Elite female track and field athletes, who naturally produce above-normal amounts of testosterone, received disheartening news Thursday. To be eligible to race in future international competitions, they could be forced to take medication to lower their testosterone levels or, if they don’t want to alter their body’s chemistry, compete against men.

The International Association of Athletics Federations (IAAF) announced new regulations that could prevent female athletes who have a condition called hyperandrogenism from competing in events ranging from 400 meters to the mile unless they reduce their blood testosterone level by taking hormonal contraceptives, such as birth control. Athletes will not be required to undergo any type of surgery to meet eligibility requirements, the governing body said in a statement.

Many of the sport’s fans and other athletes were outraged by the announcement, arguing the regulations are discriminatory and target accomplished female athletes, such as South Africa’s Caster Semenya, a two-time Olympic gold medalist in the 800 meter. Semenya, who has hyperandrogenism and specializes in a race that falls within the restricted events, would probably be affected.

The rules, which are expected to take effect Nov. 1, require athletes to lower and maintain their testosterone levels to no more than 5 nanomoles per liter of blood, the IAAF said. That’s half the amount previously allowed.

The alternatives for female athletes who choose not to lower their testosterone levels include competing against men, being restricted to the national stage, switching to shorter or longer distances, or racing in events for intersex athletes (provided that category is available), the statement said.

IAAF president Sebastian Coe said in the statement that the regulations are meant to “ensure fair and meaningful competition in the sport of athletics where success is determined by talent, dedication and hard work rather than other contributing factors.”

“Our evidence and data show that testosterone, either naturally produced or artificially inserted into the body, provides significant performance advantages in female athletes,” Coe said.

According to the statement, the regulations are not “intended as any kind of judgment on or questioning of the sex or the gender identity of any athlete.”

However, people have called the rules sexist and racist.

On Twitter one user wrote, “Make no mistake, this is the most sexist paradox in sports: a man with naturally high testosterone is gifted, but a woman with naturally high testosterone is a cheat.”

Another tweeted that the IAAF is “being sexist, racist and certainly living in the 16th Century.”

The new rules are the latest development in an ongoing effort by sports officials to create fair competition during a time when an increasing number of athletes no longer fit into traditional male and female categories.

It is not the first time the IAAF has tried to enforce regulations on female athletes. The previous attempt was struck down in 2015 by the Court for Arbitration in Sport, sport’s “Supreme Court,” after a challenge from Indian sprinter Dutee Chand, who also has hyperandrogenism. The court ruled that the IAAF didn’t prove women with naturally elevated amounts of testosterone had a competitive advantage, The Washington Post’s Cindy Boren reported. The IAAF was given two years to collect new scientific evidence.

In Thursday’s announcement the organization included documents and research to justify its decision.

Most women, including elite female athletes, usually have testosterone levels ranging from 0.12 and 1.79 nanomoles per liter of blood, documents said. In men, the normal levels can be as much as 29.4 nanomoles per liter. Female athletes with hyperandrogenism can have amounts similar to men, 20 or 25 nanomoles per liter, according to a tweet from the IAAF.

Women with elevated levels of testosterone, amounts between five and 10 nanomoles per liter, are believed to have a competitive advantage, as studies show they have a 4.4 percent increase in muscle mass, a 12 to 26 percent increase in muscle strength and a 7.8 percent increase in hemoglobin, which transports oxygen to red blood cells, according to IAAF documents.

A 2017 study commissioned by the IAAF and published in the British Journal of Sports Medicine also identified specific events in which high testosterone levels could give athletes an edge. These events included the 400 meter, 400-meter hurdles, 800 meter, the hammer throw and pole vault.

“To the best of our knowledge, there is no other genetic or biological trait encountered in female athletics that confers such a huge performance advantage,” the IAAF said.

While Chand and Semenya may be the first names that come to mind when thinking of female athletes with hyperandrogenism, Stephane Bermon, head of the IAAF’s health and science department, said in a statement that many others have the condition.

“We have seen in a decade and more of research that 7.1 in every 1000 elite female athletes in our sport have elevated testosterone levels, the majority are in the restricted events covered by these regulations,” Bermon said. “This is around 140 times what you will find in the general female population which demonstrates to us in statistical terms a recruitment bias.”

But the organization’s data and scientific explanations haven’t seemed to convince many who see the new regulations as singling out Semenya. (Chand will not be affected by the rules because she competes in shorter distances).

In a statement Thursday, Athletics South Africa, the sport’s national governing body, said it understood the IAAF has the “authority” to develop rules and regulations but voiced its support for “all our athletes who may be affected by this new ruling.”

The African National Congress also released a statement on Twitter, claiming the IAAF is intentionally targeting Semenya, who they say has been “constantly put under undue pressure.”

“We call on government to challenge this grossly unfair, unjust and blatant racist attempt by the IAAF to the Court of Arbitration for Sport (CAS) and have these regulations set aside. The ANC will stand with Caster Semenya in yet another attempt by international sport bodies to exclude and discriminate against her.”

Chris Mosier, a transgender triathlete and duathlete, also took to Twitter. Mosier wrote that the new rules send the message that female athletes “can be strong but not too strong.”

Others rallied behind Semenya, decrying the decision as “appalling” and “inhumane.”

The athlete herself has yet to explicitly address Thursday’s announcement but did tweet a photo of text that read “I am 97% sure you don’t like me, but I’m 100% sure i don’t care.” The statement ended with an angry-looking emoji.

The court could again consider the rules. It is also unclear what Semenya and other athletes like her plan to do if the regulations go unchallenged.

“I am natural,” Semenya told the BBC in an interview in 2015. “I am just being Caster. I don’t want to be someone I don’t want to be. I don’t want to be someone people want me to be. I just want to be me. I was born like this. I don’t want any changes.”

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