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Task-Dependent Effectiveness of a Quasi-Direct-Drive Upper-Limb Exoskeleton: Shoulder Muscle Offloading Versus
Yongxuan Hong1,2, Jiying Du3, Sida Du2
1College of Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
Bioengineering (Basel, Switzerland)
|May 4, 2026
Summary
This study found that a quasi-direct-drive exoskeleton can reduce shoulder muscle activity during static overhead tasks. However, it increases metabolic cost and reduces movement smoothness in both static and dynamic assembly work.
Area of Science:
- Occupational health
- Biomechanics
- Robotics
Background:
- Work-related shoulder disorders are a significant challenge in overhead assembly tasks.
- Active upper-limb exoskeletons are being explored to mitigate these issues.
Purpose of the Study:
- To evaluate the effectiveness of a quasi-direct-drive (QDD) active upper-limb exoskeleton during simulated overhead work.
- To assess the impact of the QDD exoskeleton on metabolic cost, muscle activity, and kinematics.
Main Methods:
- Seven healthy males performed simulated static holding (3 kg) and dynamic screwing tasks with and without the QDD exoskeleton.
- Simultaneous metabolic, electromyographic (EMG), and kinematic data were collected.
Main Results:
- The exoskeleton significantly reduced shoulder muscle activity (Upper Trapezius: -68.2%, Anterior Deltoid: -43.6%) and improved postural stability during static holding.
- Metabolic cost increased significantly in both static (+57.2%) and dynamic (+30.6%) conditions.
- Movement smoothness decreased with exoskeleton use.
Conclusions:
- QDD exoskeletons show task-dependent effectiveness, beneficial for prolonged static overhead holding.
- The device's mass incurs whole-body energy penalties, limiting its current utility for dynamic assembly.
- Improvements in mass reduction and control refinement are needed for broader application in dynamic tasks.
