Systematic Evaluation of Hip Exoskeleton Assistance Parameters for Enhancing Gait Stability During Ground Slip...

Falls are the leading cause of injuryrelated hospitalization and mortality among older adults. Consequently, mitigating age-related declines in gait stability and reducing fall risk during walking are critical goals for assistive devices. Lower-limb exoskeletons have the potential to support users in maintaining walking stability. However, most exoskeleton controllers are optimized to reduce the energetic cost of walking rather than to improve stability. Existing stability-focused controllers use a fixed, heuristic assistance profile, limiting understanding of how to optimize and personalize assistance strategies.

To address this gap, we systematically modulated the magnitude and duration of torque provided by a bilateral hip exoskeleton during slip perturbations in eight healthy adults, quantifying stability using whole-body angular momentum (WBAM).

WBAM responses were governed by a significant interaction between assistance magnitude and duration, with duration determining whether exoskeleton assistance was stabilizing or destabilizing relative to not wearing the exoskeleton device. Compared to an existing energy-optimized controller, experimentally identified stability-optimal parameters reduced WBAM range by 27.4% on average. Notably, substantial inter-subject variability was observed in the parameter combinations that minimized WBAM during perturbations.

We found that optimizing exoskeleton assistance for energetic outcomes alone is insufficient for improving reactive stability during gait perturbations. Stability-focused exoskeleton control should prioritize temporal assistance parameters and include user-specific personalization.

This study represents an important step toward personalized, stability-focused exoskeleton control, characterizing the effects of assistance on reactive stability in young adults and motivating future investigations in aging populations.