Temporal Associations of Physical Activity Volume, Intensity, and Timing With Sleep in Preschool-Aged Children.

This study aimed to investigate the temporal relationships between accelerometer-derived physical activity metrics-specifically volume, intensity, and timing-with the preceding and subsequent nights' sleep in preschool-aged children. This analysis used the baseline data from a randomised controlled trial among 93 children (53 boys) aged 3-5.9 years who provided daily, repeated measures for at least four days. Open-source R package GGIR was used to generate daily measures of average acceleration, intensity gradient, timing of the most active 10 h (M10 start), sleep duration, sleep efficiency, and sleep midpoint. Linear mixed models were performed to examine temporal associations between waketime physical activity and the subsequent night's sleep, and between nocturnal sleep and physical activity the following day, at both within- and between-person levels. A higher intensity gradient compared to the personal average during the day predicted a lower sleep efficiency on the subsequent night (β = -10.71, 95% CI: -17.20, -4.21). At the between-person level, children with longer sleep duration (β = 0.87, 95% CI: 0.45, 1.29), a later sleep midpoint (β = 1.03, 95% CI: 0.79, 1.27), or lower sleep efficiency (-0.09, 95% CI: -0.14, -0.03) were more likely to have their active periods later in the following day. These findings suggest that the timing of physical activity and sleep midpoint showed consistent bidirectional associations at both within- and between-person levels. The findings suggest that incorporating lower intensity activities that are scheduled at appropriate times into daily routines may be crucial for better sleep for young children.