Bone, muscle, and fat: Sex-related differences in prepubertal children

PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: Together, these data indicate that sex is an important determinant of the morphology in humans well before the beginning of puberty. (C) RSNA, 2002.