Chest
Volume 124, Issue 4, October 2003, Pages 1494-1499
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Clinical Investigations
Pediatrics
Influence of Body Composition, Hemoglobin Concentration, and Cardiac Size and Function of Gender Differences in Maximal Oxygen Uptake in Prepubertal Children

https://doi.org/10.1378/chest.124.4.1494Get rights and content

Objective

To determine the relative contribution of the gender difference in body composition, blood hemoglobin concentration, and cardiac dimension and function at rest and exercise of the gender difference in maximal oxygen uptake ( V˙o2max) in 10- to 12-year-old children.

Subjects

Thirty-five healthy children (17 girls and 18 boys; mean ± SD age, 10.5 ± 0.4 years).

Experimental design

An anthropometric evaluation (body surface area, body fat content, and lean body mass [LBM]), assessment of hemoglobin concentration, echocardiographic evaluation at rest (left ventricular dimensions, and diastolic and systolic indexes at rest), and cardiovascular evaluation during a maximal cycle exercise (stroke volume [SV], total peripheral resistance).

Results

The boys exhibited a higher mass-relative V˙o2max than the girls (47.9 mL/kg/min vs 40.9 mL/kg/min, respectively); but when normalized for LBM (allometric equation), the difference totally disappeared (19.0 mL/kg LBM1.33/min vs 18.9 mL/kg LBM1.33/min, respectively). No significant gender differences were seen in maximal heart rate and arteriovenous oxygen difference; however, maximal SV (SVmax) was significantly higher in boys than in girls, but when expressed relative to LBM, the difference was no longer significant.

Conclusions

These findings demonstrate that contrary to adults, the sole limiting factor of V˙o2 that distinguished boys from girls was a lower SVmax in the latter; however, this gender difference totally disappeared when normalized for LBM. Consequently, the gender difference in heart size and cardiac function during exercise should be interpreted as only one aspect of the lower LBM in girls and not as reflective of a more basic functional gender difference.

Section snippets

Subjects

Thirty-five healthy children (17 girls and 18 boys) participated in the entire experiment. All were volunteers from a local school who were examined clinically on the day of the test, and their pubertal status was assessed.14 Any child exhibiting signs of pubertal development was excluded from taking part. This study received approval from the local ethics committee, and written informed consent was obtained from all the children’s parents. All children were active but not participating in

Results

The physical characteristics of the children are reported in Table 1 . No significant differences were observed between the boys and girls in height and body mass. Girls tended to have higher body fat mass content, but the difference failed to reach statistical significance; however, LBM was higher in the boys than in girls. Hemoglobin concentration was similar in both groups.

Resting echocardiographic data are outlined in Table 2 . The aortic diameter was higher in the boys than in the girls,

Discussion

The major finding of the present study was that gender differences in V˙o2max in children were due principally to absolute SV differences given that HR and DAVO2 were similar in boys and girls. However, allometric normalization of absolute SV for LBM totally eliminated this gender difference, and according to power calculation the group size was sufficient. Consequently, gender difference in V˙o2max in children only appears to be a reflection of differences in body composition but not

ACKNOWLEDGMENT

We thank Mrs. Margaret Manson for her assistance with the English.

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