title: Tracking of physical activity with accelerometers over a 2-year time period.
abstract: BACKGROUND
  Limited data exist of tracking and changes in accelerometer-measured physical activity in children.
  
  
  METHODS
  Physical activity was assessed by accelerometers for 4 days in 167 children (boys, n = 90; girls n = 77) age 9.8 ± 0.6 years. Follow-up measurement was made 2.0 ± 0.1 yrs later (range 1.9-2.1 yrs). General physical activity (GPA) was defined as mean count/minute. Minutes of inactivity; light, moderate, and vigorous physical activity (LMVPA); moderate and vigorous physical activity (MVPA); and vigorous physical activity (VPA) per day were calculated both as absolute values and as percentage of total registration time.
  
  
  RESULTS
  Spearman rank order correlation indicated low tracking of MVPA and VPA in girls (r = .25-0.33, P < .05), and low-moderate tracking of GPA, inactivity, LMVPA, MVPA and VPA in boys (r = .23-0.40, P < .05). Time in inactivity increased at follow-up by 5%-14%. Most of the assessed physical activity variables were decreased at follow-up by 6% to 30%.
  
  
  CONCLUSIONS
  Physical activity tracks at a low-moderate degree from age 10-12 years, which confirm previous investigations that have used self-report assessments. The low-moderate tracking of physical activity variables indicate that those who were most active initially remained most active. Increasing inactive behavior was observed and that several other physical activity variables were decreased at follow-up.
authors.affiliation: Dept of Clinical Physiology and Nuclear Medicine, Skane University Hospital, Malmo, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Dencker
authors.forename: Tina
authors.initials: T
authors.lastname: Tanha
authors.forename: Per
authors.initials: P
authors.lastname: Wollmer
authors.forename: Magnus K
authors.initials: MK
authors.lastname: Karlsson
authors.forename: Lars Bo
authors.initials: LB
authors.lastname: Andersen
authors.forename: Ola
authors.initials: O
authors.lastname: Thorsson
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D000367:Age Factors; D015992:Body Mass Index; D002648:Child; D015444:Exercise; D005260:Female; D005500:Follow-Up Studies; D015438:Health Behavior; D006801:Humans; D008297:Male; D012737:Sex Factors; D018709:Statistics, Nonparametric; D013997:Time Factors