Increases in Ball Weight and Size Decrease Elbow Varus Torque During Baseball Pitching.

Background: The rates of ulnar collateral ligament injury and surgery continue to rise in baseball. Increased ball velocity and elbow varus torque may correlate with the increased risk of injury.

Hypothesis: Increased ball weight and/or size correlate with decreased elbow varus torque during pitching.

Study design: Controlled laboratory study.

Methods: Motion capture data of 20 healthy professional and high-level collegiate baseball pitchers pitching fastballs with 4 types of baseballs were collected. The baseballs were 5 oz (standard weight) or 6 oz, with a circumference of 9 inches (standard size) or 5% larger. Five kinetic parameters, 25 kinematic parameters, and 7 ball movement parameters were calculated. Differences for each parameter were compared using 2-factor (ball weight × size) repeated-measures analysis of variance (P < .05).

Results: As hypothesized, elbow varus torque decreased with increased ball weight and with increased ball circumference. Ball velocity, shoulder internal rotation velocity, elbow extension velocity, and shoulder kinetics also decreased with increased ball weight and/or increased ball circumference. Ball break decreased with increased ball weight, while ball location as it crossed home plate was also affected by ball weight and/or size. There were no clinically important differences in pitching kinematics with the different baseballs.

Conclusion: Increasing the weight of baseballs from 5 oz to 6 oz and/or the circumference by 5% may reduce elbow varus torque. Future research in league play or simulated play is warranted.

Clinical relevance: As elbow varus torque has been staassociated with UCL injury risk, increasing ball weight and/or size may reduce the rate of injury.