Throwing Kinematics in Youth Pitchers and Field Players

Abstract

Little league elbow is a common injury in youth baseball players no matter which position they play. Several throwing kinematic variables were mentioned to be associated with increasing elbow valgus stress, whether pitchers and fielders in youth players have similar throwing kinematics has not been well explored. PURPOSE: To determine the differences in throwing kinematics between pitchers and field players in youth baseball players. METHODS: Ten pitchers (age: 11.1±0.7 years; height: 149.5±10.2 cm; weight: 43.3±11.6kg) and 10 field players (age: 11.2±0.8 years; height: 146.6±6.3cm; weight: 38.5±8.8kg) with overhead throwing pattern were recruited for this study. Throwing kinematics were assessed using a 3D electromagnetic motion tracking system. A foot switch was used to determine the instant of foot strike. The instant of ball release was defined as the instant when wrist acceleration phase was becoming deceleration phase. Three fast balls that hit a target placed 14.63m away were recorded for data analysis. Independent t-tests were performed for comparing the differences in throwing kinematics, bady height, and weight between the two groups. Significant level was set at p<0.05. RESULTS: Only maximum upper torso rotational velocity during acceleration phase of throwing was found to be greater in pitchers when compared to the field players. (1015.4+74.4 vs. 906.0+104.6°/s; p= 0.015). No significant differences in shoulder abduction angle at foot strike, maximum elbow flexion angle, shoulder abduction angle at ball release, trunk side-bending at ball release, and maximum velocity of shoulder horizontal adduction, shoulder internal rotation, upper and lower torso rotation, and elbow extension were found between the two groups. There were also no significant differences in body weight and height between the two groups. CONCLUSION: Throwing kinematic variables observed in this study were similar between youth pitchers and field players except that pitchers had greater maximum upper torso rotational velocity that was not one of the kinematic variables significantly affecting elbow valgus stress based on the previous studies.