Nonlinear model of human ankle joint dynamics with electrical muscle stimulation

We examined the dynamic characteristics of the ankle joint during electrical stimulation of the soleus by applying perturbations to ankle position during stimulation. Using experimental data from a population of 10 spinal cord injured (SCI) and 10 neurologically intact (NI) subjects, we developed a nonlinear 5-element model to describe the relationship between joint position, velocity and applied torque. Model parameter values were obtained by modified steepest descent minimization [1] of the squared error between measured and modelled torque.