Electrical stimulation of the sural nerve partially compensates effects of central fatigue.

Abstract

Depression of motor evoked potentials (MEPs) following transcranial magnetic stimulation (TMS) may be a sign of central motor fatigue. Abnormal fatigue can be observed in MS patients. We have examined whether post-exercise MEP depression can be compensated by application of sensory stimuli prior to TMS. We studied 15 healthy volunteers (aged 21 to 28 years) who were required to perform an exercise protocol of ankle dorsiflexion until force fell below 66% of maximum force. MEPs were recorded from the right tibialis anterior muscle. Prior to TMS, electrical stimuli were applied to the ipsilateral sural nerve with an individual interstimulus interval between 50 to 80 ms. MEP areas decreased after exercise. When a sensory stimulus was administered MEPs did not change. We conclude that the effects of central fatigue may be--at least partially compensated--by application of sensory stimuli. Sensory stimulation (e.g. by implantation of a neurostimulator) might be a useful therapy for abnormal central fatigue.