Functional electrical stimulation of the triceps surae during gait

Every year stroke affects approximately 15 million people worldwide. It is the leading cause of disability in the western world. Gait relearning has high priority for stroke survivors. One of the most commonly treated effects of stroke gait is drop-foot (the inability to raise the toes during the swing). However, push-off is also severely diminished during stroke gait. Electromyography (EMG) results show that all muscles of the affected (paretic) side have decreased physiological activation. Reduction and premature activation of the triceps surae leads to poor push-off. Our goal was to stimulate the triceps surae using functional electrical stimulation to increase the activation of this muscle group. EMG of the stimulated muscle and other leg muscles of legs was measured, simultaneously. The aim was to evaluate how stimulation influences the activation patterns of the stimulated and non-stimulated muscles. Tests were first carried out on healthy subjects. Surface stimulation was applied to the tibial nerve, which activates the triceps surae. Stimulation timing was controlled using a uniaxial gyroscope on the lateral shank. Stimulation bursts of 300ms duration, 50Hz was applied at each step. EMG of the medial gastrocnemius, tibialis anterior, semitendinosus and rectus femoris of both legs was measured at 2048Hz. Responses between each stimulation pulse were analysed, for motor and reflexive signals. Additionally, the amplitude changes and the on and offset times of EMG bursts were analysed. Results: While FES influenced the activation patterns of healthy and stroke subjects on the stimulated and non-stimulated sides, the effects were considerably varied. Motor and or reflexive responses in the stimulated gastrocnemius were observed in healthy and stroke. In healthy subjects, responses were also observed in the tibilais anterior of the stimulated side. Less clear changes were seen in the physiological on and offset timings. Future studies should involve a larger test group with more strictly defined patient criteria. Using percutaneous or implantable stimulation electrodes, stimulation levels can be reduced; by-passing cutaneous sensation and preventing recruitment instability since the electrode would be in direct contact with the nerve. Finally, subjects should undergo a training program to facilitate gait while using FES.