Gatlin maintains innocence

Olympic 100 metres champion Justin Gatlin, bidding to get an eight-year doping ban overturned, told an arbitration hearing he never knowingly took performance-enhancing drugs.

Gatlin and around seven others testified at the hearing including therapist Chris Whetstine and Jeff Novitzky, the lead investigator in the Bay Area Laboratory Cooperative (BALCO) case, according to Gatlin's lawyer John Collins.

"Justin testified and told his story and explained to everyone how he never knowingly used a prohibited substance," Collins said.

The American joint world record-holder tested positive for testosterone or its precursors in April 2006, but has always denied knowingly taking banned substances.

Collins said it was unclear how the banned substance had entered Gatlin's system.

"It wasn't through a shot and it wasn't orally so it only leaves through his skin," Collins said.

Gatlin would not be eligible to run until July 2014 unless he receives a shorter ban.

Gatlin also tested positive in 2001 for an amphetamine contained in a medication he took for 10 years for Attention Deficit Disorder.