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Phase-Specific Analysis of Arm–Leg Load Sharing in Exoskeleton-Assisted Gait Using Biomechanical Indices

Authors :

Milad Hosseini¹ Negin Nasirian² Saeed Behzadipour³

1- دانشگاه صنعتی شریف، تهران، ایران 2- دانشگاه صنعتی شریف، تهران، ایران 3- دانشگاه صنعتی شریف، تهران، ایران

Keywords :

Exoskeleton-assisted gait،Arm–leg load sharing،Upper-limb support،Load-sharing indices،Upper-limb loading

Abstract :

This study investigated the redistribution of support between the arms and legs during exoskeleton-assisted gait with forearm crutches, using the Exoped lower-limb exoskeleton. A full-body skeletal model was developed by synchronized motion capture, ground force reaction measurement, and instrumented crutch data to compute phase-specific indices of load sharing. The modeling framework had been previously validated against experimental ground reaction forces, ensuring reliable estimation of joint kinetics and external loads. Results showed that the arms carried approximately 10% of body weight on average (ULSF ≈0.10), with transient peaks of ~0.18 during mid stance. The Vertical Impulse Share (VIS) indicated increased cumulative arm contributions in pre-swing and initial swing (~0.12–0.13), while the Arm Asymmetry Index (AAI) reached values near 1 during loading response (the initial double support phase immediately after heel strike, when the limb begins accepting body weight) and terminal swing, reflecting reliance on a single arm. Peak Support Timing (PST) consistently occurred at ~28–30% of the gait cycle, corresponding to late mid stance. These findings demonstrate that although arm forces remain modest in absolute terms, their phase-dependent nature makes them critical for stability and may predispose the upper limbs to repetitive high-load exposure. The proposed framework offers practical insights for safer exoskeleton design and rehabilitation strategies aimed at reducing upper-limb overuse.