Simultaneous Perturbation of Knee and Ankle Joints during Stance Phase of Walking: Towards Biological Joint Impedance Estimation

Characterization of lower limb joint impedance during locomotion is crucial for advancing our understanding of walking biomechanics, while also guiding the development of assistive technologies and rehabilitation strategies. Identification of impedance parameters is dependent on perturbation strategies which elicit measurable responses at the joint of interest. However current perturbation methodologies applied during locomotion either work in the swing phase or employ exoskeleton based setups which can add complexity and weight to the leg. This study introduces and evaluates a perturbation methodology using a custom-designed pusher system to elicit multi-joint-level torque and angular responses during the stance phase of gait for different conditions. Controlled perturbations applied behind the tibia revealed measurable dynamic response at the knee and ankle joint, while preserving the gait cycle's overall pattern. Torque-angle and torque-velocity graphs reveal insights into energy and power changes between perturbed and unperturbed gait cycles. The method can be adapted to various walking speeds, perturbation intensities, and durations, providing the first step for future estimation of joint impedance during locomotion.