Study objectives: To determine whether within-person changes in total physical activity (PA), moderate-to-vigorous physical activity (MVPA), and sedentary time from ages 6 to 18 predict changes in sleep duration and insomnia symptoms, and vice versa.
Methods: Seven waves of biennially collected data from a birth cohort study were used, capturing ages 6-18 years (n = 880). Every second year, objective data on PA, sedentary time, and sleep duration were collected using accelerometers, while insomnia symptoms were assessed through clinical interviews. Random Intercept Cross-Lagged Panel Models were estimated to test the within-person relations between PA/MVPA/sedentary time and sleep. Potential sex and age differences were also examined.
Results: We found no evidence for within-person relations between the study variables, nor for any sex or age differences.
Conclusions: Children and adolescents who become more physically active or spend less time in sedentary activities are probably not more likely to sleep longer or better than they typically would. Statement of Significance Increased physical activity (PA) or reduced sedentary time is assumed to improve sleep, and improved sleep is expected to promote PA. While some short-term studies on daily variations in these behaviors partially support this assumption, longer-term studies are few and have substantial methodological limitations. This study is the first to test within-person relations between PA/sedentary time and sleep in children and adolescents, analyzing seven waves of data assessed by objective measures and clinical interviews. No evidence for long-term relations between PA and sleep at the individual level was revealed, thus the findings suggest that individual-level interventions targeting one behavior may not improve the other over the long term.
Keywords: bidirectional relation; insomnia; physical activity; sleep duration; within-person relation.
© The Author(s) 2025. Published by Oxford University Press on behalf of Sleep Research Society.