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Why do athletes cheat?

The World Anti-Doping Agency has a list of over 100 banned substances. The athletes know they'll be tested for these substances over and over. So why risk getting caught? NBC's George Lewis reports.

Floyd Landis, accompanied by his wife, was on the morning talk shows Monday, denying use of performance enhancing drugs.

"Floyd, did you cheat to win the Tour de France?" the 'Today' show's Matt Lauer asked.

"No, Matt, I did not," said Landis.

"Floyd, unquestionably, has a long uphill climb to restore his name and his reputation," says Alan Abrahamson, a sportswriter with The Los Angeles Times.

As do many athletes. Whether it's Barry Bonds, who claims he never used steroids, or runner Justin Gatlin, who also denies doping.

The World Anti-Doping Agency has a list of over 100 banned substances. The athletes know they'll be tested for these substances over and over. So why risk getting caught?

John Hoberman, the author of "Testosterone Dreams" and a professor at the University of Texas, says for many it's a basic business decision.

"There are major financial incentives in some of our high profile sports, and doping is part of the price of doing business," he says.

But former marathoner Frank Shorter, later head of the U.S. Anti-Doping Agency, says he believes public disgust will compel a crackdown by sports that have tolerated the problem, until now.

"The public is fed up with doping," he says, "and to use an old analogy, the emperor has no clothes."

Floyd Landis says he will fight the doping charges until his appeals are exhausted. If the appeals fail, he'll lose his Tour de France title and face a four-year ban from cycling, in his case, a potential career-ender.