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

The purpose of this study was to examine the strength of the relationship b etween different variables of physical activity and aerobic fitness and bod y fat in adolescent boys and girls. Activity energy expenditure (AEE), time spent in a sedentary state, and time spent engaged in moderate and vigorou s physical activity (MVPA, greater than or equal to 50% peak oxygen uptake, (V)over dotO(2peak)) were assessed by the minute-by-minute heart rate moni toring method in 82 randomly selected 14- to 15-year olds (42 boys, 40 girl s). Body fat was determined by measuring skinfold thicknesses. (V)over dotO (2peak) was measured by indirect calorimetry. Somatic maturity level was de termined by percentages of adult (i.e. 18 years) height attained at examina tion. 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 relations hip between maturity level and (V)over dotO(2peak) (r=0.48, P<0.001). For b oth genders, body fat was significantly and negatively related to (V)over d otO(2peak) (r=-0.48 and r=0.43, P<0.01). Body fat and maturity explained 47 % of the variation in i(V)over dotO(2peak) in boys, whereas AEE and body fa t explained 22% of the variation in (V)over dotO(2 peak) in girls. No signi ficant associations between physical activity variables and the data on bod y fat were observed. The total amount of physical activity (AEE) was relate d to (V)over dotO(2peak), at least in adolescent girls. Although (V)over do tO(2peak) seems to be influenced by the maturity level in adolescent boys, the data support the promotion of a daily active lifestyle among young peop le.