Phenytoin does not influence postexercise facilitation of motor evoked potentials.

Postexercise facilitation of motor evoked potentials (MEPs) elicited to transcranial magnetic stimulation occurs after brief, nonfatiguing muscle activation. This phenomenon may be related to post-tetanic potentiation or long-term potentiation (LTP) observed in animal studies. Phenytoin reduces post-tetanic potentiation but does not block LTP. We studied the effects of phenytoin on postexercise MEP facilitation and its decay over time. Phenytoin did not result in either significant change in postexercise MEP facilitation nor significant change in the decay of facilitation. We conclude that postexercise MEP facilitation is unlikely to be secondary to post-tetanic potentiation.