"It's impossible to win the Tour de France without doping because the Tour is an endurance event where oxygen is decisive. To take one example, EPO (erythropoetin) will not help a sprinter to win a 100m but it will be decisive for a 10,000m runner. It's obvious," he was quoted as saying.
Armstrong, who won the Tour a record seven times between 1999 and 2005, was last year exposed as a serial drug cheat in a devastating US Anti-Doping Agency report that plunged cycling into crisis about the extent of drug-taking in the peloton.
He then admitted in a television interview that he used a cocktail of banned substances, including the blood booster EPO, testosterone and blood transfusions, to win the Tour.
Armstrong told Le Monde that he was not the first athlete to dope and there would always be a doping culture.
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"I simply took part in this system. I'm a human being," he said, admitting that he could never erase the past but would strive to make up for it for the rest of his life.
"We've got to stop thinking that all cycle racers are thugs and druggies. It depresses me to hear all this. I think that when people do exactly what they have to do, in other words, proper testing in all sports, we're going to be rolling around laughing for five minutes," he told BFM TV.
"Stop saying it's cultural for God's sake. It's impossible. There are plenty of young riders who've had dope tests and not tested positive. It's constant suspicion," he told the channel from Corsica, where the Tour gets under way tomorrow.