Olympic gold medallist Caster Semenya has lost her appeal against rules designed to decrease naturally high testosterone levels in some female runners.

The Court of Arbitration for Sport's panel of three judges gave a complex verdict and "dismissed both requests for arbitration" from Semenya and the International Association of Athletics Federations (IAAF).

In a landmark judgment, the court said the IAAF's proposed rules on athletes with "differences of sex development (DSD)" are discriminatory but "necessary".

The IAAF is the world athletics governing body.

Semenya and her legal team say they will consider appealing against the decision.


Image: Semenya outside the Court of Arbitration for a hearing in February

Judges ruled 2-1 that "on basis of the evidence submitted by the parties, such discrimination is a necessary, reasonable and proportionate means of achieving the IAAF's aim of preserving the integrity of female athletics in the restricted events".

The IAAF believes female runners with high testosterone levels have an unfair advantage in events from 400m to the mile.

South African athlete Semenya responded to the verdict with a tweet which read: "Sometimes it's better to react with no reaction."

The 28-year-old and Athletics South Africa had claimed the rules, which would force athletes with naturally-occurring high levels of testosterone to take medication to lower them, were unlawful.

Image: Semenya is a two-time Olympic 800m champion

Semenya, a two-time Olympic 800m champion, has one of the various genetic conditions collectively known as differences or disorders of sex development (DSD).

She will now be forced to medicate to suppress her testosterone levels if she wants to defend her world title in September in Doha, Qatar.

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However, the CAS judges say the IAAF should not yet apply the rules to the 1,500m.

Semenya has been the subject of intense scrutiny ever since she burst onto the scene at the 2009 World Championships in Berlin, where she won the first of her three world titles.

Aged just 18, she achieved that feat despite the emotional strain caused by international media speculation about a gender verification test following complaints from rivals about her muscular build.

Despite the award in favour of the IAAF, the CAS said its panel "expressed some serious concerns as to the future practical application" of the DSD regulations.