How to estimate physical activity prevalence in children and adolescents?

This study examined whether children and adolescents meet the guideline of 60 min of daily moderate-to-vigorous physical activity by analyzing the proportion of active days on school and non-school days.

Cross-sectional study.

Data from three Finnish school-aged physical activity studies (n = 3,221; ages 7-15 years) were analyzed. Participants wore hip accelerometers for seven consecutive days and completed questionnaires. Moderate-to-vigorous physical activity was derived from accelerometer data using mean amplitude deviation in 6-second epochs, further processed with 1-10-minute exponential moving averages. A day met guidelines if it included at least 60 minutes of moderate-to-vigorous physical activity, based on data from the accelerometer, questionnaire or both.

Overall, the mean number of days meeting the recommendation was 5.3 (standard deviation 2.1) days per week according to the questionnaire, and 6.3 (1.2) days with 6-second epochs, 5.3 (1.8) days with the 1-minute exponential moving average, and 4.2 (2.1) days with the 10-minute exponential moving average according to the accelerometer. From 1st to 9th grades, boys' proportion of active days decreased from 96% to 64% on school days and from 92% to 40% on non-school days using the 1-minute exponential moving average. Similarly, girls' proportion of active days dropped from 95% to 53% on school days and from 81% to 30% on non-school days.

The proportion of active days approach captures day-to-day variation in physical activity. The closest agreement between questionnaire and accelerometer estimates was observed when using a 1-minute exponential moving average.