Gait-Symmetry-Based Human-in-the-Loop Optimization for Unilateral Transtibial Amputees With Robotic Prostheses

Gait asymmetry due to unilateral limb loss increases the risk of injury or progressive joint degeneration. The development of wearable robotic devices paves the way for improving the gait symmetry of unilateral amputees. However, the state-of-the-art studies on human-in-the-loop optimization strategies with an optimization task of reducing the metabolic cost face several challenges, e.g., an excessively long optimization period and the infeasibility of optimization for unilateral amputees who have a deficit of gait symmetry. Herein, we propose a gait-symmetry-based human-in-the-loop optimization method to reduce the risk of injury or progressive joint degeneration for unilateral transtibial amputees. Experimental results (N = 3) indicated that convergence took the range of 388s to 821s. After optimization, compared with using passive prostheses, the gait-symmetry indicator of subjects wearing the robotic prostheses was improved by the range of 6.0% to 52.0%, and the net metabolic energy consumption was reduced by the range of 3.0% to 13.4%. Additionally, the rationality of gait indicators based on kinematics rather than kinetics was assessed. The results indicated that the human-in-the-loop strategy can improve the gait symmetry by reducing the metabolic cost and thus reduce the risk of joint injury for unilateral amputees.