Changes In Appendicular Skeletal Muscle Mass In Division I Collegiate Baseball Pitchers

Skeletal muscle mass (SKM) plays a critical role in sports performance and injury risk. For baseball players, maintaining SKM throughout the in-season is challenging given the large number of games played (50 to 56), shortened recovery time and travel. Of concern, pitchers rely heavily on the repeated use of their dominant arm followed by between-game resting periods. Quantifying changes in SKM from pre- through in-season is understudied, especially using gold standard methodology. PURPOSE: To quantify the changes in SKM from pre- through in-season in Division I collegiate baseball pitchers and evaluate differences between dominant and non-dominant upper and lower body limbs METHODS: Seventeen, male baseball players aged 20.9 ± 1.3 yrs with an average height and weight of 186.3 ± 3.8 cm and 92.7 ± 6.5 kg, respectively, participated in the study. Appendicular SKM mass, the summed SKM masses of the upper and lower limbs, was quantified via DEXA scans at two, time points, pre- (February 2024) and late, in-season (April 2024). Participants followed the established pre-testing guidelines and were eligible for DEXA scans (e.g., fasted, hydrated). All scans were completed in the morning. Changes in SKM mass were quantified for the dominant and non-dominant limbs and compared via studentized paired t-tests. RESULTS: In pitchers, appendicular SKM significantly declined (1.9 ± 0.7 kg; 95% CI: 1.5, 2.3 kg; p < 0.001) from pre through late, in-season. Similarly, significant reductions in the dominant (0.5 ± 0.5 kg; 95% CI: 0.3, 0.8 kg; p < 0.001) and non-dominant upper limbs (0.3 ± 0.4 kg; 95% CI: 0.08, 0.4 kg; p = 0.004) and dominant (0.5 ± 0.4 kg; 95% CI: 0.3, 0.7 kg; p < 0.001) and non-dominant (0.6 ± 0.4 kg; 95% CI: 0.3, 0.8 kg; p < 0.001) lower limbs. The SKM mass of the dominant arm decreased 11.2% compared to 5.8% in the non-dominant arm, this difference, however, did not reach statistical significance. CONCLUSIONS: Significant decrements in total appendicular SKM mass in collegiate baseball pitchers were observed. Pitchers also exhibited a nearly 2-fold non-statistically significant decrease in SKM mass in their dominant relative to their non-dominant arm. Tracking changes in SKM mass throughout pre- and in-seasons of collegiate baseball may provide coaches information critical to their pitchers’ performance and risk of injury.