A Stochastic Model of Knee Angle in Response to Electrical Stimulation of the Quadriceps and Hamstrings Muscles

A novel stochastic model of knee angle in response to stimulation of the quadriceps and hamstrings muscle groups is presented. This model includes uncertainty due to fatigue and day-to-day changes in the stimulated muscles. The model consists of a normally distributed random variable whose mean and standard deviation vary with time and is characterized using data from a complete spinal cord injuries subject. The experimental data show a significant difference between the left and right legs under certain conditions, and suggest that fatigue-related and day-to-day variation may also be important. The purpose of this model is to generate more realistic electrically stimulated knee movements. This stochastic modeling technique could be incorporated into a comprehensive model of a joint actuated with electrical stimulation, and has great potential as a tool for analyzing closed-loop performance of electrically stimulated systems.