Cycling:WHAT WAS already a stressful day for Lance Armstrong turned worse shortly after 7pm yesterday evening when he crashed early in the fourth stage of the Tour of California, hitting the deck. Race commentators initially didn't think the fall was serious and he remounted, returning to the peloton, but several kilometres later he withdrew from the race.

Team manager Johan Bruyneel reported that he was going to hospital to get X-rays.

Armstrong’s mishap came minutes after an outdoor questions and answers session held with huge numbers of media in the town of Visalia, the scheduled start for the day’s race. In a tense exchange, the Texan vehemently denied some stunning – and unexpected – allegations made by former team-mate Floyd Landis, who competed with Armstrong between 2002 and 2004.

Landis’s revelations came in a email exchange between himself, USA Cycling chief executive Steve Johnson and Travis Tygart, the chief executive of the US Anti Doping Agency. Dated April 30th and May 1st, it was leaked from an anonymous email account to the media on Wednesday evening. Landis said that it was issued without his knowledge.

In it, he both admitted having doped for much of his professional career, and also said that Armstrong and US Postal Service team manager Johan Bruyneel advised and facilitated him on how to use banned performance enhancers.

The email alleges that in 2002, Bruyneel instructed him in how to use testosterone patches during the Dauphiné Libéré race, and that he had illegal blood transfusions prior to that year’s Tour. He also claimed that Armstrong spoke to him about the dangers of using EPO due to a new test, and that the Texan had advised him to use transfusions only at that time.

The following year, Landis claimed that Armstrong asked him to stay at his house in Girona, Spain, while he went away for several weeks training. Landis alleges that he was asked to watch blood bags belonging to himself, Armstrong and their team-mate George Hincapie, ensuring that they remained properly refrigerated and there were no power shortages that could have affected their safe storage.

Later that season, he said that Armstrong personally supplied him with EPO.

He also made the accusation, which was “categorically rejected” by the UCI, that the Texan had tested positive during the 2002 Tour of Switzerland but that it was concealed after an agreement was reached between the rider, his director sportif Bruyneel and former UCI president, Hein Verbruggen. Armstrong did not ride in Switzerland in 2002 – it is believed Landis intended to refer to 2001.

Speaking at the start of yesterday’s stage, Armstrong rejected Landis’ claims outright. “We have nothing to hide. We have nothing to run from and if anyone has any questions we would be more than happy to answer them,” he told the journalists present.

“Obviously everyone has questions about Floyd Landis and his allegations. I would say that I’m a little surprised, but I am not; this has been going on for a long time. The harassment and threats from Floyd started a few years ago and really, at that time, we largely ignored him.”

He also alleged that Landis had threatened the organisers of the Tour of California in order to try to get his small Ouch-Bahati Racing Team into the race.

At the time of writing, Landis had yet to reply to Armstrong’s counter-claims. However, his accusations follow on from previous suggestions by others of doping within the US Postal team, plus claims that Armstrong was implicated in doping with EPO during his first Tour de France victory, back in 1999. The Texan has long faced accusations that his Tour wins were not clean. He has repeatedly denied this, and has never been sanctioned.

Landis’s own history in the sport is an extremely convoluted one, by virtue of the fact that he is the only Tour de France winner to have been disqualified from the race due to doping. The Pennsylvanian jumped to worldwide prominence in 2006 when he won the race after an outlandish display in the Alps.

One day after a collapse in form saw him lose a chunk of time, he launched an improbable solo attack on the mountainous road to Morzine and finished well over five minutes clear of the next rider. That set him up for overall victory in the race but, several days after taking the yellow jersey to the finish in Paris, he tested positive.

For the next three and a half years he vigorously fought the charge that he had taken synthetic testosterone in the race, successfully winning the sympathies of large numbers of the American public with his charismatic denials, townhall meetings explaining the facts of the case, plus an autobiography laying out reasons why he felt there was a conspiracy against him.

He was also given a large amount of donations to help him in the fight to clear his name, but lost all appeals and incurred a two year ban.

The email sent this week was an abrupt turn-around, with the 34- year-old admitting for the first time that he had doped.

Speaking to ESPN late on Wednesday, he explained the reason for his volte-face. “I want to clear my conscience. I dont want to be part of the problem any more,” he stated, saying that he was suffering psychologically and emotionally from repeated lying about doping.

“With the benefit of hindsight and a somewhat different perspective, I made some misjudgments,” he said, speaking of what went on in recent years. “And of course, I can sit here and say all day long, ‘If I could do it again I’d do something different,’ but I just dont have that choice.”

He said that coming forward with the information about his doping past and that of other team-mates was a way for him to both move on and to try to help improve the future for the sport.

Armstrong portrayed Landis as mentally unstable yesterday, but what may be of worry to the Texan is that his claims are being investigated thoroughly. USADA has been in communication with Landis for several weeks, and WADA has also pledged to fully investigate the information that has been given.

The New York Times also said yesterday that federal agent Jeff Novitzky was also looking into the allegations. He previously spearheaded the investigation into the BALCO affair, which ended the careers of Marian Jones and other athletes.

It also raises further questions about his reign at the top of cycling, with fans of the sport being completely divided as to his innocence yesterday.

For some, they feel certain that Landis is lying and has lost all credibility after years of protesting his Tour win was clean.

For others, the claims fuel the suspicion they have about Armstrong’s achievements, and their view that the sport needs to break its links with the past in order to finally ensure it has a viable future.