Upper limb disorders among biomedical laboratory workers using pipettes

Laboratory workers engaged with biomedical work often process series of specimens by repetitive or static manual activities. The widespread use of stamp pipettes has in particular been suspected to entail upper-limb disorders. Our primary aim was to test, if cumulated pipette work is associated with self-reported and clinically examined upper-limb disorders. Additionally we explored, if non-pipette repetitive or static laboratory tasks are associated with upper-limb complaints. We also explored, if use of electrically driven pipettes (reducing the forces needed to activate the pipette) are in lesser degree associated with upper limb complaints than manually driven pipettes. In all, 1,398 female laboratory technicians at two workplaces were included in a questionnaire survey. Among 1,202 respondents, 167 cases with significant upper-limb symptoms and 134 controls without participated in a case-control study. Amount of pipette work (especially when cumulated over the last 2 years) was associated with symptoms in dominant upper limb, especially in the hand/wrist and thumb, and with impingement syndrome and muscle pain in dominant shoulder. Use of electrical pipettes did not modify this association. The non-pipette tasks were at highest vaguely related to upper-limb symptoms. In biomedical laboratory work, intensive pipette use seems to constitute a dominating major ergonomic problem.

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title: Ergonomic intervention: its effect on working posture and musculoskeletal symptoms in female biomedical scientists.
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title: Epidemiologic screening of occupational neck and upper limb disorders. Methods and criteria.
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title: Musculoskeletal disorders of the neck and upper limb among sewing machine operators: a clinical investigation.
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title: Healthy Work : Stress, Productivity, and the Reconstruction of Working Life
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title: Explaining socioeconomic differences in sickness absence: the Whitehall II Study.
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title: Thumb Force and Muscle Loads Are Influenced by the Design of a Mechanical Pipette and by Pipetting Tasks
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title: Laboratory work with automatic pipettes: a study on how pipetting affects the thumb.
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title: An ergonomic design and performance evaluation of pipettes.
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title: Ergonomic evaluation of ten single-channel pipettes.
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Participants were laboratory technicians and scientists at the Lawrence Berkeley National Laboratory with experience performing pipetting tasks.



Twenty-one experienced pipette users completed a standardized pipetting task with 5 manual and 5 electronic pipettes. After using each pipette, the user rated it for attributes of comfort and usability.



Although no single pipette was rated significantly better than all of the others for every attribute tested, some significant differences were found between pipettes. The Rainin Pipet-Lite received the highest overall quality score among manual pipettes, while the Thermo Scientific Finnpipette Novus was the top-ranked electronic pipette. Features correlated with greater hand and arm comfort were lower tip ejection force, lower blowout force, and pipette balance in the hand.



The findings, when considered with participant comments, provide insights into desirable pipette features and emphasize the value of user testing and the importance of the interactions between task, workplace layout, and pipette design.

title: An investigation of hand forces and postures for using selected mechanical pipettes
abstract: The present study evaluated thumb, hand forces, wrist, forearm and shoulder postures used for pipetting with three selected mechanical pipettes. Twelve pipette users in a large university health system participated in pipetting simulation in their own laboratories to investigate the effects of pipette type, body posture (standing/seated), sample volume (200/1000 μL) and pipetting task on the physical risk factors. The thumb and hand forces were measured with 19 Flexiforce™ sensors. Wrist and forearm postures were measured with an electrogoniometer and a torsiometer, respectively. Humeral elevation as shoulder postural stress was assessed by observations from videos recorded during pipetting simulation. The study results showed several advantages of using the non-axial pipette over the traditional axial ones. The non-axial pipette was associated with approximately 2–6 times less thumb and hand force than the traditional axial pipettes. In addition, there were approximately 20–30% reductions in ulnar deviation and 30–70% reductions in humeral elevation to operate the non-axial pipette for most of the pipetting actions. One disadvantage of using the non-axial pipette appears to be increased forearm pronation by approximately 100–150% for the entire pipetting cycle, as compared to the axial pipettes. The results of the study may provide useful information regarding design of pipettes for reducing physical risk factors associated with pipetting. Relevance to industry This paper demonstrated hand forces and postures for common pipetting tasks with selected mechanical pipettes. The hand force and postural data for using axial and non-axial pipettes may provide key information for hand injury prevention due to pipetting in the industry.

title: The effect of two alternative arm supports on shoulder and upper back muscle loading during pipetting.
abstract: Pipetting involves static upper arm positions with the pipette held away from the body for sustained periods of time, putting increased musculoskeletal load on the shoulder and upper back. This study explores the effect of using two alternative arm supports while pipetting on muscle loading in the shoulder/neck region.



15 experienced pipette users participated in this study.



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Both arm support conditions resulted in significantly lower mean muscle activity of the anterior deltoid and upper trapezius muscles (p<0.001) and significantly higher subjective comfort ratings (p<0.001) compared to the control condition. The freely moving forearm support resulted in significantly lower peak muscle activity in the anterior deltoid compared to the control condition (p<0.001). Productivity was not affected by the arm supports. These findings suggest that arm support may be beneficial in reducing muscle loading and improving comfort in the shoulder and upper back during pipetting. Future studies are needed to measure the impact of these arm supports in the workplace.

title: Inverse dynamic analysis of the biomechanics of the thumb while pipetting: a case study.
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title: Ergonomics and the usability of mechanical single-channel liquid dosage pipettes
abstract: The aim of this study was to compare the ergonomics and usability of five mechanical single-channel pipettes as healthy female laboratory workers ( N = 1 1 ) performed pipetting tasks in simulated work situations. The muscular activity, wrist angle, perceived musculoskeletal strain, perceived features of usability, and work efficiency of each worker were measured during 1 day. Muscular activity of the musculus flexor pollicis longus ( p 0.0 0 1 ), ulnar deviation of the right wrist ( p 0.0 0 1 ), and perceived strain of the shoulder, forearm, wrist and thumb ( p 0.0 1 ) after the pipetting task were the least when the shortest and lightest pipette with the thickest handle and with three different sizes (small, medium, large) was used. The longest pipette and the second heaviest pipette caused the least perceived strain in the right-hand fingers. The shortest and lightest pipette with the thickest handle and with three different sizes earned the best average assessments for most of the usability features. No differences were found in work efficiency when the different pipette models were used. Relevance to industry The results of this study can be of value when pipettes are being designed and tested and when the ergonomics of work in laboratories is under development.

title: Risk factors in the onset of neck/shoulder pain in a prospective study of workers in industrial and service companies
abstract: To quantify the relative contribution of work related physical factors, psychosocial workplace factors, and individual factors and aspects of somatisation to the onset of neck/shoulder pain.  Four year prospective cohort study of workers from industrial and service companies in Denmark. Participants were 3123 workers, previously enrolled in a cross sectional study, where objective measurement of physical workplace factors was used. Eligible participants were followed on three subsequent occasions with approximately one year intervals. Outcomes of interest were: new onset of neck/shoulder pain (symptom cases); and neck/shoulder pain with pressure tenderness in the muscles of the neck/shoulder region (clinical cases).  During follow up, 636 (14.1%) participants reported neck/shoulder pain of new onset; among these, 82 (1.7%) also had clinical signs of substantial muscle tenderness. High shoulder repetition was related to being a future symptom case, and a future clinical case. Repetition was strongly intercorrelated with other physical measures. High job demands were associated with future status as a symptom case, and as a clinical case. A high level of distress predicted subsequent neck/shoulder pain, and neck/shoulder pain with pressure tenderness.  High levels of distress, and physical and psychosocial workplace factors are predictors of onset of pain in the neck and/or shoulders, particularly pain with pressure tenderness in the muscles.

title: Associations between work-related factors and specific disorders of the shoulder--a systematic review of the literature.
abstract: Our aim was to provide a quantitative assessment of the exposure-response relationships between work-related physical and psychosocial factors and the occurrence of specific shoulder disorders in occupational populations.



A systematic review of the literature was conducted on the associations between type of work, physical load factors, and psychosocial aspects at work, on the one hand, and the occurrence of tendinitis of the biceps tendon, rotator cuff tears, subacromial impingement syndrome (SIS), and suprascapular nerve compression, on the other hand. Associations between work factors and shoulder disorders were expressed in quantitative measures as odds ratio (OR) or relative risk (RR).



The occurrence of SIS was associated with force requirements >10% maximal voluntary contraction (MVC), lifting >20 kg >10 times/day, and high-level of hand force >1 hour/day (OR 2.8-4.2). Repetitive movements of the shoulder, repetitive motion of the hand/wrist >2 hours/day, hand-arm vibration, and working with hand above shoulder level showed an association with SIS (OR 1.04-4.7) as did upper-arm flexion > or =45 degrees > or =15% of time (OR 2.43) and duty cycle of forceful exertions > or =9% time or duty cycle of forceful pinch >0% of time (OR 2.66). High psychosocial job demand was also associated with SIS (OR 1.5-3.19). Jobs in the fish processing industry had the highest risk for both tendinitis of the biceps tendon as well as SIS (OR 2.28 and 3.38, respectively). Work in a slaughterhouse and as a betel pepper leaf culler were associated with the occurrence of SIS only (OR 5.27 and 4.68, respectively). None of the included articles described the association between job title/risk factors and the occurrence of rotator cuff tears or suprascapular nerve compression.



Highly repetitive work, forceful exertion in work, awkward postures, and high psychosocial job demand are associated with the occurrence of SIS.

title: Hand wrist cumulative trauma disorders in industry.
abstract: A total of 574 active workers from six different industrial sites were categorised into four force repetitive exposure groups. Workers in low force-low repetitive jobs served as an internal comparison population for the three other groups. Videotapes and surface electromyography were used to estimate hand force and repetitiveness. The presence of cumulative trauma disorders (CTD) was determined by structured interview and standardised non-invasive physical examination. Only workers who had been working on the study jobs for at least one year at the time of evaluation were eligible for selection. Categorisation of jobs and identification of CTDs were carried out independently by investigators who were appropriately blinded to exposure and outcome. The analysis of associations between CTDs and exposure categories were performed using Mantel-Haenszel plant adjusted odds ratios and unconditional multiple logistic regression. Significant positive associations were observed between hand wrist CTDs and high force-high repetitive jobs. These associations were independent of age, sex, years on the specific job, and plant.

title: User-oriented evaluation of mechanical single-channel axial pipettes.
abstract: Hand tools should be designed so that they are comfortable to use, fit the hand and are user-oriented. Six different manual, single-channel axial pipettes were evaluated for such objective outcomes as muscular activity, wrist postures and efficiency, as well as for subjective outcomes concerning self-assessed features of pipette usability and musculoskeletal strain. Ten experienced laboratory employees volunteered for the study. The results showed that light and short pipettes with better tool comfort resulted in reduced muscular activity and perceived musculoskeletal strain when they were compared with a long and heavy pipette. There were no differences in the efficiency between the different pipettes. Combining both the objective and subjective measures enabled a broader evaluation of product usability. The results of this study can be used both in product development and as information on which to base the purchase of new pipettes for laboratory work.

title: Effect of speed and precision demands on human shoulder muscle electromyography during a repetitive task
abstract: Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied during a hand movement task where five points were marked repeatedly with a pencil. Six female subjects performed with three precision demands and at four speeds. Three of the speeds were predefined, while the last speed was performed as fast as possible. The EMG were recorded from 13 shoulder muscles or parts of muscles. Elbow velocity, acceleration and rectified EMG were calculated for each task. The mean elbow velocity and acceleration increased with speed and precision demands. There was an increase in EMG as the speed demand increased for all three precision demands (P < 0.001), and as the precision demand increased for the two highest predefined speed demands (P < 0.05). The combination of a high speed and a high precision demand resulted in the highest EMG. Different EMG levels were attained for the 13 muscles and the supraspinatus muscle always showed the highest normalized EMG. However, analysis of variance showed the same relative increase for all muscles with speed and precision demands. The EMG changes in response to precision demand can only be explained in part by the differences in movement velocity and acceleration, and other factors such as increased co-contraction must also be taken into account.

title: Ergonomics and cumulative trauma disorders.
abstract: Chronic tendon and nerve disorders of the upper extremity, such as tendinitis and carpal tunnel syndrome, are a common problem among persons who routinely perform hand-intensive work. This article summarizes the most commonly reported occupational risk factors: repetitiveness, forcefulness, certain postures, mechanical stresses, exposure to vibration, and exposure to low temperatures. It describes how to look for these factors and how to control them through the design of work equipment and procedures.

title: Validity of a Self-Administered Questionnaire for Assessing Physical Work Loads in a General Population
abstract: Learning ObjectivesDescribe the design and rationale for this study evaluating eight questions on perceived physical load that are commonly a part of public health questionnaires.Recount the findings on validity of the eight physical-load questions, and the implications for which questions may be retained and which should be redesigned.Explain whether and how these findings were influenced by gender, type of work, and the presence of musculoskeletal complaints. The aim of the study was to evaluate eight questions concerning physical loads, used in public health questionnaires. Working women and men (203) completed a self-administered questionnaire twice, following a test-retest method. The questions were also validated with a structured interview. Response agreement was calculated with Cohen’s &kgr; statistics with quadratic weights (&kgr;w). Test-retest agreement varied from 0.74 to 0.92, and inter-method agreement from 0.38 to 0.81. The lowest coefficients were for the questions concerning bent/twisted work postures (&kgr;w 0.38) and repetitive movements (&kgr;w 0.39). The results did not indicate any substantial influence of gender, type of work or musculoskeletal complaint. The questions concerning general physical activity and sitting work postures, and physical exercise/sports during leisure times, had good validity. The questions concerning bent/twisted work posture and repetitive movements need to be re-designed.

title: Validity of self-reported physical work load in epidemiologic studies on musculoskeletal disorders.
abstract: This study assessed the validity of self-reported physical work load by questionnaire and logbook against task analysis and observation. It also investigated factors (job type and low-back or neck pain) affecting the self-assessment of physical work load and compared the assessments between the questionnaire and the logbook.



A self-administered questionnaire including 10 questions (ordinal scales) on physical work load and musculoskeletal symptoms was filled out by 2756 men in the forest industry. From this population, 36 men were selected for task analysis and observation. Logbooks including 10 continuous variables were analyzed for 386 men.



The Spearman rank correlation coefficients between the self-assessments and observations for the frequency of manual handling, duration of trunk flexion, neck rotation, hand above shoulder level, and squatting or kneeling ranged between 0.42 and 0.55. The correlation coefficients for the questionnaire items were higher in general, and the accuracy better, for those with no low-back pain than for those with pain. The duration of trunk flexion, neck flexion and hand above shoulder level was overestimated in the questionnaires and less so in the logbooks.



Self-administered questionnaires may help to classify groups with heterogeneous occupational tasks according to some work-load factors. The accuracy of the assessments is not good for studying quantitative exposure-effect relationships, however. The logbook method might give more valid information. The perception of musculoskeletal pain may bias the self-assessment of work load.

title: Interview versus questionnaire for assessing physical loads in the population-based MUSIC-Norrtälje Study.
abstract: MUSIC-Norrtälje study is a case-referent study, the aim of which is to find risk and health factors for low back and neck/shoulder disorders. In this part of the study, the interview technique and the self-administered questionnaire used for assessment of physical loads are described and the inter-method reliability of parts of the self-administered questionnaire is estimated. The distribution of exposure levels in a general population is also described.



The study period was three years from November 1993 to November 1996, and the study subjects totaled 2,480 persons (813 female and 610 male referents, 380 female and 315 male low back cases, 252 female and 106 male neck/shoulder cases). The interview concerned "a typical working day" during the preceding 12 months and comprised assessment of energy expenditure, work postures, and manual materials handling for work and leisure time, including regular sport activities. The self-administered questionnaire comprised 18 questions, each covering 5 different points of time: right now, 5, 10, 15, 20 years ago. The answers to eight of the questions about current conditions were compared to corresponding interview responses. The interview was considered as the "gold standard."



Ninety-eight percent of the subjects completed the interview without any great difficulties. According to the interview, the distributions of different exposure levels were generally positively skewed, i.e., the frequency of highly exposed subjects was low in the study base. The correlation between interview and questionnaire responses among the referents was high for time spent "sitting at work" (r = 0.82), "VDU work" (r = 0.87), and work related "motor vehicle driving" (r = 0.80). The correlation was moderate for work-related "hands above shoulder level" (rs = 0.63), and "hands below knee level (trunk flexion)" (rs = 0.66). The correlation was lower for leisure time activities such as "domestic work" (r = 0.55), "time for own activities" (r = 0.39), and "sitting during leisure time" (r = 0.38). Subjects seeking care for low back or neck/shoulder disorder estimated equally correctly or not, as had the referents. However, non-differential misclassification was present in all questions, which will attenuate observed estimates of the relative risk.



Even though interview data are preferable, questionnaire data may be useful for assessing well-defined work tasks and for "sitting at work."

title: Physical exposure assessment in monotonous repetitive work--the PRIM study.
abstract: A program called the Project on Research and Intervention in Monotonous Work (PRIM) was initiated in 1994 as a prospective cohort study of work-related musculoskeletal disorders. The group-based exposure assessment strategy, focusing on task-related exposure and used to obtain baseline measures of physical exposures, is reported in this paper.



Monotonous, repetitive worktasks were evaluated at 19 factories. Tasks with an estimated similarity in physical exposure were aggregated before 103 exposure groups were formed. Subjects from the exposure groups were randomly sampled for measurements, and task-related exposure levels were quantified by 43 single exposure items using a real-time video-based observation method that allowed computerized estimates of repetitiveness, body postures, force, and velocity. In combination with questionnaire-based data on task distribution, the duration of exposure was calculated at the individual level.



The video-based observational method and the large number of exposure variables enabled the establishment of detailed quantitative exposure profiles in 103 task-based exposure groups. However, methodological problems associated with the use of grouped exposure assessment were revealed. Despite efforts to optimize group homogeneity, the within-group variance was larger than the between-group variance for several shoulder postural variables.



A task-based exposure-assessment strategy can be successful in solving some of the main problems associated with the assessment of physical workplace exposures. The large within-group variance in exposure to nonneutral shoulder postures may eventually require individual assessment or the inclusion of groups with maximal contrast in exposure or both.

title: Validity of generic risk factors and the strain index for predicting nontraumatic distal upper extremity morbidity.
abstract: Nine individual generic risk factors, eight combinations of generic risk factors, the presence of any generic risk factor, and the Strain Index were evaluated for 56 jobs by 2 evaluators blinded to morbidity measures. Jobs then were assigned to dichotomous hazard classifications (problem versus safe) according to recommendations from the literature. OSHA 200 logs were used to ascertain historical evidence of distal upper extremity (DUE) morbidity, and jobs were assigned to a dichotomous morbidity classification (positive versus negative) using none versus one or more recorded cases as the criterion. Evidence of association and measures of predictive validity were evaluated by comparing hazard and morbidity classifications using 2 x 2 contingency tables. Five individual generic risk factors, three generic risk factor combinations, and the presence of any generic risk factor were not associated with morbidity classification. The odds ratio estimates among the four individual generic risk factors and the five combinations of generic risk factors associated with DUE morbidity varied from 3.3-36.0. The Strain Index had the largest estimated odds ratio of any exposure factor at 108.3. The exposure methods were grouped according to patterns of predictive validity. With one exception, the individual generic risk factors and their combinations had high sensitivity with low specificity (many false-positives), low sensitivity with high specificity (many false-negatives), or low sensitivity with low specificity. The only generic risk factor that demonstrated reasonable predictive validity was the use of gloves--its sensitivity, specificity, positive predictive value, and negative predictive value were equal to 0.75. The Strain Index performed better than any of the individual or combinations of generic risk factors. Its sensitivity, specificity, positive predictive value, and negative predictive value were all approximately 0.90.

title: Can we rely on retrospective pain assessments?
abstract: The objective of this paper was to study whether subjects in a workplace setting are able to assess the intensity of musculoskeletal pain retrospectively for a period of 3 months. The intensity of average pain and maximum pain in eight anatomic regions was assessed on a numeric rating scale. The results of 12 consecutive weekly pain recordings were compared with a final retrospective assessment of pain intensity covering the same 3-month period (119 subjects). The degree of agreement was good or excellent. The subjects were able to distinguish between the worst complaints and average complaints, and the subjective perception of aggravations or improvements corresponded to the direction of a change in score. Current complaint status slightly influenced the memory of pain. The reproducibility of the questionnaire was also assessed and showed kappa coefficients between 0.44 and 0.91 (36 subjects). The results suggest that subjects are able to accurately recall and rate the severity of pain or discomfort for a period of 3 months. These findings are of practical importance in epidemiologic studies, because they imply that retrospective reports on pain intensity are sufficiently reliable.

title: Implementation of neck/shoulder exercises for pain relief among industrial workers: A randomized controlled trial
abstract: BackgroundAlthough leisure-time physical activity is important for health, adherence to regular exercise is challenging for many adults. The workplace may provide an optimal setting to reach a large proportion of the adult population needing regular physical exercise. This study evaluates the effect of implementing strength training at the workplace on non-specific neck and shoulder pain among industrial workers.MethodsCluster-randomized controlled trial involving 537 adults from occupations with high prevalence of neck and shoulder pain (industrial production units). Participants were randomized to 20 weeks of high-intensity strength training for the neck and shoulders three times a week (n = 282) or a control group receiving advice to stay physically active (n = 255). The strength training program followed principles of progressive overload and periodization. The primary outcome was changes in self-reported neck and shoulder pain intensity (scale 0-9).Results85% of the participants followed the strength training program on a weekly basis. In the training group compared with the control group, neck pain intensity decreased significantly (-0.6, 95% CI -1.0 to -0.1) and shoulder pain intensity tended to decrease (-0.2, 95% CI -0.5 to 0.1, P = 0.07). For pain-cases at baseline (pain intensity > = 3) the odds ratio - in the training group compared with the control group - for being a non-case at follow-up (pain intensity < 3) was 2.0 (95% CI 1.0 to 4.2) for the neck and 3.9 (95% CI 1.7 to 9.4) for the shoulders.ConclusionHigh-intensity strength training relying on principles of progressive overload can be successfully implemented at industrial workplaces, and results in significant reductions of neck and shoulder pain.