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OBJECTIVE: This study aimed to describe levels of physical activity in a representative sample of preschool children and to quantify tracking of activity over 1 year. RESEARCH METHODS AND PROCEDURES: Physical activity (mean accelerometry counts/minute) was assessed over 3 days using the Computer Science and Applications accelerometer in 3- to 4-year-old children (n = 104; 52 boys; mean age, 3.7 +/- 0.4 years). In 60 children (30 boys), measurements were repeated 1 year later. RESULTS: Mean total activity at baseline was 777 +/- 207 counts/minute in boys and 657 +/- 172 counts/minute for girls; this gender difference was significant (p < 0.001). In the cross-sectional analysis, total activity was significantly positively related to age (r = 0.37, p = 0.007). In the sample followed up for 1 year, mean total activity was 849 +/- 252. The longitudinal analysis confirmed that total physical activity increased over the 1-year period (paired Student's t test, p < 0.001). The tracking rank order correlation coefficient of total activity count over 1 year was r = 0.40 (p < 0.001). DISCUSSION: This study suggests that total activity increases during the preschool period in Scottish children and that gender differences in total activity are present early in life. Tracking of total activity was only modest, but adequate assessment of tracking requires methodological research aimed at elucidating the biological meaning of accelerometer output.
Jackson et al. (Sat,) studied this question.