Using inertial measurement units to characterize musculoskeletal risk factors in a pilot study of a passive shoulder...

Exoskeletons have been considered for mitigating ergonomic risks of work-related musculoskeletal disorders (WMSDs), but they are not consistently utilized in initial deployments as workers in some facilities have not voluntarily used them. In this study, we investigated the impact of a passive shoulder exoskeleton on a drilling-fastening task with participants (n = 13) from a manufacturing training facility who have a little or no experience in using an exoskeleton. The direct measures of joint angles (shoulder and torso) and user perceptions of discomfort were analyzed. Inertial Measurement Units (IMUs) were used to estimate the shoulder and torso posture, with the orientations mapped to the Rapid Upper Limb Assessment (RULA) risk regions to support posture interpretation. Key actions (e.g., drilling and countersinking) were characterized within the work to understand how well a passive upper-body exoskeleton aligned with the task. Exoskeleton presence decreased the observed torso flexion for a subset of tasks, indicating decreased injury risk from the perspective of the torso, but limitations in selected postures. Exoskeleton presence did not have a large influence on the shoulder elevation, suggesting workers could perform the necessary tasks with the exoskeleton. However, the exoskeleton did not support a consistent positive influence on user perceptions. Importantly, participant postures show that the passive exoskeleton did not align with the dynamic shoulder movement for these tasks and created times when workers moved against the exoskeleton. These findings help explain potential barriers to exoskeleton acceptance reported in past studies. Factors such as limited postural adaptability, no linked decrease in perceived discomfort, and misalignment between exoskeleton support and the dynamic movements required by specific tasks may contribute to workers' reluctance to adopt exoskeletons. There are opportunities to extend shoulder exoskeletons to be more aligned with the nature of work, such as adding controllers to adjust the exoskeleton support to align with the user's actions.