Is early trunk rotation really hazardous for shoulder biomechanics in baseball throwing?

BACKGROUND AND HYPOTHESIS: Early trunk rotation (ETR), which is a unique kinematics of the trunk that occurs during baseball throwing, is thought to be related to shoulder injuries. Pelvic rotation is a confounder when studying the effects of trunk rotation on shoulder biomechanics. The purpose of this study was to understand the "pure" effects of trunk rotation on shoulder biomechanics, with pelvic rotation under control. Our hypotheses were as follows: (1) throwers with ETR have a different shoulder kinematics pattern compared with throwers without ETR; (2) throwers with ETR have a lower ball speed performance than do throwers without ETR; and (3) throwers with ETR have a greater value of shoulder forces and moments, which may increase risks of shoulder injury, than do throwers without ETR. METHODS: Fifty-seven elite throwers were enrolled and divided into 2 groups (non-ETR and ETR) using an outdoor motion analysis. Several kinematics and kinetics parameters of the shoulder were analyzed and compared between the 2 groups. RESULTS: Ball velocity was faster in the non-ETR group (127 km/h) compared with the ETR group (120 km/h). The shoulders of throwers in the ETR group showed pathokinematics of "horizontal adduction lag" and "dropped elbow." The increases in maximal posterior force, inferior force, horizontal abduction moment, and vertical adduction moment were 9.2%, 13.6%, 21.3%, and 24.3%, respectively, in the shoulders of throwers in the ETR group. These results indicate that ETR may be hazardous for the throwing shoulder. With lower ball velocity and higher shoulder joint loading, ETR is not a proper pitching pattern for kinetic energy transfer. CONCLUSION: Improper pitching mechanics among baseball throwers, such as ETR, may result in higher shoulder joint loading and increased risk of shoulder injuries. When treating throwers with shoulder injuries, it is important not only to address shoulder anatomy and pathology but also to understand the possible pathomechanics and pathogenesis of the shoulder caused by ETR. Furthermore, special training programs focusing on trunk flexibility and core muscle strengthening should be implemented to prevent ETR and decrease the risk of shoulder injuries. Motion analysis is useful for the screening and early detection of improper pitching mechanics in throwers.

Change in pitching biomechanics in the late-inning in Taiwanese high school baseball pitchers.

Repetitive overhead throwing may result in overuse injuries and a change in the pitching mechanics of a baseball pitcher. Accordingly, the purpose of this study is to quantify the changes in the muscle strength and pitching motion kinematics in the late-innings stage of a baseball game. Sixteen healthy baseball pitchers (16.77 ± 0.73 years) recruited from a high school, which won the National High School Baseball Championship in Taiwan in 2011; each performed 100 pitches in a bullpen throwing session. Isometric muscle strength measurements and joint kinematic data were obtained before and after the throwing session. The mean Borg's Rating of Perceived Exertion index was found to have a value of 14.14, indicating a medium-to-large degree of perceived tiredness. The results showed that the ball velocity and horizontal abduction angle decreased significantly as the pitchers became tired. Moreover, the upper torso forward tilt and knee flexion angle both increased significantly at the moment of ball release. Finally, the muscle strength of the upper extremity remained decreased 2 days after the bullpen throwing session. Overall, the results suggest that an adequate amount of rest and specific strengthening programs for the shoulder external rotator, shoulder internal rotator, shoulder flexor, shoulder extensor, shoulder adductor, and shoulder abductor muscles are recommended to the coaches and for adolescent baseball pitchers. In addition, the changes in pitching mechanics noted in this study should be carefully monitored during the course of a baseball game to minimize the risk for overuse injuries.