title: Moderate-to-vigorous physical activity is associated with decreases in body mass index from ages 9 to 15 years.
abstract: OBJECTIVE
  The purpose of this study is to determine whether time spent in objectively measured physical activity is associated with change in body mass index (BMI) from ages 9 to 15.
  
  
  METHODS
  The participants were enrolled in the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (n = 938). At ages 9, 11, 12, and 15 the time spent in moderate-to-vigorous physical activity (MVPA) was objectively measured, and BMI was calculated (kg/m(2) ). Longitudinal quantile regression was used to analyze the data. The 10th, 25th, 50th, 75th, and 90th BMI percentiles were modeled as the dependent variables with age and MVPA (h/day) modeled as predictors. Adjustment was also made for gender, race, sleep, healthy eating score, maternal education, and sedentary behavior.
  
  
  RESULTS
  A negative association between MVPA and change in BMI was observed at the 90th BMI percentile (-3.57, 95% CI -5.15 to -1.99 kg/m(2) per hour of MVPA). The negative association between time spent in MVPA and change in BMI was progressively weaker toward the 10th BMI percentile (-0.27, 95% CI -0.62 to 0.07 kg/m(2) per hour of MVPA). The associations remained similar after adjusting for the covariates, and when the analyses were stratified by gender.
  
  
  CONCLUSIONS
  Time spent in MVPA was negatively associated with change in BMI from age 9 to 15. The association was strongest at the upper tail of the BMI distribution, and increasing time spent in MVPA could help reduce the prevalence of childhood obesity.
authors.affiliation: Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA. jmitch@mail.med.upenn.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Mitchell
authors.forename: R R
authors.initials: RR
authors.lastname: Pate
authors.forename: V
authors.initials: V
authors.lastname: España-Romero
authors.forename: J R
authors.initials: JR
authors.lastname: O'Neill
authors.forename: M
authors.initials: M
authors.lastname: Dowda
authors.forename: P R
authors.initials: PR
authors.lastname: Nader
mesh_terms: D000293:Adolescent; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002648:Child; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology* / Q000517:prevention & control*; D015995:Prevalence; D057185:Sedentary Behavior; D014481:United States / Q000453:epidemiology