SHOULDER MUSCLE FIRING PATTERNS DURING THE WINDMILL SOFTBALL PITCH

The purpose of this study was to describe the activity of eight should er muscles during the windmill fast-pitch softball throw. Ten collegia te female pitchers were analyzed with intramuscular electromyography, highspeed cinematography, and motion analysis. The supraspinatus muscl e fired maximally during arm elevation from the 6 to 3 o'clock positio n phase, centralizing the humeral head within the glenoid. The posteri or deltoid and teres minor muscles acted maximally from the 3 to 12 o' clock position phase to continue arm elevation and externally rotate t he humerus. The pectoralis major muscle accelerated the arm from the 1 2 o'clock position to ball release phase. The serratus anterior muscle characteristically acted to position the scapula for optimal glenohum eral congruency, and the subscapularis muscle functioned as an interna l rotator and to protect the anterior capsule. Although the windmill s oftball pitch is overtly different from the baseball pitch, several su rprising similarities were revealed. The serratus anterior and pectora lis major muscles work in synchrony and seem to have similar functions in both pitches. Although the infraspinatus and teres minor muscles a re both posterior cuff muscles, they are characteristically uncoupled during the 6 to 3 o'clock position phase, with the infraspinatus muscl e acting more independently below 90 degrees. Subscapularis muscle act ivity seems important in dynamic anterior glenohumeral stabilization a nd as an internal rotator in both the baseball and softball throws.