Characterization of postexercise facilitation and depression of motor evoked potentials to transcranial magnetic stimulation

Abstract

We studied the effects of exercise on motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES). Subjects performed 30-second periods of isometric exercise of the extensor carpi radialis until fatigue, which was defined as the inability to maintain half maximum force. The amplitude of MEPs to TMS recorded from the resting muscle after each exercise period was on average more than twice the pre-exercise value (postexercise MEP facilitation). After fatigue occurred, the MEP amplitudes were approximately 60% of the pre-exercise value (postexercise MEP depression). There was a gradual recovery of the depressed MEPs to pre-exercise values over several minutes of rest. Postexercise MEP facilitation was constant when exercise intensity ranged from 10 to 50% of maximum voluntary contraction and it decayed to baseline over several minutes after the end of exercise. There was no postexercise MEP facilitation to TES. We hypothesize that both postexercise MEP facilitation and MEP depression are due to intracortical mechanisms.

Delayed facilitation of motor cortical excitability following repetitive finger movements

“…Such differences may explain the absence of post-exercise depression of MEPs in our present study. However, other investigators who have examined motor cortical excitability following`nonfatiguing' exercise (Brasil-Neto et al, 1993Samii et al, 1996Samii et al, , 1997 have identi®ed a transient period of facilitation immediately after completing the exercise. This facilitation ended after 4 min of rest, well short of the 15 min de®ned in the present study for the appearance of delayed facilitation of MEPs.…”

“…The subjects were instructed to make this contraction with 20% of maximal force (since it has been demonstrated that from 10 to 50% of maximal contraction post-exercise facilitation does not change, Samii et al, 1996) and to imagine the¯exion of the index ®nger before initiating the movement. The level of the ongoing EMG activity during contraction was then monitored both by acoustic feedback and by asking the subjects to try and keep within a band displayed visually on a video screen.…”

“…Motor cortex excitability is affected immediately before movement onset (Starr et al, 1988;Reynolds and Ashby, 1999), continues during the course of movement (Ljubisavljevic et al, 1996;Sacco et al, 1997;Aranyi et al, 1998;Tinazzi and Zanette, 1998), and may even persist following movement (Brasil-Neto et al, 1993McKay et al, 1995;Zanette et al, 1995;Bonato et al, 1996;Liepert et al, 1996;Samii et al, 1996Samii et al, , 1997. If movements are continued until`exhaustion' (de®ned by an inability to maintain at least 50% of maximal force), MEPs are reduced for up to 15 min, a phenomenon termed post-exercise depression (Brasil-Neto et al, 1993McKay et al, 1995;Liepert et al, 1996;Samii et al, 1996Samii et al, , 1997.…”

“…The duration of post-exercise depression is extended in patients with central nervous system lesions (Liepert et al, 1996). If the exercise is non-exhausting, an early transient facilitation of MEPs can occur for up to 4 min after completing the exercise (Brasil-Neto et al, 1993Samii et al, 1996Samii et al, , 1997. The neural mechanisms underlying both facilitation and depression of MEPs following exercise are believed to reside within the motor cortex.…”

“…The neural mechanisms underlying both facilitation and depression of MEPs following exercise are believed to reside within the motor cortex. These changes of motor cortical excitability have been considered relevant for the experience of`fatigue' or well-being accompanying motor activity (Brasil-Neto et al, 1993McKay et al, 1995;Liepert et al, 1996;Samii et al, 1996).…”