Abstract
Introduction: Kinetic and kinematic variables of the shoulder during throwing motions are a common subject in association with shoulder injury. However, research regarding swinging and striking motions, for example volleyball attacks, is limited. Volleyball has four types of high-speed attacks, the straight swing, cross body swing, and away swing. Shoulder mechanics can be evaluated for injury risk potential based upon previous research conducted with baseball throwing mechanics. Purpose: The purpose of this study was to determine the kinetic and kinematic values of the different volleyball arm swings, evaluate injury risk for each swing, and propose solutions to minimize that risk. A second purpose of this study was to evaluate any gender differences in injury risk based on mechanics of motion. Methods: The motion during each type of swing of ten high level volleyball players was recorded using an 8 camera Vicon motion capture system. Kinetic and kinematic data of 5 swings of each type was analyzed using Visual 3D software. Inverse dynamics were used to determine loads applied to the shoulder joint and comparisons with previous literature was used to estimate injury potential. Results: Statistically significant differences were found between the internal rotation torque after ball contact between the straight swing and the cross body swing conditions (p=0.033). Maximum internal torque, which occurs at the beginning of the acceleration phase, was statistically significantly different (p=0.017) between the cross body swing and the away swing. No statistically significant differences were found between conditions for the maximum abduction angle or normalized distraction force. No statistically significant effect of gender was found across conditions (p=0.534, p=0.544, p=0.243, p=0.195 respectively). Conclusions: The hypotheses of this study were not supported by the present results. The data shows that there is no difference in injury risk between males and females and that the cross body swing creates a higher risk for rotator cuff injuries. Minimizing the cross body swing at high velocities would aid athletes to avoid injury. Further research into this topic is warranted, including similar studies with increased sample size, higher skilled athletes, or comparisons with strength ratios.