# Evaluation of fatigue progression during overhead tasks and the effects of exoskeleton assistance

## TL;DR

This study shows that using exoskeletons during overhead tasks significantly reduces muscle and cardiovascular fatigue in workers.

## Contribution

The study introduces a novel evaluation of how different levels of exoskeleton assistance affect shoulder fatigue and physiological strain.

## Key findings

- Higher exoskeleton assistance reduced muscle fatigue by up to 67% compared to no assistance.
- Heart rate variability metrics indicated reduced physiological strain with medium and high assistance levels.
- Exoskeletons showed significant benefits in reducing fatigue during overhead occupational tasks.

## Abstract

Upper-limb occupational exoskeletons reduce injuries during overhead work. Previous studies focused on muscle activation with and without exoskeletons, but their impact on shoulder fatigue remains unclear. Additionally, no studies have explored how exoskeleton support levels affect fatigue. This study investigates the effects of assistive profiles on muscular and cardiovascular fatigue. Electromyographic (EMG) and electrocardiographic signals were collected to compute EMG median frequency (MDF), heart rate (HR), and heart rate variability (HRV). Fatigue was assessed using three MDF and HR metrics: relative change (

,

), slope (

,

), and intercept (

,

) of the linear regression. Results showed

decreased 64% (p = 0.0020) with higher assistance compared to no exoskeleton;

decreased 40% (p < 0.0273) with lower assistance,

decreased up to 67% (p = 0.0039) and

by 43% (p < 0.0098) with higher and medium assistance. HRV metrics included root mean square of successive differences (RMSSD) and low-frequency to high-frequency power ratio (LF/HF). RMSSD indicated parasympathetic dominance, while rising LF/HF ratio suggested physiological strain. Findings support occupational exoskeletons as ergonomic tools for reducing fatigue.