Biomechanical study of the pitching elbow

Abstract

Medial-tension injuries of the pitching elbow are well recognized. One contributing factor is the extreme valgus which has been noted to occur during the acceleration phase of throwing. It is hypothesized that breaking pitches generate higher medial loading because of the pronation and supination required to impart spin to the ball. The pitching motion is a complex action of all body segments to produce maximum linear and angular acceleration of the ball. The purpose of this study was to correlate elbow loading with pitching style. We measured the forearm segment for axial and tangential (varus-valgus plane) acceleration using accelerometers attached to the forearm and hand. Muscle activity was measured by EMG. Forearm rotation was assessed by stroboscopic photography. Despite different delivery styles when throwing breaking pitches, each pitcher demonstrated patterns of muscle activity and acceleration which were similar. Deceleration forces were lower than acceleration forces. Pronation and supination were documented and contribute to the direction of ball spin. Accelerometers can be used to evaluate pitching mechanics. We suggest that the main factors causing an elbow injury are the amount of throwing and the force with which the ball is thrown.