title: School-day and overall physical activity among youth.
abstract: BACKGROUND
  Increasing school-day physical activity through policy and programs is commonly suggested to prevent obesity and improve overall child health. However, strategies that focus on school-day physical activity may not increase total physical activity if youth compensate by reducing physical activity outside of school.
  
  
  OBJECTIVE
  Objectively measured, nationally representative physical activity data were used to test the hypothesis that higher school-day physical activity is associated with higher overall daily physical activity in youth.
  
  
  METHODS
  Accelerometer data from 2003-2004/2005-2006 National Health and Nutrition Examination Surveys were analyzed in 2012 to estimate physical activity levels during the school day (8AM-3PM) among youth aged 6-19 years (n=2548). Fixed-effects regressions were used to estimate the impact of changes in school-day minutes of moderate-to-vigorous physical activity (MVPA) on changes in total daily MVPA.
  
  
  RESULTS
  Each additional minute of school-day MVPA was associated with an additional 1.14 minutes (95% CI=1.04, 1.24; p<0.001) of total daily MVPA, or 0.14 additional minutes (95% CI=0.04, 0.24; p=0.008) outside the school day, controlling for total daily accelerometer wear time and age, gender, race/ethnicity, and other non-time varying covariates. There were no differences in the effect of school-day MVPA on total MVPA by age group, gender, race/ethnicity, poverty status, or degree of change in MVPA.
  
  
  CONCLUSIONS
  Higher school-day MVPA was associated with higher daily MVPA among U.S. youth with no evidence for same-day "compensation." Increasing school-based physical activity is a promising approach that can improve total daily physical activity levels of youth.
authors.affiliation: Department of Social and Behavioral Sciences, Harvard School of Public Health, Boston, MA, USA. michael.long@mail.harvard.edu
authors.forename: Michael W
authors.initials: MW
authors.lastname: Long
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Sobol
authors.forename: Angie L
authors.initials: AL
authors.lastname: Cradock
authors.forename: S V
authors.initials: SV
authors.lastname: Subramanian
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Blendon
authors.forename: Steven L
authors.initials: SL
authors.lastname: Gortmaker
mesh_terms: D061725:Accelerometry / Q000379:methods / Q000706:statistics & numerical data; D000293:Adolescent; D002648:Child; D002669:Child Welfare; D006291:Health Policy; D006293:Health Promotion / Q000379:methods*; D006801:Humans; D007899:Leisure Activities; D016014:Linear Models; D009043:Motor Activity; D009749:Nutrition Surveys / Q000706:statistics & numerical data; D009765:Obesity / Q000517:prevention & control; D010809:Physical Fitness; D012572:School Health Services / Q000458:organization & administration*; D012574:Schools; D012959:Socioeconomic Factors; D013997:Time Factors; D014481:United States