Gluteal muscle group activation and its relationship with pelvis and torso kinematics in high-school baseball pitchers.

The purpose of this study was to examine the activation patterns of the gluteal muscle group and their relationship to pelvis and torso kinematics throughout the high-school pitching motion. A single group, repeated-measures design was used to collect gluteus maximus and gluteus medius muscle activity through surface electromyography for the preferred and nonpreferred sides during the various phases of the pitching motion. In addition, data describing the kinematics of the pelvis and torso were collected at foot contact, maximum shoulder external rotation, ball release, and maximum shoulder internal rotation. For all pitchers, preferred gluteus maximus activity was observed to be in excess of 100% of their maximum voluntary isometric contraction throughout the stride and arm-cocking phases of the pitching motion. The observed means for the preferred gluteus medius, nonpreferred gluteus maximus, and nonpreferred gluteus medius, although different in magnitude, were similar in pattern. From the conclusion of the stride phase, through the conclusion of the arm-cocking phase, muscle activity increased for all pitchers. In examining the relationship between the rate of axial pelvis rotation and gluteal activity, several significant relationships were observed. In contrast, no significant relationships were observed with gluteal activity parameters and the rate of axial torso rotation. However, because the pitching motion progresses sequentially from the pelvis to the torso, variability in pelvis rotation may be directly related to variability in torso rotation. The findings from this study indicate that during the baseball pitch, there is a need for greater control of gluteal activation throughout the pitching motion.