IAAF president Sebastian Coe is "grateful" to the Court of Arbitration for Sport after the landmark ruling against Caster Semenya.
he double Olympic 800m champion challenged new IAAF rules which attempt to restrict testosterone levels in female runners.
She lost her appeal and Semenya and athletes with differences of sexual development (DSD) must now take medication to suppress their testosterone to compete in some track events or change to another distance.
Speaking at a Diamond League press conference ahead of the season-opener in Doha, Lord Coe said: "It's pretty straightforward. Athletics has two classifications, it has age and gender.
"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."
South African Semenya must now either take medication in order to compete in track events from 400m to the mile or change to another distance.
Cas found that the rules for athletes with DSD were discriminatory - but that the discrimination was "necessary, reasonable and proportionate" to protect "the integrity of female athletics".
But the decision was split 2-1 as one of the three CAS judges agreed with Semenya, who was backed in her appeal by Athletics South Africa, and the IAAF was told there were significant caveats to the court's approval of its 'eligibility regulations for female classification (athletes with differences of sex development)'.
"I know that the IAAF's regulations have always targeted me specifically," Semenya said in a statement after the ruling was announced 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."
Triple European champion Dina Asher-Smith added: "Caster is my friend and I hope she is going to be OK."
The rules will come into effect on May 8.