Source: Robert E. Sallis, MD. Kaiser Permanente, Fontana, California, USA The shoulder exam continues by checking the strength of the rotator cuff muscles and biceps tendons. The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) act as compressors, holding the humeral head in place against the glenoid. Injury and degeneration of the rotator cuff tendons are the most common sources of shoulder pain. The strength testing of the rotator muscle is performed by testing motions against resistance applied by the examiner. Pain with these resisted motions suggests tendonitis; weakness suggests a rotator cuff tear. The strength tested is followed by tests for impingement syndrome, shoulder instability, and labrum injury. It is important to test both of the shoulders and compare between the sides. The opposite shoulder should be used as the standard to evaluate the injured shoulder, provided it has not been injured as well.