By Duncan Mackay

Levi Leipheimer_Beijing_2008June 18 - Four of America's top road cyclists, including the Beijing 2008 bronze medallist Levi Leipheimer, have all ruled themselves out of competing for the United States at London 2012 seemingly because of their links to Lance Armstrong, who is being investigated for allegedly taking banned performance-enhancing drugs.

The seven-time Tour de France winner was last week suspended from taking part in triathlons after the United States Anti-Doping Agency (USADA) announced that they had opened proceedings against Armstrong.

Leipheimer, George Hincapie, Christian Vande Velde and David Zabriskie asked that they be taken out of the running for places on the road cycling team for the Olympics, USA Cycling announced in a brief statement.

"USA Cycling will not speculate on the reasoning behind their requests and will not have further comment," the statement said.

"Any questions related to their decision should be directed to the individual athletes."

All four riders spent time on the US Postal team with Armstrong and are expected to be called as witnesses in the case.

The 40-year-old Chris Horner, who won the 2011 Amgen Tour, will instead lead the US team in London along with several younger riders who have no connection with Armstrong. 

They include Tyler Farrar, who was tenth in last year's World Championships in Copenhagen. 

The 21-year-old Taylor Phinney (pictured) will be the youngest member of the team, having had the same distniction in Beijing four years ago when he competed on the track, finishing seventh in the individual pursuit event won by Britain's Bradley Wiggins.

Taylor Phinney_in_Team_USA_kit
Armstrong has denied the USADA charges and claimed that he is a victim of a conspiracy.

He claims the case is based upon the same evidence that was used by Federal investigators during a two-year probe which eventually ended without any criminal charges being brought.

"USADA only initiates matters supported by the evidence," said Travis T. Tygart, the chief executive of USADA. 

"We do not choose whether or not we do our job based on outside pressures, intimidation or for any reason other than the evidence.

"Our duty on behalf of clean athletes and those that value the integrity of sport is to fairly and thoroughly evaluate all the evidence available and when there is credible evidence of doping, take action under the established rules.

"As in every USADA case, all named individuals are presumed innocent of the allegations unless and until proven otherwise through the established legal process.

"If a hearing is ultimately held then it is an independent panel of arbitrators, not USADA that determines whether or not these individuals have committed anti-doping rule violations as alleged."

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