Physical activity in relation to aerobic fitness and body fat in 14- to 15-year-old boys and girls

Abstract.

The purpose of this study was to examine the strength of the relationship between different variables of physical activity and aerobic fitness and body fat in adolescent boys and girls. Activity energy expenditure (AEE), time spent in a sedentary state, and time spent engaged in moderate and vigorous physical activity (MVPA, ≥50% peak oxygen uptake, $\dot V{\rm O}_{{\rm 2peak}}$ ) were assessed by the minute-by-minute heart rate monitoring method in 82 randomly selected 14- to 15-year olds (42 boys, 40 girls). Body fat was determined by measuring skinfold thicknesses. $\dot V{\rm O}_{{\rm 2peak}}$ was measured by indirect calorimetry. Somatic maturity level was determined by percentages of adult (i.e. 18 years) height attained at examination. AEE was related to aerobic fitness for both genders (boys, r=0.30, P=0.056; girls, r=0.45, P=0.003). For boys, there was a significant relationship between maturity level and $\dot V{\rm O}_{{\rm 2peak}}$ (r=0.48, P<0.001). For both genders, body fat was significantly and negatively related to $\dot V{\rm O}_{{\rm 2peak}}$ (r=–0.48 and r=–0.43, P<0.01). Body fat and maturity explained 47% of the variation in $\dot V{\rm O}_{{\rm 2peak}}$ in boys, whereas AEE and body fat explained 22% of the variation in $\dot V{\rm O}_{{\rm 2peak}}$ in girls. No significant associations between physical activity variables and the data on body fat were observed. The total amount of physical activity (AEE) was related to $\dot V{\rm O}_{{\rm 2peak}}$ , at least in adolescent girls. Although $\dot V{\rm O}_{{\rm 2peak}}$ seems to be influenced by the maturity level in adolescent boys, the data support the promotion of a daily active lifestyle among young people.