Maximum oxygen uptake and objectively measured physical activity in Danish children 6-7 years of age: the Copenhagen school child intervention study

Objectives: To provide normative data on maximum oxygen uptake (V^·O₂MAX) and physical activity in children 6-7 years of age and analyse the association between these variables.

• Methods: VO₂MAX was measured in 366 boys (mean (SD) 6.8 (0.4) years of age) and 332 girls (6.7 (0.4) years of age) from preschool classes in two suburban communities in Copenhagen, during a progressive treadmill exercise. Habitual physical activity was measured with accelerometers.
• Results: Boys had higher VO₂MAX both in absolute values (1.19 (0.18) v 1.06 (0.16) litres/min (+11%), p<0.001) and relative to body weight (48.5 (6.0) v 44.8 (5.6) ml/kg/min (+8%); p<0.001) than girls. The difference in VO₂MAX between boys and girls decreased to +2% when expressed relative to lean body mass (LBM). Absolute VO₂MAX was related to LBM, body mass, and stature (all p<0.001). Boys were more physically active than girls (mean counts +9.4%, p<0.001), and even when boys and girls with the same VO₂MAX were compared, boys were more active. The difference in physical activity between the sexes was higher when sustained activity of higher intensity was compared.
• Conclusions: VO₂MAX is higher in boys than girls (+11%), even when related to body mass (+8%) and LBM (+2%). Most of the difference in VO₂MAX relative to body mass was explained by the larger percentage body fat in girls. When boys and girls with the same VO₂MAX were compared, boys engaged in more minutes of exercise of at least moderate intensity.