Aussie swimmer Jack vows to clear her name after positive drug test

Australian relay world-record holder Shayna Jack Sunday revealed the drug she tested positive for was a banned substance that aids muscle mass, while maintaining her innocence and vowing to clear her name.

The 20-year-old, part of Australia's 4x100m freestyle team that set a world record at last year's Commonwealth Games, failed an out-of-competition test late last month.

But it only came to light on Saturday, initially in a media report, before Jack confirmed it. She had returned home days before the start of the world championships in South Korea citing "personal reasons".

The revelation was hugely embarrassing for Australian swimming, coming just days after Olympic champion Mack Horton's high-profile protest against Chinese rival Sun Yang in Gwangju over salacious claims he smashed vials of blood following a test last year.

In an emotional Instagram post on Sunday evening, Jack said she tested positive to Ligandrol, also known as selective androgen receptor modulator, intimating that it can be found in contaminated supplements.

"I was in complete shock, asking myself how and why is this happening to me. My brain repeated over and over: 'I have always checked my substances', 'I didn't do this', 'why is this happening to me?', 'I've done nothing wrong'," she said.

"I didn't intentionally take this substance; I didn't even know it was in my system. It just didn't make any sense, and still doesn't to this day." She added that "the day I found out was the day I began my fight to prove my innocence".

Swimming Australia chief executive Leigh Russell Sunday called the test result "bitterly disappointing and embarrassing".

She said she knew of the failed test on June 26, but maintained the governing body was required to keep the details confidential "until such time as either ASADA or the individual athlete release details of an adverse test result" Richard Ings, the former head of the Australian Sports Anti-doping Authority (ASADA), questioned this in a tweet late Saturday and called Jack's explanation for missing the world championships "an untruth".

In a follow-up tweet Sunday, he added: "If Swimming Australia and ASADA have a policy of not announcing provisional suspensions then they should quickly change it.

"Major global sports all announce provisional suspensions. You can't hide suspended athletes. It always gets out. Transparency is permitted by WADA (World Anti-Doping Authority)." Russell insisted the rules were "very, very clear" and they prevented her from speaking out earlier.

"I accept this is a frustrating position... it makes it very tough for national sporting organisations to be transparent," she said in Melbourne.

The Australian team was only told of Jack's test result on Saturday, and Russell insisted Horton would have taken the same stance even if he had known earlier.

"I think that Mack has made a stand for something that he truly believes in," she said.

"And I think actually we have the same stance -- we absolutely do not want drugs in our sport.