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Kids' Exercise Interventions Show Negligible Impact

Interventions like extra exercise classes that aim to increase physical activity levels in children as a way to tackle the rising problem of obesity and overweight in youngsters appears to be having only a small, almost negligible effect, according to a review published online in BMJ on Thursday.

We have known of the rising obesity and overweight crisis for some time, and researchers have done numerous studies that show the more physically active children are, the more likely they are to have a healthy weight (as measured by body mass index, BMI) and to stay active and maintain a healthy weight through adulthood.

This has led to the development of interventions, or programs that deliberately aim to increase levels of physical activity in children by providing them with extra exercise sessions, for instance in school time or afterwards.

But so far, studies of those interventions show they are not successful in improving children's BMI. Hard Measures of Total Daily Activity In this latest study, researchers from Plymouth and Exeter Universities in the UK, carried out a systematic review, believed to be the first, of studies that did not rely on data extracted from questionnaires, but used "hard" measures of actual physical activity obtained from accelerometry devices, and also took into account whole day activity, or total bodily movement across waking hours.

For their review, the authors searched recognized databases and references lists for peer-reviewed journal studies that matched their requirements. They had to be examining interventions designed to increase activity levels in children aged 16 and under that lasted for at least four weeks, and measured results objectively, using accelerometers.

30 randomized controlled trials that took place between January 1990 and March 2012 matched these requirements. All the studies were matched on age, ethnicity, and socio-economic status, and the results were adjusted for gender and activity levels at the start of the intervention period.

Eight of the studies had included only overweight or obese children, while the rest included children from all BMI ranges.

The researchers assessed the effect of interventions on total physical activity and time spent on moderate or vigorous physical activity. Example Studies Reviewed One of the studies they reviewed was of an intervention in the US that sought to increase physical activity in 729 youngsters of average age 11 by giving them three 90-minute after-school sessions per week. Each session included 60 minutes of high intensity physical activity.

But the results were disappointing: measures taken half way through the trial showed in terms of total activity, the children were only doing an extra five minutes of walking or running per day, and by the end of the trial, even these few minutes had gone down to zero.

Another study the researchers reviewed was a 24-week intervention in 268 pre-schoolers attending Scottish nursery schools who were given three 30-minute sessions per week during nursery hours.

The results here were also disappointing: the children's physical activity levels didn't rise, and if anything, went down slightly. The data showed they spent on average one minute less per day walking or running, compared to children in the control group who did not attend the intervention sessions. Small-to-Negligle Effects The researchers conclude that the interventions had a "small-to-negligible" impact: there was little increase in total activity volume and only a small increase in time spent in moderate or vigorous intensity activity (about the same as four minutes of walking or running per day).

Such tiny improvements in physical activity levels would not be sufficient to make significant reductions in children's BMI or body fat. Such a small effect would result in a reduction for instance of only 2mm in waist size.

Previous studies have suggested such interventions don't achieve reductions in BMI and body fat because they make children eat more calories.

The authors suggest another reason for the failure to impact BMI: the interventions could be displacing equally active periods, such as after-school clubs, which would usually take place outdoors.

While it is understandable for us to jump to the conclusion that the answer to the obesity crisis in kids is to make them do more exercise, the authors suggest we think carefully first, and urge future studies to take into account the effect of any interventions on whole day activity as well as activity-specific periods, as "small increase gained from formal interventions seems insufficient to improve the body mass / fat of children." Focus On All Children In an accompanying commentary, Mark Hamer and Abigail Fisher from University College London, say although the reviewers' chosen methods have "inherent limitations", their evidence is the best so far.

They ask researchers not to focus on overweight and obese children but concentrate instead on what helps to improve health in children regardless of their weight.

They also call for more studies that look at how changes to outdoor and indoor environments affect children's physical activity.

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