title: Timing of the decline in physical activity in childhood and adolescence: Gateshead Millennium Cohort Study.
abstract: OBJECTIVE
  There is a widely held and influential view that physical activity begins to decline at adolescence. This study aimed to identify the timing of changes in physical activity during childhood and adolescence.
  
  
  METHODS
  Longitudinal cohort study (Gateshead Millennium Study) with 8 years of follow-up, from North-East England. Cohort members comprise a socioeconomically representative sample studied at ages 7, 9, 12 and 15 years; 545 individuals provided physical activity data at two or more time points. Habitual total volume of physical activity and moderate-to-vigorous intensity physical activity (MVPA) were quantified objectively using the Actigraph accelerometer over 5-7 days at the four time points. Linear mixed models identified the timing of changes in physical activity across the 8-year period, and trajectory analysis was used to identify subgroups with distinct patterns of age-related changes.
  
  
  RESULTS
  Four trajectories of change in total volume of physical activity were identified representing 100% of all participants: all trajectories declined from age 7 years. There was no evidence that physical activity decline began at adolescence, or that adolescent declines in physical activity were substantially greater than the declines during childhood, or greater in girls than boys. One group (19% of boys) had relatively high MVPA which remained stable between ages 7 and15 years.
  
  
  CONCLUSIONS
  Future policy and research efforts to promote physical activity should begin well before adolescence, and should include both boys and girls.
authors.affiliation: Physical Activity for Health Group, School of Psychological Sciences & Health, University of Strathclyde, Glasgow, UK.|Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Mohammed Abdulaziz
authors.initials: MA
authors.lastname: Farooq
authors.affiliation: Institute of Health & Society, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Kathryn N
authors.initials: KN
authors.lastname: Parkinson
authors.affiliation: Institute of Health & Society, Newcastle University, Newcastle upon Tyne, UK.|Human Nutrition Research Centre, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Ashley J
authors.initials: AJ
authors.lastname: Adamson
authors.affiliation: Institute of Health & Society, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Pearce
authors.affiliation: Human Nutrition Research Centre, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Reilly
authors.affiliation: Physical Activity for Health Group, School of Psychological Sciences & Health, University of Strathclyde, Glasgow, UK.
authors.forename: Adrienne R
authors.initials: AR
authors.lastname: Hughes
authors.affiliation: Physical Activity for Health Group, School of Psychological Sciences & Health, University of Strathclyde, Glasgow, UK.
authors.forename: Xanne
authors.initials: X
authors.lastname: Janssen
authors.affiliation: Human Nutrition Research Centre, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Basterfield
authors.affiliation: Physical Activity for Health Group, School of Psychological Sciences & Health, University of Strathclyde, Glasgow, UK.
authors.forename: John J
authors.initials: JJ
authors.lastname: Reilly
mesh_terms: D056044:Actigraphy; D000293:Adolescent; D002648:Child; D004739:England; D015444:Exercise; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D057185:Sedentary Behavior; D013997:Time Factors
keywords: Physical activity; adolescent; child; exercise; longitudinal study