Marissa L. Ebersole

Incidence of carpal tunnel syndrome among automobile assembly workers and assessment of risk factors.

Objectives: This study defined the incidence rate of carpal tunnel syndrome (CTS) among active assembly workers and evaluated risk factors. Methods: This study followed 189 automobile assembly workers over 1 year. Incident cases were defined as workers who had no current or prior history of CTS and were subsequently diagnosed with CTS by means of active surveillance during the study. Results: The estimated annual incidence rate ranged from 1% to 10%, depending on the case definition. Significant predictors for CTS include a higher baseline median-ulnar peak latency difference, history of wrist/hand/finger tendonitis, history of diabetes, nonneutral wrist and elbow postures, and a lower self-reported social support. Conclusions: This is similar to other prospective studies that demonstrate both ergonomic and medical history are independent risk factors for development of CTS.

Predictors of Persistent Elbow Tendonitis Among Auto Assembly Workers

Introduction: Lateral and medial epicondylitis associated with work activity is a common upper extremity musculoskeletal disorder with a prevalence of 4–30% depending upon the work setting and diagnostic criteria. The influence of treatment, ergonomic factors, medical history, psychosocial variables, and aging on the improvement of symptoms has not been well defined. Methods: This was a prospective cohort study of a cohort of 45 workers with active elbow tendonitis for an average of 13 months. Complete resolution of symptoms was the defined outcome measure. Results: The predictive factors for persistent elbow tendonitis included older age (OR = 1.1, 95% CI: 0.99, 1.33), higher hand repetition level for their job(s) (OR = 2.5, 95% CI: 1.00, 6.25), more deviation from a neutral wrist position during the work activity (OR = 2.0, 95% CI: 0.80, 5.56), and lower perceived decision authority on the job (OR = 0.9, 95% CI: 0.79, 0.98). Other ergonomic, psychosocial, and electrophysiologic measures were not predictive. The models had relatively high sensitivity and specificity. Treatment effects could not be evaluated due to incomplete data available. Conclusions: Older workers with jobs requiring more repetition and awkward wrist postures, and less decision authority were less likely to have resolution of their elbow tendonitis. Implications: Workers at highest risk for persistent elbow tendonitis should be placed at jobs with lower repetition levels and that use more neutral wrist postures. Effective interventions must address both the ergonomic and psychosocial risk factors in a multifaceted approach to this problem.

Verbal Estimation of Peak Exertion Intensity

The objectives of this research were to investigate the accuracy and precision with which trained and untrained participants estimate the magnitude of forceful exertion and to evaluate the mathematical relationship between actual and estimated exertion. Three groups of participants estimated, as a percentage of maximum voluntary contraction (%MVC), the magnitude of submaximal exertion for 12 simulated tasks. In addition to the control group, one group was exposed to one physical benchmark (100% MVC) and another to three benchmarks (25%, 75%, and 100% MVC) prior to force estimation. Error (estimated minus actual) significantly decreased (p < .0001) from 14% MVC to 4% MVC with one benchmark and to -3% MVC with three benchmarks, as compared with the control group. Furthermore, the standard deviation decreased significantly (p < .0001) from the control group (16.6% MVC) to the one-benchmark group (13.8% MVC) to the three-benchmark group (11.6% MVC), indicating improved precision. Significant interaction effects were observed, but their impact on main effects was negligible. Also, linear, power, and logarithmic regression models described the relationship between perceived and actual exertion equally well (R2 = .64-.81). Applications of this research include improving the accuracy and precision of field-based psychophysical estimates of forceful exertion for epidemiological research and other field-based analyses.

Analysis of an Observational Rating Scale for Repetition, Posture, and Force in Selected Manufacturing Settings

Objective: The aim of this work was to quantify the interrater reliability of a set of scales that assess repetition, posture, and force as used on site when examining industrial work. Background: Interrater reliability of observational assessment methods can vary depending on the definition of the methods and situations in which they are used. Method: In several industries, 846 jobs were assessed using pairs of analysts to rate the repetition, force, and posture of the upper limbs. Twelve analysts with varying experience levels participated. Results: Using an interclass correlation coefficient (ICC), force and repetition had reliability values of .60 and .71 before and .82 and .87 after discussion, respectively. After discussion, peak posture ratings had ICCs of .60 to .83. ICCs for average posture ratings ranged from .31 to .51 initially to .55 to .67 in final ratings. Less experienced analysts changed their initial ratings more than did the senior investigators. Conclusion: The high interrater reliability of the repetition and force metrics indicates that a single analyst is appropriate for basic job assessment. Posture ratings benefit greatly from a two-analyst system. Average postures should be assessed across a full range of the scale for interrater reliability assessment. Analyst pairs should be rotated to avoid forming biases. Application: For basic assessments of forceful exertions and repetitive motions, a single analyst can be used, reducing the resource requirements for both industry and large epidemiological studies.

Inter-Rater Reliability for Hand Activity Level (HAL) and Force Metrics

Observational rating methods are used frequently in ergonomic job analysis because they are less costly and time consuming than other methods. The ACGIH recently published a threshold limit value (TLV) for repetitive work. This TLV suggests the use of one such observational method developed by Latko et al. (1997) for rating Hand Activity Level (HAL) and peak force. One criticism of Latkos method is the unknown reliability and consistency of the raters during the analysis process. Latko suggests the use of two or more trained observers to increase this consistency. This study analyzed 410 jobs at an automotive assembly plant using 2 observers recording initial and final ratings. A weighted kappa was calculated for the HAL and peak force before and after discussion. Before discussion, HAL reliability was rated as moderate and peak force as fair. After discussion, both HAL and peak force kappa values were rated as good.

A Task Analysis Approach to Assessing Exposure

Lean manufacturing has created an environment where industrial jobs are continually changing and becoming more complex in nature. In current practice, each of these job changes would require a new ergonomic analysis. This research proposes that the analysis of individual tasks within a job can be added to understand the overall exposure of the job. Using this relationship, one can obtain an understanding of job exposure without a complete reanalysis. In this study, nine jobs were analyzed using observational techniques in which generic ergonomic stresses were rated on a scale from 0 to 10 at both a task and job level. When the task observations were added together and compared to the entire job, the ratings of radial/ulnar deviation differed by an average of 1.4 points on a 10-point scale. Peak force differed by an average of 1.1 points. The other ratings were all within 1 point on a 10-point scale, which is considered within consensus as defined by the scales. These support the proposed method.

Task-Based Measurement of Force in Automotive Assembly Using Worker Self-Assessment, Observational Analysis and Electromyography:

Worker self-assessments of force and observational assessments are convenient and efficient ways of assessing force demands. Past studies have criticized the accuracy and reliability of these methods of assessment. This study related worker perceptions of peak hand force, observational ratings of peak hand force and peak finger flexor and extensor EMG to understand the reliability and accuracy of these subjective methods when used at a subtask level. Worker and observer ratings of force had moderate correlation (R2 = 0.49). While the correlation of these subjective ratings to peak subtask EMG values was poor at an aggregate level, the percent agreement showed that workers and observers were within 1 point on a 10-point scale at least 61% of the time. This suggests that certain types of tasks were more suited to comparisons with the finger flexor and extensor EMG than others, and further investigation of these relationships is required.

Verbal Estimation of Peak Force

This study investigated the precision and accuracy with which individuals could estimate the magnitude of submaximal, upper extremity forceful exertions over a range of tasks typical of occupational/industrial settings. Without training, the average estimation errors were 15.3, 23.2, and 11.8%Max for low, medium, and high levels of force, respectively. When subjects were first exposed to a single, maximum exertion, these error levels improved to 9.8, 14.3, and 10.6%Max. When exposed to two additional benchmarks of 25% and 75%Max, error improved further to 6.8, 11.8, and 9.4%Max.