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

Area of Science:

• Biomechanics
• Human-robot interaction
• Occupational health

Background:

• Overhead tasks pose significant ergonomic challenges, leading to muscle fatigue and potential injury.
• Passive arm-support exoskeletons (ASE) are designed to mitigate these challenges by providing external torque.
• Understanding the optimal torque levels for ASE is crucial for effective ergonomic support.

Purpose of the Study:

• To investigate the impact of varying passive arm-support exoskeleton (ASE) torque levels on upper extremity muscle activity.
• To assess the influence of ASE torque on perceived exertion and fatigue during dynamic overhead (DO) tasks.
• To determine user preferences for ASE torque levels during simulated drilling tasks.

Main Methods:

• Twenty participants performed a 20-cycle dynamic overhead (DO) drilling task under four conditions: no ASE, and ASE torque at 50%, 75%, and 100% support.
• Surface electromyography (sEMG) was used to measure activity in six shoulder muscles bilaterally.
• Participants reported subjective ratings of perceived exertion (RPE) and shoulder fatigue, along with torque preferences.

Main Results:

• Increasing ASE torque significantly reduced shoulder agonist muscle activity by up to 47% during the arm ascent phase.
• Higher torque levels led to significant decreases in perceived exertion (RPE) and fatigue during the ascent phase.
• Conversely, elevated torque levels increased antagonist muscle activity during the arm descent phase.

Conclusions:

• ASE torque levels of 75% and 100% were rated most favorably by participants.
• A 75% torque setting is suggested as an effective support level, balancing reduced flexor activity during ascent with minimized antagonist activity during descent.
• ASEs show potential for reducing musculoskeletal load in overhead tasks, but careful calibration is needed to optimize performance across different movement phases.