Hamstring Injuries in MLB Are Not Lateralized to the Throwing Arm or Inside Leg: An Analysis of 1435 In-Game Injuries (2011–2017)

Hamstring injuries in professional baseball remain incompletely understood related to laterality in being either ipsilateral or contralateral to the throwing arm. General and specific injury comparisons were investigated with respect to independent lower-limb, environmental conditions, position, throwing arm side relationship, and age. More left and non-dominant-sided hamstring injuries were hypothesized in baserunning with greater injury presence in infielders and younger players. Between 2011 and 2017, 1435 hamstring injuries were identified within the major league baseball Health and Injury Tracking System. Data included laterality (left versus right, contralateral versus ipsilateral to the throwing arm), position, time of season, days missed, mechanism of injury, and age. Chi-Square, t-tests and Mann–Whitney U tests evaluated significant findings with an a priori of p < 0.05. No significant differences in injury laterality (right vs. left) with baserunning (p = 0.797) or in total (p = 0.367) or contralateral vs. ipsilateral injury laterality in total (p = 0.770) were seen. No significant laterality differences were seen by position, days missed, or time in the season. In general, most injuries occurred in the first half of the season (67.8%, 973/1435). Outfielders were the most injured position (34%, 495/1435). Athletes under 25 years were the most injured age group as compared to the 30–34 group (p = 0.037), 35–39 group (p = 0.038), and the 40+ group (p = 0.024). No statistically significant hamstring injury asymmetries were identified among major league baseball players despite biomechanical theories suggesting potential differences in lower-limb loading during baseball activities. Younger athletes demonstrated greater injury susceptibility, highlighting the need for future investigation into factors that may contribute to elevated injury incidence in younger professional baseball players.