The effects of relative trunk rotation velocity on ball speed and elbow and shoulder joint torques during baseball pitching.

In baseball pitching, suppressing trunk rotation while rotating the pelvis in the early phase of arm cocking is important for throwing a fast ball. However, quantitative evaluation of trunk rotation during pitching has not been established, and its associations with elbow and shoulder torques are unclear. The purpose of this study was to examine the correlation of a new measure of trunk rotation suppression with ball speed and elbow and shoulder torques during pitching. Eighteen adult male baseball pitchers (21.7 ± 1.2 years old) participated. Three qualified pitches were analysed using a three-dimensional motion capture system. Trunk rotation velocity, normalised to the peak velocity, was derived at the time of peak pelvic velocity. Pearson's correlation coefficient was used to determine correlations. The normalised trunk rotation velocity at the peak pelvic velocity was significantly correlated with elbow valgus torque ( R  = -0.508, P  = 0.032), shoulder external rotation torque ( R  = -0.507, P  = 0.032) and ball speed ( R  = -0.504, P  = 0.033). A smaller normalised trunk rotation angular velocity at the time of peak pelvic rotation velocity could increase ball speed but may also increase elbow and shoulder torques among pitchers who demonstrate trunk rotation after foot contact.