Asafa Powell and Tyson Gay painstakingly built their record-setting careers and untainted reputations by resisting shortcuts and exercising tight control over who gained entrance to their inner circles.

Then they turned 30, and with age and injuries taking their toll, they made exceptions.

And now they are paying a price.

Both sprinters have run afoul of anti-doping rules. They claim they failed drug tests because they put their fate in the hands of people they didn't know very well.

"Sometimes, a human being just naturally, generally, trusts somebody," explained the 30-year-old Gay, who has pulled out of next month's World Championships while the US Anti-Doping Agency reviews his case. "That's just what people do," he said.

And therein lies the problem. People can call themselves trainers, nutritionists or doctors, some with legitimate credentials, some not, but with virtually no vetting, and get close enough to gain the confidence of some of the world's best athletes.

While Gay would not reveal the new person in his inner circle, Powell and his agent have placed the spotlight on the former 100-metre world record-holder's new trainer, Christopher Xuereb of Canada. They are exchanging accusations, with Powell claiming he never tested positive until he started working with Xuereb, and Xuereb insisting he did nothing wrong, saying it's difficult "to assist some athletes without risk of being made the scapegoat".

Xuereb worked at the Toronto clinic run by Anthony Galea, the sports physician whose clients included Tiger Woods. Galea pleaded guilty to bringing unapproved and mislabelled drugs into the United States for house calls.

Nothing new

Xeureb was fired from the clinic three years ago, Galea's attorney, Steve Greenspan, told The Associated Press.

"The guy was a physio assist," Greenspan said. "He was not qualified to do anything. The clinic, said if you want to do anything more, you have to go get qualifications."

Steve Roush, the former chief of sport performance at the US Olympic Committee (USOC), says this ritual of the athlete blaming someone else for a doping positive is nothing new. Nor, Roush says, is the underwhelming amount of research many athletes perform before hiring their new training or nutrition guru.

"Most of them, it's simply word of mouth," Roush said.

"You've got Marion Jones learning about it from (ex-husband) C.J. Hunter, that type of stuff. There's this little community, I guess you'd call it. They pretty much share information. Of course, then, when something goes wrong, they immediately start pointing the finger."

Gary Wadler, the past chairman of the World Anti-Doping Agency's banned-substances list, said athletes are susceptible to what he calls "the culture of the guru".

"They come to the athletes with the scientific literature, come up with some apparent justification for recommending whatever they recommend," Wadler said.

"And because it's pronounced as the stuff to use by the guru, it's deemed to be the last word, particularly when the guru talks in technical jargon," he added.

In his position at USOC, Roush dealt extensively with accrediting and managing athlete entourages, though the USOC's ability to control credentials comes mainly at the Olympic Games.

He said that, shortly before he left the USOC in 2008, management considered putting together a registry of sorts for athletes, who could use the list to see if their potential hire had ever been found dealing in performance-enhancing drugs. Nothing ever came of the idea, and the USOC, which guides national governing bodies on a wide range of issues, including marketing and sex-abuse prevention, largely stays out of the business of monitoring athlete entourages.