Debbie Nicholson

Study reveals interventions have little impact on overall activity levels and body mass index

Program interventions such as extra exercise classes geared to children in order to increase their physical activity have failed according to a new study.

Studies have demonstrated that greater activity levels are linked to lower levels of body mass index (BMI) however; physical activity interventions have been failing when it comes to improving BMI.

View slideshow: Moderate and vigorus activities

We have all read about it by now that the obesity rate for children and teens has continued to rise in the past two decades. The more physically active children are the healthier weight they have and remaining active and staying a healthy weight will extend into adulthood. Many past reviews had not limited their analysis to the entire day of activity and some had used questionnaire’s instead of objective measures of physical activity such as using pedometers. This is the first systemic review to measure physical activity using accelerometry devices which provide a measure of total bodily movement across waking hours.

The study’s authors from Plymouth and Exeter, England, looked at 30 randomized controlled studies or controlled clinical trials, all participants were 16 and under and the intervention had lasted for at least four weeks and measured results objectively, using accelerometers.

All trials were matched on age, ethnicity and socio-economic status and were adjusted for gender and baseline activity. Effects of intervention were calculated on both total physical activity and time spent in moderate-or-vigorous physical activity. Eight of the studies involved only overweight/obese children and the rest of the studies involved children from all BMI categories.

The researchers assessed the effect of interventions on total physical activity and time spent on moderate or vigorous physical activity.

Physical interventions analyzed included one the United States that looked to increase physical activity of 729 children by giving the children three ninety minute after school activity-related sessions each week. Each session consisted of sixty minute high intensity activity but halfway through the trial the children were only doing an extra five minutes of walking or running each day and by the end of the trial it disappeared totally.

In Scotland, another intervention was conducted over a period of 24 weeks with 268 nursery-schools aged children by giving them thirty minute sessions during the week during nursery hours. This intervention also did not increase the activity of the children and seemed to make them less active as they spent one minute less each day walking or running compared to the control group.

The review revealed interventions achieved increases in children's total activity volume with small improvements in time spent in moderate-or-vigorous intensities (equal to four more minutes walking or running per day), which would have minimal impact on children BMI or body fat (equal to a reduction of 2mm in waist circumference). The authors suggested the interventions could be replacing periods of equally intense activity such as after school activity that would usually be spent outside.

The authors concluded “This 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.” The authors suggest that further studies should obtain both whole day activity and activity related to intervention-specific periods.

This study was published online in BMJ.

In an accompanying editorial Dr. Mark Hamer, Epidemiology & Public Health, Div of Population Health and Dr. Abi Fisher, research associate, from University College London, have asked researchers not to focus on overweight/obese children but to focus on what improves health in children indifferent of their weight. They are also calling for more studies to examine how changes to outdoor and indoor environments affect children’s activities.

According to the Centers for Disease Control and Prevention children and adolescents should get one hour or more of physical activity a day. This physical activity should include aerobic activity such as brisk walking or running, muscle strengthening activities such as gymnastics or push-ups and bone strengthening activities, such as jumping rope.