Seasonal changes in the volume and intensity of children’s school year physical activity

Background Assessing 24-hour movement behaviours with accelerometry captures patterns of physical activity, sedentary behaviour, and sleep. Average acceleration (AvAcc) and intensity gradient (IG) are accelerometer outcomes which describe the volume and intensity distribution of these movement behaviours across the 24-hour cycle. Little is known about trajectories of children’s AvAcc and IG over time, and how these outcomes differ by season and between weekdays and weekends. This study describes school year trajectories of children’s weekday and weekend AvAcc and IG. Methods During the 2023-24 school year 249 children (8-9 years old; 51.4% girls) wore accelerometers for 24 hours×day ^-1 over 7-days at three time points (TP; Autumn, Winter, Summer). AvAcc and IG were calculated to represent physical activity volume and intensity distribution across the day, respectively for weekdays and weekends. K-means cluster analyses were performed on TP-Autumn weekday and weekend data to group participants according to their combined physical activity volume and intensity distribution profiles. Linear mixed models examined school year weekday and weekend AvAcc and IG trajectories for the whole sample (Aim 1) and for the clusters (Aim 2). Results Aim 1: Weekday AvAcc, but not IG, significantly increased from TP-Autumn to TP-Summer (b = 4.44, 95%CI=2.47, 6.40). Weekend AvAcc and IG were relatively stable, with non-significant school year increases observed. Aim 2: For weekday and weekend physical activity outcomes there were 3-cluster groupings (Most Active, Somewhat Active (weekdays) / Active (weekends), and Least Active). Weekday and weekend physical activity volume and intensity distribution trajectories were relatively consistent for each cluster, although it was evident that the Least Active children had the most positive AvAcc and IG trajectories. Conclusions Weekday physical activity volume but not intensity increased over the school year, while both dimensions of weekend activity had stable trajectories. Children’s physical activity intervention programming should leverage seasonal influences and employ different strategies for targeting physical activity volume and intensity distribution on weekday and weekend days. Weekday and weekend cluster groups had distinct physical activity profiles which followed subtly different AvAcc and IG school year trajectories. The presence of sub-groups characterised by different physical activity patterns may require differentiated intervention strategies.