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Study question How effective are physical activity interventions at increasing the activity of children?
Summary answer Physical activity interventions achieve a small to negligible increase in total activity, with a small improvement in the time spent at moderate or vigorous intensities amounting to around four more minutes walking or running per day.
What is known and what this paper adds Physical activity interventions have little effect on the prevention of childhood obesity, but the reasons for this have been unclear. The finding that physical activity interventions have little effect on the overall activity of children provides one explanation.
Selection criteria for studies
We searched Embase, Medline, PsycINFO, and SPORTDiscus electronic databases up to March 2012 for trials that sought to increase the physical activity of children/adolescents. To be included, the trials needed to have measured whole day physical activity objectively with accelerometers at both baseline and follow-up. They also needed to have been at least four weeks in duration and to have incorporated a control group.
We focused on the total amount of physical activity and the time spent in moderate or vigorous physical activity. Both outcomes were expressed as standardised mean differences.
Main results and role of chance
Thirty studies, incorporating 6153 children with accelerometer measured physical activity, met the inclusion criteria. 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 physical activity (0.16, 0.08 to 0.24; P<0.001, equivalent to approximately four more minutes walking or running per day). The pooled intervention effect did not differ significantly when restricted to studies of higher methodological quality (standardised mean difference 0.09 for total physical activity and 0.11 for moderate or vigorous physical activity).⇓
Bias, confounding, and other reasons for caution
Not all of the included studies reported both of the outcome measures of interest, yet both are likely to have been collected. This may have led to reporting bias whereby, for example, authors selected the outcome measure that showed the greatest effect. We cannot rule out publication bias either. The absence of small 'unsuccessful' trials in the presence of small 'successful' trials may reflect the reluctance of editors to publish negative results. Both sources of bias may have caused us to overestimate the true effect of the interventions.
Study funding/potential competing interests
EarlyBird (BM and TW) is supported by the Bright Future Trust, the Kirby Laing Foundation, the Peninsula Foundation and the EarlyBird Diabetes Trust. WH is supported by the National Institute for Health Research (NIHR) Collaborations for Leadership in Applied Health Research and Care (CLAHRC).
▸ This article is an abridged version of a paper that was published on bmj.com. Cite this article as: BMJ 2012;345:e5888
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