International athletics is in turmoil after some of the biggest names in sprinting returned positive doping tests.

Former 100m world record-holder Asafa Powell of Jamaica, American champion Tyson Gay and Jamaican Olympic gold medallist Sherone Simpson face suspension for testing positive for banned substances, puncturing the myth that the sport has cleaned up its act.

“I am not now nor have I ever been a cheat,” Powell tweeted.

Powell called for an investigation as to how a stimulant called oxilofrine entered his system and caused a positive test at Jamaica’s national championships in June.

Simpson, who tested positive for the same stimulant, said she “would not intentionally take an illegal substance of any form into my system.”

Gay, who has gone out of his way to promote himself as an anti-drug athlete, was more contrite but wasn’t taking full responsibility.

“I don’t have a sabotage story. I don’t have any lies. I don’t have anything to say to make this seem like it was a mistake or it was on USADA’s hands, someone playing games,” said Gay. “I don’t have any of those stories. I basically put my trust in someone and I was let down.”

Gay said he would pull out of the world championships.

Generally, first-time offenders are hit with two-year bans, though reduced penalties are sometimes given if there are extenuating circumstances, which both Gay and his coach, Lance Brauman, said there were.

“He mentioned that he (trusted) someone and that person was untrustworthy at the end the day,” Brauman told The Associated Press in a phone interview. “Maybe I’m naive, but I believe him.”

More In: Other Sports | Sport