Intervening on the Determinants of Mechanical Exposures: The Effects of a Redesigned Production System on Physical Demands and Worker Perceptions

Abstract

OCCUPATIONAL APPLICATIONS Biomechanical analyses confirmed that workers on an existing production system experienced substantial trunk and shoulder loads. The production system design was a major determinant of these high exposures. To reduce these exposures, workplace stakeholders (including local and corporate management and organized labor) engaged with researchers in a participatory design process. Process elements included biomechanical modeling simulations to develop potential configurations, which were subsequently tested by workers during user trials with mock-ups. Based on stakeholder feedback, a new tilted production system was implemented. Formal analyses following installation of the tilted line demonstrated significant decreases in trunk flexion, spinal compression, and muscle activity for the low back and shoulder regions. Workers perceived that the new tilted line made their work significantly easier, safer, and less tiring. The study indicates that interventions at the production system level, developed using a participatory process, can reduce mechanical exposures while improving worker perceptions of job demands.

TECHNICAL ABSTRACT Background: The design of an existing production system (flat line) was identified as the dominant driver of mechanical exposures for the low back and upper limb. A participative process was utilized in designing and implementing a tilted line that allowed workers to adopt more upright postures. Purpose: This study aimed to test the hypotheses that the new tilted production system would (1) decrease physical demands of the low back and shoulder, (2) not increase activity of the wrist musculature, (3) reduce workers’ reports of pain intensity, and (4) be perceived as a positive and beneficial change by the workforce. Methods: Eighteen of 22 tilted line workers volunteered to be videotaped (postures input into a biomechanical model of the upper limb/trunk) and have electromyography from the low back, shoulder, and forearm recorded while they worked at four tilted and flat line positions. Self-report questionnaires were used to compare pain intensity scores from workers on the tilted and flat lines. Results: Working on the tilted line was associated with statistically significant reductions in peak trunk angle (mean difference of 11°), L4/L5 spinal compression (314 N), and peak and mean electromyography for the low back (31% and 29%) and dominant shoulder (11% and 12%). No significant differences in pain scores were observed between the two lines. However, workers perceived that the tilted line made their work significantly easier, safer, less tiring, and assisted with their job. Conclusions: Tilting the production system allowed more upright postures, significantly reducing mechanical exposures for the trunk and upper limb. The participatory design approach may have contributed to workers’ positive perceptions about the newly designed production system. Ergonomic interventions that focus on workplace elements that drive mechanical exposures likely increase change impact and intervention intensity and should be an effective way to decrease musculoskeletal disorder risk factors.

KEYWORDS:

• Biomechanics
• electromyography
• intervention
• musculoskeletal disorders
• production line
• participation

ACKNOWLEDGMENTS

This study was supported by the Health Evidence and Applications Linkage Network, The Woodbridge Group, and the Canadian Auto Workers Union. The authors would like to acknowledge the efforts and contributions of Mardon Fraser, Robert W. Norman, J. Michael Smith, and all of the workplace stakeholder parties involved.