After years of denial, Floyd Landis–the cyclist who was stripped of his winning title to the 2006 Tour de France after failing a drug test–admitted last week that he did take performance enhancing drugs. And his confession is causing a stir, partly because he also implicated former teammate Lance Armstrong, seven-time-winner of the Tour de France (Armstrong denies the accusation), and partly because of the particular drugs he fessed up to taking:

Mr. Landis said in [several emails to cycling officials] that during his career, he and other American riders learned how to conduct blood transfusions, take the synthetic blood booster Erythropoietin, or EPO, and use steroids. All these practices are banned in cycling. Mr. Landis said he started using testosterone patches, then progressed to blood transfusions, EPO, and a liquid steroid taken orally. [Wall Street Journal]

EPO shook the cycling community in the 1990s, when police raids during the 1998 Tour de France (dubbed the “Tour de Dopage“) found that several riders were using EPO. It looks like the drug, believed to be thwarted by drug tests, has returned.

Our kidneys produce most of our natural erythropoietin, a hormone that leads to the creation of red blood cells. Since red blood cells carry oxygen, more cells means more oxygen in the blood. More oxygen means longer, harder workouts.

Anemics, who suffer from fatigue, naturally have low levels of the hormone. Dopers, who take a synthetic version, have high levels, which can give them endurance but also lead to dangerous side effects such as blood-thickening (and thus strokes).

Regulatory agencies like the International Cycling Union and the World Anti-Doping Agency have developed tests to combat the use of such drugs in competitive sports. For example, the biological passport program, unveiled in 2007, uses repeated sampling to make an electronic record of the cyclist’s natural levels of various hormones, which become benchmarks to test against before a particular race. And since a urine test introduced in 2000 could determine EPO levels, apparent use of the drug declined over the past decade.

But Landis’s confession forces regulatory agencies to face a loophole that helped riders pass urine tests. It’s called microdosing:

“In 2003, the athletes started to use a new procedure together with blood doping,” said Francesca Rossi, the director of antidoping at the International Cycling Union, the sport’s governing body. “I know that this microdosing strategy can be difficult to detect.” Working with doctors, cyclists discovered that carefully controlled, small doses of EPO eluded the urine test while still raising their red cell count. Microdoses of EPO let athletes put in superhuman hours of training without suffering the natural consequence of fatigue. [New York Times]

The debate over how much EPO doping is going on in competitive cycling will certainly continue in the messy aftermath of Landis’s claims. In one allegation, Landis claimed that Armstrong was caught with EPO in 2001 Tour de Suisse, but that officials had covered it up.

Landis suffered another blow to his credibility. The International Cycling Union said no riders tested positive for EPO at the 2001 Tour de Suisse, disputing comments made by the disgraced cyclist. [Boston Globe]

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Image: flickr / whileseated