Experts generally recommend that kids should get an hour per day of exercise at least to help stave off heart trouble as adults.
However a new study has suggested that even more activity may be needed.
Lead researcher Lars Bo Andersen, from the Norwegian School of Sports Science, Oslo said, 'Current guidelines for physical activity in children may underestimate the necessary level for maintaining good health. We would suggest 90 minutes per day to prevent clustering of heart disease risk factors.'
The results of his team's research are published in the July 22 issue of The Lancet.
Andersen's team conducted their study over 1,700 children, aged 9 or 15 years, from schools in Denmark, Portugal and Estonia. The team measured each child's amount of daily activity, and also risk factors for cardiovascular disease, such as weight, blood pressure, waist circumference, insulin resistance, and blood cholesterol.
Andersen's team gave children accelerometers to measure everyday activities such as walking to school and moderate-intensity play.
The accelerometer mostly picked by everyday activities and not high-intensity sports. According to Andersen, "If you think about the changes in physical activity that have happened over the years [and] which may have contributed substantially to the obesity epidemic, it is very likely that the decrease in activity is in mainly free activities."
Following four days of monitoring, Andersen's team found that the combined risk factor score for cardiovascular disease decreased with increase in physical activity. 9-year-olds who did 116 minutes of moderate to vigorous intensity activity and the 15-year-olds who did about 88 minutes daily were found to have the lowest risk factor scores.
Anderson said, "Clustering of heart disease risk factors occurs even in healthy children, and the risk is more than three times higher among sedentary children compared to the physically active. We should do more to create a society where physical activity is a natural part of everyday living, and we should find effective strategies to increase the physical activity level among children."
He said that simple changes in children's routine and environment can help towards this goal.
"We need to make it possible to live an active lifestyle, which means that children should play outside, they should walk or cycle to school, they should train their motor skills in school PE lessons," Andersen said. "Few parents or politicians have been aware of the health consequences of low habitual physical activity, because our children are not ill -- yet."
According to Dr. David L. Katz, an associate professor of public health and director of the Prevention Research Center at Yale University School of Medicine in New Haven, Conn, levels of physical activity continue to decline in industrialized countries where technology does more and more of what muscles used to do at both work and play.
He said, "The trend is especially noteworthy for children, as competing demands squeeze both physical activity and recess out of the typical school day, and [TV/computer] screen time replaces playground or backyard time."
Katz said that ensuring that kids remain active has become a matter of vital importance.
He said, "For example, when schools don't have time for a dedicated hour of physical education, bouts of brief activity could be provided in the classroom during each session of the day. We have developed just such a program at my lab, under the name 'ABC (activity bursts in the classroom) for Fitness,' and are currently evaluating its benefits."
While it seems to have become ever more difficult for adults and children alike to maintain healthful levels of physical activity, Katz said, "We must find ways to put motion into our daily routine, and especially that of our children. Nothing less than their health, quality of life, and perhaps even life expectancy is at stake."