Tracking of physical activity with accelerometers over a 2-year time period

Limited data exist of tracking and changes in accelerometer-measured physical activity in children.

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.

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%.

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.