Dexterity is not affected by fatigue-induced depression of human motor cortex excitability.

Following a fatiguing muscle contraction, motor evoked potentials (MEPs) evoked by transcranial magnetic brain stimulation remain depressed for many minutes, reflecting a reduction in the excitability of the corticospinal projection. No functional significance has been linked to this observation. We postulated that dexterity would be affected when MEPs are depressed. MEPs were recorded from the first dorsal interosseous muscle of 11 healthy subjects in resting muscles before and after a fatiguing maximum voluntary contraction. This induced significant MEP depression in all subjects. No change in dexterity was seen when MEPs were depressed or at any time point throughout the experiment. We conclude that fatigue-induced MEP depression is not associated with a decline in dexterity.