Olympic champion Caster Semenya lost her appeal Wednesday against rules governing unusually high testosterone in female runners, meaning she and other women like her will have to take medication to suppress their levels of the male sex hormone if they want to compete in certain events.
In a landmark 2-1 ruling, the highest court in world sports said the proposed rules from track's governing body, the IAAF, are discriminatory, but "such discrimination is a necessary, reasonable and proportionate means" of "preserving the integrity of female athletics."
The IAAF argued that unusually high, naturally occurring levels of testosterone in athletes like Ms. Semenya with "intersex" conditions that don't conform to standard definitions of male and female give them an unfair competitive advantage, and it decreed a maximum for females.
The South African runner whose strength and super-fast times have led others to question her accomplishments declared she will not be stopped by the ruling, issued by the Court of Arbitration for Sport.
"I know that the IAAF's regulations have always targeted me specifically," Ms. Semenya said in a statement. "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."
The two-time Olympic champion in the 800 meters will have to lower her testosterone levels if she wants to defend her world title in September in Doha, Qatar.
Ms. Semenya was traveling to Doha on Wednesday for the first Diamond League track meet of the season, where she is expected to race in the 800 on Friday. The Diamond League is an annual series of meets for the top athletes in the world, and the event is the last one before the new rules apply.
It is against the rules for athletes to inject or swallow testosterone supplements, known for strengthening muscle tone and bone mass. Some women have what is known as hyperandrogenism, meaning they have naturally occurring testosterone levels that are unusually high.
Ms. Semenya's level is considered private medical information and has not been disclosed.
The South African Sports Confederation and Olympic Committee decried the ruling, saying, "We maintain that the rules are ill-thought and will be a source of distress for the targeted female athletes."
"This decision marks a massive turning point as it now redefines what a female athlete in particular is," said Natalie du Toit, head of the organization's athletes commission, adding: "Knowing Caster and the hard work she has put into her sport, we support all her endeavors, and we are all behind her."
The IAAF went into the case arguing that female runners with high testosterone have an unfair advantage in events from 400 meters to the mile. However, the court suggested that the IAAF apply the rules only up to the 800 because the evidence was not clear that women with hyperandrogenism have an edge in the 1,500 meters.
That could give Ms. Semenya a route to compete at the world championships without taking medication, such as birth control pills.
A further appeal is possible to Switzerland's Supreme Court in Lausanne. But judges rarely overturn decisions of the world sports court.
The scrutiny of Ms. Semenya's muscular body has cast doubt on the integrity of her track achievements throughout her career. As a teenager in 2009, she won her first world title in Berlin. Hours before the race, the IAAF had asked for Ms. Semenya to undergo a gender verification test.
Ms. Semenya's case was the second attempt by the IAAF to regulate such athletes. In 2015, a panel including two of the same judges who heard Ms. Semenya's case suspended the IAAF's first attempt in an appeal brought by Indian sprinter Dutee Chand.
The judges four years ago said the IAAF did not prove hyperandrogenic women gained a significant advantage, and invited the governing body to submit new evidence. The IAAF produced a fresh scientific study.
Ms. Semenya is not the only female athlete with high natural levels of testosterone but has become an unwilling face of the issue. Two weeks ago, Olympic silver medalist Francine Niyonsaba of Burundi confirmed she has the same hyperandrogenism as her rival in the 800.
Referring to the rule, Ms. Niyonsaba said: "For me, it's about discrimination. It doesn't make sense. I didn't choose to be born like this. What am I? I'm created by God."
At the 2016 Rio Olympics, Ms. Semenya and Ms. Chand were publicly identified as women with high testosterone, but other athletes implied that other runners, including medalists in the 800 meters, also had elevated levels.
"I think that we need separate events for them and for us," said Nataliia Lupu of Ukraine said after running against Ms. Semenya. "You can see that it's easy for them." Ms. Semenya will "definitely win against us, even without using her full strength."
This story was reported by The Associated Press. Gerald Imray contributed reporting.