ADVANCE FOR WEEKEND EDITIONS, JULY 20-21 - FILE - In this July 25, 2012, file photo, the United States'Tyson Gay warms up during a training session for the 2012 Summer Olympics, in Birmingham, England. While the facts continue to be sifted in the doping cases against Gay and Asafa Powell, two key questions will linger even after things are resolved: Where do these trainers, nutritionists and doctors come from and how do they move, seemingly unvetted, into the inner circles of some of the world's best athletes? (AP Photo/Jon Super, File)

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're 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 U.S. Anti-Doping Agency reviews the case against him. "That's just what people do."

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.

"There are a lot of snake-oil salesmen who end up taking advantage of the athletes, sometimes unbeknownst to the athletes," said USADA CEO Travis Tygart.

While Gay would not reveal the new person in his inner circle, Powell and his agent have placed the spotlight on the former 100-meter world-record holder's new trainer, Christopher Xuereb of Toronto. They are now 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 mislabeled drugs into the United States for house calls.

Xuereb was fired from the clinic three years ago, Galea's lawyer, Brian 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 U.S. Olympic Committee, 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."

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.

"Whether it would've worked or not, we don't know," Roush said. "But it was an idea that could've made it a little more challenging for a bad seed to do business."

USOC spokesman Patrick Sandusky said the federation had no comment for this story.

Faced with its own drug problem, Major League Baseball took a different tack about a decade ago by tightening its policy regarding who was allowed in team clubhouses. The main target: Personal trainers who weren't officially affiliated with teams but often had spots in their inner circles, catering to Barry Bonds, Sammy Sosa and other stars.

Though the enhanced restrictions didn't prevent players from associating with independent trainers outside the stadium, it sent a strong message that only people with team credentials had baseball's seal of approval.

Olympic sports, especially those dealing in individual disciplines, have a tougher time with blanket policies.

The International Olympic Committee has an Entourage Commission that tries to keep tabs on people who surround big-time athletes. But its power to police these groups is limited.

Australian IOC member Kevan Gosper would like to change that. He says athletes found guilty of doping violations should have more than their medals stripped away.

"It should be agreed before competitions that if an athlete is caught doping, you take the money back," Gosper said. "If you take the money back, you cut the supply line to the entourage. You have to do something that really hurts. The cash flow goes beyond the athletes. You've got to hit the entourage."

USA Track and Field has a coaches' registry that requires background checks. The screening includes a national criminal database search and a sex offender registry search but makes no specific mention of an applicant's past regarding performance-enhancing drugs.

USADA, which tests American athletes, has gone after trainers and coaches before, most notably when it gave a lifetime ban to Trevor Graham, who worked with Jones, Tim Montgomery and others involved in doping scandals. But among the voluminous list of resources for athletes on its website, USADA doesn't offer anything in the way of before-the-fact vetting of athletes' potential employees.

However, USADA does make its list of banned coaches and trainers available and Tygart is hopeful that a proposed WADA rule, which would leave athletes open to sanctions for knowingly working with support personnel who have been banned, might help regulate entourages more effectively.

"It's something we've been concerned about," Tygart said. "Currently, there is no universal certification or education provided or any licensing needed for those who treat Olympic athletes. It's fertile ground for people who see opportunity, who see fame or fortune by associating with high-profile athletes, and sometimes they end up taking advantage of those athletes and leading them down the wrong path."

The best way to avoid the wrong path, experts say, is for athletes to spend more time interviewing and researching any potential members of their inner circles, especially those who might be recommending which vitamins and supplements to take.

"You ask questions," said Amy Goodson, a registered sports dietitian who is a consultant with USATF. "Ask them where they went to school, ask them what their credentials are. If it's just a personal training certification, I'd be leery of taking the information from them. Going out of your way to ask questions is going to be your best bet."

Often, they don't ask enough questions.

"If you ran your business that way, you wouldn't be in business very long," Wadler said.

Powell's agent, Paul Doyle, said the sprinter was referred to Xuereb through other physiotherapists Doyle's clients have worked with in the past.

Now, it's a relationship Powell regrets. Gay feels the same way about his connection with a still-unidentified guru who supposedly gave him the drug that caused his positive test.

"I basically put my trust in someone," Gay explained, "and I was let down."

That excuse has been predictable for decades — and never very credible.

"The burden is on us," American hurdler David Oliver said. "But most athletes know what they are getting involved in, and it starts with who they claim their 'circle' is."

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AP Sports Writer Stephen Wilson in London contributed to this report.

News from © The Associated Press, 2013