Caster Semenya has lost a landmark case against athletics' governing body meaning it will be allowed to restrict testosterone levels in female runners.
The Court of Arbitration for Sport (Cas) rejected the South African's challenge against the IAAF's new rules.
But Cas said it had "serious concerns as to the future practical application" of the regulations.
Olympic 800m champion Semenya, 28, said in response to the ruling that the IAAF "have always targeted me specifically".
Now she - and other athletes with differences of sexual development (DSD) - must either take medication in order to compete in track events from 400m to the mile, or change to another distance.
"For a decade the IAAF has tried to slow me down, but this has actually made me stronger. The decision of Cas will not hold me back," said Semenya in a statement.
"I will once again rise above and continue to inspire young women and athletes in South Africa and around the world."
Previously, she had said that she wanted to "run naturally, the way I was born".
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".
However, Cas set out serious concerns about the application of the rules, including:
- Worries that athletes might unintentionally break the strict testosterone levels set by the IAAF;
- Questions about the advantage higher testosterone gives athletes over 1500m and the mile;
- The practicalities for athletes of complying with the new rules.
Cas has asked the IAAF to consider delaying the application of the rules to the 1500m and one mile events until more evidence is available.
Semenya is still eligible to compete at the Diamond League meet in Doha on Friday and can make an appeal against the Cas ruling to the Swiss Tribunal Courts within the next 30 days.