title: Longitudinal study of physical activity and sedentary behavior in children.
abstract: OBJECTIVE
  Physical activity is thought to decline during childhood, but the extent of the decline is unknown. We made objective measures of 2-year changes in physical activity and sedentary behavior in English children who participated in the Gateshead Millennium Study to explore the nature, timing, and extent of changes in physical activity and sedentary behavior before adolescence.
  
  
  METHODS
  We conducted a longitudinal study of 405 children (207 girls), aged 7 years, in 2006/2007 and again 24 months later. Physical activity and sedentary behavior were measured with the Actigraph GT1M accelerometer. Data were analyzed in 2010. Changes in total volume of physical activity (accelerometer counts per minute [cpm]), moderate-to-vigorous-intensity physical activity (MVPA), and sedentary behavior were quantified. Factors associated with changes in physical activity and sedentary behavior were tested by using linear regression. Tracking of physical activity and sedentary behavior over the 2-year period was assessed by rank-order correlation.
  
  
  RESULTS
  Mean daily volume of physical activity declined by 83 cpm (interquartile range [IQR]: -189 to 31) over 2 years; the percentage of daily time spent in MVPA was low at baseline and declined by 0.3% (IQR: -1.4 to 0.9). The percentage of daily time in sedentary behavior was high at baseline and increased from 78.0% to 81.1% of the day (change 3.1% [IQR: -0.3 to 6.0]). The decline in MVPA and increase in sedentary behavior were significantly greater in girls and in those with higher BMI z scores at baseline. Physical activity and sedentary behavior showed moderate tracking over the 2-year period.
  
  
  CONCLUSIONS
  We report here new evidence of low and declining levels of physical activity and MVPA and increasing sedentary behavior before adolescence.
authors.affiliation: Institute of Health & Society, Human Nutrition Research Centre, Newcastle University, M1.151 Leech Building Medical School, Framlington Place, Newcastle Upon Tyne NE2 4HH, United Kingdom. laura.basterfield@ncl.ac.uk
authors.forename: Laura
authors.initials: L
authors.lastname: Basterfield
authors.forename: Ashley J
authors.initials: AJ
authors.lastname: Adamson
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Frary
authors.forename: Kathryn N
authors.initials: KN
authors.lastname: Parkinson
authors.forename: Mark S
authors.initials: MS
authors.lastname: Pearce
authors.forename: John J
authors.initials: JJ
authors.lastname: Reilly
mesh_terms: D002648:Child; D002652:Child Behavior; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D026741:Physical Therapy Modalities; D057185:Sedentary Behavior