Just weeks before the start of the showpiece World Championships in Moscow, athletics was engulfed in a spiralling drug crisis last night after it was revealed that American Tyson Gay and Jamaica's Asafa Powell, the fastest and second fastest men in the world this year, had both tested positive for banned substances.
Gay, a triple world gold medallist in 2007, admitted that a urine sample he had provided in an out-of-competition drug test on May 16 had returned a positive result and that he was pulling out of next month's World Championships in Moscow.
According to the Associated Press news agency, the Florida-based sprinter fought back tears as he confessed to the failed drug test in a phone conversation from Amsterdam.
"I don't have a sabotage story," he said. "I basically put my trust in someone and was let down."
In a separate case, Powell, the former world record-holder, also admitted that he tested positive at last month's Jamaican trials, though he insisted he had not cheated knowingly and was "reeling" from the news.
In a statement, the Jamaican said: "I will confirm that a sample I gave at the national trials in June earlier this year has returned 'adverse findings'.
"The substance oxilofrine (methylsynephrine) was found, which is considered by the authorities to be a banned stimulant.
"I want to be clear in saying to my family, friends, and most of all my fans worldwide that I have never knowingly or willfully taken any supplements or substances that break any rules.
"I am not now – nor have I ever been – a cheat. My team has launched an internal investigation and we are co-operating with the relevant agencies and law enforcement authorities to discover how the substance got in my system."
Fellow Jamaican Sherone Simpson, a silver medallist in the women's 4x100m relay at last summer's London Olympics, also tested positive at the trials for the same substance as Powell, while there were unconfirmed media reports in Jamaica that a further two unnamed Jamaicans had returned adverse findings.
The banned drug oxilofrine that top Jamaican sprinters Asafa Powell and Sherone Simpson have tested positive for is a stimulant used to boost the body's ability to burn fat.
The substance helps athletes boost their power-to-weight ratio with more lean muscle and less fat, and so increase their speed.
It may also increase the rate at which the heart reaches its maximum performance during exercise, meaning a greater supply of oxygen can get to the muscles earlier.
Oxilofrine is an agent that stimulates part of the nervous system and was previously used to treat low blood pressure. More recently, it has started to appear in combination with caffeine in dietary supplements marketed as weight loss products.
However, the superiority of using oxilofrine over an exercise warm-up to achieve this appears unconvincing.
They include the USA's Amy Dodson, one of the world's top amputee runners, who received a six-month ban in 2011 and American cyclist Flavia Oliveira who was banned for 18 months in 2009. Both said they had unknowingly ingested the stimulant via an over-the-counter supplement.
Bolt's agent, Ricky Simms, confirmed last night that the triple Olympic champion had nothing to do with the latest drug cases.
Gay, the American record-holder, had been in his best form in years this season with the three fastest 100m times in the world – an improvement he had attributed to being finally free of injury problems following surgery on a hip problem in 2011. Yesterday's revelations suggest a more sinister explanation.
The American refused to reveal the substance for which he had tested positive, but confirmed that his 'A' urine sample had recorded an adverse finding and that he would now be asking for his 'B' sample to be analysed.
Technically, he is not guilty of a doping offence until the process is complete, but Gay is clearly resigned to his fate after admitting that he would not be competing in Friday's Diamond League meeting in Monaco or on the world stage in Moscow. Rarely does a 'B' test contradict an 'A' test.
"I made a mistake," he said. "I'm pulling out of Monaco and the World Championships."
Gay added that he had informed team-mates, friends and family about the positive test, including his mother and daughter.
He said: "They already know it is some type of accident. I don't want to use certain words, to make it seem like an accident, because I know exactly what went on, but I can't discuss it right now.
"My career and my name have always been better than medals or records or anything like that. I've always wanted a clean name with anything. Unfortunately, I have to break this news, that I have a positive 'A' sample."
Gay declined to go into details about the circumstances of the failed test, but said he planned to give a full explanation to the United States Anti-Doping Agency (USADA).
"I have to go over everything with USADA first," said Gay. "I will take whatever punishment I get like a man. I do realise and respect what I put in my body, and it is my responsibility.
"I'm going to be honest with USADA, about everything, everybody I've been with, every supplement I've ever taken, every company I've ever dealt with, everything."
In a statement, the anti-doping agency said: "In response to Mr Gay's statements, USADA appreciates his approach to handling this situation and his choice to voluntarily remove himself from competition while the full facts surrounding his test are evaluated.
"The 'B' sample will be processed shortly and, as in all cases, all athletes are innocent unless or until proven otherwise through the established legal process, and any attempt to sensationalise or speculate is a disservice to due process, fair play, and to those who love clean sport."
Gay, whose American record of 9.69sec makes him the second fastest sprinter of all time, had previously taken part in a USADA campaign promoting drug-free sport.
In a testimonial on the USADA website, Gay said: "I compete clean because I really believe in fairness, and besides that, my mom would kill me! Just being honest." (© Daily Telegraph, London)