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Objective: The purpose of this study was to develop alternative Strain Index risk classification categories. Background: Strain Index scores are usually categorized into four Strain Index "risk categories." The "original" risk categories were developed in the meat-packing industry and may not be fully applicable to other industries. Method: Daily Strain Index scores were estimated among 276 manufacturing workers participating in a cohort study of occupational risk factors for hand–arm musculoskeletal symptoms. Each score was categorized using the original method and a new method based on quartiles of Strain Index score values among symptomatic participants. Models examining associations between original Strain Index risk categories and incident hand–arm symptoms were compared to models examining associations between the alternative Strain Index risk categories and incident hand–arm symptoms. Results: Compared to the respective referent categories, a twofold or greater increase in the risk of incident hand–arm symptoms was observed for the highest original Strain Index risk category (HR = 2.06, 95% CI = [1.08–3.92]) and for the second highest alternate Strain Index risk exposure category (HR = 2.21, 95% CI = [1.26–3.85]). Although significant associations between Strain Index risk category and incident hand–arm symptoms were observed for both Strain Index categorization methods, model fit statistics favored the alternate approach. Conclusion: Results from this study suggests that the Strain Index risk category structure may need to be tailored to specific populations. Application: If verified, results from this study provide a better way to identify hazardous manufacturing jobs and target them for exposure reduction.

Objective: The aim of this study was to characterize associations between psychosocial and work organizational risk factors and upper-extremity musculoskeletal symptoms and disorders. Background: Methodological limitations of previous studies of psychosocial and work organizational risk factors and musculoskeletal outcomes have produced inconsistent associations. Method: In this prospective epidemiologic study of 386 workers, questionnaires to assess decision latitude ("control") and psychological job demands ("demand") were administered to study participants and were used to classify them into job strain "quadrants." Measures of job stress and job change were collected during each week of follow-up. Incident hand/arm and neck/shoulder symptoms and disorders were ascertained weekly. Associations between exposure measures and musculoskeletal outcomes were estimated with proportional hazard methods. Results: When compared to the low-demand/high-control job strain referent category, large increases in risk of hand/arm disorders were observed for both high-demand/high- control (hazard ratio [HR] = 4.49, 95% confidence interval [CI] = [1.23, 16.4]) and high-demand/low-control job strain categories (HR = 5.18, 95% CI = [1.39, 19.4]). Similar associations were observed for hand/arm symptoms. A strong association was also observed between the low-demand/low-control job strain category and neck/shoulder disorders (HR = 6.46, 95% CI = [1.46, 28.6]). Statistically significant associations were also observed between weekly stress level and weekly job change and several musculoskeletal outcomes. Conclusion: Associations between psychosocial risk factors and work organizational factors and musculoskeletal outcomes were large and in the hypothesized direction. Application: Prevention of occupational musculoskeletal disorders may require attention to psychosocial and work organizational factors in addition to physical factors. Methods to control adverse effects of psychosocial and work organizational risk factors should be explored.