The purpose of this study was to clarify the effects of muscle damage induced by eccentric exercise on motor learning and its neurophysiological mechanism. In seven subjects, maximal voluntary contraction (MVC) and a motor learning task using pincer grip were assessed before and after eccentric exercise (ECC) of the first dorsal interosseous muscle (FDI). For the motor learning task, subjects were instructed to make a cursor follow a series of target line on an oscilloscope by precisely controlling the voluntary force. During 10% MVC, transcranial magnetic stimulations were applied at a wide range of intensities (0.8-2.0×active threshold) to obtain a recruitment curve of the motor evoked potentials (MEP) in FDI. Following ECC, MVC was decreased to 75% of the pre-exercise value without any muscle soreness. During the motor learning task, the absolute error between target line and actual voluntary force and background electromyographic (EMG) activities in FDI were significantly higher after ECC than before. Maximum value of MEP and slope, which were assessed by Bolzmann sigmoid function, were significantly increased after ECC. The calculated threshold of MEP did not change before and after ECC. These results suggest that muscle damage induced by ECC increased the corticospinal excitability which can be seen at high stimulator output levels. This could be attributed to increased EMG activities during voluntary contractions which disrupted motor learning ability after ECC.

DESCENTE SPORTS SCIENCE Vol.31/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE