Sex Differences in Muscle Morphology between Male and Female Sprinters.

There is a marked difference between males and females in sprint running performance, yet a comprehensive investigation of sex differences in the muscle morphology of sprinters remains to completed. This study compared muscle volumes of 23 individual leg muscles/compartments and five functional muscle groups, assessed with 3T magnetic resonance imaging, between male (n=31) and female (n=22) sprinters, and sub-groups of elite males (EM, n=5), elite females (EF, n=5), and performance matched (to elite females) males (PMMEF, n=6). Differences in muscle volume distribution between EM, EF and unathletic male controls (UM) were also assessed. For the full sprint cohorts, males were more muscular than females, but the differences were non-uniform and anatomically variable, with the largest differences in the hip extensors and flexors. However, amongst elite sprinters the sex differences in the volume of the functional muscle groups were almost uniform (absolute volume +47-53%), and the muscle volume distribution of EM was more similar to EF than UM (P<0.039). For PMMEF relative hip extensor volume, but not stature or percent body fat, differentiated for performance (PMMEF and EF < EM) rather than sex. In conclusion, whilst the full cohorts of sprinters showed a marked sex difference in the amount and distribution of muscle mass, elite sprinters appeared to be selected for a common muscle distribution phenotype that for these elite sub-groups was a stronger effect than that of sex. Relative hip extensor muscle volume appeared to be the primary determinant of the sex difference in performance.

The Muscle Morphology of Elite Female Sprint Running.

INTRODUCTION: A paucity of research exists examining the importance of muscle morphological and functional characteristics for elite female sprint performance. PURPOSE: This study aimed to compare lower body muscle volumes and vertical jumping power between elite and subelite female sprinters and assess the relationships of these characteristics with sprint race and acceleration performance. METHODS: Five elite (100 m seasons best [SBE 100 ], 11.16 ± 0.06 s) and 17 subelite (SBE 100 , 11.84 ± 0.42 s) female sprinters underwent: 3T magnetic resonance imaging to determine the volume of 23 individual leg muscles/compartments and five functional muscle groups; countermovement jump and 30 m acceleration tests. RESULTS: Total absolute lower body muscle volume was higher in elite versus subelite sprinters (+15%). Elite females exhibited greater muscle volume of the hip flexors (absolute, +28%; relative [to body mass], +19%), hip extensors (absolute, +22%; relative, +14%), and knee extensors (absolute, +21%), demonstrating pronounced anatomically specific muscularity, with relative hip flexor volume alone explaining 48% of sprint performance variability. The relative volume of five individual muscles (sartorius, gluteus maximus, adductor magnus, vastus lateralis, illiopsoas) were both distinct between groups (elite > subelite) and related to SBE 100 ( r = 0.553-0.639), with the combination of the sartorius (41%) and the adductor magnus (17%) explaining 58% of the variance in SBE 100 . Elite female sprinters demonstrated greater absolute countermovement jump power versus subelite, and absolute and relative power were related to both SBE 100 ( r = -0.520 to -0.741) and acceleration performance ( r = 0.569 to 0.808). CONCLUSIONS: This investigation illustrates the distinctive, anatomically specific muscle volume distribution that facilitates elite sprint running in females, and emphasizes the importance of hip flexor and extensor relative muscle volume.