Throwing with the whole body: non-uniform muscle volume profiles in collegiate baseball pitchers.

Abstract

High-speed baseball pitching imposes unique demands on the musculoskeletal system, requiring coordinated force generation across the entire body. Whilepreviousstudies have examined strength or morphology in isolated regions, the full-body distribution of muscle volume in pitchersremainspoorly characterized. This study usedin vivoMRI to quantify muscle volume across 70 upperextremity,lower extremity,and trunk muscles in 42 Division I collegiate pitchers, and compared results to a control cohort of 27 healthy, non-athlete males. A validated AI segmentation pipeline was used to extract individual muscle volumes, and linear regression models based on height × mass were used to generate size-based predictions from the control population. Z-scores were used to assessbody-size-adjusteddifferences between pitchers and controls, while muscle volume fractions and dominance-referenced asymmetries were used to assess muscle distribution and lateralization. Pitchers showed significantly larger muscle volumes than controls in most muscles, with the greatest differences in the latissimus dorsi, gluteus maximus, and erector spinae. Rotator cuff and distal forearm muscles showedrelativelysmalleror no differences. Forearm and scapular musclesexhibitedpronounced asymmetries favoring the pitching side, and differences in asymmetry patterns wereobservedbetween right- and left-handed pitchers. While most muscle volumes scaled with body size,specific muscles includingthe flexor carpiulnarisand pronatorteresshowed reduced scaling strength in pitchers, consistent with targeted differences. These findings provide a comprehensive reference for evaluating muscle development in throwing athletes and offer insight into the distributed, asymmetric, and sport-specific nature of muscular differences in elitepitchers.