One by one, the vices of youth add up. It began with television washed down with soda and a side of fries. Now, it's the Internet, Madden 2004 and Grand Theft Auto.

But as the layers of sedentary living accumulate -- and at a time when many teenagers are stereotyped as being fat and lazy -- a growing number are taking up a sport where fat and lazy just don't cut it: cross-country.

The evidence will be on display today at the Central Coast Section cross-country championships at Crystal Springs in Belmont.

Bucking societal trends, the sport continues to draw participants in an age where more than one-third of Americans do not participate in physical activity and one-quarter of U.S. children spend at least four hours a day watching TV.

``This is not just an epidemic,'' said Greg Payne, department chair for human performance at San Jose State, ``but a serious epidemic.''

In California, 75 percent of selected fifth- through ninth-grade students failed a basic fitness test last year. But 37,083 state high school students ran cross-country, a 13 percent increase over five years ago, according to a survey by the National Federation of High School Associations. Nationwide, there were 355,193 runners, an increase of more than 4,000 from the year before.

Why? The immediate answers are often superficial: body image, conditioning, making friends. But as the season progresses, the lure grows deeper: self-esteem, confidence, self-discipline.

``You can sit on a couch and play video games for five hours,'' Menlo-Atherton junior Evan Anderson said. ``And then you stand up and think, `What have I done all day?' You do this, and you feel you actually accomplished something.''

Half Moon Bay freshman Allie Hughey used to go home from school and turn on the TV. She never liked running, and she tried it only at the urging of friends.

When she won a junior varsity race, ``It was the coolest thing ever.''

``I didn't expect cross-country to be that fun,'' she said. ``Now, it's my favorite part of the day.''

Most runners, however, don't share the perspective of those such as San Lorenzo Valley's Alex Dunn, the favorite to win the Division IV title today.

``I run because it's something I'm good at,'' he said. ``It's a waste of talent not to do it.''

For others, success may be hidden to all but themselves, measured by a personal-best time or place.

Mid-Peninsula, an alternative private high school in Menlo Park with an enrollment of 135, had no cross-country team until math teacher and former UCLA runner Melinda George persuaded students to try it this fall.

``You're going to run cross-country, right?'' she'd ask good-naturedly along the corridors.

``No way,'' was a typical response.

But with more encouragement, the tone began to change.

``You want me to be on the cross-country team? But I'm not any good.''

``Yeah, I might just think about it.''

None of the 13 who came out had run competitively before. Some were smokers, some overweight. Most couldn't run for two minutes, much less complete a three-mile race.

``Hardly anybody likes to run when they start,'' George said. ``But then it becomes addicting. They see themselves improving, they see themselves getting better. No matter how hard they try, they will reach some kind of success.

``Remember, there's not just a race in the front, but also for second to last.''