Evaluating model-estimated shoulder muscle activity during overhead work with varied task demands and exoskeleton use

Passive arm-support exoskeletons (ASEs) can reduce shoulder stress during overhead work. However, the effects of ASEs are task- and device-specific, and current human-subjects evaluation protocols are time-consuming and resource-intensive. Musculoskeletal modeling could simplify ASE evaluation, such as by estimating muscle activation in place of measuring electromyographic (EMG) data. We assessed shoulder muscle activities estimated using a commercial biomechanical modeling system during dynamic overhead push tasks at different heights and force directions, performed with/without an ASE. We compared model estimates to normalized EMG using pattern similarity and magnitude difference metrics. Overall, model performance was good at lower task heights and declined at higher heights; ASE use further reduced performance, especially at higher task heights. These findings suggest that model-estimated shoulder muscle activity may be reasonably accurate under specific task conditions, but that improvements to musculoskeletal models are needed to make these models suitable for a broader range of tasks.