Suspended US Olympic relay gold medallist Crystal Cox has denied using performance-enhancing drugs.

"I can sit and preach I am innocent and have never used steroids but proving my innocence was difficult without the money or the resources, going against a Goliath like the United States Anti-Doping Agency (USADA)," said the 2004 4x400 metres relay alternate whose four-year ban has put the team's gold in jeopardy.

USADA announced Cox's suspension last weekend, saying her results since 2001 had been disqualified because of the use of prohibited anabolic agents and hormones between 2001 and 2004.

"I fought as long as I could and tearfully signed the sanction but knowing in my heart and every fibre of my being I was innocent," said Cox.

"If I did not sign the sanction, being banned (for life) from track and field would damage me more than the public scrutiny I am receiving now."

USADA chief executive Travis Tygart defended his agency's handling of the case and said Cox could have gone to an independent decision-making body rather than accept the four-year suspension.

"She acknowledged her use of anabolic agents in violation of the rules," Tygart said.

"We have a signed document."

The suspension could mean all members of the US 4x400 team, including Cox who ran in a preliminary round and finalists Monique Henderson, Monique Hennagan, Sanya Richards and Deedee Trotter, lose their medals.

Traditionally, the IOC has stripped national relay teams of medals when a team member, including alternates, has been suspended for, or admitted to, doping.

The doping case is the sprinter's second.

In 2002 she tested positive for the prohibited substance ephedrine and was given a public warning by USADA and disqualified from her race.