Sure, you think, my kid's on a football team. That takes care of his exercise needs, right? Probably not.
"There are these bursts of activity," says Jim Sallis, a professor of family and preventive medicine at the University of California, San Diego. "But if you think about it, one hour of playing football out on the field means that the vast majority of that time is spent standing around waiting for the next play."
And that's a problem, federal health officials say, because children need at least one hour of moderate to vigorous physical activity every day.
"We know that physical activity in childhood strengthens your bones, increases your muscle mass," says Tala Fakhouri, an epidemiologist with the Centers for Disease Control and Prevention. "It also has effects on psychological well-being in kids and teens. It increases their capacity for learning, their self-esteem and it may also help them deal with stress."
But just one in four young teenagers between ages 12 and 15 actually get that one hour of exercise every day, Fakhouri says. She analyzed federal health data gathered from 800 teenagers in 2012.
While kids may be active in childhood, it's typical to see a decline as they move into their teen years. "We know, for example, that sedentary behaviors like watching TV are the single biggest contributor to physical inactivity in adolescence," Fakhouri says.
But it's not that teenagers no longer enjoy sports.
In the study, teenage boys said their favorite physical activities outside of gym class were basketball, running, football, bicycling and walking. Girls favored running, walking, basketball, dancing and bicycling.
Most studies of physical activity find boys more active than girls, and this one was no different. It found that 27 percent of boys and 22.5 percent of girls got the recommended one hour of exercise daily. That includes gym class, organized activities and play.
It's not necessarily teenagers' fault that they're not more active, researchers say.
Parents worry about safety when their kids go outside. They worry about bullying from other kids and crime in urban neighborhoods. Sallis adds that a surprising number of parents are concerned about traffic. "They don't want their kids to go out because traffic is so bad. There's no safe place to cross the street," he says.
But organized classes or teams aren't the only option.
Families can make small changes in their schedule to build in more exercise, Fakhouri says. "You can take a long walk after dinner. You can take your dog on long walk. Play basketball, dance together."
And with many schools reducing or cutting out PE, Sallis says parents may have to put pressure on the schools, too.
"Look at what's happening in PE," Sallis says. "If they're not going out at all or very much, complain about that. If you see PE class and it's not very active, inform the principal that that's not acceptable."
Bottom line: Physically active kids become physically active adults. And that's another critical reason, Sallis says, to help your kids get out and get moving.