Effect of sex, body mass index and physical activity level on peak oxygen uptake among 14-19 years old adolescents

INTRODUCTION: It is recognized that peak oxygen uptake (VO2peak), the highest rate at which oxygen can be consumed during exercise, is the best single measure of young people´s cardiorespiratory fitness. Low cardiorespiratory fitness and inadequate physical activity may be associated with an unhealthy cardiovascular disease risk profile even in children and adolescents. Few longitudinal studies have examined differences in VO2peak during adolescent years while taking the potential effect of physical activity into account. To examine the effect of sex, body mass index (BMI) and physical activity level on longitudinal changes in VO2peak in Norwegian adolescents, 14 to 19 years old boys and girls were studied once a year for six years. METHODS: In total, 116 Norwegian adolescents (61 boys and 55 girls, age at entry: 14.0±0.5 yr, weight: 54.2±10.9 kg, height: 1.63±0.08 m (mean±SD)) were tested for directly measured VO2peak every spring from the year they entered secondary school at 8th grade until they finished 3rd grade at high school. Height, weight and VO2peak were measured by standardized procedures, while data about physical activity level were obtained using a self-administered questionnaire. Multiple regression and linear mixed model analysis were used to examine the relationships between VO2 peak, age, sex, BMI and physical activity level. RESULTS: Sex, BMI and the number of exercising days per week significantly and uniquely explained VO2peak, and collectively these predictors explained 58-71% of the variance in VO2peak at the different age levels. The rate of change in VO2peak over the 14–19 years age range showed a slight increase over the first three or four years, followed by a slight decrease. This pattern was most evident for boys. There was no significant gender differences in the association between VO2peak and physical activity level over time. The strength of association between VO2peak and physical activity level varied over time. The physical activity level explained nearly 30% of the total variance in VO2peak for 15 year-olds, while the corresponding figure for 18 year-olds was less than 9%. CONCLUSION: This study confirms the importance of sex, BMI, and physical activity level as highly significant and independent predictors of aerobic capacity among adolescents. Taking the decrease in VO2peak from 17 years of age into account, the findings point to the importance for adolescents to maintain a high physical activity level, emphasizing activities that increases the aerobic capacity.