<p>Disgraced former American cyclist Lance Armstrong has revealed he first started doping from the age of 21, during his first season as a professional.</p>.<p>"Wow, straight to the point, probably 21," Armstrong replied when asked how old he was when he first doped as part of an ESPN documentary.</p>.<p>The exchange with US journalist Marina Zenovich appeared in a 90-second trailer released on Monday for a two-part documentary called "Lance" which will be broadcast by ESPN on May 24 and 31.</p>.<p>During the clip, in which former US Postal Service team-mates Tyler Hamilton and George Hincapie respond to the same question about performance-enhancing drugs, Armstrong, now 48, explains there are "a bunch of ways to define doping".</p>.<p>"The easiest way to define it is breaking the rules. Were we getting injections of vitamins and other things like that at an earlier age? Yes, but they weren't illegal. I always asked (what I was being given). I always knew, and I always made the decision on my own," he said.</p>.<p>"Nobody said, 'Don't ask, this is what you're getting.' I never, ever would have gone for that. I educated myself on what was being given, and I chose to do it."</p>.<p>Armstrong dominated professional cycling in the 2000s and won the Tour de France seven years in a row from 1999 to 2005.</p>.<p>He was later stripped of those titles and received a lifetime ban from the sport in 2012 after the US Anti-Doping Agency determined he was the key figure in a sophisticated doping programme on the US Postal Service team.</p>.<p>In 2013, he confessed to doping starting in 1996 in a televised interview with US chat-show host Oprah Winfrey.</p>.<p>His latest admission could also cast doubt over his world road race title won in Oslo in 1993, having turned professional the previous season.</p>
<p>Disgraced former American cyclist Lance Armstrong has revealed he first started doping from the age of 21, during his first season as a professional.</p>.<p>"Wow, straight to the point, probably 21," Armstrong replied when asked how old he was when he first doped as part of an ESPN documentary.</p>.<p>The exchange with US journalist Marina Zenovich appeared in a 90-second trailer released on Monday for a two-part documentary called "Lance" which will be broadcast by ESPN on May 24 and 31.</p>.<p>During the clip, in which former US Postal Service team-mates Tyler Hamilton and George Hincapie respond to the same question about performance-enhancing drugs, Armstrong, now 48, explains there are "a bunch of ways to define doping".</p>.<p>"The easiest way to define it is breaking the rules. Were we getting injections of vitamins and other things like that at an earlier age? Yes, but they weren't illegal. I always asked (what I was being given). I always knew, and I always made the decision on my own," he said.</p>.<p>"Nobody said, 'Don't ask, this is what you're getting.' I never, ever would have gone for that. I educated myself on what was being given, and I chose to do it."</p>.<p>Armstrong dominated professional cycling in the 2000s and won the Tour de France seven years in a row from 1999 to 2005.</p>.<p>He was later stripped of those titles and received a lifetime ban from the sport in 2012 after the US Anti-Doping Agency determined he was the key figure in a sophisticated doping programme on the US Postal Service team.</p>.<p>In 2013, he confessed to doping starting in 1996 in a televised interview with US chat-show host Oprah Winfrey.</p>.<p>His latest admission could also cast doubt over his world road race title won in Oslo in 1993, having turned professional the previous season.</p>