The relationship between pitch velocity and shoulder distraction force and elbow valgus torque in collegiate and high school pitchers

Background: The relationship between pitch velocity, shoulder distraction force, and elbow valgus torque is not well understood. The purpose of this study was to (1) determine the association between baseball pitch velocity and shoulder distraction force and (2) determine the association between baseball pitch velocity and elbow valgus torque. A subpurpose was to determine these same associations within subgroups of college baseball and high school baseball pitchers. Methods: Collegiate and high school baseball pitchers were biomechanically analyzed; variables extracted from the pitching reports included fastball pitch velocity, shoulder distraction force, and elbow valgus torque. Linear regression was performed to analyze the relationship between fastball velocity and shoulder and elbow kinetics. Subgroup analyses were then performed for college and high school pitches. Coefficients and 95% confidence intervals (95% CI) were calculated, with R squared (r(2)) used to assess model fit. Results: Atotal of 70 pitchers (college: n = 23; high school: n = 47) were included in this study. There was a positive weak linear relationship between pitch velocity and shoulder distraction force (3.24 %body weight [BW] [95% CI: 2.07, 4.40], r(2) = 0.32, P < .001) and elbow valgus torque (0.16 %body weight x height [BW x H] [95% CI: 0.11, 0.20], r(2) = 0.44, P < .001). College pitchers did not exhibit a relationship between pitch velocity and shoulder distraction force (1.44%BW [95% CI: -2.50, 5.38], r(2) = 0.02, P < .001), whereas high school pitchers did exhibit a weak positive linear relationship between pitch velocity and shoulder distraction force (3.69 %BW [95% CI: 2.25, 5.14], r(2) = 0.36, P < .001). Both college and high school pitchers exhibited a weak positive relationship between pitch velocity and elbow valgus torque (college: 0.15 %BW x H [95% CI: 0.05, 0.25], r(2) = 0.29, P < .001; high school: 0.16 %BW x H [95% CI: 0.09, 0.22], r(2) = 0.36, P < .001). Discussion: Pitching velocity exhibited a weak positive linear relationship with both shoulder distraction force and elbow valgus torque. However, only high school pitchers were observed to have a weak positive linear relationship between pitch velocity and shoulder distraction force, whereas both college and high school pitchers exhibited a weak positive relationship between pitch velocity and elbow valgus torque. These findings suggest that older pitchers may attenuate shoulder forces with increased pitch velocity due to physical maturity or increased pitching mechanical skill in comparison with younger pitchers. (C) 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.