Identification of passive knee joint and shank dynamics in paraplegics using quadriceps stimulation

The dynamics of the knee-joint-freely-swinging-lower-leg system of three sitting paraplegic patients was identified using a parameterized analytical model. Surface electrodes were used for stimulation. The output of the knee joint-lower leg system was the angular position, velocity and acceleration. A model structure was taken from the literature and its complexity minimized based on the experiments and offline identification. The resulting model structure facilitates possible recursive identification. Model parameters of the lower leg dynamics were estimated using a least-squares algorithm in combination with the Levenburg-Marquardt algorithm. The intersubject variability in parameter values for the knee joint damping and the gravitational component appeared to be small when normalized to the inertia of the lower leg. The identified model for the knee joint and shank dynamics accurately predicted passive lower leg movement and could be used to estimate the magnitude of active knee torque due to elicited quadriceps contraction.<
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