Dynamics of the hip joint in baseball batting

Abstract

The purpose of this study was to clarify the exertion of torque and motion related to the generation of mechanical energy in both hip joints during baseball batting. The participants were 98 male amateur baseball players (body height: 172.6±5.6cm, body weight: 70.3±8.1kg, age: 19.0±1.9yr, career: 11.0±2.8yr). The batting motion was recorded using a motion capture system (10cameras, 250Hz), and the ground reaction forces acting on each foot were estimated using 2 force plates (1000 Hz). Hip joint angles were expressed as Euler angle of the thigh relative to the lower torso. Hip joint torques were calculated using inverse dynamics. Other kinetic variables-e.g. hip joint torque power, mechanical work by hip joint torque-were also calculated. The main results were as follows: 1. Throughout the analysis phase, there was no significant correlation between the bat head speed at impact and the angles of both hip joints. 2. For the hip joint on the pitcher side, the generation of mechanical energy by flexion and adduction torque was large during the phase before maximum pelvis rotational velocity. 3. For the hip joint on the catcher side, the generation of mechanical energy by extension torque was large in the phase before maximum pelvis rotational velocity. These results suggest that there are no differences in the kinematics of both hip joints depending on the bat head speed at impact. In addition, it is indicated that the ability to exert flexion and adduction torques for the hip joint on the pitcher side and the extension torque for the hip joint on the catcher side during baseball batting motion contribute to the generation of mechanical energy.