Arm Angle Moderates the Association Between Fastball Usage and Elbow/Forearm Injury in MLB Pitchers
- 1University of California, San Diego
Abstract
BackgroundNewly available arm angle data offers a new dimension to understand rising rates of arm injury in MLB pitchers.
PurposeTo evaluate the relationship between arm angle, pitch characteristics, and elbow and forearm injury in MLB pitchers.
Study DesignRetrospective cohort study; Level of evidence, 3
MethodsStatcast data from 2020 to 2025 and MLB injured list (IL) data were used to evaluate arm angle and pitch characteristics in relation to elbow and forearm injuries. Results are presented with and without requirements on prior season workload and for same-season and next-season injury incidence. A generalized additive model (GAM) was used to capture non-linear dependence and interactions between selected features and injury incidence to the elbow or forearm. Average marginal effect (AME) odds ratios are reported for main effect terms.
ResultsN = 3,812 pitcher-seasons were included. 29% pitchers who underwent UCLR did so in the same season as a forearm injury (tmean = 44, tmedian = 27 days to surgery). Arm angle, fastball usage, and their interaction were the three most predictive features. Arm angle was positively related to incidence of injury ([Formula] = 1.014), fastball usage was inversely related to incidence of injury ([Formula] = 0.243), and arm angle moderated the effect fastball usage at high arm angle, where increased usage was no longer protective. Slider velocity ([Formula] = 1.072), spin rate ([Formula] = 1.001), and usage ([Formula] = 2.039) also significantly predicted injury risk. Fastball velocity was not significant in any fit, with [Formula] = 0.999 across all fits. Fit-level Nagelkerke R2 values ranged from .019 to .052.
ConclusionFastball usage and arm angle, not velocity, predicted elbow and forearm injury risk among MLB pitchers, and arm angle was the single most predictive feature. The heterogeneity of risk factors as a function of arm angle, and the novelty of MLB arm angle data, may explain why fastball usage has been previously underexplored as a risk factor.
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BibTeX
@misc{richards2026angle,
title = {{Arm Angle Moderates the Association Between Fastball Usage and Elbow/Forearm Injury in MLB Pitchers}},
author = {C. Richards and D. T. La Salle and O. Vila Dieguez and S. R. Ward},
howpublished = {medRxiv},
year = {2026},
month = aug,
doi = {10.64898/2026.08.29.26361727},
url = {https://www.medrxiv.org/content/10.64898/2026.08.29.26361727v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Arm Angle Moderates the Association Between Fastball Usage and Elbow/Forearm Injury in MLB Pitchers
AU - C. Richards
AU - D. T. La Salle
AU - O. Vila Dieguez
AU - S. R. Ward
PY - 2026
DA - 2026/08/29
PB - medRxiv
DO - 10.64898/2026.08.29.26361727
UR - https://www.medrxiv.org/content/10.64898/2026.08.29.26361727v1
AB - BackgroundNewly available arm angle data offers a new dimension to understand rising rates of arm injury in MLB pitchers. PurposeTo evaluate the relationship between arm angle, pitch characteristics, and elbow and forearm injury in MLB pitchers. Study DesignRetrospective cohort study; Level of evidence, 3 MethodsStatcast data from 2020 to 2025 and MLB injured list (IL) data were used to evaluate arm angle and pitch characteristics in relation to elbow and forearm injuries. Results are presented with and without requirements on prior season workload and for same-season and next-season injury incidence. A generalized additive model (GAM) was used to capture non-linear dependence and interactions between selected features and injury incidence to the elbow or forearm. Average marginal effect (AME) odds ratios are reported for main effect terms. ResultsN = 3,812 pitcher-seasons were included. 29% pitchers who underwent UCLR did so in the same season as a forearm injury (tmean = 44, tmedian = 27 days to surgery). Arm angle, fastball usage, and their interaction were the three most predictive features. Arm angle was positively related to incidence of injury ([Formula] = 1.014), fastball usage was inversely related to incidence of injury ([Formula] = 0.243), and arm angle moderated the effect fastball usage at high arm angle, where increased usage was no longer protective. Slider velocity ([Formula] = 1.072), spin rate ([Formula] = 1.001), and usage ([Formula] = 2.039) also significantly predicted injury risk. Fastball velocity was not significant in any fit, with [Formula] = 0.999 across all fits. Fit-level Nagelkerke R2 values ranged from .019 to .052. ConclusionFastball usage and arm angle, not velocity, predicted elbow and forearm injury risk among MLB pitchers, and arm angle was the single most predictive feature. The heterogeneity of risk factors as a function of arm angle, and the novelty of MLB arm angle data, may explain why fastball usage has been previously underexplored as a risk factor.
ER -