Motor cortex fatigue in sports measured by transcranial magnetic double stimulation

Purpose: Besides peripheral mechanisms, central fatigue is an important fac tor limiting the performance of exhausting exercise in sport. The mechanism s responsible are still in discussion. Using noninvasive transcranial magne tic stimulation (TMS) in a double-pulse technique, we sought to assess fati gue of the motor cortex after exhaustive anaerobic strain, Methods: 23 male subjects (22-52 yr) taking part in the study were requested to accomplish as many pull-ups as possible until exhaustion. The amount of physical lifti ng work was recorded. Before and immediately after the task, intracortical inhibition (ICI) and facilitation (ICF) were measured by a conditioned-test double-pulse TMS method for the right brachioradialis (BR) and abductor po llicis brevis muscle (APB). Results: After exercise, ICF was significantly reduced in the BR but not in the APE. ICI was not altered. Changes tended t o normalize within 8 min after the task. The amount of lifting work accompl ished showed significant correlation to the values of ICF reduction (r = 0. 73). Moreover, the baseline values of ICF before exercise were also signifi cantly correlated to the lifting work (r = 0.63). Conclusions: Because doub le-pulse TMS gives access to the motor cortex independently of spinal or pe ripheral mechanisms, reduced ICF reflects decreased excitability of interne uronal circuits within the motor cortex. We suggest that ICF measures motor cortex fatigue after exhausting strain specifically for the muscles perfor ming the task, gamma -Aminobutyric acid (GABA)-ergic neurotransmission is p ossibly involved in the mechanisms mediating central fatigue. Double-pulse TMS may be a useful tool in the control of training in sports as well as in the detection of pathological central fatigue in overreaching and in the p revention of overtraining.