title: Relation between the changes in physical activity and body-mass index during adolescence: a multicentre longitudinal study.
abstract: BACKGROUND
  The 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.
  
  
  METHODS
  BMI 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.
  
  
  RESULTS
  Each 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<0.0001) for white girls. Similar results were apparent for sum of skinfold thickness. For moderately active girls, changes in BMI and sum of skinfold thickness were about midway between those for active and inactive girls.
  
  
  CONCLUSIONS
  Changes in activity levels of US girls during adolescence significantly affected changes in BMI and adiposity. Thus, preventing the steep decline in activity during adolescence is an important method to reduce obesity.
authors.affiliation: Department of Internal Medicine, University of New Mexico School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM 87131-0001, USA. skimm@salud.unm.edu
authors.forename: Sue Y S
authors.initials: SY
authors.lastname: Kimm
authors.forename: Nancy W
authors.initials: NW
authors.lastname: Glynn
authors.forename: Eva
authors.initials: E
authors.lastname: Obarzanek
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Kriska
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Daniels
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Barton
authors.forename: Kiang
authors.initials: K
authors.lastname: Liu
mesh_terms: D000293:Adolescent; D000328:Adult; D044383:Black People; D015992:Body Mass Index; D002648:Child; D002149:Energy Intake; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D009765:Obesity / Q000517:prevention & control; D012885:Skinfold Thickness; D044465:White People