LAUSANNE, Switzerland (AFP) — The Court of Arbitration for Sport (CAS) said Tuesday it had opened a probe into Caster Semenya’s challenge of controversial new IAAF rules on testosterone occurring in female athletes.

CAS said it had “registered a request for arbitration” filed by the South African two-time Olympic gold medallist against the “International Association of Athletics Federations’ (IAAF) ‘Eligibility Regulations for Female Classification (Athletes with Differences of Sex Development)’ that are due to come into effect on 1 November 2018”.

Semenya, CAS said, sought a “ruling from CAS to declare such regulations unlawful and to prevent them from being brought into force. An arbitration procedure has been opened”.

The IAAF announced its new rules targeting women who naturally produce unusually high levels of testosterone in April, arguing that hyper-androgynous competitors enjoy an unfair advantage.

Athletes classified as “hyper-androgynous”, like Semenya, will have to chemically lower their testosterone levels to 5 nanomoles per litre of blood to be eligible to run any international race of 400 metres up to the mile.

Semenya, who has undergone several sex tests since her first title in 2009, has called the rules discriminatory and violate the IAAF’s Constitution and the Olympic Charter. The 27-year-old has been at the centre of debate because of her powerful physique, one of the effects of hyper-androgenism which causes those affected to produce high levels of male sex hormones.

The IAAF said it stood “ready to defend the new regulations”.

“Sex differences in physical attributes such as muscle size and strength and circulating haemoglobin levels give male athletes an insurmountable competitive advantage over female athletes in sports where size, strength and power matter,” the IAAF said in a statement.

“These advantages (which translate, in athletics, to an average 10-12 per cent performance difference across all disciplines) make competition between men and women as meaningless and unfair as an adult competing against a child or a heavyweight boxer competing against a flyweight. Only men would qualify for elite-level competition; the best female athlete would not come close to qualifying.”

The IAAF added that evidence suggested that having levels of circulating testosterone in the normal male range rather than in the normal female range, and being androgen-sensitive, gave a female athlete a performance advantage of at least 5-6 per cent over a female athlete with testosterone levels in the normal female range.