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Getting children to be more physically active seems as if it should be so simple. Just enroll them in classes and programs during school or afterward that are filled with games, sports and other activities.

But an important new review of the outcomes of a wide range of different physical activity interventions for young people finds that the programs almost never increase overall daily physical activity. The youngsters run around during the intervention period, then remain stubbornly sedentary during the rest of the day.

For the review, which was published last week in the British medical journal BMJ, researchers from the Peninsula College of Medicine and Dentistry in England collected data from 30 studies related to exercise interventions in children that had been published worldwide between January 1990 and March 2012.

To be included in the review, the studies had to have involved children younger than 16, lasted for at least four weeks, and reported objectively measured levels of physical fitness, like wearing motion sensors that tracked how much they moved, not just during the exercise classes but throughout the rest of the day. The studies included an American program in which elementary school-age students were led through a 90-minute session of vigorous running and playing after school, three times a week. Another program involved Scottish preschool youngsters and 30 minutes of moderate physical playtime during school hours, three times a week.

In each case, the investigators had expected that the programs would increase the children’s overall daily physical activity.

That didn’t happen, as the review’s authors found when they carefully parsed outcomes. The American students, for instance, increased their overall daily physical activity by about five minutes per day. But only during the first few weeks of the program; by the end, their overall daily physical activity had returned to about where it had been before the program began. The wee Scottish participants actually became less physically active over all on the days when they had the 30-minute play sessions.

The review authors found similar results for the rest of the studies that they perused. In general, well-designed, well-implemented and obviously very well-meaning physical activity interventions, including ones lasting for up to 90 minutes, added at best about four minutes of additional walking or running to most youngsters’ overall daily physical activity levels.

The programs “just didn’t work,” at least in terms of getting young people to move more, said Brad Metcalf, a research fellow and medical statistician at Peninsula College, who led the review.

Why the programs, no matter their length, intensity or content, led to so little additional daily activity is hard to understand, Dr. Metcalf said, although he and his co-authors suspect that many children unconsciously compensate for the energy expended during structured activity sessions by plopping themselves in front of a television or otherwise being extra sedentary afterward. It is also possible, he said, that on a practical level, the new sessions, especially those taking place after school, simply replace time that the youngsters already devoted to running around, so the overall additive benefit of the programs was nil.

But the broader and more pressing question that the new review raises is, as the title of an accompanying editorial asks, “Are interventions to promote physical activity in children a waste of time?”

Thankfully, the editorial’s authors answer with an immediate and emphatic “no.” If existing exercise programs aren’t working, finding new approaches that do work is essential, they say.

They point out that active children are much more likely to be active adults and that physically active children also are far less likely to be overweight. A convincing, if separate body of scientific evidence has shown that the most physically active and fit children are generally the least heavy.

So if structured classes and programs are not getting children to move more, what, if anything, can be done to increase physical activity in the young? “It’s a really difficult problem,” said Frank Booth, a professor of physiology at the University of Missouri-Columbia, who was not involved with the review.

Determining the most effective placement of classes and programs, so that they don’t substitute for time already spent running around and instead augment it, would help, he said.

But a more vital element, he said, “involves mothers and fathers,” who can encourage children to leave the couch, subverting their drive to compensate for energy expended earlier by sitting now.

A welcoming setting may also be key, the authors of the accompanying editorial wrote, pointing to a 2011 study of same-sex twins, ages 9 to 11. In that study, the most important determinant of how much the youngsters moved — or didn’t — was their local built environment. Children with more opportunities to be outside, in a safe, well-designed space, were more likely to be outside, romping.

But none of these suggestions will be easy to put in place, Dr. Booth said, or inexpensive, and all will require scientific validation. No one expected, after all, that well-designed exercise interventions for children would prove to be so ineffective.

Ultimately, he continued, the best use of resources in this field may be to direct them toward unearthing the roots of childhood inactivity. “Kids naturally love to run around and play,” Dr. Booth said. “But they’re just not doing it as much now. And we don’t know why. So what we really need to understand is, what’s happening to our kids that makes them quit wanting to play?”