(CNN) Former Olympic swimmer Sharron Davies has backed the decision for testosterone levels to be reduced in athletes with a difference in sex development (DSD), saying that Caster Semenya has had a "huge" advantage over her opponents.

Semenya, a double Olympic champion over 800 meters, lost an appeal to the Court of Arbitration of Sport (CAS) on Wednesday, meaning she will have to take medication to reduce her testosterone levels if she wants to compete internationally at events between 400 meters and a mile.

South African Semenya is hyperandrogenous, a medical condition estimated to occur in five to 10% of women that results in elevated levels of testosterone.

"I think this is about trying to create as much of a level playing field as possible for female sport," Davies, who won a silver medal in the pool at the 1980 Olympics, told CNN Sport.

"We are talking about between eight and 12% difference which just comes from your biology. That's what we're saying. Sport needs to be about sex not gender, it's as simple as that," added Davies, referring to an athlete's biological composition.

Davies (right) has worked in the media since retiring from competitive swimming.

'Level playing field'

Davies raced against East German athletes during the 1970s and 80s who had taken performance-enhancing drugs to raise their testosterone levels. An excess of testosterone has been found to increase muscle mass within females and cause increased strength, stamina and physical energy.

While she acknowledges that Semenya's testosterone levels are natural rather than induced, Davies says the advantage has been significant.

"There were many athletes who came fourth and no one will ever remember their names and there were many people who didn't win medals that they should have done, and I just don't want to see a whole other generation of young girls end up with the same issue," she says.

"There are many young girls out there that have been training for years, and years, and years who have not won the medals they deserve on a level playing field."

Semenya has responded following the CAS verdict with a number of tweets, one reading: "They laugh at me because I am different. I laugh at them because they are the same."

Another said: "Knowing when to walk away is wisdom. Being able to is courage. Walking away with your head held high is dignity."

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The South African, who will compete at the Diamond League meeting in Doha on Friday, has 30 days to appeal the CAS ruling.

"She did not [set out to cheat]," says Davies, who retired from swimming in 1994. "But she has known for 10 years now that ... she does have an advantage on the track. So this isn't something that's coming as a surprise to her.

"And for the last 10 years that she's been winning money and signing sponsorship deals and doing very well. That's absolutely fine. But now it's very apparent that it's an unfair platform."

Semenya's representatives did not immediately respond to CNN's request for comment regarding Davies' critique.

The 28-year-old Semenya has been the most dominant female middle-distance runner from the past decade, winning three world and two Commonwealth titles on top of her two Olympic golds.

"I know that the IAAF's [International Association of Athletics Federations] regulations have always targeted me specifically," she said in a statement released by her representatives on Wednesday.

"For a decade the IAAF has tried to slow me down, but this has actually made me stronger. The decision of the CAS will not hold me back. I will once again rise above and continue to inspire young women and athletes in South Africa and around the world."

The statement ended by saying that Semenya is reviewing the decision with her legal team and is considering whether to file an appeal.

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A number of leading sport science experts have supported Semenyna, notably Ross Tucker.

"The decision was a disappointment to me, because of the scientific matters and in particular the scientific process that was followed in supporting those regulations," wrote Tucker.

"In my reading of the situation, there is insufficient evidence to support the regulations. There is concept, theory, and biological rationale, but not evidence. And the regulations are, for all intents and purposes, an evidence-based document."

Speaking ahead of the Diamond League in Doha, IAAF president Sebastian Coe said he was "grateful" that CAS had upheld the original ruling.

"It's pretty straightforward. Athletics has two classifications, it has age and gender," Coe told reporters. "We are fiercely protective of both and I am really grateful the court of arbitration has upheld that principle.

"This is a Diamond League press conference, that is as much as I really need to say."