Regional morphology of lateral abdominal muscles in collegiate softball players

Background Lateral abdominal (LA) muscles show asymmetry in batting sports, and different LA regions perform distinct functions, suggesting region-specific hypertrophy. This study examined the segmental morphology of LA muscles in male collegiate softball players. Methods Eight male college softball players with asymmetrical movement and nine male long-distance runners (symmetrical controls) participated. Magnetic resonance images were used to determine the volume of the upper, middle, and lower parts of the LA muscles. All muscle volumes were normalized by body weight. Comparisons were made between the batting side (D side) and non-batting side (ND side) for the softball group, and between the dominant (D side) and non-dominant sides (ND side) for the control group. To compare muscle volumes, a two-way ANOVA with Bonferroni post hoc correction was used to examine the effects of both groups (softball vs. control) and body side (D side vs. ND side) on LA muscle volumes. Results A significant interaction was observed at the middle region (F = 28.243, p < 0.001), with the ND side of the softball group showing significantly greater volumes than the D side ( p < 0.001). In the lower region, a significant main effect was observed (F = 12.220, p = 0.003), with the ND side exhibiting greater volumes than the D side. Conclusion Male collegiate softball players demonstrate asymmetrical, region-specific morphology of the lateral abdominal muscles, with pronounced hypertrophy in the middle region on the non-dominant side, reflecting the mechanical demands of sport-specific asymmetrical movement.