The CAS upheld new IAAF rules which attempt to restrict testosterone levels in female runners such as South Africa's Semenya.
ADVERTISEMENTIAAF President Sebastian Coe said on Thursday that he's "really grateful" to the Court of Arbitration for Sport (CAS) after the ruling against Olympic champion Caster Semenya.
The CAS upheld new IAAF rules which attempt to restrict testosterone levels in female runners.
Double Olympic 800-metre champion Semenya lost her appeal after challenging the IAAF rules.
It means the South African, as well as other athletes with differences in sexual development, must now take testosterone-reducing medication if they want to compete in some track events - from 400 metres to the mile - or switch to other disciplines.
Coe said there would be no delay in implementing the new regulations, despite CAS suggesting it had "serious concerns as to the future practical application" of them.
Athletics South Africa has said it was "reeling in shock" over the CAS decision in a show of public backing for Semenya.
The 28-year-old athlete is eligible to compete in Doha and can make an appeal against the Cas ruling within the next 30 days to the Swiss Tribunal Courts.
On Thursday she tweeted: