Optimizing passive exoskeleton torque for dynamic overhead work: Phase-specific analysis on muscle activity and...

This study investigated how different levels of torque provided by a passive arm-support exoskeleton (ASE) influence upper extremity muscle activity, perceived exertion, and fatigue during arm ascent and descent phases of a Dynamic Overhead (DO) task.

The DO task involved 20 cycles of simulated drilling and was completed by 20 individuals by using a light-duty drill in four conditions: without supporting torque (no ASE) and with three increasing levels of ASE torque (i.e., 50, 75, and 100% of the torque required to support the arm in 90° of flexion). Surface electromyography was measured bilaterally over six shoulder muscles. Moreover, participants indicated torque preference, ratings of perceived exertion (RPE), and fatigue in the shoulder.

Increasing torque levels caused significant reductions in shoulder agonist muscle activity (up to 47%) and significant decreases in RPE and fatigue during the ascent phase. In contrast, higher levels of torque increased muscular activity for some antagonist muscles during the descent phase.

While torque levels of 75% and 100% received the most positive ratings, we suggest that 75% torque could be an effective supporting condition, by reducing shoulder muscle flexor activity during arm ascent and minimizing antagonist muscle activity during arm descent.