Sex difference in peak oxygen uptake in prepubertal children

Area of Science:

• Exercise Physiology
• Pediatric Sports Medicine
• Cardiovascular Research

Background:

• Prepubertal boys typically exhibit greater aerobic fitness (peak V O(2)) than girls, often attributed to larger lean body mass (LBM) and cardiac output.
• Existing research suggests boys maintain higher aerobic fitness even when LBM is controlled, implying other physiological factors are involved.

Purpose of the Study:

• To investigate sex differences in peak V O(2), heart size, peak cardiac output, and peak arterio-venous oxygen difference (A-VO(2)) in prepubertal children with similar LBM.
• To determine if central cardiovascular factors (heart size, cardiac output) or peripheral factors (A-VO(2) difference) explain sex-based differences in aerobic capacity.

Main Methods:

• Selected prepubertal boys and girls with matched mean LBM.
• Measured left ventricular mass (LVM) and end-diastolic volume (LVEDV) using cardiac MRI.
• Assessed peak V O(2) via incremental cycle ergometry and peak cardiac output using thoracic bioimpedance.

Main Results:

• Boys demonstrated significantly higher peak V O(2) and peak A-VO(2) difference compared to girls.
• No significant sex differences were observed in peak cardiac output, LVM, or LVEDV.
• Central factors (heart size, peak cardiac output) were proportional to LBM and sex-independent.

Conclusions:

• Sex differences in prepubertal aerobic fitness are not explained by central cardiovascular factors like heart size or cardiac output, which scale with LBM.
• Peripheral factors, potentially related to muscle physiology and impacting A-VO(2) difference, likely underlie the higher peak V O(2) observed in boys.