Relation between the changes in physical activity and body-mass index during adolescence: a multicentre longitudinal study

SummaryBackgroundThe role of physical activity in preventing obesity during adolescence remains unknown. We examined changes in activity in relation to changes in body-mass index (BMI) and adiposity in a cohort of 1152 black and 1135 white girls from the USA, who were followed up prospectively from ages 9 or 10 to 18 or 19 years.MethodsBMI and sum of skinfold thickness were assessed annually, whereas habitual activity was assessed at years 1 (baseline), 3, 5, and 7–10. Each girls' overall activity status was categorised as active, moderately active, or inactive. Longitudinal regression models examined associations between changes in activity and in overall activity status with changes in BMI and in sum of skinfold thickness.FindingsEach decline in activity of 10 metabolic equivalent [MET]-times per week was associated with an increase in BMI of 0·14 kg/m2 (SE 0·03) and in sum of skinfold thickness of 0·62 mm (0·17) for black girls, and of 0·09 kg/m2 (0·02) and 0·63 mm (0·13) for white girls. At ages 18 or 19 years, BMI differences between active and inactive girls were 2·98 kg/m2 (p<0·0001) for black girls and 2·10 kg/m2 (p