When its television screens go blank on Saturday, the Nickelodeon cable network is advising its viewers not to fiddle with the buttons — but to go outside and play.

The three hours of dead air the children's network will begin broadcasting at noon (EDT/PDT) is part of its fourth annual worldwide day of play, an encouragement to kids to get outside and work on getting in shape.

Later that day, any kids who have gotten the exercise bug might tune into the network's "Let's Just Play Go Healthy Challenge" (6 p.m. EDT/PDT) and compare what they did with other kids whose exercise regimens have been spotlighted on the show.

If they have been following the program, an effort of the network and the Alliance for a Healthier Generation, they'll see that one of those kids has made some impressive gains.

The 13-year-old, identified only as Kenderick from Little Rock, Ark., was a chubby youth and self-described "couch potato who played video games and didn't go outside much" when he joined the program in April. Since then, he says he has dropped 40 pounds and learned to swim and ride a bike.

"I could have learned to swim before, but I was really scared of the water," he told The Associated Press recently. "I got a bike for Christmas. I touched it once, fell off and never rode it again."

Over the past several months, however, he overcame those fears and got in good enough shape to take part in a triathlon in which he swam 100 yards, biked four miles and ran one mile.

Kenderick, whose family has a history of heart disease and diabetes, said he hopes he might have been an inspiration to some of the 750,000 kids the network says made a promise on its Web site to do their part to fight childhood obesity.

In the meantime, he still has some goals he wants to achieve.

"I still want to lose weight but I want to work on my muscles now," he said. "I want to get ripped now."