The regulators of the sport of athletics has won its latest high profile case around the integrity of the sport, but with some long lasting implications for the future of the sport and its participants.

The Court of Arbitration for Sport (CAS) had ruled on the side of the International Association of Athletics Federations (IAAF) in its case against decorated athlete Caster Semenya, deciding that Semenya will now be obliged to take medication in order to reduce her testosterone levels to ‘below five nmol/L’.

The South African star went to court earlier this year to challenge the current rules proposed by the sporting body which have set out a revised eligibility criteria for female athletes.

The case had been dubbed as a landmark case for intersex and transgender women, with decision is expect to send shockaves throughout the sporting world.

The unexpected CAS ruling will now require athletes with a “difference of sexual development” (DSD), such as Semenya, to consume testosterone suppressants if they are to continue competing in races ranging from 400m to one mile.

This would inevitably hinder the performance of athletes such as Semenya immensely, with sport scientist Ross Tucker, claiming that the new ruling will mean Semenya will run 800m around seven seconds slower than her world-leading time.

CAS had previously agreed that the IAAF policy towards DSD athletes was “discriminatory”. Two of the three arbitrators, however, had accepted the IAAF argument that elevated testosterone levels in female athletes can lead to significant advantages in size, strength and power from puberty onwards.

The arbitrators stated that the IAAF policy was ‘necessary, reasonable and proportionate’ to ensure fair competition in women’s sport.

Semenya, in response to the ruling, has expressed hope that the DSD regulations may one day be overturned, while also suggesting that she – alongside her legal team – would be considering a legal appeal.

“I know that the IAAF’s regulations have always targeted me specifically,” she added. “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.”

CAS explained that its ruling followed a failure from Semenya’s team to sufficiently prove that the IAAF policy was “invalid” back in February, and as a result, ruled that the policy towards DSD athletes is legal – providing it can be justified.

As it explained in a statement: “The panel found that the DSD Regulations are discriminatory but that, on the 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.”

As part of the ruling, CAS expressed that there are ‘some serious concerns’ regarding the fair application of the new regulations, accepting that there may be some contention over three areas: difficulties for athletes in implementing and complying with the DSD regulations; the absence of concrete evidence supporting the inclusion of certain events under the DSD Regulations, including the 1500m and one mile; the potentially negative and harmful side effects of hormone treatment for DSD athletes.

CAS addressed the health issues regarding the hormone suppressants, commenting: “The side effects of hormonal treatment, experienced by individual athletes could, with further evidence, demonstrate the practical impossibility of compliance which could, in turn, lead to a different conclusion as to the proportionality of the DSD regulations.”