Time-varying impedance of the human ankle in the sagittal and frontal planes during straight walk and turning steps

Abstract

This paper describes the methods and experiment protocols for estimation of the human ankle impedance during turning and straight line walking. The ankle impedance of two human subjects during the stance phase of walking in both dorsiflexion plantarflexion (DP) and inversion eversion (IE) were estimated. The impedance was estimated about 8 axes of rotations of the human ankle combining different amounts of DP and IE rotations, and differentiating among positive and negative rotations at 5 instants of the stance length (SL). Specifically, the impedance was estimated at 10%, 30%, 50%, 70% and 90% of the SL. The ankle impedance showed great variability across time, and across the axes of rotation, with consistent larger stiffness and damping in DP than IE. When comparing straight walking and turning, the main differences were in damping at 50%, 70%, and 90% of the SL with an increase in damping at all axes of rotation during turning.

Towards a Generalized Model of Multivariable Ankle Impedance During Standing Based on the Lower Extremity Muscle EMG

“…In addition, to account for sensor biases and time-varying impedance, different values of , , and were estimated in small sample windows. Therefore, the vector of unknown parameters is ≡ [ , , , [1] , [2] , … , [10] ]…”

“…In parallel to these EMG studies, previous work determined the ankle mechanical impedance in the dorsi-plantarflexion (DP) and inversion-eversion (IE) directions under loaded and nonloaded scenarios [10][11][12][13][14]. The mechanical impedance of the ankle is defined as the ankle's response to an input motion and can be useful in the control design of active ankle-foot prostheses [12].…”

Estimation of Multi-Directional Ankle Impedance as a Function of Lower Extremity Muscle Activation

“…estimated the time-varying impedance in both the sagittal and frontal planes during the stance phase of straight walk and a turning maneuver [72], [80], [81], [83]. Similar changes in the ankle impedance were found throughout the gait cycle in both DP and IE directions.…”

Estimation and Prediction of the Human Gait Dynamics for the Control of an Ankle-Foot Prosthesis

“…Studies of the ankle impedance in the sagittal plane extended to functional activities, such as straight walking [22] and turning [23]. The early stance phase was studied by Rouse et al using a vibrating platform, called Perturberator, that applies torque perturbations to the ankle from the ground.…”

“…The anisotropic ankle impedance during walking was estimated with a two Degrees of Freedom (DOF) vibrating platform for the first time [23].…”