Eduardo Rodriguez turns 11 this summer. His doctor said he's in the middle of a growth spurt and Eduardo wants to make sure that continues, so he says he's trying to get in as much activity as possible.

“We do an hour of exercise and then we play some games. I sweat a lot when that happens,” said Rodriguez.

But according to a report published in the latest Journal of the American Medical Association, more and more kids his age aren't sweating it out much at all when it comes to exercise. The report from the University of California, San Diego shows a steady decline in physical activity among kids as they head into their teen years.

Most experts recommend children and adolescents get at least an hour of exercise a day, but most are barely reaching that.

“One of the most obvious things is the increased range of sedentary activities,” said Dr. Mary Jo Messito. “Computers, instant messaging, all the computer games, all the sedentary range activities.”

In the study, researchers tracked more than 1,000 kids for six years. At nine years of age, children clocked in an average of three hours of exercise a day, both during the school week and on weekends. But by age 15, the amount of physical activity was far below recommended guidelines, down to just 49 minutes on school days, and 35 minutes on weekends.

“Kids who are active, even if they are overweight, are less at risk for high blood pressure, and diabetes, and heart disease,” said Messito. “This decrease in activity that we have seen in this generation – the implications are scary for when they're adults, they really are.”

While summer may be a good time for kids to catch up on physical activity they may be lacking, Dr. Messito said it's something that needs to happen all year round.

“There is lots of evidence that shows that academics are great and that a longer school day has some advantages for kids, but that exercise helps too,” Messito said.

Doctors say some environmental factors need to change, like cuts in school recess and gym time, along with fewer parks and other places to play. But there are still simple things that can keep kids active.

“Sixty minutes a day and that doesn't mean 60 minutes a day of aerobics classes and weight lifting. It means 60 minutes of playing ball, basketball, riding your skateboard, riding your bicycle. Moderate to vigorous activity,” said. Messito.