Biomechanical analysis of the pitching characteristics of adult amateur baseball pitchers throwing standard and lightweight balls

[Purpose] The purpose of this study was to determine the relationship between pitching weight and pitching mechanics, including ball reaction force (BRF) and temporal parameters, for the prevention of throwing injury in adult amateur pitchers. [Participants and Methods] Twenty adult male amateur pitchers (mean age, height, and body mass: 26 ± 3.4 years, 1.7 ± 0.03 m, and 71.6 ± 9.5 kg, respectively) randomly pitched light (110 g) and heavy (145 g) baseballs at maximum velocity. Kinematic, kinetic, and temporal parameters were compared between the light and heavy balls. [Results] Pitching heavy balls significantly increased the BRF to 9.2 N and maximum trunk rotation angular velocity to 26.2°/sec, and decreased the ball speed to 1.4 m/sec and upper limb joint torque efficiency and shoulder internal rotation angular velocity at the moment of ball release at 250.8°/sec. Furthermore, the peak temporal kinetic parameters until ball release appeared early in the throwing of the heavy ball. [Conclusion] Adult amateur pitchers who pitched heavy balls had greater BRF; had decreased upper limb joint torque efficiency, ball speed, and arm angular velocity; and reached maximum kinetics early. Adult amateur pitchers may be at risk of throwing injuries due to throwing of heavy balls.