Demonstrating relationships between workplace demands and exposures related to musculoskeletal disorders and stress-related health outcomes

Musculoskeletal disorders (MSD) and outcomes related to stress, such as mental health disorders, are important sources of pain, distress, disability, and costs in Canadian workplaces. Recent initiatives have highlighted the importance of preventing MSD and stress-related outcomes at work, however they are typically treated separately, each having their own literature, prevention approaches, and programs; there has been a push to recognize their connected nature. The objectives of the thesis were therefore to: 1) develop a framework to guide measurement of physiological responses related to workplace demands in both the physical and psychosocial domain, 2) examine relationships between workplace demands (in the physical and psychosocial domain) and exposures related to MSD and stress-related health outcomes during simulated computer work, and 3) examine relationships between potentially straining aspects of call centre work and exposures related to MSD and stress-related outcomes through a field study.
\nThe framework was developed to recognize the connected nature of work-related MSD and stress-related outcomes. It is intended that the framework be used as a guide to measure exposure and outcome variables in a comparable manner across the physical and psychosocial domains in future laboratory and field studies. The multidisciplinary approach offered a foundation to examine common workplace risk factors for physiological responses related to MSD and stress-related outcomes in the studies comprising the thesis; an approach that could make possible more effective and efficient programs to target both work-related MSD and stress-related outcomes. The integrated and multidisciplinary framework substantially contributed to a limited body of literature. 
\nTwo laboratory studies targeted the second objective of the thesis. The aim of the first was to examine the effect of mechanical demand on scapular orientation during computer work. Maximum scapular motions for rotation, protraction/retraction, and tilt were documented while participants’ arms were in postures typical of computer work. The identification of these ranges permitted quantification of normalized mean position during different computer tasks, and will permit future research to better describe scapular orientation during sedentary work. Compared to a neutral posture, participants held a more laterally rotated and protracted position of the scapula when they carried out computer tasks, potentially compressing tissues in the subacromial space.
\nThe study also illustrated it was not the change in mechanical demand that produced statistically significant differences in the mean duration and size of scapular movements during computer work, but rather the change in cognitive demand. The second laboratory study further investigated the effect of cognitive demand on physiological responses related to MSD, as well as those associated with stress-related outcomes, during computer work. Changes in cognitive demand related to perceptions of increased workload, increased sympathetic nervous system activity, and changes in the duration and size of scapular movements. Together, the findings from the two laboratory studies showed that when cognitive demand increased, both the duration and size of scapular movements decreased, as did the change in muscle activation (for the right and left upper trapezius) associated with the movements. The observed reduction in movement during mentally demanding tasks may be associated with static postures, a risk factor for discomfort and pain among computer users.
\nThe field study was carried out in two parts. Part A explored, through semi-structured interviews, potentially straining aspects of work for call centre agents, with an emphasis on agent-client interactions, and Part B examined relationships between agent-client interactions and physiological responses monitored over a work shift. Results from Part B showed greater activation of the trapezius muscle and the sympathetic nervous system when calls were perceived to be challenging or overwhelming compared to when calls were perceived to be non-straining. Findings from Part A suggest that aspects of both the content of work, for example the regulation of emotion, and the context of work, for example workforce surveillance, condition the interactions agents have with clients every day. Future efforts should consider how these features of work might be improved to minimize agents’ exposure to situations that elicit physiological stress responses.
\nThis work provided evidence of common workplace risk factors for MSD and stress-related health outcomes: 1) cognitive demand among computer users, and 2) perceptions of psychosocial demand among call centre agents. These findings should encourage stakeholders in research and in the workplace to integrate prevention efforts for MSD and stress-related outcomes to more effectively and efficiently target primary prevention.

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