Trajectories of children's physical activity volume and intensity across the school year : the Ready, Set, Move project

Fairclough, Stuart J and Clifford, Lauren and Banks, Jordan and Edwards, Peter and Gilmour, Ayva-Mae and Tyler, Richard and Brown, Denver M Y and Rowlands, Alex V and MacDonald, Mhairi (2025) Trajectories of children's physical activity volume and intensity across the school year : the Ready, Set, Move project. Journal of activity, sedentary and sleep behaviors. ISSN 2731-4391

Abstract

Average acceleration (AvAcc) and intensity gradient (IG) are accelerometer metrics which when combined describe the volume and intensity distribution of physical activity, sedentary behaviour, and sleep across the 24-h cycle. Little is known about trajectories of children's AvAcc and IG over time on weekdays and weekends. This study describes school year trajectories of children's weekday and weekend AvAcc and IG. During 2023-24 249 children (8-9 years old; 51.4% girls) wore accelerometers for 24 h⋅day over 7-days at three time points (Autumn, Winter/Spring, Summer). AvAcc and IG were calculated for weekdays and weekends. K-means cluster analyses were performed on Autumn data to group participants according to their combined AvAcc and IG 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). Aim 1: There were significant increases in weekday AvAcc in Summer compared to Winter/Spring (β = 3.94, 95% CI = 1.20, 6.68) and Autumn (β = 4.43, 95% CI = 2.47, 6.40), but not IG. Weekend AvAcc and IG were relatively stable. Aim 2: Three cluster groupings of children were identified (Most Active, Somewhat Active (weekdays) / Active (weekends), and Least Active). Weekday AvAcc increased significantly from Winter/Spring to Summer in all groups (+ 3.6-4.6 mg, 95% CIs > 0) and from Autumn to Summer in the less active groups only (+ 5.2-5.8 mg, 95% CIs > 0). IG remained stable for the Most and Somewhat Active groups, with a significant increase from Autumn to Summer observed in the Least Active group (+ 0.05, 95% CI = 0.01-0.09). There were no significant within-cluster group changes in weekend AvAcc or IG, although the Least Active children had the most positive AvAcc and IG trajectories. Weekday physical activity volume but not intensity increased over the school year, while both dimensions of weekend activity had stable trajectories. Weekday and weekend cluster groups had distinct physical activity profiles which followed subtly different AvAcc and IG trajectories. The results reinforce the complementary insights provided by studying AvAcc and IG together and have implications for children's physical activity intervention programming.