Interaction of voluntary activity and functional electrical stimulation in the upper extremity as a method for short-term alteration of corticospinal excitability and force control

Repetitive movement training (RMT) is a well-established method for rehabilitating functional movement. However, many stroke survivors are not able to participate in RMT for the necessary duration to produce results due to rapid muscle fatigue or inability to perform the desired movement at all. Often, functional electrical stimulation (FES) is applied passively, as a rehabilitative therapy, to stroke subjects who are unable to participate in RMT. The effects of voluntary contraction and FES are not well understood for the upper extremity following a stroke. This experiment was designed to elucidate the mechanisms of functional and neurophysiological changes associated with combining FES and voluntary movement vs. the effects of each intervention alone in healthy subjects, with a within-subjects single day design. Eleven right-handed, neurologically healthy subjects participated in a series of three experimental sessions. The testing conditions were voluntary movement alone (VOL), functional electrical stimulation alone (FES), and voluntary movement supplemented by functional electrical stimulation (VOL+FES). Subjects were evaluated for changes in maximum force and force control before and after each session. Corticospinal excitability was evaluated using transcranial magnetic stimulation (TMS) at five time points throughout each session. There were no significant changes pre-post or between conditions for the maximum force or the force control. FES alone was found to immediately and significantly reduce corticospinal excitability; that reduction continued through the post measurement. Both VOL and VOL+FES increased corticospinal excitability pre-post, although not significantly. At the post measurement, both VOL and VOL+FES were significantly larger than FES, although not different from each other. These results indicate that adding voluntary movement to functional electrical stimulation may serve to increase corticospinal excitability while allowing the subject to participate in meaningful rehabilitative movements