抄録
Background: Shoulder injuries in baseball pitchers often occur at the maximum external rotation (MER). However, in the past, amounts and directions of the force applied to the shoulder at this moment during throwing motion has not been clarified. The purpose of this study was to analyze forces applied to the shoulder.
Methods: Biomechanical analysis was performed on 213 pitchers with various skill levels. Throwing motion was measured using motion capture system. To describe angular values of the upper arm relative to the trunk, Euler angle sequence was utilized. In order to estimate the resultant joint forces at the shoulder, an inverse dynamics technique was employed.
Results: The relationship between horizontal abduction/adduction angle and resultant anterior/posterior force at the MER showed significant correlation (r=-0.63, p < 0.05). The increase in horizontal abduction at this moment was associated with increased resultant anterior force. The horizontal adduction angle with minimal resultant anterior/posterior force at MER was 1.79°. Superior/inferior force at MER was poorly correlated with abduction/adduction angle, showing increased adduction angle associated with higher resultant force toward superior direction. Regarding the relationship between age and throwing kinematics, horizontal abduction angle at MER was larger in young pitchers than adult pitchers.
Conclusion: Comparison between horizontal abduction angle and anterior shear force at the MER in the throwing motion showed significant correlation. Evaluation and correction of the throwing motion focusing on horizontal abduction at MER may be a key to the reduction of harmful stresses leading to shoulder injuries among pitchers.
