OBJECTIVE: To analyze activities of left lower extremity muscles throughout phases of the golf swing, using surface electromyography. METHOD: We evaluated muscle activities during the golf swing of 5 amateur and 5 professional golfers using surface electromyography. Surface electrodes were placed in the left gluteus medius, gluteus maximus, biceps femoris, gastrocnemius, rectus femoris, peroneus longus, and tibialis anterior. RESULTS: Muscle activities of professional golfers in the left gluteus medius, gluteus maximus, biceps femoris, tibialis anterior, rectus femoris abruptly increased from top-swing phase to impact phase but muscle activities of amateur golfers in these muscles increased to top-swing phase and decreased at follow swing phase. Muscle activities of professional golfers in left peroneus longus, gastrocnemius abruptly increase from forward swing to impact but muscle activity of amateur golfers in these muscles continuously increase to impact and abruptly increase at follow swing. CONCLUSION: Our findings demonstrate the importance of the muscles in the golfer's swing.