Sat, Jul 19, 2008 (2:05 a.m.)

If you want to see energy in action, spend the day with a 9-year-old child. If you can’t handle all of that physical activity, hang out with a 15-year-old.

That’s one way to interpret the results of a study published Wednesday in The Journal of the American Medical Association.

As reported by The New York Times, researchers found the typical 9-year-old stays active for three hours a day, but by age 15 a child on average gets only 49 minutes of physical activity on weekdays and only 30 minutes on Saturdays and Sundays.

The federal government recommends children engage in at least one hour of moderate activity daily, but the researchers say they believe youngsters begin to fall below that goal around age 13. It’s downhill from there.

A check of the Clark County School District curriculum shows its students are getting at least some exercise. Middle school children are required to take at least one semester of physical education each year from grades six through eight. High school students must take at least two units of physical education out of 22 1/2 units total to graduate.

Some teens undoubtedly lack motivation to exercise if they are not part of a sports team. But it can be argued that the greater culprit has been the explosion in home entertainment systems that keep many youngsters glued to their TV sets, video game players and computers.

This should be of concern to parents because a pattern of lethargy at an early age can translate into obesity and other health problems down the road.

Moderate activity, though, can contribute to better performance in school and greater success as an adult. Parents can do their part by making sure their teens develop sound fitness habits that will give them a better chance of preserving their good health and achieving their dreams.