The ontogeny of sex differences in exercise performance.

Sex differences in adult athletic performance are driven by the 20-to 30-fold increase in testosterone production of male puberty creating larger and stronger muscle, bone and cardiorespiratory functions, and higher hemoglobin creating male physical advantages in power sports, where strength, speed, or endurance determine success. Before puberty, boys also surpass girls in age-group records despite no difference in circulating testosterone over the decade from minipuberty to puberty. However, the relative magnitude of the prepubertal, relative to pubertal, sex differences in exercise performance remain uncertain. To investigate the magnitude of these differences in a unitary dataset, this was a secondary analysis of a exercise performance of 85 347 healthy 9- to 17-year-old Australian schoolchildren between 1985 to 2009. Boys surpassed girls in 8 of 9 exercises excepting 1, a stretching exercise, in which girls surpassed boys. For each exercise the magnitude of the pubertal changes were much larger than those of prepubertal differences. These findings in normative tests extend previous studies of competitive age records of prepubertal children and compare the same tests over the pubertal transition. These findings confirm that the quantitatively dominant sex differences in exercise performance are those of puberty. That at least 1 prepubertal exercise test is dominated by girls indicates that the prepubertal differences are more likely to be biological rather than sociological, related to boy's greater habitual play or exercise. It is postulated that these prepubertal sex differences may arise from the combination of androgen imprinting during minipuberty propagated by muscle memory.