Force and torque vectors at the foot generated by surface electrical stimulation of leg muscles

MotionMakerTM is a robotic system that employs functional electrical stimulation (FES) of leg muscles to allow subjects with complete or partial paralysis of the legs to perform exercises. To achieve the greatest benefit from exercise muscles should do work. The maximum work is done if all of the force exerted by the leg acts along the direction of movement of the pedal. Therefore, it would be metabolically most efficient to minimize forces and torques on the pedal that do no work. Furthermore, FES should not destabilize the joints. The first step in achieving these goals is to characterize the mechanical output of each muscle as a function of the stimulation level and joint angles; in particular, to measure the force and torque vectors at the pedal during FES of major muscles of the ankle, knee and hip. Here we report the results of a preliminary study with these objectives, conducted with neurologically normal subjects.