ABSTRACT

　In the present study, we investigated the effects of passive heat stress on corticospinal excitability. Motor-evoked potentials （MEPs） were recorded at the right first dorsal interosseous in ten healthy males following a single-pulse transcranial magnetic stimulation（TMS） of the left primary motor cortices（M1） . MEPs were measured in four sessions:（1） before passive heat stress（Pre） ,（2） when esophageal temperature was increased by 0.5?C（Warm） and（3） 1.2?C（Heat） , and（4） after passive heat stress （Recovery） . In addition, the resting motion threshold of TMS was measured in each session, and changes in the corticospinal excitability were examined using the four levels of stimulation intensity of 100, 110, 120, and 130%. The MEP amplitudes did not differ among sessions under low-intensity stimulation （100, and 110%） , but significantly decreased under high-intensity stimulation （120, and 130%） . This suggests that high-intensity muscle contraction, in which many motor neurons are activated, is more susceptible to stress caused by a hot environment than low-intensity muscle contraction. The MEP latencies became faster under heat stress, regardless of the stimulus intensity of TMS, indicating that the conduction velocity of the descending motor output was accelerated by increases in body temperature. These findings suggest that human corticospinal excitability is affected by passive heat stress.

DECENTE SPORTS SCIENCE Vol.42/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE