Caster Semenya of South Africa and Ajee Wilson of the United States at the women’s 800 heats Wednesday. (Lucy Nicholson/Reuters)

The silence couldn’t have been louder. On the track, runners stay in their own lanes. Off it, they’re even more careful.

“I’m not talking about it,” Britain’s Lynsey Sharp said.

“I’m not here to comment on that right now,” Canadian runner Melissa Bishop offered.

The women’s 800-meter race at the Rio de Janeiro Olympics is one of the most anticipated track and field events, fraught with mixed emotions and plenty of whispers. The race will feature Caster Semenya, and many believe the sport’s oldest world record might finally fall, which would prompt only more speculation about whether the playing field in the race was fair in the first place.

The 25-year old South African runner is believed to have an intersex condition called hyperandrogenism, which means her body may be producing testosterone at levels much higher than most women. The International Association of Athletics Federation and the Court of Arbitration for Sport have wrestled with what this means, while many athletes and coaches say publicly and privately that they feel Semenya has a competitive advantage on the track. Whether she does or doesn’t, Semenya came to Rio de Janeiro with the potential to rewrite history every time she steps on the track.

“When you line up against someone like that, it’s going to be a completely different ball game,” said Justine Fedronic, a Stanford-educated runner competing for France at the Olympics. “If you’re just watching the splits they’re running, it’s not the way a woman’s 800 usually unfolds. It’s definitely changed the racing game this year.”

On Wednesday, Semenya and 64 other women arrived at Olympic Stadium for their first-round heats. Semenya looked at ease in her two trips around the track, winning her heat with a time of 1:59.31 and easily advancing to Thursday’s semifinals.

She has said little publicly about her condition, which has fueled plenty of speculation. The controversy dates to 2009, when Semenya won the world championships and was forced to submit to a gender test. Ever since then, her mere entry in a race has made her a lightning rod of sorts, especially in the months leading up to the Olympics.

Before last year, the IAAF could monitor testosterone levels and require athletes to take hormone-suppressing drugs to compete. Semenya benefited from a Court of Arbitration for Sport ruling in July 2015 that suspended the rule and eliminated any ceilings on acceptable testosterone levels in female competitors. The court said that testosterone level alone is not sufficient cause for preventing women from competing against women. The court’s ruling, though, is provisional, giving track’s governing body two years in which to study the science and possibly revisit the matter. (The IAAF has indicated it might challenge the ruling.)

Semenya has been on a tear since then and has posted three of the four fastest times in the world this season. It’s created an uncomfortable situation for many other runners. As Fedronic explained, they feel for Semenya, whose body has become a subject for public dissection. But they also compete in a sport that has struggled for years to create a level playing field for runners.

“We have doping issues, but this is not on that level. It’s a completely different issue,” Fedronic said. “It’s not anybody’s fault.

“It’s probably not something she was aware of most of her life. She’s just trying to be out there training and compete just like the rest of us. It’s really not fair to her. But it’s not fair to others, too.”

After the court ruling, there were no questions about Semenya’s eligibility to compete at the Rio Games. Richard Budgett, the International Olympic Committee’s medical director, said any athlete cleared by the sport’s international federation is allowed to vie for a medal here.

“There is no sex testing, no gender testing at the Rio Games,” he said. “There are no rules about hyperandrogenism at these Rio Games.”

Many of the 800-meter runners did not want to discuss Semenya following Wednesday’s first-round races. They preferred to discuss their own heats, their own training and their own medal prospects. But Semenya casts a specter over all of that. Her best time this year is nearly a full second ahead of anyone else’s.

“I feel as if I’m fighting for bronze rather than gold,” Sharp said before these Olympics, according to the Sun.

Bishop is the world’s third fastest runner this year, and her top time is more than two seconds slower than Semenya’s best, which might as well be an eternity in a race like the 800. She knows there’s only so much she can do when the starter’s pistol fires.

“I think we just got to focus on what we have to do and my race plan and not focus on anyone else,” she said Wednesday, shortly after posting the top first-round time, a 1:58.38 finish.

Many runners feel the debate surrounding Semenya’s eligibility only will gain steam following the Olympics. Competing on such a big stage could spur on the detractors who question her eligibility and feel she competes with an unfair advantage. But her supporters might become more vocal, as well, people who are concerned about Semenya’s privacy and her right to compete. They say her condition is no different than genetic gifts bestowed on other athletes: Kevin Durant’s height, for example, or Usain Bolt’s long legs.

Ireland’s Ciara Everard acknowledged that it’s a sensitive, complicated subject, but “people are complaining about it.”

“It’s probably something that needs to be revised after this,” she said.

Ajee Wilson was in Semenya’s heat Wednesday, and chasing Semenya pushed the American runner to post her fastest time of the year, a 1:59.44 second-place finish. She, too, feels the IAAF should try to revisit its rules that concern Semenya’s eligibility.

“I think at this point, what I think doesn’t really matter. We’re all on the track,” she said. “Whoever’s on there is racing.”

Semenya knows a bit about competing against a stacked deck. She won silver at the 2012 Olympics. The gold medalist there was Russia’s Mariya Savinova, who was embroiled in her country’s doping scandal, faces a possible lifetime ban from running and likely will lose her Olympic title.

Savinova is also the one who first cast skepticism on Semenya, losing to her at the 2009 world championships and saying, by way of explanation, “Just look at her.”

Seven years later, the sport is still looking closely at the speedy South African, watching her do amazing things on the track and sorting out whether the controversy is unfair to Semenya, her competitors — or both.

“I don’t know what the solution is,” Fedronic said. “There definitely isn’t a clear one.”