Shoulder Muscle Firing Patterns During the Windmill Softball Pitch

Abstract

The purpose of this study was to describe the activity of eight shoulder muscles during the windmill fast-pitch softball throw. Ten collegiate female pitchers were an alyzed with intramuscular electromyography, high speed cinematography, and motion analysis. The su praspinatus muscle fired maximally during arm elevation from the 6 to 3 o'clock position phase, cen tralizing the humeral head within the glenoid. The pos terior deltoid and teres minor muscles acted maximally from the 3 to 12 o'clock position phase to continue arm elevation and externally rotate the humerus. The pec toralis major muscle accelerated the arm from the 12 o'clock position to ball release phase. The serratus anterior muscle characteristically acted to position the scapula for optimal glenohumeral congruency, and the subscapularis muscle functioned as an internal rotator and to protect the anterior capsule. Although the wind mill softball pitch is overtly different from the baseball pitch, several surprising similarities were revealed. The serratus anterior and pectoralis major muscles work in synchrony and seem to have similar functions in both pitches. Although the infraspinatus and teres minor muscles are both posterior cuff muscles, they are char acteristically uncoupled during the 6 to 3 o'clock posi tion phase, with the infraspinatus muscle acting more independently below 90°. Subscapularis muscle activ ity seems important in dynamic anterior glenohumeral stabilization and as an internal rotator in both the base ball and softball throws.