Electromyographic activity of shoulder muscles during unilateral upper extremity proprioceptive neuromuscular...

Twenty-nine normal adults were tested to measure the electrical activity of the anterior, middle, and posterior portions of the deltoid muscle and sternal portion of the pectoralis major muscle during the performance of four upper extremity diagonal patterns with the elbow straight, flexing, and extending. The patterns were performed through range of motion, with an isometric contraction performed in the shortened range. With the elbow straight, the middle portion of the deltoid muscle was primarily active with shoulder flexion, abduction, and external rotation; the anterior portion of the deltoid muscle with shoulder flexion, adduction, and external rotation; the posterior portion of the deltoid muscle with shoulder extension, abduction, and internal rotation; and the sternal portion of the pectoralis major muscle with shoulder extension, adduction, and internal rotation. The middle and anterior portions of the deltoid muscle exhibited significantly greater activity in their optimal patterns with the elbow strainght, followed by patterns with the elbow flexing and significantly less activity with the elbow extending. The posterior portion of the deltoid muscle in its optimal pattern produced greatest activity with the elbow straight or extending. Findings confirm the patterns considered optimal for monitored portions of these two muscles in normal subjects. Suggestions are made for study of patients who exhibit imbalances of muscle strength.