Arm Stress Comparisons Between Common Baseball Pitch Types

Abstract

The purpose of this study was to examine differences in varus arm stress between baseball pitch types — fastballs versus a breaking ball of choice—with MotusBASEBALL’s motion capture arm sleeve. Twenty-eight males between the ages of 18 and 36 (21.4 ± 4.3) were asked to throw ten pitches of each pitch type — fastballs (n = 28), curveballs (n = 14), sliders (n = 14), and changeups (n = 18). Every subject threw fastballs and a breaking ball of their choice, and some subjects threw additional changeups. Sliders had the highest arm stress (54.6 ± 12.9 N·m) while curveballs had the lowest (46.8 ± 16.3 N·m). Fastball arm stress was 50.1 ± 16.8 N·m and changeup arm stress was 51.3 ± 15.5 N·m. There was no statistically significant difference between pitch types and arm stress (p-value range 0.08-0.92), although the proportion of outlier readings for arm stress was significant for sliders (proportion of outliers: 34%, p-value: 0.009 versus change-ups; p-value: 0.014 versus curveballs). In addition, pitch type was significant only in determining the velocity reading from the Motus App (p-value <.0001), and was not significant in determining arm speed, arm slot, or shoulder rotation.