Caster Semenya, a South African athlete, is still fighting the regulations placed on the testosterone levels of competitors in mid-range women’s track events imposed by the International Association of Athletics Foundation (IAAF).

The IAAF’s testosterone regulations come from an ongoing debate over regulating gender in sports. Because athletes are divided by gender, sports leagues have the challenge of defining what qualifies an athlete as a man or a woman.

Men’s sports leagues typically have no defining regulations, whereas women’s leagues are considered a “protected class.” This differentiation is predicated on the idea that men are typically athletically superior. For women to have a chance at competing, this belief suggests, they must be limited to competing against other women. This has led to fears of male athletes lying about their identities to medal in female competitions.

This debate over ‘gender checks,’ has been going on since the 1930’s. Many athletes were required to show physicians confirmations of their gender before being allowed to compete. Later, more stringent regulations required female athletes to undergo medical examinations, chromosomal analysis, and eventually, genetic testing.

Going into the 21st century, most sports leagues allowed women to compete without any testing — unless their gender was ‘challenged.’ If someone contested that an athlete was not actually a woman, as a fellow athlete did with Semenya, the athlete could be required to prove their gender. Semenya’s exact medical information was not made public for her privacy, but she returned to competition in 2010 after the testing.

Some sports organizations, including the IAAF, have used testosterone levels as a regulating factor for athletic participation in women’s sports. This decision has been based on the belief that testosterone is responsible for giving some athletes a competitive edge over others, due to the link between testosterone and muscle growth in men.

Some have argued that the limitations placed on women’s sports in an effort to make competition more fair are purely sexist, as no such limitations exist for men’s sports, even though a number of prominent male competitors have specific advantages, such as height or the ability to process lactic acid. Those in favor of regulating the sex characteristics of female athletes but not the other physical traits of male athletes argue that this difference is necessary because sports are divided into different categories for men and women, but not for tall people and short people. They believe that without this division, women would be pushed out of athletics, and thus restrictions are necessary to provide women with a fulfilling opportunity to compete.

Arguments do exist for combining men’s and women’s sports leagues and separating athletes by other athletic factors, but no action has been taken on these proposals.

Semenya is not the first woman who has had to contend with these physical regulations. Dutee Chand, an Indian athlete, was found to have particularly high levels of testosterone. She fought back against rules preventing her from competing and provided medical evidence that she was “testosterone insensitive,” meaning her body cannot use the excess testosterone it produces.

Debates over the practical role that testosterone actually plays in the abilities of athletes exist, and in 2015, the IAAF was given two years to provide evidence that their regulations on testosterone levels were scientifically warranted.

Chand was eventually allowed to continue racing, and the IAAF adjusted the guidelines, abolishing testosterone level limits on shorter racing events that they believed were not significantly affected by testosterone. The IAAF maintains, however, that an athlete’s testosterone levels can play a defining role in longer events — including the events that Semenya is most known for.

Due to the history of challenges leveled against Semenya in the wake of her success, some believe that the regulations are attempting to specifically target the athlete. There is also speculation that it may be linked to non-athletic ways Semenya has inadvertently challenged certain norms in her everyday life, including some of her more traditionally masculine attributes and preferences and her marriage to Violet Raseboya.

Semenya challenged the regulations, but the Court of Arbitration for Sport (CAS) ruled against her, claiming that there was significant proof that testosterone would give her an advantage. Actual reports of what this advantage is vary — some claiming it would help her run less than 1% faster, while others claimed it could help her run as much as 9% faster. The study used in the ruling is under scientific contention. The CAS told Semenya that, should she wish to continue competing in the regulated events (her primary events), she would have to take testosterone suppressing medication. These medications can have side effects such as hot flashes and osteoporosis — a disorder where bones degenerate.

The issue of testosterone level regulations has also played a role in the discussion of the place of trans athletes — especially trans women — in sports. Some have hoped to use testosterone levels as a benchmark for allowing trans women to participate in women’s sports. Others argue that this does not account for the natural variability of testosterone in all humans, including cisgender women.

Semenya herself was told she could participate in the men’s variations of her events if she did not wish to lower her testosterone, which could create an odd precedent for an individual competing in some events as a ‘man’ and others as a woman.

Recently, some news outlets such as NBC have reported that Semenya has intersex traits — meaning some biological traits associated with both sexes. However, Semenya was raised as a cisgender girl and continues to live as a woman. Although exact medical details are not known, Semenya lived the majority of her life unaware of the condition, which leads some to believe that it has a relatively mild effect. This has left people wondering if this case could have larger ramifications for intersex athletes.

Some feel that the entire issue goes back to a larger problem surrounding the ways society attempts to define what it means to be a woman. Others have linked the debate to a history of women of color — especially black women — being seen as less female, because the regulations specifically target “middle-distance running events, the events in which women from the global south have excelled in for decades,” says the Guardian.

A further aspect of the issue is the way many people feel the regulations violate women’s autonomous bodily rights by forcing them to go through medically unnecessary hormone alterations in order to participate in certain events.

Semenya has refused to take any form of testosterone suppressing medication and currently plans to run in the 3000 meters race at the Prefontaine Classic — an event that does not fall under the contentious testosterone regulations.