Bone, Muscle, and Fat: Sex-related Differences in Prepubertal Children

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Abstract
To determine whether there are sex-related differences in vertebral cross-sectional dimensions, in paraspinous muscle area, and in the amount of fat in the subcutaneous and visceral compartments of prepubertal boys and girls. Subcutaneous fat, visceral fat, paraspinous musculature, and vertebral cross-sectional dimensions were studied in 31 pairs of prepubertal healthy white girls and boys 5-10 years of age, rigorously matched for age, height, and weight. Data were analyzed with the Student t test and multiple regression analysis. Sex had a differential effect on fat accumulation and musculoskeletal development. Compared with boys, girls had, on average, 28% greater total fat and 30% higher subcutaneous fat (P <.001 for both), but 10% less paraspinous musculature (P =.002) and 15% smaller vertebral cross-sectional dimensions (P <.001). In contrast, the sexes were monomorphic for visceral fat (P =.24). Stepwise regression analysis indicated that only 22% of the difference in vertebral cross-sectional area could be explained by sex-related differences in paraspinous musculature. Together, these data indicate that sex is an important determinant of the morphology in humans well before the beginning of puberty.