The banned hormone erythropoietin, or EPO, wasn't detectable by cycling's doping controls until 2001 and so was widely abused because it prompts the body to produce oxygen-carrying red blood cells, giving a big performance boost to endurance athletes.
Armstrong was clearly talking about his own era, rather than the Tour today. Le Monde reported that he was responding to the question: "When you raced, was it possible to perform without doping?"
"That depends on which races you wanted to win. The Tour de France? No. Impossible to win without doping. Because the Tour is a test of endurance where oxygen is decisive," Le Monde quoted Armstrong as saying. It published the interview in French.
Some subsequent media reports about Le Monde's interview concluded that Armstrong was saying doping is still necessary now, rather than when he was winning the Tour from 1999-2005. That suggestion provoked dismay from current riders, race organizers and the sport's governing body, the International Cycling Union or UCI. Five-time champion Bernard Hinault, who works for Tour organizer ASO, said: "We have to stop thinking that all riders are thugs and druggies and all that."
Asked later by The Associated Press to clarify his comments, Armstrong said on Twitter he was talking about the period from 1999-2005. He indicated that doping might not be necessary now.
"Today? I have no idea. I'm hopeful it's possible," Armstrong tweeted.
In a statement issued before that clarification, UCI President Pat McQuaid called the timing of Armstrong's comments "very sad."
"I can tell him categorically that he is wrong. His comments do absolutely nothing to help cycling," McQuaid said in a statement. "The culture within cycling has changed since the Armstrong era and it is now possible to race and win clean.