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

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 (MDFΔ,HRΔ), slope (MDFslope,HRslope), and intercept (MDFintercept,HRintercept) of the linear regression. Results showed MDFΔdecreased 64% (p = 0.0020) with higher assistance compared to no exoskeleton; HRΔ decreased 40% (p < 0.0273) with lower assistance, MDFslope decreased up to 67% (p = 0.0039) and HRslope 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.