A Study of Control Mechanism of Ball Spin Rate by Upper Limb in Baseball Pitching Based on Kinetic Synergy

Abstract

This study aims to examine the mechanism how ball spin rate during baseball pitching is controlled by central nervous system. The participants were seven baseball players. The kinematics and kinetics of the finger, wrist, elbow, and shoulder were calculated using an inverse dynamics method. Kinetic synergies were calculated for joint angles and torques using singular value decomposition. The similarity of spatial pattern of kinetic synergy in each subject was evaluated by cosine similarity. It was indicated that there were three types of synergies: 1) Two pitchers had a synergy that was primarily based on shoulder internal rotation torque, 2) two pitchers had a synergy that was primarily based on elbow extension torque, 3) three pitchers had a synergy that was primarily based on shoulder horizontal adduction torque. In particular, pitchers with a high spin rate relative to ball velocity (SPV) were of the shoulder internal rotation type. On the other hand, pitchers with a low SPV were of the shoulder horizontal adduction type. It is considered that pitchers with a high SPV executed synergy of the shoulder internal rotation torque, which is the same as the direction of ball spin, based on hierarchical control in order to increase ball spin rate. These results suggest that between pitchers with high SPV and low SPV have different spinal nerve activity and motor patterns, respectively.