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Inverse Dynamics Analysis of the Crutch-Assisted Gait with a Lower-Limb Robotic Exoskeleton

Authors :

Negin Nasirian¹ Milad Hosseini² Reza Norouzzadeh³ Saeed Behzadipour⁴

1- دانشگاه صنعتی شریف، تهران، ایران 2- دانشگاه صنعتی شریف، تهران، ایران 3- دانشگاه صنعتی شریف، تهران، ایران 4- دانشگاه صنعتی شریف، تهران، ایران

Keywords :

Inverse dynamics،Crutch-assisted gait،Upper limb biomechanics،Exoskeleton modeling،Joint torque estimation

Abstract :

This study presents a comprehensive inverse dynamics framework for evaluating upper-limb joint loading during crutch-assisted gait with Exoped, a lower-limb robotic exoskeleton. To address the absence of integrated biomechanical models capturing the combined interactions of the user, exoskeleton, and assistive devices, a full-body skeletal model was developed. Motion capture and force plate data were collected from a paraplegic user walking with instrumented forearm crutches, each equipped with a single-axis load cell and reflective markers. The crutch system was validated against force plate measurements, showing high accuracy in vertical ground reaction force (GRF) estimation with a maximum RMS error of 7.01% for axial forces, with shear forces remaining below 10% throughout the gait cycle. The skeletal model was further validated by comparing model output and recorded foot GRFs, demonstrating close agreement in both magnitude and timing of loading patterns with average relative errors of 14.34% for the left foot and 15.86% for the right foot. Inverse dynamics analysis revealed physiologically plausible torques, with peak values of approximately –12 Nm at the elbow and 20 Nm at the shoulder, primarily in the pitch (flexion/extension) and roll (abduction/adduction) axes. These magnitudes align with previously reported ranges for assisted gait and remain within physiological capacity, supporting the model validity. The results identify critical phases of the gait cycle-particularly early and mid-stance-where torque demands peak, providing actionable insights for clinical gait training and exoskeleton control strategies aimed at minimizing upper-limb exhaustion and pathological risks