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1 Department of Pediatrics, University of California, Irvine College of Medicine, Orange 92868; 3 Harbor-University of California Los Angeles Medical Center, Torrance, California 90509; and 2 Connecticut Children's Medical Center and Department of Pediatrics, University of Connecticut Health Center, Farmington, Connecticut 06030
Little is known about the relationship among training,
energy expenditure, muscle volume, and fitness in prepubertal
girls. Because physical activity is high in prepubertal
children, we hypothesized that there would be no effect of training.
Forty pre- and early pubertal (mean age 9.1 ± 0.1 yr) nonobese
girls enrolled in a 5 day/wk summer school program for 5 wk and were randomized to control (n = 20) or training groups
(n = 20; 1.5 h/day, endurance-type exercise). Total
energy expenditure (TEE) was measured using doubly labeled water, thigh
muscle volume using magnetic resonance imaging, and peak O2
uptake (
O2 peak) using cycle ergometry.
TEE was significantly greater (17%, P < 0.02) in the
training girls. Training increased thigh muscle volume (+4.3 ± 0.9%, P < 0.005) and
O2 peak (+9.5 ± 6%,
P < 0.05), effects surprisingly similar to those
observed in adolescent girls using the same protocol (Eliakim A,
Barstow TJ, Brasel JA, Ajie H, Lee W-NP, Renslo R, Berman N, and Cooper
DM, J Pediatr 129: 537-543, 1996). We further
compared these two sample populations: thigh muscle volume per weight
was much lower in adolescent compared with prepubertal girls (17.0 ± 0.3 vs. 27.8 ± 0.6 ml/kg body mass; P < 0.001), and allometric analysis revealed remarkably low scaling factors
relating muscle volume (0.34 ± 0.05, P < 0.0001), TEE (0.24 ± 0.06, P < 0.0004), and
O2 peak (0.28 ± 0.07, P < 0.0001) to body mass in all subjects. Muscle and
cardiorespiratory functions were quite responsive to brief training in
prepubertal girls. Moreover, a retrospective, cross-sectional analysis
suggests that increases in muscle mass and
O2 peak may be depressed in nonobese
American girls as they mature.
exercise; doubly labeled water; magnetic resonance imaging; oxygen uptake
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