The effect of FES of the tibial nerve on physiological activation of leg muscles during gait.

The effects of surface functional electrical stimulation (FES) of the tibial nerve of healthy subjects were evaluated. The FES was applied at three different times during gait: early, mid and late stances. The purpose of this work is to understand the effect of unilateral stimulation on the bilateral activation patterns of leg muscles, because FES is used in practice to improve gait, while associated neuromuscular change is not often measured. The experimental protocol presented here will be transferred to stroke subjects, who could benefit from improved push-off during gait. Results show that FES of the tibial nerve changes the offset timing of the tibialis anterior muscle on the stimulated side and the on- and offset timings of the tibialis anterior muscle of the leg contralateral to stimulation. Additionally, activity levels of the semitendinosus ipsilateral and tibialis anterior contralateral to the stimulated leg significantly decreased, with respect to the non-stimulated condition. For the semitendinosus, this was a difference of 6-7microV, with p<0.05. For the tibialis anterior, this was a difference of 7-15microV, with a significance of p=0.00, respectively. This information is important for future applications of stimulation as it means that stimulation not only affects the stimulated muscle but also the physiological motor control by the CNS.

Interaction of artificial and physiological activation of the gastrocnemius during gait.

Objectives. The purpose of this research was to understand the effects of surface functional electrical stimulation (FES) of the tibial nerve on the activation of the gastrocnemius medialis of the stimulated side. Methods. FES was carried out on six healthy subjects, initiated at three different times during gait: early, mid, and late stance. Each stimulation burst consisted of 15 pulses, applied for 300 msec, at 50 Hz stimulation frequency. Mixed model statistical analysis was carried out on the median onset and offset times of the gastrocnemius medialis and the root mean square of the interpulse interval responses. Results. Results indicate that the electromyography response to FES is dependent on the time of application. The most prominent effects found in the intervals between the stimulation pulses (interpulse intervals) were found when stimulation was applied early in the stance phase. This study revealed that the only statistically significant effect on burst timing was a delay in offset timing due to mid-timed stimulation. Conclusions. We conclude that additional activation may have been compensated, at least in part, by blocking of the physiological activation during the stimulation burst.