Using dynamic surface electrode electromyography, we evaluated muscle activity in 13 male professional golfers during the golf swing. Surface electrodes were used to record the level of muscle activity in the right abdominal oblique, left abdominal oblique, right gluteus maximus, left gluteus maximus, right erector spinae, left erector spinae, upper rectus abdominis, and lower rectus abdominis muscles during the golfer's swing. These signals were synchronized electronically with photographic images of the various phases of the golf swing; the images were recorded in slow motion through motion picture photography. The golf swing was divided into five phases: take away, forward swing, acceleration, early follow-through, and late follow-through. Despite individual differences among the subjects' swings, we observed reproducible patterns of trunk muscle activity throughout all phases of the golf swing. Our findings demonstrate the importance of the trunk muscles in stabilizing and controlling the loading response for maximal power and accuracy in the golfer's swing. This study provides a basis for developing a rehabilitation program for golfers that stresses strengthening of the trunk muscles and coordination exercises.