Narrator: This is Science Today. A lack of vigorous activity is the primary reason for obesity in adolescents ages 11 to 15. Dr. Kevin Patrick, a professor of family and preventive medicine at the University of California, San Diego, led a study of 900 adolescents.

Patrick: We think it’s one of the largest to look at diet and activity factors with both self-report and objective measurements of activity – especially a very multi-cultural, multi-ethnic group of kids.

Narrator: Patrick used an activity monitor called an accelerometer for a week and found that the average adolescent watched about four hours of TV per day and participated in very little vigorous physical activity.

Patrick: That’s the type of exercise that really causes somebody to break a sweat – get real active and get out there and do something. Kids just don’t walk as much as they used to, they don’t get out and ride their bike. Of course, there are logical reasons – parents are concerned about safety and concerned about other issues, but this really gets into the question of how we design and manage our environments.

Narrator: For Science Today, I’m Larissa Branin.