title: Determinants of Three-Year Change in Children's Objectively Measured Sedentary Time.
abstract: BACKGROUND
  Sedentary behaviours (SB) are highly prevalent in young people and may be adversely associated with physical and mental health. Understanding of the modifiable determinants of SB is necessary to inform the design of behaviour change interventions but much of the existing research is cross-sectional and focussed upon screen-based behaviours.
  
  
  OBJECTIVE
  To examine the social, psychological and environmental determinants of change in children's objectively measured sedentary time from age 11 to 14 years.
  
  
  METHODS
  Data are from the second (2008) and third (2011) waves of assessment in the Sport, Physical Activity, and Eating Behaviour: Environmental Determinants in Young People (SPEEDY) study, conducted in the county of Norfolk, United Kingdom. Longitudinal data on accelerometer assessed sedentary time were available for 316 (53.5% female, 11.2±0.3 years at baseline) and 264 children after-school and at the weekend respectively. Information on 14 candidate determinants, including school travel mode and electronic media ownership, was self-reported. Change in the proportion of registered time spent sedentary was used as the outcome variable in cross-classified linear regression models, adjusted for age, sex, body mass index and baseline sedentary time. Simple and multiple models were run and interactions with sex explored.
  
  
  RESULTS
  Daily sedentary time increased by 30-40 minutes after-school and at the weekend from baseline to follow-up. Participants who travelled to school by cycle exhibited smaller increases in after-school sedentary time (beta; 95%CI for change in % time spent sedentary: -3.3;-6.7,-0.07). No significant determinants of change in weekend sedentary time were identified.
  
  
  CONCLUSIONS
  Time spent sedentary increased during the three-year duration of follow-up but few of the variables examined were significantly associated with changes in sedentary time. Children's mode of school travel may influence changes in their sedentary time over this period and should be examined further, alongside broader efforts to identify modifiable determinants of SB during childhood.
authors.affiliation: MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, United Kingdom.
authors.forename: Andrew J
authors.identifier: http://orcid.org/0000-0002-3819-3448
authors.initials: AJ
authors.lastname: Atkin
authors.affiliation: MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, United Kingdom.
authors.forename: Louise
authors.initials: L
authors.lastname: Foley
authors.affiliation: MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, United Kingdom.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Corder
authors.affiliation: MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, United Kingdom.|Department of Sports Medicine, Norwegian School of Sports Sciences, Ullevål Stadion, Oslo, Norway.
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
authors.affiliation: MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge School of Clinical Medicine, Institute of Metabolic Science, Cambridge Biomedical Campus, Cambridge, United Kingdom.
authors.forename: Esther M F
authors.initials: EM
authors.lastname: van Sluijs
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D015444:Exercise; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D057185:Sedentary Behavior; D012737:Sex Factors; D012959:Socioeconomic Factors; D013334:Students / Q000706:statistics & numerical data*; D006113:United Kingdom