Sex difference in peak oxygen uptake in prepubertal children

Prepubertal boys' greater aerobic fitness (peak (V) over dotO(2)) has been attributed to their larger lean body mass (LBM) this bestowing a greater heart size and consequent larger maximum cardiac output. No difference in peak arterio-venous (A-VO(2)) difference is thought to exist. However other work indicates that boys' aerobic fitness remains 5% higher even after controlling for differences in LBM. Consequently the purpose of this Study was to investigate whether peak (V) over dotO(2), heart size. peak cardiac output and peak A-VO(2) difference Would be comparable between a group of boys and girls with a similar LBM. A group of 9 prepubertal boys and 9 prepubertal girls with a similar mean LBM (27.0 +/- 1.4 boys vs. 27.0 +/- 2.0 kg girls) were selected. Left ventricular mass (LVM) and end diastolic volume (LVEDV) were measured using cardiac magnetic resonance imaging, Peak (V) over dotO(2) was determined on a cycle ergometer following an incremental exercise protocol to exhaustion. and cardiac Output wits recorded using thoracic bioimpedance. Boys' peak (V) over dotO(2) (1.41 +/- 0.18 L min(-1) vs. 1.23 +/- 0.08 L min-1) and A-VO(2) difference (14.8 +/- 2.1 mL 100 mL(-1) vs. 12.6 +/- 1.6 mL 100 mL(-1)) were significantly (p < 0.05) higher than girls' values, but there were no significant sex differences in peak cardiac Output (10.0 +/- 1.4 L min(-1) vs. 9.9 +/- 1.40 L min(-1)), LVM (97 +/- 13 g vs. 93 +/- 20 g) or LVEDV (77 +/- 8 mL vs. 70 +/- 13 mL). Central factors of heart size and peak cardiac output are Proportional to the LBM of the individual and sex independent. Sex differences in peripheral factors; such as muscle fibre type profile, may affect A-VO(2) difference and underlie prepubertal boys' higher peak (V) over dotO(2). (C) 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.