• Brad Metcalf, William Henley, and Terence Wilkin.
• Department of Endocrinology and Metabolism, Peninsula College of Medicine and Dentistry, Plymouth University Campus, Plymouth, UK. brad.metcalf@nhs.net
• BMJ. 2012 Jan 1;345:e5888.

ObjectiveTo determine whether, and to what extent, physical activity interventions affect the overall activity levels of children.DesignSystematic review and meta-analysis.Data SourcesElectronic databases (Embase, Medline, PsycINFO, SPORTDiscus) and reference lists of included studies and of relevant review articles.Study SelectionDesign: randomised controlled trials or controlled clinical trials (cluster and individual) published in peer reviewed journals.Interventionincorporated a component designed to increase the physical activity of children/adolescents and was at least four weeks in duration.Outcomesmeasured whole day physical activity objectively with accelerometers either before or immediately after the end of the intervention period.Data AnalysisINTERVENTION effects (standardised mean differences) were calculated for total physical activity, time spent in moderate or vigorous physical activity, or both for each study and pooled using a weighted random effects model. Meta-regression explored the heterogeneity of intervention effects in relation to study participants, design, intervention type, and methodological quality.ResultsThirty studies (involving 14,326 participants; 6153 with accelerometer measured physical activity) met the inclusion criteria and all were eligible for meta-analysis/meta-regression. The pooled intervention effect across all studies was small to negligible for total physical activity (standardised mean difference 0.12, 95% confidence interval 0.04 to 0.20; P<0.01) and small for moderate or vigorous activity (0.16, 0.08 to 0.24; P<0.001). Meta-regression indicated that the pooled intervention effect did not differ significantly between any of the subgroups (for example, for total physical activity, standardised mean differences were 0.07 for age <10 years and 0.16 for ≥ 10 years, P=0.19; 0.07 for body mass index across the entire range and 0.22 for exclusively overweight/obese children, P=0.07; 0.12 for study duration ≤ 6 months and 0.09 for >6 months, P=0.71; 0.15 for home/family based intervention and 0.10 for school based intervention, P=0.53; and 0.09 for higher quality studies and 0.14 for lower quality studies, P=0.52).ConclusionsThis review provides strong evidence that physical activity interventions have had only a small effect (approximately 4 minutes more walking or running per day) on children's overall activity levels. This finding may explain, in part, why such interventions have had limited success in reducing the body mass index or body fat of children.

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