Objective: To examine the role of gender differences in
cardiac functional capacity in explaining higher mean values for
maximal oxygen uptake (V̇o2max) in boys
than in girls.
Design: Comparative group exercise
Setting: Pediatric exercise testing
Subjects: Twenty-five prepubertal boys
(mean [± SD] age, 12 ± 0.4 years) and 24 premenarcheal girls
(mean age, 11.7 ± 0.5 years).
Maximal incremental upright cycle exercise.
results: Mean values for V̇o2max
were the following: boys, 47.2 ± 6.1 mL/kg/min; and girls,
40.4 ± 5.8 mL/kg/min (16.8% difference; p < 0.05). The average
maximal stroke index with Doppler echocardiography was 62 ± 9
mL/m2 for boys and 55 ± 9 mL/m2 for girls
(12.7% difference; p < 0.05). No significant gender differences
were seen in maximal heart rate or arterial venous oxygen difference.
When V̇o2max and maximal stroke volume
(SV) were expressed relative to lean body mass, gender differences
declined but persisted, falling to 6.2% and 5.2%, respectively.
Conclusions: These findings indicate that differences in SV
as well as in body composition contribute to gender-related variations
in V̇o2max during childhood. Whether this
reflects small gender differences in relative heart size or dynamic
factors influencing ventricular preload and contractility during
exercise is unknown.