U.S. Olympic swimmer Jessica Hardy told The Associated Press Friday that she has no idea how she tested positive for a banned substance.

In the final days of training camp with her U.S. Olympic teammates, Jessica Hardy was trying to nap between practices when she got the most dreaded of phone calls for any athlete:

She had tested positive for an illicit drug.

"My main emotion at that point was confusion," Hardy said Friday. "I had never even heard of this drug."

In an interview with The Associated Press, Hardy professed her innocence and said she has no idea how she tested positive for Clenbuterol during the U.S. Olympic trials. She also talked hopefully about getting the ruling overturned in time to compete at the Beijing Olympics.

"I'm innocent," said Hardy, who spoke by telephone from California accompanied by her attorney, Howard Jacobs. "That's all I can say to everybody. Whether or not people chose to believe me, I'm innocent."

Hardy was tested three times during the trials in Omaha, Neb., Jacobs said. The results were negative for the samples taken on July 1, after she won the 100-meter breaststroke, and on July 6, shortly after she claimed another individual race at the Olympics by finishing second to Dara Torres in the 50 freestyle.

But Hardy's "A" and backup "B" samples both came back positive — for what her attorney said was low amounts of the drug — from a test on July 4, when she finished fourth in the 100 freestyle.

Clenbuterol is usually prescribed to those with breathing disorders, such as asthma, and also is well-known in horse racing circles as a treatment for respiratory ailments. More recently, it's been touted as a weight-loss drug.

But it's also a stimulant that increases aerobic capacity and the flow of oxygen in the bloodstream, which is why it landed on the list of banned substances for athletes.

Hardy said she can't figure out how Clenbuterol wound up in her system — if, in fact, the test was accurate.

"It's pretty much the hardest thing in my life that I've ever had to go through," she said. "I've cried every single day since I found out. I even vomited from anxiety. This is absolutely the worst time of my life."

Unless the positive test is overturned through an expedited arbitration process, Hardy will miss what was supposed to be her first Olympics and face a mandatory two-year doping ban.

The positive test between two negative tests certainly will be a major point in Hardy's appeal.

"I would definitely say it's unusual," Jacobs said. "As far as how it will play into the arbitration case, I don't know. But it's out of the norm."

The 21-year-old Hardy set a world record in the 100 breaststroke as a high school senior and was a four-time NCAA champion at the University of California before turning pro last year. After her performance at the Olympic trials, she was expected to be a key member of the U.S. women's team in Beijing with her two individual events, plus likely spots on the 400 free relay and the 400 medley relay.

Now, her whole life is on hold, though Hardy continues to train on her own in Southern California in hopes that her doping case will be overturned. The rest of the U.S. team left Friday for Singapore, where they will hold their final workouts before heading to Beijing.

"My training and my practices are really the only thing I have control over right now," she said, shortly after a morning workout. "Honestly, I'm working as hard as possible. That's really the only thing I can do for myself."