Abstract des Autors

This study aimed to clarify the effects of changing to a short bat grip position from the long bat grip position on baseball bat swing timing, peak ground reaction force with the front leg, and activation of the upper and lower limb muscles. Nine male college baseball players participated in this study. By using a batting simulator, the coincident timing task was to swing the bat coincidentally with the arrival timing of a moving target by using the long or short bat grip position. The batter performed 10 sets of four swings for a total of 40 swings for the coincident timing task. During the four swings, the batter swung the bat by using the long grip position in the first, second, and fourth swings. Only in the third swing did the batter use the short grip position. The ground reaction force with the front leg was measured, and electromyograms of the upper and lower limb muscles were obtained during the coincident timing task. Our results indicated no significant differences in absolute and variable timing errors between the long and short bat grip positions. In contrast, the constant timing error was significantly increased with the short bat grip position. Moreover, the time to peak ground reaction force and time to peak muscle activation of both the upper and lower limb muscles were significantly delayed when the short bat grip position was employed. Significant positive relationships were observed between the constant timing error and time to peak ground reaction force, which showed differences between the second and third swings. No significant difference in swing time was observed between the long and short bat grip positions. These findings indicate that changing to the short bat grip position from the long bat grip position will not improve the batter's swing timing. Furthermore, changing to the short bat grip position could delay the batter's swing timing, probably because the change causes a delay in swing preparation.