Relationships between Bat Swing Speed and Muscle Thickness and Asymmetry in Collegiate Baseball Players

The purpose of the present study was to examine the relationships between bat swing speed (BSS), muscle thickness, and muscle thickness asymmetry in collegiate baseball players. Twenty-four collegiate baseball players participated in this study. Maximum BSS in hitting a teed ball was measured using a motion capture system. The muscle thicknesses of the trunk (upper abdominal rectus, central abdominal rectus, lower abdominal rectus, abdominal wall, and multifidus lumborum), upper limb, and lower limb were measured using a B-mode ultrasonography. Lateral asymmetry between each pair of muscles was determined as the ratio of the thickness of the dominant side to that of the non-dominant side. Statistically significant positive correlations were observed between BSS and muscle thicknesses of the abdominal wall and multifidus lumborum on the dominant side (r = 0.426 and 0.431, respectively; p < 0.05), whereas only trends against this significance were observed between BSS and muscle thicknesses on the non-dominant side. No statistical correlations were found between BSS and the lateral asymmetry of any muscles. These findings indicate the importance of the trunk muscles for bat swing, and the lack of association between BSS and lateral asymmetry of muscle size.