Relationship between Muscle Activity in the Shoulder Girdle Area and Trunk Rotation during Pitching

Abstract

[Purpose] The purpose of this study was to investigate the relationship between muscle activity in the shoulder girdle area and trunk rotation during pitching. [Subjects and Methods] Subjects were high school baseball pitchers. The subjects were divided into two groups: having a history of shoulder pain (n=8), and controls (n=10). Items of investigation were the angles of rotation of the chest and pelvis, changes in these angles, and muscle activities in the vicinity of the shoulder girdle during pitching, which were determined by surface electromyography frequency analysis. [Results] Those with a history of shoulder pain showed a significantly lower amount of change in the angle of rotation of the chest during the cocking phase and a significantly higher amount during the acceleration phase, a significantly lower amount of change in the angle of rotation of the pelvis during the cocking phase, and significantly lower muscle activity of the lower trapezius and serratus anterior muscles in the shoulder girdle area during the cocking phase. [Conclusion] As a strategy to prevent further injury to shoulders already injured by pitching, it is necessary to increase the qualitative function of the muscles to improve the balance between shoulder girdle muscle activity and trunk rotation.