title: Trends in physical activity and sedentary behaviour in adolescence: ethnic and socioeconomic differences.
abstract: OBJECTIVE
  To assess developmental trends in physical activity and sedentary behaviour in British adolescents in relation to sex, ethnicity and socioeconomic status (SES).
  
  
  METHODS
  A 5-year longitudinal study of a diverse cohort of students aged 11-12 years at baseline in 1999.
  
  
  METHODS
  36 London schools sampled using a stratified random sampling procedure.
  
  
  METHODS
  A total of 5863 students categorised as white, black or Asian, and stratified for SES using the Townsend Index.
  
  
  METHODS
  Number of days per week of vigorous activity leading to sweating and breathing hard. Hours of sedentary behaviour, including watching television and playing video games. Data were analysed using multilevel, linear, mixed models.
  
  
  RESULTS
  Marked reductions in physical activity and increases in sedentary behaviour were noticed between ages 11-12 and 15-16 years. Boys were more active than girls, and the decline in physical activity was greater in girls (46% reduction) than in boys (23%). Asian students were less active than whites, and this was also true of black girls but not boys. Black students were more sedentary than white students. Levels of sedentary behaviour were greater in respondents from lower SES. Most differences between ethnic and SES groups were present at age 11 years, and did not evolve over the teenage years.
  
  
  CONCLUSIONS
  Physical activity declines and sedentary behaviour becomes more common during adolescence. Ethnic and SES differences are observed in physical activity and sedentary behaviour in British youth that anticipate adult variations in adiposity and cardiovascular disease risk. These are largely established by age 11-12 years, so reversing these patterns requires earlier intervention.
authors.affiliation: Cancer Research UK Health Behaviour Unit, Department of Epidemiology and Public Health, University College London, London WC1E 6BT, UK.
authors.forename: Naomi Henning
authors.initials: NH
authors.lastname: Brodersen
authors.forename: Andrew
authors.initials: A
authors.lastname: Steptoe
authors.forename: David R
authors.initials: DR
authors.lastname: Boniface
authors.forename: Jane
authors.initials: J
authors.lastname: Wardle
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000208:ethnology / Q000502:physiology*; D015992:Body Mass Index; D002318:Cardiovascular Diseases / Q000517:prevention & control*; D002648:Child; D015331:Cohort Studies; D005006:Ethnicity; D015444:Exercise / Q000502:physiology*; D005260:Female; D015438:Health Behavior / Q000208:ethnology; D006801:Humans; D008019:Life Style / Q000208:ethnology; D008137:Longitudinal Studies; D008297:Male; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors