Objectives The objectives of this study were to (1) assess whether the Pitch Timer was associated with the incidence of upper extremity injury (UEI) in Major League Baseball (MLB) Pitchers and (2) assess the association between UEI and Pitcher `Tempo` between 2021 and 2024 in the MLB. Methods This study was a retrospective review of all MLB Pitchers who pitched in at least three out of four seasons between 2021 and 2024. Players were assessed for time spent on the injury list (IL) due to shoulder and/or forearm/elbow-associated pathology. With the Pitch Timer starting in the 2023 season, the incidence of UEI was calculated in pre- and post-Timer cohorts. Games missed per injury were also assessed pre- and post-Timer. Average Pitching Tempo was assessed in pitchers with shoulder injuries, forearm/elbow injuries, and uninjured pitchers. Continuous variables were compared using two-tailed t-tests, and categorical variables were compared using the chi-squared test with a statistical significance set at p < 0.05. Results There were no significant differences in the incidence of shoulder injuries (p = 0.94) or forearm/elbow injuries (p = 0.24) in MLB pitchers between any year from 2021 to 2024. Pitchers who sustained shoulder injuries in 2023-2024 missed significantly more games per injury than pitchers who sustained shoulder injuries in 2021-2022 (p = 0.007). The same trend did not exist in the elbow (p = 0.57). Average Pitch Tempo was similar between pitchers with shoulder and forearm/elbow injuries versus uninjured pitchers (16.72-17.09 s, p = 0.14-0.20). Conclusions The incidence of UEI did not increase in MLB Pitchers following the implementation of the Pitch Timer prior to the 2023 MLB season. Following the introduction of the Pitch Timer in 2023, MLB Pitchers averaged significantly greater games missed per shoulder injury than previous seasons, suggesting there may be a link between the Pitch Timer and shoulder injury severity. Pitching Tempo was not associated with UEI.
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