Changes in corticomotor excitation and inhibition during prolonged submaximal muscle contractions.
Changes in motor evoked potential (MEP) amplitude, post-MEP silent period duration, and interpolated twitch torque were measured using transcranial magnetic (TMS) and electrical (TES) stimulation during a 20% maximum voluntary contraction of the elbow flexors sustained to exhaustion. TMS- and TES-induced MEP amplitude increased progressively over the contraction period up until the point of exhaustion. The TMS-induced silent period was prolonged only during the second half of the contraction period, the time course being different from that of the MEP responses, whereas the TES-induced silent period did not change. The findings indicate that corticomotor excitability increases during a sustained submaximal voluntary contraction and that, as fatigue develops, there is a progressive buildup of intracortical inhibition. This may represent a mechanism whereby corticomotor output is maintained at an appropriate level to preserve optimal motor unit firing frequencies during a fatiguing contraction.
Sacco
P
P
Department of Human Movement, Edith Cowan University, Australia.
Thickbroom
G W
GW
Thompson
M L
ML
Mastaglia
F L
FL
D000328:Adult; D001132:Arm; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009433:Neural Inhibition; D010807:Physical Endurance; D010812:Physical Stimulation; D013997:Time Factors; D019415:Torque