Changes in corticomotor excitability after fatiguing muscle contractions

To investigate whether the type and duration of activity influences cortico motor excitability following fatiguing exercise, we compared motor evoked p otential (MEP) responses of the biceps brachii to transcranial magnetic sti mulation (TMS) during recovery from two different exercise regimens. Respon ses were recorded in both the resting state and during a weak contraction. Ten subjects performed a 60-s maximal voluntary contraction (MVC) and, on a subsequent occasion, a sustained 20% MVC to the point of exhaustion. Resti ng MEP amplitude declined following maximal and submaximal protocols, reach ing 34% and 31% of pre-exercise means, respectively (P < 0.001 for both). I n contrast, mean facilitated MEP amplitude showed a smaller and more transi ent decrement following the sustained submaximal effort (64%; P < 0.05), bu t not the 60-s MVC. Abolition of the postexercise depression in resting MEP amplitude by a weak tonic contraction indicates that decreases in excitabi lity at the spinal level contribute to the reduced corticomotor excitabilit y observed after fatiguing exercise. (C) 2000 John Wiley & Sons, Inc.