The purpose of this study was to investigate gender- and event-related differences in trunk muscle size in high school athletes. Magnetic resonance images of the trunk region were obtained for a total of 204 female and male athletes majoring in sprinting, long-distance running, throwing events, volleyball, badminton, boat events, canoeing and judo. Thirty-six untrained high school students (Control) also participated. From the images, muscle volumes of the rectus abdominis (RAV), internal and external oblique muscles (OBV), psoas major, quadratus lumborum, erector spine muscles, and the total muscle compartment (TotalV) were estimated. Fat-free mass (FFM) was also measured by air-plethysmography, and the estimated muscle volumes per FFM were compared to assess gender- and event-related differences in trunk muscularity. Predominant development of trunk muscles on the non-dominant side was observed in athletes involved in throwing events, badminton and volleyball, regardless of gender. While males showed significantly larger values than the females for all of the estimated muscle volumes in terms of absolute values, there was no gender difference in RAV/FFM, although males still showed significantly larger values in the other muscles after taking difference of body size into account. Judo and throwing-event athletes showed the largest TotalV in terms of absolute value; however, sprinters and badminton players showed the largest values of TotalV/FFM, suggesting predominant development of trunk muscles in these sports events. Judo athletes showed predominant development of only OBV, and no difference in trunk muscularity was found among volleyball athletes, long-distance runners and untrained control groups. These results demonstrate that trunk muscle size in high school athletes depends on the specialist sport event, and it is assumed that sport-specific motions/training could affect the development of trunk muscularity.
