Golf is a popular sport throughout the world, yet there is little in the literature that discusses the mechanics of the swing. The purpose of this study is to analyze the EMG activity in eight shoulder muscles of both the right and left arms during the golf swing. The results reveal that the infraspinatus and supraspinatus act predominantly at the extremes of shoulder range of motion, the subscapularis and pectoralis major during acceleration, the latissimus dorsi during forward swing, and the anterior deltoid during forward swing and follow-through. The middle and posterior deltoids appear to be relatively noncontributory, without any specific timing patterns. This data is an expansion of an earlier pilot study and allows us to more accurately develop an exercise program for optimal performance as well as for prevention and rehabilitation.