not to the study as a whole but rather to a detailed 
analysis of the data to identify potential risk factors that might be 
used to predict low back pain. The authors describe a detailed process 
for focusing on factors most likely to have caused the observed reports 
of low back pain. Second, OSHA disagrees that the authors were vague in 
their methods. Various aspects of the study, such as the selection of 
study subjects, data collection, and data analysis, were described in 
clear enough detail that would allow the reader to assess the results 
reported. Finally, the authors noted that causality cannot be 
established with this study. However, the purpose of the study was to 
identify possible risk factors for low back pain among these workers 
that might aid in the identification of hazardous components in the 
work that can guide effective primary intervention. In this regard, the 
authors report positive associations that show that certain 
occupational risk factors can be predictive of low back pain.
    Gibson, Dunn & Crutcher criticize a study by Punnett et al. ``A 
comparison of Approaches to Modeling the Relationship between Ergonomic 
Exposures and Upper Extremity Disorders'' (2000, Ex. 500-71-43). This 
is a methodology study concerning approaches for combining independent 
and dependent variables for the purpose of exposure-response analysis. 
This study uses the information on upper extremity disorders in vehicle 
manufacturing found in an earlier Punnett et al. (1998, Ex. 26-38) 
study), which these same commenters criticized previously (Ex. 32-241-
4, pg. 144). OSHA has responded to those criticisms elsewhere in this 
preamble.
    Gibson, Dunn & Crutcher have two main criticisms of the Kurppa et 
al., (1991, Ex. 26-53) study concerning the incidence of tenosynovitis 
or peritendinitis and epicondylitis in a meat-processing factory. The 
commenters claim that the diagnostic definition of the response 
tenosynovitis or peritendinitis (agreed to by the plant physician), 
``boils down to focal soreness/tenderness and nothing more specific or 
mysterious than that.'' (Ex. 500-118, pg. 71). In response, OSHA notes 
that, in order to be included as a response in the study, the condition 
needed to be severe enough in each case to qualify for sick leave (Ex. 
26-53, pg. 33). As a result, OSHA believes that the response is a 
meaningful health effect, i.e., because it was serious enough to 
warrant time away from work for recuperation. Gibson, Dunn & Crutcher 
(Ex. 500-118 pg 71) also claim that, ``By its very nature, a 
surveillance study perturbs the experience of discomfort.'' However, 
this type of physiological biasing factor would appear to have only a 
minimal or no effect on the end results since the rate of occurrence of 
tenosynovitis or peritendinitis and epicondylitis, for both men and 
women, was shown typically to be an order of magnitude higher for 
strenuous compared to non-strenuous meat processing jobs (Ex. 26-53, 
pg. 34).
    Gibson Dunn & Crutcher correctly point out (Ex. 500-118, pg. 72-73) 
that the utility of participatory ergonomics was not evaluated in the 
Roquelaure et al. (1997, Ex. 38-96) study. However, OSHA used this 
study only to show an association between stress variables and carpal 
tunnel syndrome (CTS). The role of participatory ergonomics in reducing 
CTS was not alluded to by OSHA.
    Gibson Dunn & Crutcher correctly point out (Ex. 500-118, pg. 73) 
that in the Viikari-Juntura et al. (1994, Ex. 26-873) study what is 
defined as severity of neck trouble is in fact the frequency of self-
reported symptoms (pain, ache, stiffness or numbness). As a result, 
Gibson Dunn & Crutcher believe the possibility exists that the 
subject's statements concerning severe neck trouble could be 
misleading. OSHA used the Viikari-Juntura et al. study to only show an 
association between neck symptoms and stress factors. OSHA did not 
comment on the severity of the symptoms.
    Gibson Dunn & Crutcher note (Ex. 500-118, pgs. 73-74) that the 
authors of the Kearns et al. (2000, Ex. 500-71-34) study did not intend 
that the results of the study on the prolongation of median motor and 
sensory nerve latency be generalized beyond the effects of work related 
to pork processing. OSHA agrees that the study supplies limited 
information about the relationship between workplace physical factors 
and CTS.

Stenlund et al.studies, Exs. 26-733 and 26-1479

    Gibson Dunn & Crutcher (Ex. 500-118 pg. 70-71) have criticized the 
1992 study by Stenlund et al. (Ex. 26-733) of osteoarthrosis and the 
1993 Stenlund et al. (Ex. 26-1459) of shoulder tendinitis. First, the 
1992 Stenlund et al. study is criticized for its conclusion that 
radiographic evidence of osteophytes (spurs) in the acromioclavicular 
joint is a predictor of osteoarthrosis causing cartilage loss and 
abnormal reparative processes. Gibson Dunn & Crutcher argue that in 
other joints, such as the knee, increased usage leads to osteophytosis 
(spurs) and increased preservation of cartilage, which is good. They 
question whether the Stenlund et al. (1992) paper is detecting a 
``bad'' outcome. Gibson Dunn & Crutcher also criticize the 1993 
Stenlund et al. paper for using shoulder tendinitis as an adverse 
effect measure, arguing that shoulder tendinitis is subject to overt 
reporting and recording bias. They conclude that these types of outcome 
measures are not appropriate to be used in epidemiological studies.
    With regard to the 1992 Stenlund et al. study, the critics are 
comparing minimal changes commonly observed with habitual usage of a 
joint such as the knee (e.g., increased preservation of cartilage) to 
severe osteoarthrosis, from heavy manual work and vibration, of a 
joint, in this case the shoulder. In the Stenlund study, radiographs 
were classified into 5 grades of osteoarthrosis (0 = normal; 1= minimal 
changes; 2 = moderate changes, more severe changes to cartilage and 
bone structure begins to be affected; 3 = severe osteoarthrosis, and 4 
= totally destroyed joint). Those classifying the radiographs were 
blinded as to exposure. The authors did not find significant 
differences in lower grade changes. However, they did observe that 
among rock blasters and bricklayers who had exposure to heavy load and 
vibration compared to foremen who did not, there was a significant 
increase in grade 2 and 3 osteoarthrosis. Therefore, OSHA believes that 
Gibson Dunn & Crutcher are actually confusing two different health 
outcomes in their criticism. The study by Stenlund et al. (1992) would 
support the hypothesis that normal habitual use of the shoulder might 
cause increased preservation of the cartilage. However, shoulder joints 
exposed to heavy loads and vibrations such as those examined in the 
study show radiographic evidence of severe osteoarthrosis.
    With regard to the 1993 Stenlund et al. study, the authors noted 
the potential for misclassification when using tendinitis as a measure 
of outcome. They agree that in some epidemiological studies, clinical 
diagnosis of tendinitis may not be an appropriate measure of prevalence 
in the population, since some individuals with tendinitis may not see a 
physician for their symptoms, thus creating a selection bias. However, 
the authors assert that this type of bias is overcome in their study by 
the use of a cross sectional study design. In order to further lessen 
the potential for misclassification, the authors also

[[<strong>Page</strong> 68538]]

included symptoms of pain during the last year that could have 
originated from structures other than the tendons or muscle attachment 
inflamation in addition to using palpation and isometric contraction. 
They reasoned that persons experiencing pain in their shoulder in the 
last year and who on examination have pronounced pain reaction to 
palpation and contraction, have probably had a disorder in the muscle 
attachment or tendon, that in clinical practice would have been 
classified as tendinitis. OSHA believes that, with proper study design 
and control for misclassification, as was done in the Stenlund study, 
clinically diagnosed shoulder tendinitis is an adequate measure of 
effect. Thus, the Stenlund et al., 1993 study can be used with other 
studies in the record to form a reliable weight of evidence on which to 
base the agency's health effects conclusions.
    Gibson Dunn & Crutcher also criticized the 1990 study on 
degenerative disc disease among concrete workers and house painters by 
Riihimaki et al. (Ex. 502-455). They argue that the results of this 
study are ``not compelling'' because the authors found insignificant 
risk ratios and, thus, are very likely to be influenced by unmeasured 
variables. OSHA finds this argument unconvincing for the following 
reasons. Number one, the authors did, in fact, find a statistically 
significant risk of detectable degenerative changes in the lumbar spine 
among concrete workers (38%) compared to house painters (26%). 
(Relative Risk=1.4, (CI 1.1-1.8; p0.01)) In this study, concrete 
reinforcement workers were compared to house painters. The authors 
noted that the load on the back is distinctly different among concrete 
workers compared to house painters. The authors also note that in 
Finland, persons in these trades have very similar socio-economic 
status and lifestyles, thus making it more likely that the detected 
difference between these groups is due to occupational exposures rather 
than other factors. Moreover, as a part of the study design the 
concrete reinforcement workers and house painters were matched by age, 
earlier back accidents, height, body mass index and smoking. These 
covariates were included in a mutivariate logistic regression to 
perform the statistical analysis to control for possible confounding 
factors likely to affect disc degeneration. After controlling for these 
factors, the authors still reported statistically significant effects. 
In addition, the authors noted that workers, to be included in the 
study, had to have at least 5 years seniority, thus creating the 
possibility for negative bias due to health-based self-selection of 
workers in the more physically demanding job (i.e. concrete workers). 
The effect of this negative bias, however, would underestimate the risk 
ratios. In an attempt to understand the underlying etiology of this 
disc degeneration, the authors did additional analyses looking at 
different segments of the lumbar region and different degenerative 
spinal changes (e.g. disc space narrowing, spondylophytes, and endplate 
sclerosis). In some of these sub-analyses for certain lumbar regions, 
there was no statistically significant effect. Overall, however, the 
authors found a significant association between work and disc 
degeneration while controlling for confounders. Therefore, OSHA does 
find these results compelling and generally supportive of its health 
effects assessment.
    Gibson Dunn & Crutcher criticized the 1994 study of sciatic pain 
among men in machine operating, dynamic physical work and sedentary 
work by Riihimaki et al. (1994, Ex. 26-1188). They claim that the 
associations observed in this study are ``barely significant'' (Ex. 
500-197, pg. 69) and are no more significant than the associations 
observed with physical exercise. In addition, they state that the 
observed increases are negatively influenced by workers' self reporting 
of tasks, ``an inadequate definition of sciatica'' and recall bias.
    OSHA is unsure as to what these critics mean by ``barely'' 
significant. The authors reported a statistically significant increase 
in sciatic pain among machine operators and carpenters compared to 
office workers. For machine operators the relative risk =1.6 (95% CI 
1.2-2.2) and for carpenters was 1.7 (95% CI 1.3-2.4). This statistical 
significance remained even after controlling for a variety of risk 
factors (e.g., age, seniority, education, physical exercise, smoking, 
car driving, and prior back accidents). Adjusted relative risks were 
1.4 and 1.5.
    The authors do acknowledge that the reporting of symptoms of 
sciatica can be subjective, as can a worker's perception of physical 
task. In order to minimize this type of bias, they used explicit 
descriptions of symptoms and tasks to ensure uniform understanding of 
the concepts. The authors also recognize the potential of recall bias 
to negatively influence the results. However, they note that this 
misclassification also depends not only on the recall error but also 
the incidence rate of the symptoms. They conclude that the recall error 
bias in the observed risk ratios is small if ``by the end of follow-
up'' the rate of reporting symptoms among the misclassified subjects 
does not deviate much from the overall incidence rate. Thus, while OSHA 
acknowledges the potential bias pointed out by the critics of this 
study, the agency believes that these sources of bias have been taken 
into consideration in this study to such an extent that the observed 
increased risk ratios can be accepted with some confidence. In 
addition, OSHA believes that these observed risk ratios are more than 
barely significant and, when viewed in the context of other positive 
epidemiological evidence, contribute to the weight of evidence and the 
strength of the agency's overall health effects assessment.
    Gibson Dunn & Crutcher also criticize four other epidemiology 
studies OSHA relied on in contributing to the strength of the agency's 
overall health effects assessment: two studies by Silverstein et al. 
(Exs. 26-34 and 26-1404), a study by Venning et al. (Ex. 500-41-49), 
and a study by Punnett et al. (Ex. 26-39). OSHA responds to criticisms 
of these 4 studies in on Section G:3-Exposure-Response.

VI. Risk Assessment

A. Introduction

    The United States Supreme Court, in the Benzene decision 
(Industrial Union Department, AFL-CIO v. American Petroleum Institute, 
448 U.S. 607 (1980)), has ruled that the OSH Act requires, prior to the 
issuance of a new standard, that a determination be made that there 
exists a significant risk of material impairment and that issuance of 
the new standard will substantially reduce that risk. The Court stated 
that ``before he can promulgate any permanent health or safety 
standard, the Secretary is required to make a threshold finding that a 
place of employment is unsafe in the sense that significant risks are 
present and can be eliminated or lessened by a change in practices'' 
(448 U.S. 642). The Court also stated that ``the Act does limit the 
Secretary's power to require the elimination of significant risks'' 
(448 U.S. 644).
    In the Cotton Dust case (American Textile Manufacturers Institute 
v. Donovan, 452 U.S. 490 (1981)), the Court reaffirmed the position it 
had previously taken in the Benzene decision that a risk assessment is 
not only appropriate but required to identify significant health risks 
in workers and to determine if a new standard will reduce those risks. 
Although the Court did not require OSHA to perform a quantitative risk 
assessment in every case, the Court implied, and OSHA as

[[<strong>Page</strong> 68539]]

a matter of policy agrees, that assessments should be put into 
quantitative terms to the extent possible.
    The weight of evidence presented in the Health Effects section of 
this preamble (Section V) demonstrates a causal relationship between 
exposure to workplace risk factors and work-related musculoskeletal 
disorders. As discussed in that section, the major workplace risk 
factors include exposure to repetitive motion, force, awkward postures, 
contact stress, and segmental vibration. The Health Effects section 
also demonstrates that the risk associated with occupational exposure 
to these risk factors increases with frequent or prolonged exposure to 
these risk factors, and that the risk is increased when workers are 
exposed to more than one risk factor in a job.
    OSHA has determined that there is substantial evidence that 
exposure to these biomechanical stressors at work can cause or 
contribute to the development of MSDs and that reductions in these 
stressors can reduce the number and severity of these work-related 
MSDs. The underlying evidence falls into three broad categories:

    Studies of groups of workers showing a relationship between 
exposure to biomechanical risk factors in the workplace and an 
increased incidence or prevalence of MSDs;
    Biomechanical studies that show that adverse tissue reactions 
and damage can occur when tissues are subjected to high forces and/
or a high number of repetitive movements, which occur when workers 
are substantially exposed to biomechanical risk factors; and
    Scientific and case studies that demonstrate that workplace 
interventions designed to reduce exposures to biomechanical risk 
factors are effective in reducing the internal forces imposed upon 
tissues and the incidence and severity of MSDs.

    In the Health Effects section of this preamble, OSHA summarizes 
data and findings from more than 170 epidemiological studies of the 
incidence or prevalence of MSDs in groups of workers who are exposed to 
physical risk factors in their jobs. In most of these studies, the MSD 
prevalence of a group of exposed workers is compared to that in another 
worker group that is not exposed to the risk factors of interest. If 
the exposed group shows a higher MSD prevalence than does the reference 
group, the study provides evidence of an association between exposure 
and an increased risk of developing MSDs, particularly if the study is 
of good quality and adequately controlled for potentially confounding 
factors (such as age and gender) and biases.
    Many of these epidemiological studies were reviewed by the National 
Institute for Occupational Safety and Health (NIOSH) in 1997 (Ex. 26-1) 
to evaluate the strength of the evidence for a causal relationship 
between several types of MSDs and the workplace risk factors of force, 
repetitive motion, awkward posture, and vibration. More than 600 peer-
reviewed studies were critically reviewed, making this one of the 
largest human data bases ever built to examine work-related adverse 
health outcomes. NIOSH found that for most combinations of MSDs and 
risk factors, the evidence in humans that a causal relationship existed 
between workplace exposure to risk factors and the development of MSDs 
was either ``sufficient'' or ``strong.'' For a few MSD/risk factor 
combinations, there was insufficient evidence of a causal relationship, 
but in no case did NIOSH determine that there was evidence for the 
absence of a relationship between exposure to workplace risk factors 
and the development of MSDs. NIOSH concluded that `` * * * a 
substantial body of credible epidemiologic research provides strong 
evidence of an association between MSDs and certain work-related 
physical factors when there are high levels of exposure and especially 
in combination with exposure to more than one physical factor * * *'' 
(NIOSH 1997, ES p. xiv, Ex. 26-1).
    A similar conclusion was reached by the experts participating in a 
workshop conducted by the National Academy of Sciences/National 
Research Council (NRC) (Ex. 26-37). For the NRC report, a panel of 
experts critically reviewed the methods used to select and evaluate the 
human studies relied on in the 1997 NIOSH study (Ex. 26-1). The 1999 
NRC report concluded as follows:

[the association between MSDs and exposure to risk factors at work 
that have been] identified by the NIOSH review * * * as having 
strong evidence are well supported by competent research on heavily 
exposed populations.
    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 level of exposure to physical 
loading than for those employed in occupations with lower levels of 
exposure. (Ex. 26-37)

    In this context, NAS's use of the phrases ``heavily exposed'' and 
``high level of exposure'' does not refer to any specific 
quantitatively defined level of exposure to biomechanical risk factors, 
but simply reflects that, in the epidemiological studies, groups of 
workers who were considered to be ``exposed'' to biomechanical risk 
factors experienced higher intensities and durations of exposure than 
did the comparison, or referent, groups of workers. In general, workers 
in the exposed groups were exposed to biomechanical risk factors on a 
nearly daily basis, and were usually exposed for most of each work 
shift. However, as shown by OSHA's summary of exposure-response data in 
the Health Effects section (Section V), many of these epidemiological 
studies placed workers in the exposed group even if they were exposed 
for only about one-quarter to one-half of the work shift. Later in this 
section, OSHA defines ``higher-risk'' workers as those who are exposed 
in excess of the final rule's job screening criteria, which generally 
reflects those workers as having two or more hours per shift of 
exposure to biomechanical risk factors.
    Since the NIOSH and NAS reports, many additional epidemiological 
studies have been published and are contained in the rulemaking record. 
These studies have been reviewed by OSHA in detail in the Health 
Effects section, and their results add to the already substantial 
weight of evidence originally evaluated by NIOSH and NAS. OSHA is not 
alone in its determination that the epidemiological data base for 
ergonomics convincingly establishes a causal relationship between 
workplace exposure to risk factors and MSDs. Many experts who provided 
testimony in the record and appeared at OSHA's informal hearing agreed 
that sufficient epidemiological evidence exists to conclude that 
biomechanical factors at work cause or contribute to MSDs. These 
experts included researchers, medical professionals, and ergonomists 
(Exs. 37-1, 37-2, 37-9, 37-10, 37-13, 37-10, 37-15, 37-16, 37-17, 37-
18, 37-21, 37-27; Tr. 843, Tr. 1048; Tr. 1112, Tr. 1103-1103, Tr. 1367, 
Tr. 9808-9809, Tr. 16802, Tr. 17566-17567, Tr. 8261, Tr. 2834, Tr. 
9297, Tr. 16145, Tr. 1959-1960, Tr. 17358, Tr. 13330-13331, Tr. 3412).
    That exposure to workplace risk factors can cause or contribute to 
MSDs is made more plausible by the growing body of studies of 
biomechanical effects, also summarized in the Health Effects section 
(Section V of this preamble), that are designed to explore how tissues 
react to mechanical stress and how those reactions are related to 
disease processes. OSHA presented detailed scientific information on 
the biomechanics and pathophysiology of MSDs in its Health Effects 
Appendicies, prepared at the time of the proposed rule (Ex. 27-1); the 
discussion below briefly summarizes the information

[[<strong>Page</strong> 68540]]

reviewed in the Health Effects Appendicies and in the Health Effects 
section.
    Although all soft musculoskeletal tissue can tolerate certain 
physical loads, these tissues will respond adversely if the load 
becomes excessive. Muscles, ligaments, tendons, and tendon sheaths can 
become inflamed with repetitive or prolonged loading, cartilage can 
deteriorate when subjected to abnormal loads, and nerves can exhibit 
dysfunction and eventually permanent damage if compressed or subjected 
to extended tension. Other studies have shown that the kinds of risk 
factors present in many industrial occupations can impose internal 
forces on soft musculoskeletal tissue sufficient to cause the kinds of 
physiologic responses described above. The relationships between 
external and internal loads have been demonstrated using both 
biomechanical models and direct measurement and observation in the 
workplace (see Section V, Health Effects).
    Finally, evidence of the work-relatedness of MSDs comes from 
several studies and case reports that document the effectiveness of 
ergonomic interventions in reducing exposures to risk factors and the 
successes of individual companies' ergonomics programs in reducing the 
incidence or prevalence of MSDs and the severity of MSDs among their 
workers. After reviewing intervention studies, including both field and 
laboratory studies, the NRC (1998, Ex. 26-37) concluded that

    * * * specific interventions can reduce the reported rate of 
musculoskeletal disorders for workers who perform high-risk tasks. 
No known single intervention is universally effective. Successful 
interventions require attention to individual, organizational, and 
job characteristics, tailoring the corrective action to those 
characteristics.

The scientific evidence and case studies demonstrating that ergonomic 
interventions reduce excessive tissue loads and the associated tissue 
pathology, and reduce MSD incidence and severity, are summarized later 
in this section).
    In addition to biomechanical risk factors present at work, the risk 
of developing an MSD is also influenced by individual, organizational, 
and social factors. Factors that affect individual susceptibility 
include age, general conditioning, and pre existing medical conditions. 
Although some of these individual factors have been identified in human 
studies as being statistically significant predictors of disease, they 
are generally much weaker predictors than are biomechanical factors of 
force, repetition, posture, and vibration (NRC 1998, Ex. 26-37). 
Organizational factors that have been linked to MSDs include poor job 
content (e.g., lack of job variety) and job demands (e.g., excessive or 
highly variable workload and time pressure). The importance of poor job 
content is difficult to evaluate, since this factor can coexist with 
biomechanical factors (for example, excessive workload can result in a 
worker needing to increase repetitive movement and/or force). Social 
factors refer to a lack of social support from management and 
supervisors, which can lead to psychological stress and dissatisfaction 
with work, both associated with an increased prevalence of MSDs. 
However, after evaluating the nature of psychosocial factors and their 
role in contributing to the risk of MSDs, OSHA has determined that, 
although psychosocial factors appear, at least in some studies, to have 
some relationship to the observed increases in the incidence of MSDs 
among workers exposed to risk factors, their effect is independent of 
that of biomechanical factors and is generally not as predictive of MSD 
risk as are biomechanical factors. The evidence reviewed by the Agency 
suggests that psychosocial factors may have a greater influence in 
determining the length of disability following development of an MSD 
than do biomechanical factors, but have shown weaker associations with 
the prevalence or incidence of MSDs than have biomechanical factors 
(see Section V.G.5 of the Health Effects Section for a discussion of 
the literature dealing with psychosocial effects). OSHA's finding is in 
accord with that of the NAS review (1999, Ex. 26-37).
    OSHA believes that the human epidemiologic studies, the 
biomechanical and physiological studies, and the studies of the 
effectiveness of workplace ergonomic interventions together constitute 
a compelling body of evidence that demonstrates that exposure to risk 
factors at work is a major factor in the development of MSDs, and that 
reducing or eliminating exposures to these risk factors will reduce the 
number and severity of these MSDs.
    The epidemiological data base that describes the associations 
between exposure to workplace risk factors and increased prevalence or 
incidence of MSDs is vast. The nature of the hazard and of the 
available data require OSHA to perform a different type of risk 
assessment than it performs to assess occupational risks from chemical 
exposures. There are many reasons for this, in particular the complex 
interactions among different kinds of exposures that lead to tissue 
injury and disorders and the difficulty of defining exposure metrics 
that reflect all of the various combinations of risk factors to which 
workers are exposed across industry. This is not to say that exposure-
response relationships have not been observed or cannot be defined in 
specific circumstances; in fact, there are many cases in which the risk 
of MSDs has been quantitatively related to the degree and intensity of 
exposure. In the Health Effects section of this preamble (Section V), 
OSHA describes scientific studies that demonstrate a positive 
association between the magnitude and/or duration of exposure to 
workplace risk factors and the prevalence of MSDs, including upper 
extremity disorders and back injuries. OSHA concludes that these 
studies provide compelling evidence of the work-relatedness of MSDs, 
since a finding of positive exposure-response trends is one of the key 
findings necessary to establish a causal relationship between exposure 
and disease.
    Using data on the incidence of work-related MSDs, risk can be 
quantified using a population-based approach similar to the one used by 
OSHA to quantify the risk of Hepatitis B among workers with frequent 
occupational exposure to blood and other potentially infectious 
material (56 FR 64004). For this final ergonomics program rule, OSHA 
uses a similar approach in its final risk assessment. In this 
assessment, OSHA relies on data from the Bureau of Labor Statistics 
(BLS) to estimate the annual incidence of work-related MSDs in 
different industry sectors and occupations, by type of injury and type 
of exposure. A description of these data and OSHA's analytical approach 
are described in part B below, and the results of this analysis appear 
in part C.
    Having quantified the risk, it is important to determine the extent 
to which the standard is likely to reduce that risk. In the case of 
this ergonomics program standard there is abundant evidence of the 
effectiveness of ergonomic programs. This evidence comes from a variety 
of published studies, articles, and unpublished data that describe the 
reductions in risk ergonomics programs have actually achieved in the 
workplace. Most commonly, this evidence is expressed in terms of 
reductions in injury rates and decreases in the numbers of lost 
workdays caused by MSDs. OSHA's discussion of these data appears in 
part D, below. The Agency presents the results of its risk analysis in 
parts C and D; comments on the preliminary risk

[[<strong>Page</strong> 68541]]

assessment (64 FR 65926) follow these sections.

B. Data Sources and Analytical Approach

    The annual Survey of Occupational Injuries and Illnesses conducted 
by the Bureau of Labor Statistics (BLS) is the principal data source 
for evaluating the risks to employees of developing a work-related 
musculoskeletal disorder. This survey is conducted under a joint 
federal/state program that collects workplace injury and illness data 
from about 165,000 private industry establishments. The survey requests 
information only on non-fatal injuries and illnesses, and excludes the 
self-employed, farms with fewer than 11 employees, private households, 
and employees in federal, state, and local government agencies.
    For this survey, selected employers are required to provide 
statistics on the total number of injuries and illnesses recorded on 
the OSHA Form 200 (the ``OSHA Log''), as well as information describing 
the nature and causes of their lost workday injuries and illnesses. 
Thus, according to the BLS, the data provided by employers ``* * * 
reflect not only the year's injury and illness experience, but also the 
employer's understanding of which cases are work-related under current 
record keeping guidelines of the U.S. Department of Labor.'' 
Information from employers is provided in sufficient detail to permit 
the BLS to systematically code each reported case and develop estimates 
of the numbers and incidence of each specific type of LWD injury and 
illness for the United States as a whole, by industry sector and by 
occupation.
    Although the BLS data are the best available data on the number and 
kinds of job-related injuries and illnesses occurring among U.S. 
workers in any given year, there is no single BLS-reported number that 
represents all employer-reported musculoskeletal injuries and illnesses 
occurring in that year. Instead, employer-reported injuries and 
illnesses are coded by the BLS according to a classification system 
that categorizes each incident by type of injury or illness and by 
nature of the exposure event leading to the injury or illness (Ex. 26-
1372). The types of disorders that are addressed by the standard fall 
into several of these BLS injury and illness categories.
    To use these data, OSHA identified the kinds of cause-specific 
injuries and illnesses, as coded by the BLS, that reflect MSDs of the 
kinds that will be covered by the ergonomics program standard. An OSHA 
panel, which included an occupational physician and two professional 
ergonomists, examined the BLS listing of occupational injury and 
exposure event codes and their definitions from the manual provided to 
state personnel who code the data from the BLS employer survey. The 
table contained in Appendix VI-A at the end of this Risk Assessment 
section provides the list of injury categories that were initially 
selected by this panel as being likely to include at least some work-
related MSDs. From this initial list, the panel selected a subset of 
injury categories that predominately included work-related MSDs of the 
type that has been associated with exposure to the biomechanical risk 
factors addressed by the final rule; these categories appear in Table 
VI-1. Of the injury categories selected, OSHA chose to base its 
analysis exclusively on six injury categories that were deemed by these 
experts to be most relevant and most likely to represent a large 
proportion of lost workday MSDs; in other words, OSHA deliberately 
excluded several categories such as ``traumatic injuries to bones, 
nerves, and spinal cord,'' ``symptoms involving nervous and 
musculoskeletal systems, unspecified,'' and ``disorders of the 
peripheral nervous system, unspecified.'' The injury categories 
included by OSHA for the risk assessment were:

Sprains, Strains, and Tears;
Back Pain, Hurt Back;
Soreness, Hurt, except back;
Carpal tunnel syndrome;
Hernia; and
Musculoskeletal and connective systems diseases and disorders.

[[<strong>Page</strong> 68542]]

[GRAPHIC] [TIFF OMITTED] TR14NO00.000

[[<strong>Page</strong> 68543]]

[GRAPHIC] [TIFF OMITTED] TR14NO00.001

    For this analysis, OSHA is interested in capturing only those 
injuries and illnesses that are associated with exposure to the risk 
factors addressed in the final rule. These risk factors are repetitive 
motion, excessive force,

[[<strong>Page</strong> 68544]]

awkward postures, contact stress, and segmental vibration. The annual 
BLS survey does not break out the causes of injuries and illnesses 
captured by the survey in a manner that precisely matches the kinds of 
risk factor exposures covered by the rule. However, the OSHA panel did 
identify the three exposure event categories defined by the BLS that 
are the most closely related to these risk factors. These are:
    <bullet> ``Repetitive motion,'' which reflects the risk factors of 
repetitive motion, sometimes combined with force and/or awkward 
posture, and contact stress, which is a combination of repetitive 
motion and force;
    <bullet> ``Overexertion,'' which includes activities such as 
lifting/lowering, pushing/pulling, holding/carrying, and throwing, and 
thus reflects the risk factor of force, sometimes combined with 
repetitive motion and/or awkward posture; and
    <bullet> A subcategory of ``bodily reaction'' that includes 
``bending, climbing, crawling, reaching, twisting,'' which reflects the 
risk factor of awkward posture.
    The BLS definitions for these exposure event categories appear in 
Table VI-2. Note that musculoskeletal injuries and illnesses caused by 
acute events such as slips, trips, falls, being struck by objects, or 
by motor vehicle accidents are excluded from the data relied on in 
OSHA's risk analysis (because they are not included in the coverage of 
the final rule (see paragraph (a) of the regulatory text)). The process 
used by OSHA to identify those injury and exposure event categories 
from which to select the BLS data represents the closest approximation 
possible from the data available to OSHA of the MSDs that the final 
rule will actually cover.
    The BLS injury and illness coding system also includes two exposure 
event categories that reflect exposure to vibration involving damage to 
the nerves or circulatory system (Ex. 26-1372). They include:
    <bullet> Event code 05, rubbed or abraded by friction or pressure; 
this code includes injuries caused by rubbing or abrasion by ``objects 
being handled,'' and includes ``superficial injuries such as blisters, 
scratches, or abrasions,'' as well as those involving nerve or 
circulatory damage, and
    <bullet> Event code 06, rubbed, abraded, or jarred by vibration, 
which includes injuries caused by vibration of mobile equipment or 
vehicles, as well as other machines or equipment.

[[<strong>Page</strong> 68545]]

[GRAPHIC] [TIFF OMITTED] TR14NO00.002

[[<strong>Page</strong> 68546]]

[GRAPHIC] [TIFF OMITTED] TR14NO00.003

    MSDs caused by segmental vibration are thus included with those 
caused by whole-body vibration in both event categories, which makes it 
difficult to separate out those vibration-induced injuries and 
illnesses related only to

[[<strong>Page</strong> 68547]]

segmental vibration, one of the risk factors covered by the standard. 
The BLS estimated that a total of 5,465 injuries related to exposure 
events classified under these two categories (excluding injuries 
involving the eyes) had occurred in 1996 (see BLS Table R32 for 1996, 
available at <A HREF="http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://www.bls.gov/oshc_d96.htm">http://www.bls.gov/oshc_d96.htm</A>). Because it is not 
possible to identify the number of injuries associated with segmental 
vibration, OSHA has included in its analysis only those MSDs related to 
the three event codes of overexertion, repetitive motion, and the 
subcategory of bodily reaction described above. The injury/illness and 
event codes used by OSHA in the Risk Assessment and Significance of 
Risk sections for the final rule are the same as those used to support 
these analyses of the proposed rule. OSHA's decision not to include 
vibration-induced injuries and illnesses in the universe of MSDs means 
that the risks estimated in the final Risk Assessment section, and the 
estimates in the Significance of Risk section, are understated.
    OSHA received numerous comments on its selection of injury/illness 
and exposure event codes from those used in the BLS classification 
system. In particular, several commenters objected to OSHA's inclusion 
of injuries categorized as ``strains, sprains, and tears,'' because, in 
their view, such injuries reflect acute injury events, while OSHA's 
ergonomics program standard was intended to address injuries that arise 
from cumulative damage through long-term exposure to risk factors. 
These commenters include, among others, the Chamber of Commerce (Ex. 
30-1722), the American Iron and Steel Institute (Exs. 30-3951, 32-206), 
Gibson, Dunn, & Crutcher on behalf of numerous clients (Exs. 500-197, 
32-241), the National Coalition on Ergonomics (Ex. 32-368), the 
American Forest & Paper Association (Ex. 30-3865), the AEI-Brookings 
Joint Center (Ex. 30-3911), Edison Electric Institute (Ex. 32-300-1), 
the Center for Office Technology (Ex. 30-2208), Integrated Waste 
Services Association (Ex. 30-3853), Organization Resources Counselors 
(Ex. 30-3813), the American Meat Institute (Ex. 30-3677), Guilford 
Mills (Tr. pp. 11519-11520, 11566-11567), the Puerto Rico Manufacturers 
Association (Ex. 30-3348), and the National Paint and Coatings 
Association (Ex. 30-4340). In support of their views, these commenters 
point to the BLS's definition of ``strains, sprains, and tears,'' which 
appeared on Table VI-1 of the preamble to the proposal (64 FR 65928--
65929) and reads as follows:

    This nature group classifies cases of sprains and strains of 
muscles, joints, tendons, and ligaments. Diseases or disorders 
affecting the musculoskeletal system, including tendinitis and 
bursitis, which generally occur over time as a result of repetitive 
activity should be coded in Musculoskeletal System and Connective 
Tissue Diseases and Disorders, major group 17. (Ex. 26-1372)

Based on this definition, Gibson, Dunn, & Crutcher conclude that cases 
classified as sprains, strains, and tears represent single-incident 
traumatic injuries and ``are not MSDs'' (Ex. 500-197, p. I-166).
    To further support their view that strains, sprains, and tears 
reflect acute injury events and not cumulative trauma, Gibson, Dunn, & 
Crutcher note that most of the strain, sprain, and tear injuries 
described in OSHA's preliminary risk assessment were associated with 
overexertion, which is defined by the BLS as follows:

    Overexertion applies to cases, usually non-impact, in which the 
injury or illness resulted from excessive physical effort directed 
at an outside source of injury or illness * * * Free bodily motions 
that do not involve an outside source of injury or illness are 
classified either in major group 21, Bodily Reaction, or in major 
group 23, Repetitive Motion. (Ex. 26-1372)

Thus, Gibson, Dunn, and Crutcher argue that

    Clearly, nothing in this definition suggests that overexertion 
injuries develop gradually over time. To the contrary, this 
definition expressly excludes injuries that result from repetitive 
motion. There is simply no evidence that sprains, strains, and tears 
associated with overexertion meet the definition of an MSD. (Ex. 
500-197, p. I-167)

Similarly, the Chamber of Commerce stated: ``It is not difficult to 
imagine that many, if not most of these injuries * * * may well have 
occurred as the result of a single instantaneous event.'' (Ex. 30-1722)
    Gibson, Dunn & Crutcher (Ex. 500-197), AISI (Exs. 32-206, 30-3951), 
the American Forest & Paper Association (Ex. 30-3865), the American 
Meat Institute (Ex. 30-3677), and the Hon. David M. McIntosh of the 
U.S. House of Representatives (Ex. 30-542) all objected to the 
inclusion of cases from BLS category 0972 (back pain, hurt back) in the 
universe of MSDs on the grounds that these are traumatic injuries as 
well. To support this position, Gibson, Dunn, & Crutcher pointed to 
OSHA's Record Keeping Guidelines for Occupational Illnesses and 
Injuries, commonly known as the ``Blue Book.'' These guidelines 
instruct employers how to record occupational injuries and illnesses on 
their OSHA 200 logs. Gibson, Dunn & Crutcher argued that, in the Blue 
Book, OSHA ``concedes'' that back cases should be categorized as 
injuries rather than illnesses. According to Gibson, Dunn and Crutcher 
(Ex. 500-197):

    OSHA states that back cases are ``injuries'' that are ``usually 
triggered by an instantaneous event'' for purposes of OSHA 200 
recording, [but] converts them into ``illnesses'' that develop 
``gradually over time'' for purposes of its MSD statistics * * * The 
bottom line is that OSHA has no reliable data regarding the causes 
of back pain and back injuries. OSHA allows employers to 
``generalize'' about back pain for purposes of OSHA 200 recording 
precisely because its causes are often indeterminate.

    OSHA has carefully considered these comments and finds them 
unpersuasive. It is necessary and appropriate to include these BLS 
categories to arrive at an accurate estimate of the risk posed by the 
biomechanical risk factors addressed in this standard.
    First and foremost, OSHA is issuing its final ergonomics program 
standard because of substantial evidence that workers who are regularly 
exposed to biomechanical risk factors are at an increased risk of MSDs 
and the pain and disabilities associated with them. Whether these 
injuries and illnesses come about because of an acute event or because 
of pathology that develops over a longer term is not germane to the 
issue of whether workers who are regularly exposed need protection. The 
sole consideration is that increased exposure to biomechanical risk 
factors increases the risk to the worker. For example, a worker whose 
job involves heavy lifting on a regular basis is at an elevated risk of 
suffering a low back disorder. Such a disorder may arise either because 
repeated lifting is causing cumulative wear resulting in degenerative 
changes to the disc, or because the stress imposed on the spine during 
lifting can overcome the capacity of the disc to withstand compression, 
resulting in acute structural failure (see Section V.E on the health 
evidence for low-back disorders). Although a worker who lifts heavy 
loads infrequently may be at risk from acute failure, the worker who 
lifts frequently as part of their regular job is at greater risk via 
either mechanism.
    Furthermore, there is substantial evidence in the record that many 
of the injuries coded as strains, sprains, and tears in fact develop 
gradually over time. Several commenters believed that it was 
appropriate for OSHA to include statistics on strains, sprains, and 
tears in its assessment of MSD risks. For example, the AFL-CIO, in 
their post-hearing brief, stated that

[[<strong>Page</strong> 68548]]

    The industry is just plain wrong on this point [that back 
injuries are traumatic injuries]. The BLS survey is based on 
employer reports of injuries. To simplify recording, OSHA recording 
criteria specifically specify that back injuries, one major source 
of MSDs, should be recorded as injuries, even if they result from 
chronic exposure conditions. Disorders related to repeated trauma, 
including carpal tunnel syndrome are to be recorded as illnesses. * 
* * Thus, it is OSHA's recording criteria and BLSs coding rules and 
definitions that result in many MSDs, particularly back injuries, 
being classified as sprains, strains, and tears. This category 
includes injuries that may result from a single exposure and those 
that result from repeated activities. OSHA has limited the types of 
strains, sprains, and tears that are covered [in its risk 
assessment] to those * * * associated with] exposures that are 
covered by the rule (e.g., overexertion, repetition). (Ex. 500-218, 
p. 13-14)

Testimony from Dr. Frank Mirer of the United Auto Workers, who is also 
a member of the BLS Labor Research Advisory Committee, explained why 
MSDs of the back are frequently recorded as sprains and strains:

    You have to understand the reality of this BLS database, which 
is derived from [the] OSHA 101 form submitted by management medical 
departments to OSHA or to the BLS. Now when a worker goes up to the 
medical department * * * all they know is they hurt. And most of 
them see a nurse and their disorder is just thrown into a bin. Back 
conditions are all injuries. They come as strain and sprain * * *. 
[W]e have acute flare ups, just as a back injury is a chronic 
condition and has an acute flare up. So standard practice in the 
industry * * * is [that] cases [considered to be] of ergo interest * 
* * [include] sprain and strain injuries that are not accompanied by 
a fall or some other traumatic [event] * * *. (Tr. 5896-5897)

When asked whether strains and sprains due to overexertion or 
repetition were likely to be related to the risk factors covered by the 
standard, both Dr. Rosecrance and Mr. Alexander agreed. Dr. Rosecrance 
testified that injuries classified as sprains or strains are 
appropriately considered MSDs, depending on the events leading to the 
injury:

    * * * I look at an MSD * * * as a disorder affecting muscles, 
tendons, ligaments, bone, connective tissue. And certainly in my 
definition of MSD, a sprain would meet that because a sprain is a 
tear to a ligament * * * [It] perhaps [might] be a traumatic one or 
from an acute injury like a slip or a trip * * *. When we review, 
let's say, the OSHA 200 Log and there is a strain or sprain on 
there, I will ask * * * what was the cause of that sprain or strain? 
Was the strain from repetitive use or was it a strain from an acute 
type of injury?

    Some rulemaking participants provided evidence to the record 
documenting that back disorders were frequently recorded as strains and 
sprains without regard to the nature of the exposure or events 
associated with each case. For example, the post-hearing submission of 
the United Food and Commercial Workers Union (UFCW) (Ex. 500-133), 
which contained copies of OSHA-200 logs (Ex. 500-133-2), reported 
finding MSDs categorized as strains and sprains, back pain, hurt back, 
carpal tunnel syndrome, hernia, and disorders associated with repeated 
trauma. According to the UFCW, retail stores primarily categorized such 
MSDs as sprains and strains, back pain and hurt backs, and injuries, 
and seldom classified MSDs as illnesses. In contrast, the UFCW stated 
that meatpacking industry logs more often accurately record MSDs as 
illness, reflecting the greater experience this industry has in dealing 
with ergonomic issues. A review of OSHA 200 logs submitted by the 
Teamsters (Ex. 500-146) also shows that disorders that are clearly 
recognized as MSDs, such as carpal tunnel syndrome and tendinitis, are 
nevertheless often recorded by employers as injuries, which in turn 
would be described in the BLS statistics as strains and sprains.
    Other rulemaking participants described the use of sprain and 
strain injury categories for ergonomic injuries in other injury 
classification systems. In describing the province of Victoria's 
(Australia) 1999 ergonomics regulation, which combined Victoria's 
earlier manual handling and occupational overuse syndrome (OOS) 
regulations, Mr. David C. Caple, Director, David Caple & Associates Pty 
Ltd., testified that both repetitive injuries and back injuries were 
combined under one generic sprain and strain category by that 
regulation (Tr. 2723-2724). The Ford Motor Company's injury 
classification system also combines strain and sprain injuries with 
cumulative trauma disorders and other disorders of interest to the 
company's ergonomics committee (Tr. 5826). When asked whether sprains 
and strains are included within the category of repetitive motion 
disorders under Oregon's workers' compensation law, Mr. Goodman replied 
that they are often classified in that category, depending on the 
events leading to the injury. He explained that Oregon's law defines an 
injury as ``sudden and unexpected in onset'; thus, strains and sprains 
would be considered repetitive motion disorders if the onset was slow 
and insidious rather than sudden (Tr. 13694).
    As described by the AFL-CIO submission and Dr. Frank Mirer's 
testimony, all back disorders are classified as injuries rather than 
illnesses, under OSHA's recordkeeping rules; as a result, back 
disorders are commonly classified as strains and sprains, regardless of 
whether the disorder arose from an acute, traumatic event or from 
cumulative damage caused by prolonged exposure to risk factors. 
Evidence in the record indicates that most cases of back pain arising 
from exposure to risk factors of the type covered by the final rule do 
not develop suddenly but are instead cases involving gradual onset, 
which makes it difficult to identify or relate the back pain to a 
single precipitating event. OSHA's witness, Dr. Stover Snook, testified 
that

    I am of the view and most scientists are of the view that that 
is not typically how low back pain develops through traumatic things 
like playing football on a weekend. It usually develops gradually 
and insidiously, most of it, not all of it, but most of it does. 
(Tr. 884)

In a study of back braces, Walsh and Schwartz (Ex. 30-3857-7) also 
characterized the nature of work-related back disorders as being of 
gradual onset:

    Most back injuries are not the result of a single traumatic 
incident but rather a compilation of minor traumatic events 
occurring during normal working conditions for reasons that are 
seldom obvious to the individual worker. Successive injuries result 
in more severe impairment and increase the probability of long-term 
disability * * *. In fact, improper body mechanics and unhealthy 
work habits may take their toll on a daily basis. In recent years, 
there has evolved a body of evidence that suggests that the etiology 
of most but not all back pain is due to insidious and chronic 
deterioration of the intervertebral disc, facet joints, and 
ligaments in the back caused by biomechanical wear and tear. (Ex. 
30-3857-7, p. 245)

OSHA's analysis of the biomechanical and pathological literature 
dealing with work-related back pain leads to conclusions that are 
consistent with these characterizations (see Section V, Health 
Effects).
    Because back disorders are recorded as injuries, notwithstanding 
the mechanistic evidence described above that characterizes most back 
disorders as being of chronic onset, practicing ergonomists believe 
that it is important to investigate the underlying events associated 
with recorded cases of strain or sprain to determine whether the injury 
is related to excessive exposure to ergonomic risk factors. This 
practice was described in the testimony of Dr. John Rosecrance, 
Assistant Professor, University of Iowa and Mr. David Alexander, 
President of Auburn

[[<strong>Page</strong> 68549]]

Engineers, Inc. and reflects an understanding that the classification 
of back disorders as strains and sprains often does not mirror the true 
nature of these disorders.
    OSHA's final risk assessment (like its proposed assessment) relies 
on statistics for strains and sprains that are associated only with 
overexertion (i.e., lifting/lowering, pushing/pulling, holding/
carrying), repetitive motion, and bodily reaction (i.e., awkward 
postures). Thus, OSHA's treatment of the BLS data exclude strains and 
sprains that were determined by ergonomists or health care 
professionals to arise from accidents, such as slips or falls. Based on 
the evidence and testimony reviewed above, strains and sprain injuries 
captured by the BLS system and classified under these three exposure 
event codes properly reflect musculoskeletal disorders that arise as a 
result of exposure to the risk factors covered in the final rule. 
Further, as described below in part C of the risk assessment, OSHA has 
refined its analysis, based on data in the record, to estimate the 
number and incidence of MSDs occurring among those workers who are 
exposed to risk factors at levels that meet the final rule's screen; 
OSHA believes that this refinement will ensure that the Agency is 
accurately stating the risks posed to employees covered by the final 
rule.
    The United Auto Workers (Ex. 32-185), argued that OSHA was 
underinclusive, not overinclusive, in its choice of the BLS categories 
that represent MSDs. In addition to the six categories chosen by OSHA, 
the UAW argued that OSHA should have included a substantial fraction of 
the injuries and illnesses categorized as ``other'' and ``multiple 
injuries'' as well. OSHA agrees that these injury categories contain 
MSDs that are relevant to OSHA's risk analysis. However, since data are 
not available to describe the proportion of the injuries classified 
under these categories that are, in fact, MSDs, the Agency has not 
included them in its revised risk assessment. This decision also means 
that the risks presented by OSHA in its Risk Assessment section and 
estimated in the Significance of Risk section are understated.
    As explained by OSHA in its preliminary risk assessment for the 
proposed rule, risk estimates based on the BLS data understate the true 
risk of incurring a work-related MSD posed to employees who are exposed 
to workplace risk factors that are associated with the development of 
MSDs, for several reasons. First, the BLS data include only those lost 
workday (LWD) cases that resulted in at least 1 day spent away from 
work, and thus do not capture either non-lost workday MSD cases nor MSD 
cases that resulted in the employee being temporarily reassigned to 
another job. Second, some LWD MSDs reported to the BLS by employers are 
likely to have been coded in BLS injury categories that are excluded 
from OSHA's categories of overexertion, repetition, and bodily reaction 
(bending, climbing, crawling, reaching, twisting); for example, 
injuries due to segmental vibration are included in BLS event 
categories other than those included by OSHA in its analysis, and, as 
pointed out by the UAW (Ex. 32-185), the non-specific BLS injury 
categories of ``other'' and ``multiple injuries'' are also likely to 
contain MSDs.
    Finally, the incidence of MSDs reported by the BLS is the reported 
incidence of MSDs occurring among all workers in the industries 
surveyed (on a full-time-equivalent basis); that is, the incidence for 
each industry sector is calculated by BLS as the number of MSD cases 
reported in 1996 divided by the total number of full-time equivalent 
employees in that industry sector in 1996. Expressing the incidence in 
this way has the effect of diluting the estimated incidence of 
disorders that are actually occurring among exposed employees, i.e., 
those who routinely are exposed to workplace risk factors that have 
been associated with the development of work-related MSDs. The risk to 
exposed employees is substantially higher than the risk reflected by 
the BLS estimates of MSD incidence, because most of the injuries 
reported to the BLS will in fact have occurred among that subset of 
workers whose jobs expose them to these risk factors (that is, if the 
incidence were calculated using the much smaller denominator that 
reflects the number of exposed employees, the resulting incidence 
estimate would be higher). Evidence that workers exposed to workplace 
risk factors are at substantially higher risk than other workers in 
their industry comes from the large data base of formal scientific 
studies of exposed worker populations that have demonstrated a positive 
relationship between exposure to workplace risk factors and the 
relative risk of developing an MSD (see the Health Effects section of 
this preamble). These studies show that the prevalence of MSDs among 
exposed employees is often 2- or 3-fold higher, and can be as much as 
10 to 20 times higher, as the prevalence among workers who are not so 
exposed.
    In the next part of the Final Risk Assessment, OSHA presents two 
alternative approaches to quantifying risks posed to workers who are 
exposed to biomechanical risk factors on the job. The first approach is 
the same as that used in the Preliminary Risk Assessment presented in 
with the proposed rule. In that approach, OSHA's estimates of the risk 
are based on the numbers and incidence of MSDs reported by BLS (based 
on OSHA's definition of MSDs) by industry sector and by occupation. 
OSHA's second approach responds to a number of comments made in the 
record that the Agency's Preliminary Risk Assessment did not (1) 
properly subtract out MSD cases that occurred among employees who were 
not heavily exposed to physical risk factors, and (2) did not properly 
account for background risk (i.e., that part of the risk that could not 
be attributed to workplace exposure or that occurs among the general 
population). To address these comments, the Agency was able to use data 
that became available in the record to more precisely characterize the 
MSD risk in the subset of employees who are the most heavily exposed to 
risk factors covered in the final rule, and to account for background 
risk. OSHA's underlying rationale is explained fully in part C below.

C. Results

    Table VI-3 provides the BLS estimates of the number of injuries and 
illnesses reported nationwide by employers for 1996, by nature of 
injury and type of workplace exposure, for all injury and exposure 
event categories determined by OSHA to represent the MSDs covered by 
the standard. Overall, OSHA estimates that there were a total of 
647,344 lost workday MSDs that occurred in 1996, as derived from 
employer reports of thoseTable VI-3 here illnesses and injuries. These 
disorders represent about 34.4 percent of the 1.88 million LWD injuries 
and illnesses reported by employers in 1996 (BLS press release 97-453, 
12/17/97).

[[<strong>Page</strong> 68550]]

    Table VI-3.--Estimates of the Number of Lost Workday Musculoskeletal Disorders (MSDs) in 1996, by Nature of Injury and Type of Workplace Exposure
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                            Type of workplace exposure
                                                         -----------------------------------------------------------------------------------------------
            Nature of injury                 BLS Code      Total for all                                   Subtotal  (O       Bodily
                                                             exposures     Overexertion     Repetition        and R)       Reaction \a\      Subtotal
--------------------------------------------------------------------------------------------------------------------------------------------------------
Total for all lost workday injuries.....  ..............  ..............         526,594          73,796         600,390          79,475         679,865
Musculoskeletal Disorders:
    Sprains, Strains, Tears.............             021         819,658         424,290          12,872         437,162          66,068         503,230
    Back Pain, Hurt Back................            0972          52,046          28,046             861          28,907           4,646          33,553
    Soreness, Hurt, except back.........            0973          73,542          17,984           5,811          23,795           2,896          26,691
    Carpal tunnel syndrome..............            1241          29,937  ..............          29,809          29,809  ..............          29,809
    Hernia..............................             153          29,624          25,819             322          26,141             670          26,811
    Musculoskeletal and connective                    17          35,238           7,761          18,278          26,039           1,211          27,250
     system diseases and disorders......
                                         ---------------------------------------------------------------------------------------------------------------
        Total Number of MSDs............  ..............       1,040,045         503,900          67,953         571,853          75,491        647,344
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Data from BLS included only those injuries reporeted to have been associated with ``Bending, climbing, crawling, reaching, twisting.'' Source: BLS-
  reported estimates for BLS nature-of-injury codes 021, 0972, 0973, 1241, 153, and 17, and for BLS exposure events of overexertion, repetition, and
  bodily reaction (1996).

    For 1998, the BLS estimated that there were 592,500 MSDs that 
occurred throughout U.S. industry, representing an 8.5-percent decline 
from 1996 (``Lost-Worktime Injuries and Illnesses: Characteristics and 
Resulting Time Away From Work, 1998,'' U.S. Bureau of Labor Statistics, 
available at <A HREF="http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://www.bls.gov/news.release/osh2.nr0.htm">http://www.bls.gov/news.release/osh2.nr0.htm</A>). This 
decline is consistent with the pattern seen from 1992-1996, when both 
MSD and overall injury rates declined. For the final risk assessment, 
OSHA has continued to use 1996 BLS data in order to be consistent with 
the economic analysis, which uses 1996 as a base year throughout. For 
example, 1996 is the base year from which data are used to estimate 
numbers of establishments and employees, revenues, profits, and costs 
associated with the final rule.
    About 66 percent of the estimated number of MSDs reported to the 
BLS in 1996 were categorized by BLS coders as ``sprains, strains, and 
tears'' due to overexertion. As discussed in part B above, OSHA 
received many comments on the use of BLS data on injuries classified by 
the BLS as sprains, strains, and tears; these commenters objected to 
including these injuries in the risk assessment on the grounds that 
injuries classified as strains, sprains, and tears reflect acute 
injuries that cannot be considered MSDs. Based on the evidence and 
testimony presented in part B above, however, OSHA has determined that 
it is appropriate to include strains, sprains, and tears that are 
associated with the exposure events of overexertion, repetitive motion, 
and bodily reaction in the universe of relevant MSDs because these 
injuries arise from exposure to relevant risk factors. Furthermore, 
OSHA believes that, when MSDs result from exposure to the biomechanical 
risk factors covered in the final rule, it is not important to make any 
distinction between whether those injuries arose from acute or chronic 
events. The purpose of the standard is to reduce the risk of MSDs 
resulting from exposure to risk factors, regardless of the duration of 
the exposure preceding to those injuries and illnesses.
    As further evidence of the appropriateness of including strain, 
sprain, and tear injuries in the risk assessment, OSHA presented BLS 
data in the preliminary risk assessment that provides additional 
information on the nature of the injuries and the exposure events 
associated with those injuries [64 FR 65931]; these data are reproduced 
in Table VI-4. For this analysis, OSHA obtained from the BLS a breakout 
of the estimated number of injuries, by body part and by type of 
overexertion event. This breakout appears in Table VI-4 and shows that 
about 89 percent of these sprain, strain, and tear injuries (379,615) 
are comprised of injuries due to lifting /lowering, pushing/pulling, 
holding/carrying, or throwing, all of which are activities involving 
force. For the remaining 11 percent of the BLS-coded sprain, strain, 
and tear injuries, the exact nature of the overexertion exposure was 
either not reported by the employer or did not fall into any other 
exposure classification under the BLS system. Of the 379,615 injuries 
for which the nature of the overexertion exposure was reported, the 
majority (88 percent) affected body parts that are consistent with the 
kinds of injuries addressed by the final standard, such as the upper 
extremities, neck and shoulder, lower extremities, and back. Fifty-two 
percent of these injuries represent back injuries due to lifting or 
lowering. Only a small proportion (12 percent) of sprain, strain, and 
tear injuries reported by the BLS in 1996 affected body parts that are 
not relevant to MSDs. Therefore, OSHA is confident that the vast 
majority of BLS-coded sprain, strain, and tear injuries are 
appropriately included in the estimated number of MSDs for 1996, and 
that the judgment of the OSHA expert panel in selecting appropriate BLS 
injury and event categories for Table VI-4 here the risk analysis is 
confirmed by this additional breakout and review of the BLS data.

[[<strong>Page</strong> 68551]]

[GRAPHIC] [TIFF OMITTED] TR14NO00.004

    The data summarized above have been broken out by the BLS both by 
industry sector and by occupation code. In addition, the BLS provided 
OSHA with estimates of the incidence of MSDs, as defined above by 
injury type

[[<strong>Page</strong> 68552]]

and cause, for each 2-digit SIC. As explained above, the BLS-calculated 
incidence estimates are based on the incidence among all employees 
(full-time equivalents) in each industry sector, and therefore 
understate the true incidence of work-related MSDs occurring among 
workers who are highly exposed to workplace risk factors, i.e., exposed 
in jobs that meet the standard's action trigger. Nevertheless, OSHA 
believes that these incidence estimates are useful for characterizing 
industry-specific MSD risks and for comparing the extent of the problem 
between industry sectors covered by the ergonomics program standard. 
Table VI-5 provides estimates of the number and incidence of LWD MSDs 
in each general industry 2-digit SIC group for which the BLS provided 
data. Industries having the highest incidence of MSDs include the 
following:

Air transportation (36.6 cases/1,000 workers);
Local and suburban transit (14.7 cases/1,000);
Motor freight transportation and warehousing (14.4 cases/1,000);
Health services (13.8 cases/1,000);
Transportation equipment (13.4 cases/1,000); and
Food and kindred products (12.2 cases/1,000).

    Table VI-6 provides estimates of the number and incidence of LWD 
MSDs by occupation code for the 75 occupations having the highest 
estimated annual incidence of employer-reported MSDs. Because the BLS 
does not provide incidence estimates by occupation, OSHA calculated the 
incidence using employment estimates from the Bureau of the Census 
Employment and Earnings (1996). Occupations having the highest 
incidence include:

Driver--sales workers (42.4 cases/1,000 workers);
Machine feeders and offbearers (34.6 cases/1,000);
Public transportation attendants (32.1 cases/1,000);
Nursing aides, orderlies, and attendants (31.6 cases/1,000);
Punching and stamping machine operators (30.4 cases/1,000 workers);
Laborers, except construction (29.1 cases/1,000);
Sawing machine operators (18.9 cases/1,000);
Furnace, kiln, and oven operators, except food (18.0 cases/1,000);
Grinding, abrading, polishing machine operators (17.9 cases/1,000);
Health aides, except nurses (16.9 cases/1,000); and
Licensed practical nurses (16.5 cases/1,000).

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[[<strong>Page</strong> 68556]]

    Of the Census Employment and Earnings (1996). Occupations having 
the highest incidence include:

    Driver--sales workers (42.2 cases/1,000 workers);
    Machine feeders and offbearers (34.6 cases/1,000);
    Public transportation attendants (32.1 cases/1,000);
    Nursing aides, orderlies, and attendants (31.6 cases/1,000);
    Punching and stamping machine operators (30.4 cases/1,000 workers);
    Laborers, except construction (29.1 cases/1,000);
    Sawing machine operators (18.9 cases/1,000);
    Furnace, kiln, and oven operators, except food (18.0 cases/1,000);
    Grinding, abrading, polishing machine operators (17.9 cases/1,000);
    Health aides, except nurses (16.9 cases/1,000; and
    Licensed practical nurses (16.5 cases/1,000).
    Of the 225 occupations for which BLS provided estimates of the 
numbers of employer-reported MSDs and total employment, the annual 
incidence of MSDs was 1 LWD case or more per 1,000 workers per year for 
178 (79 percent) of the occupations. The data described above reflect 
the annual incidence of MSDs estimated to have occurred in 1996 within 
general industry sectors and within occupations within this sector.
    Past risk assessments conducted by OSHA in other health standards 
rulemakings have typically estimated the lifetime risk to workers based 
on the assumption that they are exposed to the hazard in question for a 
full 45-year working lifetime. These past risk assessments dealt 
primarily with chronic, fatal diseases such as cancer. Unlike the 
impairments of health caused by many other OSHA-regulated hazards, 
however, MSDs are not fatal, although they are often debilitating. 
Moreover, a worker can experience more than one work-related MSD over a 
working lifetime. As a result, the lifetime risk associated with 
exposure to risk factors on the job can be expressed in a number of 
ways. One way of doing this is to define lifetime risk as the 
probability that a worker will experience at least one work-related 
musculoskeletal disorder during his or her working lifetime (45 years). 
This probability is calculated as 1-(p),<SUP>45</SUP> where p is the 
probability that a worker will not experience a work-related MSD in any 
given year (i.e., p is one minus the estimated MSD incidence for 1996 
in the industry sector of interest).\1\ For example, the estimated 
incidence of MSDs in 1996 for SIC 80, Health Services, is 13.847 lost 
workday cases per 1,000 workers. The probability that a worker in SIC 
80 will not experience an MSD in any given year is calculated as 
1-.013847, or 0.9862 (almost 99 percent). Over 45 years, the 
probability that a worker will never experience a work-related MSD is 
(.9862)<SUP>45</SUP>, or 0.534 (i.e., 53 percent). Therefore, the 
probability that a worker in SIC 80 will experience at least one work-
related MSD is 1-0.534, or 0.466 (i.e., 466 per 1,000 workers).
---------------------------------------------------------------------------

    \1\ OSHA used two simplifying assumptions when calculating the 
probability of experiencing no work-related MSDs in a working 
lifetime: (1) Employment in an industry was used as a surrogate for 
exposure to ergonomic hazards in that industry. (2) The probability 
of experiencing a work-related MSD in any given industry was treated 
as if it were identical for workers in that industry who had never 
previously experienced a work-related MSD and those who had 
previously experienced a work-related MSD.
---------------------------------------------------------------------------

    Alternatively, lifetime risk could be defined as the expected 
number of work-related MSDs an employee entering an industry will 
experience over a working lifetime in that industry. Unlike a 
probability, the expected value in such cases can exceed 1. (That is 
why, in the table below, one industry is identified in which an 
individual who works for 45 years can expect to experience, on average, 
more than one work-related MSD during that time.) The expected value 
represents the experience of the ``average'' individual, a measure that 
reflects the aggregate experience of many individuals.
    Both approaches \1\ taken by OSHA to estimate lifetime risk assume 
that the risk to a worker is independent from one year to the next, 
i.e., that a worker's injury experience in any one year does not modify 
his or her risk in any subsequent year. Although this is a reasonable 
assumption for the purpose of estimating an average lifetime risk, it 
is likely to be the case that the risk will be higher for workers who 
have had an MSD and continue to be exposed since musculoskeletal tissue 
has already been damaged. Among workers who have not experienced 
symptoms of an MSD, the risk to any individual worker in subsequent 
years depends on the amount of tissue damage sustained from exposure to 
risk factors and that worker's individual ability to repair or resist 
continued injury to the point of experiencing an MSD. In addition, 
OSHA's approach also assumes that each worker within a given industry 
sector (defined by 2-digit SIC) has the same risk. For the same reasons 
as discussed above, a relatively small number of workers will, in fact, 
experience injury rates far in excess of the average, while a 
comparatively large number will experience injury rates below the 
average. At this time, data are not available that would allow OSHA to 
determine the lifetime MSD risks for subpopulations of workers within 
each industry sector, i.e., those subpopulations with higher than 
average or lower than average risks, respectively.
---------------------------------------------------------------------------

    \1\ In written comments (Ex.32-185-3), the UAW expressed a 
strong preference for estimating the lifetime risk as the 
probability that a worker will experience at least one MSD in a 
working lifetime rather than as an estimate of the lifetime risk 
expressed as the expected number of MSDs a worker will experience in 
a working lifetime.
---------------------------------------------------------------------------

    Another meaning or interpretation of expected value may be more 
intuitive: The expected value is the total number of MSDs that may be 
expected to occur in a cohort of 1000 workers all of whom enter an 
industry sector at the same time and all of whom work for 45 years in 
the industry. The expected value of the number of MSDs occurring among 
these 1,000 workers over 45 years of employment is calculated as the 
annual MSD incidence multiplied by 45. For example, the estimated 
incidence of work-related MSDs in 1996 for SIC 80 (Health Services) is 
13.847 cases per 1,000 workers, or a frequency of 0.01387. The expected 
value of the number of work-related MSDs predicted to occur among those 
1,000 workers over 45 years is estimated to be (0.01387*45), or 0.623 
(623 per 1,000 workers).
    Table VI-7 presents OSHA's estimates of the lifetime risk of 
experiencing work-related MSDs, by industry sector. Based on the 
probability approach, the estimated probability of experiencing at 
least one work-related MSD during a working lifetime ranges from 24 per 
1,000 to 813 per 1,000, depending on the industry sector. Based on the 
expected value approach, the expected number of work-related MSDs that 
will occur in a cohort of workers all entering an industry at the same 
time ranges from 24 per 1,000 to 1646 per 1,000, since this approach 
recognizes that it is possible for a worker to experience more than one 
work-related MSD in a working lifetime.
    Several rulemaking participants criticized OSHA's preliminary risk 
assessment on the grounds that the Agency's risk estimates made no 
allowance or correction for background risk. These participants (see, 
for example, Exs. 32-206, 500-223, Tr. pp.10248-9, Exs. 30-3865, 30-
3356, 32-368, 30-4185, 30-3813, 30-1722, 500-221) argued that MSD risks 
for specific industries and occupations based on

[[<strong>Page</strong> 68557]]

BLS data should be compared to the background rate of MSD risk in the 
general population to calculate the excess risk associated with work. 
Some of these stakeholders asserted that, because OSHA has not done so, 
the Agency's estimates here represent only the average MSD risk posed 
to a worker in a particular industry or occupation by exposure to ``all 
of life's activities.'' OSHA does not agree; the BLS data reflect only 
cases that employers have deemed to be work-related. It would be 
inappropriate to adjust the MSD rates estimated on the basis of the BLS 
data by subtracting from these rates the MSD rates that have been 
reported in the general population. When excess risk is calculated by 
comparing a population of concern (in this case the employed 
population) to a reference population (e.g., the general population), 
the proper approach is to compare the total incidence in the population 
of concern to the total incidence in the reference population (see 
Rothman and Greenland, Ex. 38-240). That is, to estimate the excess 
risk of MSDs among workers using the approach suggested by these 
commenters, one must have data that describes the incidence of all 
MSDs, both work-and non-work-related, in the working population. 
Assuming that the MSD rate for the general population is the non-work-
related rate, and then subtracting this rate from the BLS-based rate, 
would yield estimates of the work-related, or excess, risk to workers 
only if the BLS data truly represented all MSDs occurring among workers 
(both on the job and off the job). This is clearly not the case, since 
the BLS data are designed only to capture those injuries that are work-
related; the BLS system does not capture those MSDs that occur among 
workers that are unrelated to work. Therefore, adjusting the BLS data 
by subtracting out MSD rates for the general population would not yield 
meaningful estimates of the excess MSD risk to workers.

[[<strong>Page</strong> 68558]]

[GRAPHIC] [TIFF OMITTED] TR14NO00.008

    Some commenters (see, e.g., Ex. 30-3813, Tr. 4102-4108, Exs. 30-
3356, 30-46-28, 30-4564, 30-3865, 30-4185, 30-3368, 30-1897) argued 
that, despite screening out some of the background risk, the BLS data 
are still overinclusive.

[[<strong>Page</strong> 68559]]

They pointed out that under the applicable OSHA and BLS guidelines, a 
case is considered ``work-related'' if an event or exposure in the 
workplace made any contribution to the injury or illness, regardless of 
the extent of that contribution. For example, Frank White of ORC 
testified that

    ORC [and others] question OSHA's ability to make quantitative 
determinations of workplace risks based on data that do not allow 
OSHA to differentiate between the respective contributions of 
workplace and non-workplace factors. In the face of OSHA's own 
acknowledgment of the special difficulties associated with 
establishing MSD causation compared ``to more traditional workplace 
exposures and disorders,'' the use of data that inherently include 
conditions caused by both work and non-work exposures to determine 
workplace risk is unacceptable. The result, once again, is an 
overreaching by OSHA--this time in its estimation of the true 
workplace risk--that has the effect of permeating, and effectively 
invalidating, the entire proposal. (Tr. 4102)

OSHA interprets Mr. White's comment as saying that, although strictly 
non-work-related MSDs are not captured by the BLS system, some 
proportion of cases in the system nevertheless represent MSDs that 
occur among workers who are not regularly exposed to risk factors, or 
whose exposures arise from tasks that are not ``core elements'' of the 
job (using the language contained in the proposed rule). In other 
words, although there may be some contribution from work to these 
cases, exposure to risk factors on the job are no greater that those 
encountered during non-work activities.
    In this risk assessment for the final ergonomics program standard, 
OSHA has relied on BLS injury and illness data in much the same way it 
does when evaluating the risks associated with safety hazards. Because 
the statistics relied upon by OSHA reflect work-related injuries and 
illnesses reported by employers and determined by OSHA to have been 
associated with exposure to the risk factors addressed by the final 
rule, there is no ``background'' number of injuries and illnesses in 
the OSHA data in the sense that BLS data are capturing non-work-related 
injuries. In other words, the total number of MSDs that occur in the 
workforce are either work-related or non-work-related; BLS counts the 
first and the second represents background. Thus, OSHA does not agree 
with these commenters that it is necessary to adjust the BLS data per 
se to account for such background risk.
    However, OSHA does recognize that some fraction of the number of 
MSDs estimated from the BLS data represents injuries and illnesses 
occurring among employees in jobs that would not be covered by the OSHA 
standard. That is, some of the MSDs being captured by the BLS's annual 
survey reflect injuries to workers who are not in jobs that meet the 
action trigger, e.g., those who may be exposed to risk factors only 
infrequently or those whose exposures were not of sufficient duration. 
OSHA does not intend the final ergonomics program standard to apply to 
these kinds of jobs. Instead, OSHA intends the standard to apply to 
those jobs where MSDs have occurred and the employee's exposure to risk 
factors was of sufficient duration, magnitude, and frequency to have 
contributed to the injury. This concept is reflected in the final rule 
in the form of the Basic Screening Tool, which explicitly identifies 
those exposure conditions that must be present on the job, along with 
an employee's report of an MSD incident, before the employer is 
obligated to implement the program. Employers have no obligation to 
establish an ergonomics program under the final rule if employees are 
not exposed to risk factors at least at the level(s) reflected in the 
Basic Screening Tool. Thus, OSHA adjusted, as an alternate analysis, 
its estimates of risk based on the BLS data to include only that 
portion of the risk that will be addressed by an ergonomics program 
developed under the final rule, i.e., that portion of the risk that is 
occurring among employees who are exposed to risk factors at least to 
the extent reflected in the final rule's screening tool. OSHA is thus 
estimating the risk of MSDs occurring among employees who would be 
covered in an ergonomics program, i.e., those who are more highly 
exposed to biomechanical risk factors.
    As explained by OSHA above, the BLS-reported incidence of MSDs 
reflects the number of MSDs reported per 1,000 full-time equivalent 
workers employed in industry. This incidence figure distributes the 
MSDs evenly across all workers in an industry sector or occupation. 
However, as demonstrated by the scientific evidence presented in the 
Health Effects section (Section V), OSHA has determined that the work-
related risk of MSDs increases with the intensity and/or duration of 
exposure. Because of this, MSDs are not, in fact, evenly distributed 
across all workers, but are concentrated among the proportion of 
workers who are the more highly exposed to biomechanical risk factors. 
Thus, the incidence of MSDs among the more highly exposed workers is 
greater than that among the lesser-exposed workers; this has been shown 
in the almost 200 epidemiological studies reviewed in the Health 
Effects section. It is for this reason that OSHA believes that the risk 
estimates presented in the first analysis above, which relied on the 
BLS-reported incidence estimates by industry and occupation, understate 
the true risk among the workers who are more highly exposed to physical 
risk factors (while overstating it for workers who are not highly 
exposed to risk factors).
    OSHA's second approach to estimating work-related MSD risks takes 
account of this risk differential between more highly exposed (i.e., 
higher-risk) workers and lesser-exposed (i.e., lesser-risk) workers to 
estimate more precisely the risk among those workers who would most 
benefit from an ergonomics program. In addition, the risk among the 
higher-risk workers is estimated in two forms. One assumes that all of 
the risk among the higher-risk workers can be attributed to their 
exposure to biomechanical risk factors, i.e., all of the risk is work-
related. OSHA believes this is reasonable because the data used to make 
these estimates are the BLS data, which represents MSDs reported by 
employers to be work-related. The second form assumes that, despite the 
fact that the data derive from reports of work-related injuries, only 
part of the risk can be attributed to workplace exposure to physical 
risk factors because of the presence of some ``background'' risk among 
the higher-risk workers. This background risk represents MSDs that are 
not work-related and are attributed to some unknown non-work exposure 
to risk factors. OSHA believes that making such an adjustment to the 
estimated risk among higher-risk workers leads to an overly 
conservative estimate of risk among workers whose jobs will be screened 
in under the final rule; however, the Agency is nevertheless making 
this adjustment in response to addresses the concerns of those 
commenters who argued that OSHA should take account of the 
``background'' incidence of MSDs.
    The first step in OSHA's second approach to estimating work-related 
MSD risks is to estimate the incidence of MSDs for higher-risk and for 
lesser-risk workers. OSHA considers the higher-risk workers to be those 
workers who are exposed to risk factors at levels that meet the final 
rule's basic screening tool; all other workers are considered lower-
risk in the sense that they are exposed to risk factors at levels below 
the final rule's screen.
    To accomplish this analysis, OSHA relied on data contained in the 
record from Washington State's industry-wide survey of workplace 
exposure to

[[<strong>Page</strong> <strong>68560</strong>]]

physical risk factors (Ex. 500-41-118); details of this survey are 
presented in Chapter 3 (Benefits Assessment) of the Final Economic 
Analysis. Data from this survey were used to estimate the percentage of 
employees in each major industry group who are exposed to risk factors 
that at least meet the level of a ``caution zone'' job under Washington 
State's ergonomics standard. The kinds and durations of risk factor 
exposures contained in Washington State's definition of a ``caution 
zone'' job are similar to those contained in OSHA's Basic Screening 
Tool, e.g., generally 2 or more hours per shift of exposure to 
repetitive motions, awkward postures, contact stress, or segmental 
vibration, or 4 or more hours per shift of keyboarding activity. Both 
tools also use the same lifting weight and frequency-of-lift criteria 
to screen jobs for force associated with manual handling. Because of 
the similarities between OSHA's screening tool and the Washington State 
criteria, OSHA believes it reasonable that use of the Washington State 
survey data on workplace exposures to biomechanical risk factors will 
yield reasonable estimates of the numbers of workers who are exposed to 
risk factors at the levels that meet the action trigger of the final 
rule. OSHA has used these data, along with data derived from the 
epidemiology studies reviewed in the Health Effects section (Section V 
of the final rule's preamble), to estimate the number and incidence of 
MSDs occurring annually among employees who are exposed to risk factors 
at levels meeting the action trigger in the final rule. OSHA's Final 
Economic Analysis contains a detailed description of the Washington 
State survey data and OSHA's use of these data to estimate the 
percentage of workers in each covered industry sector who are exposed 
to risk factors at levels that meet the final rule's action trigger.
    OSHA's approach to estimating the excess risk of MSDs among exposed 
workers is summarized in Table VI-8. From the Washington State survey 
data, OSHA estimated the percentage of employees who are exposed to 
risk factors that meet the final rule's screen criteria (Column D of 
Table VI-8) in each 2-digit industry sector, as well as the number of 
higher-risk workers (Column E).
    To estimate the incidence of MSDs separately for higher-risk as 
compared with lower-risk workers, OSHA assumes that the annual 
incidence of MSDs among the higher-risk workers is three times that of 
low-risk workers. The justification for this assumption can be found in 
the many epidemiology studies reviewed in the Health Effects section of 
this preamble (Section V). These studies compared the prevalence or 
incidence of MSDs among workers who are regularly exposed to the risk 
factors addressed by the final rule with the prevalence or incidence 
among the referent (or less-exposed) worker populations. Typically, 
these epidemiological studies report observed differences in these 
rates as ratios (such as odds ratios, incidence ratios, prevalence 
ratios, or other relative risk measures). A compilation of the risk 
measures identified in these studies appears in the form of estimated 
median and mean risk ratios in Table VI-9, separated by part of body. 
As the table shows, median risk ratios for back disorders, neck and 
shoulder disorders, and upper extremity disorders are 1.85, 2.7 to 3.3, 
and 2.8 to 6.6, respectively. Mean values for back disorders, neck and 
shoulder disorders, and upper extremity disorders are 2.4, 4.5 to 5.2, 
and 4.4 to 12.6, respectively. Based on these values, OSHA finds that, 
in general, employees who are regularly exposed to the risk factors 
covered by the final rule are at three times higher risk or, put 
another way, will experience a 3-fold higher incidence of MSDs than is 
the case for workers who are not so exposed.

[[Continued on <strong>page</strong> 68561]]
</PRE>