TITLE:
Assumption of Fixed Ball at the Centre of Mass of the Hand Results in Underestimation of Wrist Muscle Flexion Torque Component Owing to Ball Kinetics Immediately before Ball Release in Baseball Throwing
AUTHORS:
Takeji Kojima
KEYWORDS:
Baseball Throwing, Wrist Joint, Non-Conventional Inverse Dynamics, Non-Fixed Ball at Hand
JOURNAL NAME:
Advances in Physical Education,
Vol.15 No.2,
May
31,
2025
ABSTRACT: In conventional inverse dynamics analyses of the human body, the locations of the centre of pressure (COP) of external forces acting on the body segments are necessary to solve problems. In the analysis of baseball throwing, the location of the COP of the forces acting from the baseball on the palm and/or fingers remains unclear, and the centre of mass (COM) of the ball may be fixed at a point in the hand until ball release: at the COM or third metacarpal joint of the hand, for instance. This study aimed to investigate possible errors of the muscle flexion torque at the wrist joint due to an assumption that a ball is fixed at the COM of the hand until ball release in baseball throwing. Seven male collegiate baseball players each threw a baseball with their supreme effort at a target in a laboratory. The markers attached to the throwing arm and ball were captured at 500 fps with eight cameras of a motion capture system. Wrist muscle flexion torques were determined using an inverse dynamics analysis, which does not necessitate the COP location, under the following two conditions: an actual ball position and motion were considered (C1), and the COM of the ball was fixed at the COM of the hand until the release (C2). The torque determined under C1 was significantly different from (p