We used dynamic electromyography and a motion analysis system to describe the muscle firing patterns in 10 shoulder muscles and the basic kinematics of a two-handed overhead medicine ball throw. Ten healthy male subjects with no history of shoulder injury were evaluated. The two-handed medicine ball throw was divided into three phases for analysis: cocking, acceleration, and deceleration. The average duration of the throw was 1.92 seconds; the cocking phase represented 56%, the acceleration phase 15.5%, and the deceleration phase 28.5% of the throw. In the cocking phase, the upper trapezius, pectoralis major, and anterior deltoid muscles showed high activity ( > 40% to 60% maximum manual test), and the rotator cuff muscles had moderate activity ( > 20% to 40%). In the acceleration phase, five of the muscles demonstrated high levels of activity ( > 40% to 60%) and the upper trapezius and lower subscapularis muscles had very high levels of activity ( > 60%). Analysis of the deceleration phase revealed high activity in the upper trapezius muscle and moderate activity in all other muscles except the pectoralis major. Our findings support the use of medicine ball training as a bridge between static resistive training and dynamic throwing in the rehabilitation of the overhead athlete. This training technique provides a protective method of strengthening that closely simulates portions of the throwing motion.