Prepubescents' ventilatory responses to exercise with reference to sex and body size

Abstract

Study objectives: To examine the ventilatory responses of prepubescent children to submaximal and peak exercise using appropriate allometric modeling to control for differences in body size. Design: Cross-sectional study of a representative sample of children. Setting: Middle schools (8 to 11 years) in Exeter, UK. Participants: We studied 101 boys and 76 girls aged 11.1 (0.4) years and classified Tanner stage 1 for pubic hair (no true pubic hair). Measurements: At rest: stature, mass, sum of skinfolds, hemoglobin concentration, FVC, and FEV1. During treadmill exercise at 7, 8, 9, and 10 km/h, and at peak exercise: oxygen uptake (V̇O2), minute ventilation (V̇E), tidal volume (VT), and respiratory frequency (Rf). Results: At peak exercise, boys' V̇O2, V̇E, and VT were significantly (p<0.01) higher than girls' values and remained so even when the influence of body size was controlled using allometric principles. There were no significant (p>0.05) sex differences in Rf or the ratios VT/FVC or V̇E/V̇O2. When data were compared at the same relative exercise intensity (ie, 70 to 75% or 80 to 85% peak V̇O2), no significant (p>0.05) sex differences in Rf, VT/FVC, or V̇E/V̇EO2 were detected. Boys' higher (p<0.001) V̇O2 values were reflected by their higher V̇E which remained higher than values for girls at both submaximal levels even when the influence of body size was covaried out. Conclusions: Prepubescent boys demonstrate higher peak V̇O2 than girls and this is supported by a higher V̇E and VT, even when the influence of body size is accounted for using allometry. Other ventilatory responses to both peak exercise and exercise at the same relative intensity are remarkably similar in both boys and girls.