Association of Fatigue and Ulnar Collateral Ligament Injury in Professional Baseball Pitchers

Little is known about the subclinical changes to the ulnar collateral ligament (UCL) throughout an entire competitive season. This knowledge gap is due to limitations of how physical workload measures are defined and collected. This study provides a proof of concept for the development of a novel measurement of physiological fatigue. It will further investigate whether there is an association between physiological workload and UCL injury probability. This study collected demographic, environmental, performance and injury history information on 1,633 pitchers during the 2018 and 2019 seasons. Fatigue Adjusted Pitch Count was formulated and quantified from these measures. Time-to-event analysis was used on the 2018-2019 season data to validate the hypothesis that consistently elevated FAPC during a competitive season is an indicator of UCL injury risk. A Cox Proportional Hazards analysis found FAPC in its current version to have a weak, negative association with UCL injury. A posthoc inspection found FAPC to have a slightly stronger association with UCL injury than actual pitch count. Pitching status (starter versus reliever) was a finding of statistical and contextual relevance, warranting further research. This study provides the initial steps towards the validation and potential adoption of this real-time, performance-based measure of fatigue. Further validation and refinement of the FAPC calculation can provide coaches, teams, and clinicians holistic, data-informed guidance for the surveillance of injury, maximizing sport-specific and overall health