Estimating Lower Limb Impedance during Gait Using Treadmill-Induced Perturbations*

Human walking involves simultaneous control of multiple joints, such as the ankle and knee, while regulating stiffness and viscosity, which collectively form joint impedance. Understanding joint impedance, crucial for enhancing energy efficiency and stability, can inform the design of biomimetic support technologies and control strategies for assisting robots. Previous studies focused on perturbing single joints to estimate impedance, but determining impedance during walking requires the simultaneous perturbation of multiple joints. This study estimated knee and ankle joint impedance through perturbations induced by a treadmill, considering the interlocking of multiple joints during walking. The results of estimation of the stiffness of the knee and ankle using this proposed method appropriately reflect variations in muscle activity status.