title: They go straight home - don't they? Using global positioning systems to assess adolescent school-travel patterns.
abstract: BACKGROUND
  Active travel to school is a potential source of physical activity for adolescents, but its assessments often rely on assumptions around travel patterns. Global positioning system (GPS) and accelerometry provide an objective assessment of physical activity from school-travel and the context in which it occurs (where, when, how long).
  
  
  OBJECTIVE
  To describe school-travel patterns of adolescents and to compare estimates of physical activity during the hour before/after school - a commonly used proxy for school-travel time - with physical activity accrued during school trips identified through GPS ('GPS-trips').
  
  
  METHODS
  Adolescents (n=49, 13.3±0.7 years, 37% female) from Downtown Vancouver wore an accelerometer (GT3X+) and GPS (Qstarz) for 7 days (October 2012). Minutes of moderate-to-vigorous physical activity (MVPA) during the hour before/after school and during GPS-trips were calculated for then=130 school-trips made by 43 students. We used multilevel linear regression to assess the association between MVPA during GPS-trips and MVPA during the hour/before school.
  
  
  RESULTS
  Only 55% of school-trips were from/to home and within the hour before/after school ('normal'). Estimates of MVPA during the hour before/after school were higher than during GPS-trips (12.0 vs. 8.0 min). On average, MVPA during GPS-trips was linearly associated with MVPA during the hour before/after school, suggesting that physical activity levels during the hour before/after school are broadly reflective of physical activity from school-travel.
  
  
  CONCLUSIONS
  GPS and accelerometry provide context-rich information relating to school-travel. The hour before/after school may - on average - provide a simple means to crudely estimate physical activity from school-travel when GPS are not available.
authors.affiliation: University of British Columbia - Department of Orthopaedics, Centre for Hip Health and Mobility, 684C-2635 Laurel Street, Vancouver, BC, Canada V5Z 1M9.
authors.forename: Christine
authors.initials: C
authors.lastname: Voss
authors.affiliation: Simon Fraser University - Faculty of Health Sciences, Blusson Hall, Rm 11522, 8888 University Dr, Burnaby, BC, Canada V5A 1S6.
authors.forename: Meghan
authors.initials: M
authors.lastname: Winters
authors.affiliation: University of British Columbia - Department of Family Practice, Centre for Hip Health and Mobility, 7/F, 2635 Laurel Street, Vancouver, BC, Canada V5Z 1M9.
authors.forename: Amanda D
authors.initials: AD
authors.lastname: Frazer
authors.affiliation: University of British Columbia - Department of Orthopaedics and Family Practice, Centre for Hip Health and Mobility, 7/F, 2635 Laurel Street, Vancouver, BC, Canada V5Z 1M9.
authors.forename: Heather A
authors.initials: HA
authors.lastname: McKay
keywords: Adolescent; Health promotion; Physical activity; Spatial behavior; Transportation