Longer bouts of exercise help prevent childhood obesity

Children who exercise in bouts of activity lasting five minutes or longer are less likely to become obese than those whose activity levels are more sporadic and typically last less than five minutes each, Queen's University researchers have discovered.

Led by Kinesiology and Health Studies professor Ian Janssen, the new study supports Canada's Physical Activity Guidelines for Children and Youth, which call for children to accumulate at least 90 minutes of moderate-to-vigorous physical activity over the course of the day, in bouts of at least five to 10 minutes' duration. Until now there has been no scientific evidence to support the recommendation of sustained, rather than sporadic exercise.

"Even in 60-minute physical education classes or team practices, children are inactive for a large portion of the time and this would not necessarily count as sustained exercise," says Dr. Janssen. "When children engage in longer periods of sustained physical activity, there is a smaller likelihood that they will be overweight or obese."

The findings appear in the May issue of the American Journal of Preventive Medicine .

Conducted by Dr. Janssen and graduate student Amy Mark, the study analyzed data from 2,498 youth aged eight to 17, who participated in the National Health and Nutrition Examination Survey. Sporadic (one to four minutes), short (five to nine minutes) and medium-to-long (10 minutes and longer) bouts of moderate-to-vigorous physical activity were measured using motion sensors. Participants' body mass index (BMI) was used to classify them as normal weight or obese.

Two-thirds of the physical activity measured in the young people took place in short, sporadic sessions that lasted less than five minutes. Within the most active children, 25 percent of those who tended to accumulate their physical activity in bouts were overweight or obese, compared with 35 percent in those who tended to accumulate their activity in a sporadic manner.

"Our findings have important public health implications with respect to the promotion of physical activity in young people," says Dr. Janssen, noting that current U.S. and international guidelines do not stipulate how daily physical activity should be accumulated.

The researchers say that further studies will be required to determine the optimal length of exercise time, and to examine the influence of bouts of physical activity on other aspects of health.