Post-exercise depression of motor evoked potentials as a function of exercise duration.
Post-exercise facilitation and post-exercise depression are phenomena described in motor evoked potentials (MEPs) elicited to transcranial magnetic stimulation. Brief, non-fatiguing muscle activation produces post-exercise facilitation, and prolonged fatiguing muscle activation produces post-exercise depression. We studied 12 normal subjects to determine whether post-exercise depression occurs before fatigue is reached. We recorded MEPs from the resting extensor carpi radialis muscle after increasing the duration of isometric wrist extension, at 50% of maximum voluntary contraction, until the muscle fatigued. Fatigue was defined as the inability to maintain that force. The mean exercise duration before the muscle fatigued was 130 s, and post-exercise depression occurred only beyond 90 s of exercise. We conclude that post-exercise depression is detectable only after prolonged muscle activation.
Samii
A
A
Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-1428, USA.
Wassermann
E M
EM
Hallett
M
M
D000328:Adult; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D013997:Time Factors