Time-specific intervention effects on objectively measured physical activity in school children

AimIt is unclear whether intervention effects on school-aged children's physical activity differ across specific periods of the week or day. This study aimed to assess the time-specific intervention effects on accelerometer-measured physical activity in primary school children.Subject and methodsThis was a nested study in a cluster-randomized controlled trial conducted from September 2018 to June 2019 in Beijing, China. The intervention group included four schools (119 children) and the control group included four schools (99 children). The obesity prevention intervention engaged schools and families to improve children's physical activity. Outcome measures included accelerometer-assessed intensity and amounts of physical activity within specific periods of a week (weekday/weekend day) or a day (in-school/out-of-school periods). Linear mixed models were used to estimate intervention effects.ResultsThe intervention led to an increase in time engaged in moderate-to-vigorous physical activity (MVPA) within in-school periods of a day (adjusted mean difference 0.54 minutes/hour; 95% confidence interval 0.13, 0.94, P = 0.012) but it did not improve physical activity within out-of-school periods (P > 0.05) compared with the control group. There was no evidence of difference across sex, body mass index, physical activity, and accelerometer compliance. No intervention effects were observed in physical activity within the whole weekday or weekend day (P > 0.05).ConclusionsThe intervention effectively increased MVPA within in-school periods but did not improve out-of-school physical activity. Findings support the tailoring of intervention components to specific periods of a day to improve school-aged children's whole pattern of physical activity.