Post-exercise facilitation and depression of M wave and motor evoked potentials in healthy subjects

Objectives: To characterize so-called central fatigue, the effect of various levels of exercise on central and peripheral motor potentials were compared. Methods: Thirteen healthy subjects performed 4 levels of exercise following isometric dorsiflexion of the foot. Post-exercise recordings from the anterior tibial muscle of motor evoked potentials (MEP) evoked by transcranial magnetic stimulation (TMS) and M wave evoked by electrical stimulation of the peroneal nerve were performed. Results: After 5 s the post-exercise MEP amplitude increased. The increase was related to the degree of work performed. Subsequently, there was a gradually decrease of amplitude reaching statistical significance after 15 min. The area of the M wave increased significantly after 10 s and returned to baseline after 2–3 min. Conclusions: Facilitation and depression of MEP after fatiguing exercise is at least partly a peripheral phenomenon dependent on the level of exercise performed.