Background Since the policy of “keeping trash off of the ground” in Taiwan, long-term exposure to repetitive motion in waste collection process results in high risk of upper extremity musculoskeletal disorders (UEMDs). Thus, we assessed the moderation and mediation effects of job-related stress and job support on work-related UEMDs among municipal waste collectors. Methods A cross-sectional study was conducted in two cities located at northern Taiwan during 2018–2019. 626 municipal waste collectors voluntarily participated and anonymously filled out a structured questionnaire. The moderation and mediation effects of effort-reward imbalance (ERI) and social support on UEMDs were analyzed by Haye’s Process Macro Model. Results Prevalence of UEMDs in municipal waste collectors were 43.4% for neck, 56.0% for shoulder, 24.1% for upper back, and 33.1% for hand/wrist. There was high prevalence of shoulder (72.2%), neck (48%), and upper back (30%) in female workers compared to male, most significantly in shoulders. In univariate and multivariate analysis, high ERI and low job support were significantly associated with ORs of 3.11 (95% CI:1.58–6.13) for elbow, 2.79 (95% CI:1.39–5.56) for shoulder, 3.39 (95% CI:1.64–7.00) for upper back and 3.83 (95% CI:1.98–7.41) for hand/wrist. Prevalent UEMDs were positively associated with high ERI in municipal waste collectors but negatively with job support. The moderation effects of ERI and job support on UEMDs, of which the measured synergy index exceeded one, were 18.24 for shoulder, 3.32 for elbow, and 2.45 for hand/wrist, but mediation effects were not significant. Conclusions This study found municipal waste collectors with work-related upper extremity disorders were significantly associated with work-related psychological risk factors. Therefore, waste collection cannot only to be improved by semi-automatic and automatic processes but immediate intervention programs for the reduction of psychological risk factors is needed promptly.

Despite repetitive activities and the frequency of high workload for municipal solid waste (MSW) collectors, the risks of work-related stress on upper extremity pain are inconclusive. The objective of this study is to assess the moderation and mediation effect of effort-reward imbalance (ERI) and over-commitment (OC) on upper back and hand/wrist disorders in MSW collectors. Methods: A cross-sectional study was conducted with MSW collectors from two cities in Taiwan. Each participant was asked to anonymously fill out a structured questionnaire. Work-related stress, including ERI and OC, was assessed by a Chinese version of the Job Content Questionnaire (C-JCL). Upper back and hand/wrist disorders were assessed using the Nordic musculoskeletal questionnaire. Multivariate analysis was used to assess moderation and mediation effect of OC and ERI on upper extremity pain. Results:The moderation effect of ERI and OC on upper back and hand/wrist disorders in MSW collectors was found. Disorders were higher in the group with both ERI ≥1 and high OC (OR (odds ratio) = 3.25 and OR = 3.00) than in the group with ERI ≥1 and low OC (OR = 2.66 and OR = 1.87) and in the ERI <1 and high OC group (OR = 2.27 and OR = 1.26). Synergy indexes were 0.77 and 1.77, respectively. Using multivariate analysis after adjusting for covariates, the mediation effect of OC was significant for the association between ERI and upper back and hand/wrist pains. The indirect effects of OC for upper back and hand/wrist pains accounted for 35% and 42%, respectively, and OC appears to mediate the relationship between ERI and upper back and hand/wrist disorders in MSW collectors. Conclusion: Work-related stress measured ERI and OC may play a role in moderating and mediating effects on upper extremity pain. Encouraging provisions of work modification and stress management is needed to mitigate the occurrence of upper extremities pain in MSW collectors.