Human-in-the-Loop Optimization of Hip Exoskeleton Assistance During Stair Climbing

• Published in: IEEE transactions on biomedical engineering Vol. 72; no. 7; pp. 2147 - 2156
• Main Authors: Park, Dongho, An, Jimin, Lee, Dawit, Kang, Inseung, Young, Aaron J.
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.07.2025; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adult; Bayesian optimization; Biomechanical Phenomena - physiology; Climbing; Convergence; Costs; Exoskeleton; Exoskeleton Device; Exoskeletons; Female; Flexible printed circuits; Hip; Hip - physiology; hip exoskeleton; human-in-the-loop optimization; Humans; Legged locomotion; Male; metabolic cost; Metabolic rate; Metabolism; Optimal control; Optimization; Parameter identification; Pelvis; personalized assistance; stair climbing; Stair Climbing - physiology; Stairs; Statistical analysis; Timing; Torque; Young Adult
• ISSN: 0018-9294; 1558-2531; 1558-2531
• DOI: 10.1109/TBME.2025.3536516

Objective: This study applies human-in-the-loop optimization to identify optimal hip exoskeleton assistance patterns for stair climbing. Methods: Ten participants underwent optimization to individualize hip flexion and extension assistance, followed by a validation comparing optimized assistance (OPT) to biological hip moment-based assistance (BIO), no assistance (No-Assist), and no exoskeleton (No-Exo) conditions. Results: OPT reduced metabolic cost by 4.5% compared to No-Exo, 11.44% compared to No-Assist, and 5.02% compared to BIO, demonstrating the effectiveness of the optimization approach. Statistical analysis revealed distinct characteristics in optimal assistance timing and magnitude that deviated systematically from biological hip moment patterns. Compared to BIO, OPT exhibited later peak flexion timing (76.4 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 3.7% vs 65.0%), shorter flexion duration (29.2 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 3.6% vs 40.0%), later peak extension timing (26.7 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 3.8% vs 20.0% of gait cycle), and higher peak flexion magnitude (11.1 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 1.5 Nm vs 10.0 Nm). While individual optimal assistance profiles varied across participants, comparison between individually optimized parameters and the best subject-independent parameters identified through post-hoc analysis showed consistency. On average, metabolic rate convergence was achieved after 18 iterations, while most exoskeleton control parameters did not reach our convergence criteria within 20 iterations. Conclusion: These findings demonstrate that human-in-the-loop optimization can effectively identify task-specific assistance patterns for stair climbing, while the consistency between individual and subject-independent parameters suggests the potential for developing generalized assistance strategies. The systematic differences between optimized and biological moment-based assistance underscore the fundamental distinctions between biological torque-based control and optimal control for exoskeleton assistance.