Impact of a passive upper-body exoskeleton on muscular activity and precision in overhead single and dual tasks: an explorative randomized crossover study

Gräf, Julia; Grospretre, Sidney; Argubi-Wollesen, Andreas; Wollesen, Bettina · 2024 · Crossref

DOI: 10.3389/fneur.2024.1405473

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Summary

This exploratory randomized crossover study investigates the impact of a passive upper-body exoskeleton on muscular activity, fine motor control, and cognitive performance during overhead industrial tasks. The research addresses the prevalence of work-related musculoskeletal disorders (WMSDs) caused by overhead work, which often leads to fatigue and pain. While exoskeletons are known to reduce physical strain, their influence on fine motor control (specifically the speed-accuracy trade-off) and cognitive-motor interference remains underexplored. The study aimed to determine how exoskeleton use affects these factors in both single-task (ST) and dual-task (DT) scenarios, both before and after inducing muscle fatigue. The study involved 10 healthy participants (five male, five female) who performed an overhead nailing task using a nail gun. The task was designed based on Fitts’ law, requiring participants to hit targets of varying difficulty indexes to assess the speed-accuracy trade-off. Participants performed the task under four conditions: with and without the exoskeleton, and before and after a fatiguing exercise protocol involving shoulder and leg weights. In the dual-task condition, participants simultaneously counted auditory beats from a metronome to assess cognitive load. Surface electromyography (sEMG) was used to measure muscle activity in the M. deltoideus, M. trapezius, and M. erector spinae. Statistical analyses included repeated measures ANOVA to compare muscle activation, task completion times, and error rates across conditions. The results indicated that the exoskeleton significantly reduced muscle activity in the M. deltoideus and M. trapezius, particularly when comparing single-task to dual-task conditions, suggesting a reduction in physical effort. However, the exoskeleton did not significantly affect the speed-accuracy trade-off in single-task conditions, regardless of fatigue status. In dual-task conditions, the exoskeleton influenced performance differently depending on the fatigue state. Generally, dual tasks resulted in longer completion times than single tasks. Notably, cognitive performance, measured by errors in the auditory counting task, was significantly better (fewer errors) when using the exoskeleton after fatigue compared to all other conditions. This suggests that the exoskeleton may alleviate cognitive-motor interference under fatigued conditions. The study concludes that passive upper-body exoskeletons offer supportive benefits for industrial overhead tasks by reducing muscular effort in key shoulder muscles. While they do not inherently improve motor precision in non-fatigued states, they may help maintain cognitive performance and manage the speed-accuracy trade-off more effectively when users are fatigued. These findings highlight the potential of exoskeletons to mitigate both physical strain and cognitive-motor interference, supporting their integration into workplace safety strategies to reduce WMSDs and maintain productivity during demanding tasks.

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• physical impairment