Influence of cardiac functional capacity on gender differences in maximal oxygen uptake in children

Objective: To er;examine the role of gender differences in cardiac function al capacity in explaining higher mean values for maximal oxygen uptake (VO2 max) in boys than in girls. Design: Comparative group exercise testing. Setting: Pediatric exercise testing laboratory, Subjects: Twenty-five prepu bertal boys (mean [+/- SD] age, 12 +/- 0.4 years) and 24 premenarcheal girl s (mean age, 11.7 +/- 0.5 years). Interventions: Maximal incremental upright cycle exercise, Measurements and results: Mean values for VO(2)max were the following: boys , 47.2 +/- 6.1 mL/kg/min; and girls, 40.4 +/- 5.8 mL/kg/min (16.8% differen ce; p < 0.05), The average maximal stroke index with Doppler echocardiograp h, was 62 +/- 9 mL/m(2) for boys and 55 +/- 9 mL/m(2) for girls (12.7% diff erence; p <0.05). No significant gender differences were seen in maximal he art rate or arterial venous oxygen difference. When VO(2)max and maximal st roke volume (SV) were expressed relative to lean body mass, gender differen ces declined but persisted, falling to 6.2% and 5.2%, respectively. Conclusions: These findings indicate that differences in SV as well as in b ody composition contribute to gender-related variations in VO(2)max during childhood. Whether this reflects small gender differences in relative heart size or dynamic factors influencing ventricular preload and contractility during exercise is unknown.