Olympic gold medalist Caster Semenya received bad news about her racing career last week, news that centered on the particulars of her body. Those probing, intimate details shaped a controversial rule of the International Association of Athletics Federations, the governing body of the running world. And they are now determining the fate of other athletes.

The Court of Arbitration for Sport decided last week to uphold an IAAF rule that would require Semenya to take testosterone suppressants to compete in the women’s division in her best events, the 800-meter and 1,500-meter races. Almost immediately the decision rippled out to other runners. Athletics Kenya announced on Friday that it had dropped two female sprinters from its team for the IAAF World Relays championship this weekend, after blood tests revealed high levels of testosterone.

The dispute, however, is about much more than testosterone. Semenya's medical status as an intersex person was leaked to the press in 2009. Semenya herself has never referred to herself as intersex, instead simply stating, “I am a woman and I am fast.” The bottom line is that her body naturally produces more testosterone than the average woman, and some of her competitors and some athletics experts believe this gives her an unfair advantage.

But others question whether testosterone is the athletic miracle worker it has been made out to be. In fact, even the CAS has said this: When, in 2015, it ruled on the case of Indian sprinter Dutee Chand, who also has uncommonly high testosterone, the CAS determined that the IAAF had not mustered sufficient scientific support to justify a policy against naturally high testosterone.

The reality is that although testosterone plays a role in elite performance, the details of the science get murky very quickly. The athletes with the highest testosterone are not always the winners. Ones with lower levels can also take home gold. With the science unresolved, some of Semenya’s defenders see the CAS’s ruling as the latest salvo in a broader backlash against people who have bodies that defy stereotypes of womanhood.

“This decision is biased, not only based on the fact that Caster is intersex, but that she is from South Africa, she’s a Black South African, she’s queer, and she’s gender non-conforming,” says Sean Saifa Wall, cofounder of the Intersex Justice Project. “We’ve only seen this kind of humiliation and shaming of Black and brown intersex athletes, particularly Caster Semenya and two other runners,” including Chand.

Advocates point out that scientific-seeming methods of separating the sexes can often be weaponized against gender and sexual minorities, such as intersex people. “Science is a tool and a method, but of course that can be in anyone’s hands,” says Hans Lindahl, communications director at intersex advocacy group InterACT. “It’s hard to take socially constructed categories like gender and sex and try to clump them into science. It doesn’t work.”

Historically, the weight of sex testing has always fallen on women's sports. So it is also the place where the extremely difficult questions of defining gender boundaries are now being hashed out. “People want to believe that there’s some essential difference between women and men that makes them completely distinct and explicit categories,” says trans author Julia Serano, who also has a PhD in biology. “That essence doesn’t exist in real life.”

Sex testing of female athletes began with the intent of trying to catch men masquerading as women to try to win medals, though no man has ever been caught doing so. Instead, it was intersex women who were often thrown out of sports as a result of these tests.