Predictors of Throwing Velocity in Youth and Adolescent Pitchers

Sgroi, T., et. al. J Shoulder Elbow Surg. 24(9): 1339-1345, 2015

Purpose: To determine the demographic and biomechanical factors that predict throwing velocity in youth and adolescent pitchers.

Subjects: 420 pitchers between the ages of 12.1 and 17.3 years with a mean age of 14.7 +/- 2.6 years. Mean height was 67.5 +/- 5.3 inches. Mean weight was 145.4 +/- 39.2 pounds. Mean velocity was 64 +/- 10 mph.

Procedures: Demographic data collected included age, height and weight. Biomechanical data were obtained from video motion analysis at 210 Hz while pitching from a regulation practice mound and distance from home plate appropriate for the subject’s level of play. Throwing velocity was measured with a JUGS Sports radar gunwith an accuracy of +/- 0.5 mph. Biomechanical factors measured included: 1) did the pitcher lead with his hips; 2) did he have his hand on top of the ball during the stride phase; 3) did he have his arm in the throwing position at front foot contact; 4) were his shoulders closed at the hand-set position; 5) did he have a closed foot orientation at front foot contact; 6) did he separate the rotation of his hips and shoulders, i.e., during the cocking phase, was his pelvis rotated to face home plate while his shoulders continued to face third base (RHP); and 7) was he in a fielding position at follow-through.

Analysis: Data were analyzed using an Excel X and SPSS 21 software for Student t test, Mann-Whitney test and Pearson correlation coefficients.

Results:

• Pitch velocity was significantly correlated with age, height, weight, stride length as a percentage of height, foot angle at front foot contact and shoulder – hip separation.

• Subjects with a closed shoulder position at front foot strike had a significantly higher velocity than those with an open shoulder position.

• Subjects with separation of shoulders and hips had a significantly higher pitch velocity than those without a separation of shoulders and hips.

• Age, height, shoulder-hip separation and stride length as a percentage of height explained 78% of the variance in pitch velocity.

• Each year of age was associated with a 1.5 +/- 0.1 mph increase in velocity.

• Each one-inch increase in height was associated with a 1.2 +/- 0.2 mph increase in velocity

• Each increase in stride length by 10% of subject height was associated with a 1.9 +/- 0.4 mph increase in velocity.

Discussion:

• The correlation between height and velocity is likely due to a longer lever arm that allows pitchers to transfer more force to the ball.

• A pitcher with a short stride length and without shoulder and hip separation would be able to increase velocity by 4.3% by increasing stride length and shoulder-hip separation, i.e., a 70-mph pitcher could increase velocity to 73 mph.

• Adding separation of shoulders and hips without increasing stride length increased velocity by 2.6 +/- 0.5 mph. The importance of hip and shoulder separation to velocity relates to the “summation of forces” principle, i.e., the greatest transfer of force occurs when the subsequent segment begins rotating at the moment at which the prior segment reaches max angular velocity. Therefore,proximal trunk rotation ideally begins at the moment of max angular velocity of the pelvis. This explains why a strong core is essential for high-velocity pitching.

Takeaway:

• Correlation does not imply cause, but the data strongly suggest that age and height are related to pitch velocity.

• Data also suggest that pitchers who want to increase velocity should improve hip and shoulder separation and increase stride length.