Rotator cuff weakness has been implicated as a cause of subacromial impingement. Numerous exercises have been advocated to strengthen the rotator cuff, particularly the supraspinatus. The clinical rationale and two exercises advocated for strengthening the supraspinatus, the empty can and the full can, were evaluated. By understanding how these exercises vary from a biomechanical perspective, it is hoped that clinicians can minimize the forces experienced by the supraspinatus during the rehabilitation process.