Functional electrical therapy for assisted treadmill training: use of passive dynamics

The purpose of this study was to assess the feasibility of a new technique for assisted treadmill training in incomplete spinal cord injury using surface functional electrical stimulation (FES). A limitation of surface FES is that hip flexors cannot be directly stimulated. By having the subject walk downhill on a treadmill while supported in an overhead harness, the passive dynamics of the legs can be exploited, and gravitational forces will facilitate hip flexion. A computer model for the swing phase of gait was developed. It was used to optimize the torque profiles for the knee and ankle, while eliminating the hip flexor moment. To determine the appropriate stimulation current that would be applied by the neuroprosthesis during downhill walking, the torque at the knee was measured as it moved through its range of motion for a variety of applied currents and a variety of speeds. These data allowed the torque versus time plots to be translated into current versus time, which would be applied by the neuroprosthesis to generate locomotion on the inclined treadmill. The implementation of this new technique will be the subject of future study.