Longitudinal changes in body composition, physical capacities and energy expenditure in boys and girls during the onset of puberty

Background: The onset of puberty is a period of rapid anatomical and physio logical alterations expected to induce changes in metabolic rate and energy requirements of children. Aim of the study: To evaluate the changes in anthropometrical features, bod y composition, physical capacities, and energy expenditure (EE) of boys and girls during the period of onset of puberty. Methods: Sixteen children (8 boys and 8 girls were recruited in the same sc hool-class and studied both at 10.4 and 12.8 years of age. Body composition was assessed by bioimpedance analysis. Peak oxygen uptake (peak VO2) was m easured using an automated on-line system during exercising on a cycle ergo meter. Energy expenditure (EE) was determined by whole-body indirect calori metry over a 24-h period after a 12-h period of adaptation to the calorimet ers. Volunteers followed the same activity programme that included four 15- min periods of exercise. Results: During the onset of puberty, boys and girls gained 4.7 +/- 2.1 kg. y(-1) (P < 0.0003) fat-free mass (FFM), whereas fat mass gain was 1.0 +/- 1 .2 kg.y(-1) (P < 0.05) in girls and 0.20 +/- 0.66 kg.y(-1) in boys (NS). Pe ak VO2 adjusted for differences in FFM was not significantly affected by ge nder or pubertal stage. However, adjusted external mechanical power perform ed at peak VO2 was higher in pubertal than in prepubertal children, by 40% (P < 0.0001) and 22% (P < 0.003) in boys and girls, respectively. It was al so 17% (P < 0.0002) higher in pubertal boys than in pubertal girls. Daily a nd sleeping EE increased by 38% and 32% in boys and girls, respectively, du ring the 2.4-y period (P < 0.0001). Adjusted EEs were also significantly hi gher in pubertal than in prepubertal boys (P < 0.05 and P < 0.003), but not in girls. The main significant determinants of daily EE were FFM (r(2) = 0 .866, P < 0.0001), peak VO2 (r(2) = 0.017, P < 0.04), and age (r(2) = 0.014 , P < 0.05). Tanner's stage was an additional determinant of sleeping EE (r (2) = 0.025, P < 0.006). Conclusions: The increases in physical capacities and EE during the onset o f puberty indicated clear gender differences, which could be explained main ly by alterations of body composition in boys and girls, and by changes in hormonal status in boys. They also stressed the significant increase in ene rgy requirements of children, especially boys, at an early stage of puberty .