Fine wire EMG of the shoulder was performed on 11 swimmers; 5 performed during dry land studies and 7 during aquatic studies. One individual underwent both studies. A cinematographic analysis was synchronized with the EMG data to determine what muscles were firing at each phase of the swim stroke. Eight muscles were studied: biceps, subscapularis, latissimus dorsi, pectoralis major, supraspinatus, infraspinatus, serratus anterior, and deltoid. Three strokes were analyzed: freestyle, breaststroke, and butterfly. The freestyle and butterfly are frequently associated with impingement type syndromes in swimmers. It was determined that the supraspinatus, infraspinatus, middle deltoid, and serratus anterior were predominately recovery phase muscles. The latissimus dorsi and pectoralis major were predominately pull-through phase muscles. The biceps had mixed inconsistent activity during both phases. From dry land quantifications of the EMG signal it was determined that the serratus anterior functions near maximal muscle test during each stroke, and theoretically may fatigue with repetition. It is hoped that a training program aimed to strengthen the scapular rotators may help alleviate impingement syndrome in swimmers.