Caster Semenya won an interim ruling in her battle against the IAAF when the Swiss supreme court ordered athletics' governing body to suspend its testosterone regulations on Monday, raising the prospect of her competing at the world championships without having to take hormone suppressing medication.
The decision temporarily lifts the contentious rules, at least until the IAAF responds with arguments to the supreme court, known as the Swiss Federal Tribunal, to restore them. The IAAF has until June 25 to do that.
Should the IAAF fail to overturn the ruling, the regulations will remain suspended until Semenya's full appeal is heard by a panel of Swiss federal judges. That could take up to a year or more, meaning the 28-year-old South African might be cleared to run unrestricted in her favored event in remaining Diamond League meetings and the worlds in Doha, Qatar, in September and October.
"I am thankful to the Swiss judges for this decision," Semenya said. "I hope that following my appeal I will once again be able to run free."
The supreme court appeal is the second time the two-time Olympic 800-meter champion has challenged the IAAF rules. Semenya lost her case against the IAAF at the Court of Arbitration for Sport on May 1 and the rules came into effect on May 8.
They meant that Semenya wasn't allowed to run in any top-level 800-meter race unless she medically reduced her elevated testosterone levels before Monday's decision.
Dorothee Schramm, the Swiss-based lawyer leading Semenya's appeal, said the supreme court "has granted welcome temporary protection to Caster Semenya."
"This is an important case that will have fundamental implications for the human rights of female athletes," Schramm said.
The ruling has implications for other athletes, too. Francine Niyonsaba of Burundi and Margaret Wambui of Kenya, both Olympic medalists in the 800, have said they are also affected by the rules.
The regulations apply only to some races, from 400 meters to one mile. Semenya is the reigning Olympic champion and a three-time world champion in the 800. She also has a world championships bronze medal in the 1,500 meters, which the IAAF also made a restricted race.
Semenya has battled track authorities for the right to run in what she describes as her natural form for a decade, ever since she was subjected to gender verification tests by the IAAF at the age of 18 when she won her first world title in 2009.
The dispute is viewed as one of the most controversial and complex to face sport.
The IAAF rules apply to female athletes with medical conditions known as "differences of sex development" (DSD) and specifically those born with the typical male XY chromosome pattern. The athletes also have testosterone levels higher than the typical female range, which the IAAF argues gives them an unfair athletic advantage over other women because the hormone helps build muscle and increases oxygen levels in the blood.
To compete in the Olympics, world championships or other international athletics events, each athlete must reduce her testosterone level and keep it within the acceptable range for six months prior to competing. The IAAF gives three medical options to do that: A daily contraceptive pill, a monthly testosterone-blocking injection, or surgery. The treatments could inhibit athletic performance but by how much is uncertain, while also posing risks of other negative side effects.
Prescribing medical treatments solely for sports eligibility reasons has been labelled as unethical by an array of experts, including the World Medical Association, which represents doctors across the world.
Semenya's lawyers say her appeal to the Swiss supreme court will focus on human rights, with the rules forcing her to take medication or have surgery to be eligible to compete.
Since the rules came into effect last month, Semenya and Wambui publicly refused to take medication. Semenya has been forced to medically suppress her testosterone level before, under previous IAAF rules that were dropped in 2015.
Athlete medical records and details of DSD tests are confidential but Semenya and Indian sprinter Dutee Chand have fought testosterone regulations and Niyonsaba and Wambui have both publicly criticized the rules recently. Niyonsaba won the silver medal behind Semenya in the 800 meters at the 2016 Olympics in Rio de Janeiro and Wambui won the bronze.
It's unclear how many other female athletes are affected. The IAAF says it will not identify athletes with DSD but says there are dozens in elite athletics.