title: The tracking of active travel and its relationship with body composition in UK adolescents.
abstract: BACKGROUND
  To examine the tracking of active travel through adolescence, and its association with body mass index (BMI) and fat mass at age 17 in a UK cohort.
  
  
  METHODS
  We analysed data collected from the Avon Longitudinal Study of Parents and Children (ALSPAC). The analyses include all participants with self-reported travel mode to school at ages 12, 14 and 16 years, and measured height, weight and body composition at age 17 (n=2,026). Tracking coefficients were calculated for individual travel behaviours (including walking and cycling) through adolescence using Generalised Estimating Equations. Linear regression analyses examined associations between travel pattern (consistently passive, consistently active, active at two time points or active at one time point), BMI, and DXA-measured fat mass (expressed as internally derived standard deviation scores) at 17 years. Analyses were adjusted for height (where appropriate), sex, age, parental social class, and maternal education with interaction terms to assess sex differences.
  
  
  RESULTS
  There was substantial tracking in active travel through adolescence, with 38.5% of males and 32.3% of females consistently walking or cycling to school. In males, a consistently or predominantly active travel pattern was associated with a lower BMI SD score at age 17 (consistently active: adjustedβ=-0.23; 95% CI -0.40, -0.06; active at two time points: adjustedβ-0.30; 95% CI -0.50, -0.10) compared to those with a consistently passive pattern. No associations were seen in females.
  
  
  CONCLUSIONS
  Maintenance of active travel behaviours throughout adolescence may help to protect against the development of excess BMI in males. In addition to encouraging the adoption of active travel to school, public health messages should aim to prevent drop out from active travel to promote good health in youth.
authors.affiliation: National Institute for Health Research, Bristol Biomedical Research Unit in Nutrition, Diet and Lifestyle, Level 3 University Hospitals Bristol Education and Research Centre, Upper Maudlin Street, BS2 8AE, Bristol, UK; Centre for Exercise, Nutrition and Health Sciences, School for Policy Studies, 8 Priory Road, University of Bristol, BS8 1TZ, Bristol, UK.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Falconer
authors.affiliation: National Institute for Health Research, Bristol Biomedical Research Unit in Nutrition, Diet and Lifestyle, Level 3 University Hospitals Bristol Education and Research Centre, Upper Maudlin Street, BS2 8AE, Bristol, UK.
authors.forename: Sam D
authors.initials: SD
authors.lastname: Leary
authors.affiliation: Centre for Exercise, Nutrition and Health Sciences, School for Policy Studies, 8 Priory Road, University of Bristol, BS8 1TZ, Bristol, UK.
authors.forename: Angie S
authors.initials: AS
authors.lastname: Page
authors.affiliation: National Institute for Health Research, Bristol Biomedical Research Unit in Nutrition, Diet and Lifestyle, Level 3 University Hospitals Bristol Education and Research Centre, Upper Maudlin Street, BS2 8AE, Bristol, UK; Centre for Exercise, Nutrition and Health Sciences, School for Policy Studies, 8 Priory Road, University of Bristol, BS8 1TZ, Bristol, UK.
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Cooper
keywords: Active travel; Adolescence; Body composition; Cycling; School; Walking