Olympic gold medalist Caster Semenya loses testosterone fight.

GENEVA — The sports world’s highest court ruled Wednesday that Olympic gold medalist Caster Semenya and other female runners like her with unusually high testosterone must take medication to reduce their levels of the male sex hormone if they want to compete in certain events — a landmark decision with far-reaching ramifications for other women’s sports.

In a 2-1 ruling, the Court of Arbitration for Sport upheld proposed rules issued by track’s governing body, the IAAF, saying that they are discriminatory but that “such discrimination is a necessary, reasonable and proportionate means” of “preserving the integrity of female athletics.”

The IAAF argued that high, naturally occurring levels of testosterone in athletes like Semenya with “intersex” characteristics that don’t conform to standard definitions of male and female give them an unfair competitive advantage, and it decreed a maximum level for females.

The court decision could open the way for similar rules in other women’s sports where size, speed and power make a difference, such as weightlifting, boxing, swimming, rugby, field hockey and soccer.

Semenya — a 28-year-old South African whose sculpted biceps and super-fast, blow-away-the-competition times have led others to question her accomplishments — declared she will not be deterred.

“I know that the IAAF’s regulations have always targeted me specifically,” 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 by such means as birth control pills or prostate cancer drugs if she wants to defend her world title in September in Doha, Qatar. Semenya is expected to race in the 800 on Friday at a track meet in Doha in what will be the last world-class event before the new rules apply.

Testosterone strengthens muscle tone and bone mass. Because of that, it is against the rules for athletes to use testosterone supplements. Some women have what is known as hyperandrogenism, meaning they have natural testosterone levels that are unusually high.

The IAAF rules require women to reduce their levels below 5 nanomoles per liter of blood. According to the IAAF, most females, including elite athletes, have levels of testosterone circulating naturally in their bodies of 0.12 to 1.79 nanomoles per liter, while men have levels that can be dozens or even hundreds of times higher — typically 7.7 to 29.4.

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.”

Under the rule, female athletes whose medical profiles previously showed high testosterone will be subject to blood tests to prove they have complied.

An appeal to Switzerland’s Supreme Court is possible. But judges rarely overturn decisions of the world sports court.