A failed drug test this week left a star middle-distance runner decrying her resulting suspension and raised a debate over the fairness of Olympic sports’ anti-doping measures on the eve of the U.S. track and field trials and a month ahead of the Tokyo Games.

At issue is whether advances in drug-testing technology are having unintended consequences. In the arms race against drug cheats, laboratories have developed measures that can detect ever-smaller quantities of banned substances in blood or urine — so sensitive that trace amounts in contaminated food and medication can trigger positive results. An athlete who ingests a banned substance without knowledge or perceptible benefit can fail a test and thus be difficult to distinguish from someone trying to gain an illegal advantage.

Since 2016, the U.S. Anti-Doping Agency (USADA) has found almost 30 cases of what could be called “innocent-source positives.” It has demonstrated that failed tests could occur because of tainted meat.

That’s what Shelby Houlihan, a 2016 Olympian and the American record holder in the 1,500 and 5,000 meters, claims happened to her. In revealing the four-year suspension that will prevent her from running in Tokyo or even in the Paris Games in 2024, Houlihan said this week she had never heard of nandrolone, the anabolic steroid she tested positive for in December. On the night before her test, she said, she ate a burrito from a Mexican food truck that served pig offal, a meat that World Anti-Doping Agency studies showed could contain nandrolone.

Houlihan’s appeal of the suspension was denied by the Court of Arbitration for Sport (CAS), which has not released details or its reasoning. That ruling could shed additional light on Houlihan’s account, but anti-doping experts viewed her claim as feasible.

“Athletes need to be able to trust the anti-doping system in sport if they’re going to really get behind it,” said Oliver Catlin, co-founder of the Banned Substances Control Group and the son of anti-doping guru Don Catlin. “I think the problem is, if you have situations like this, it almost does the opposite. It makes innocent athletes fear that the system could roll over them. That’s a principal problem that we face.”

Oliver Catlin knows more about the chemicals in our food than he wants. He has read studies that found traces of performance-enhancing drugs in vegetables that arrived via herbicides, pesticides and treated wastewater.

For years, those drugs would not have registered on drug tests. Two decades ago, tests measured the presence of drugs in nanograms, or parts per billion. A failed test now could be triggered by six picograms, which is parts per trillion. The sensitivity has improved 1,000-fold. The enhancement was critical because it enlarged the window of detection. The instruments can find drugs in an athlete’s system for much longer after the athlete took them, a powerful tool against cheaters.

“In most situations, that would be perceived as a good thing from a standpoint of anti-doping,” Catlin said. “The other side of that issue is, people ask the question, how low is too low? … In some instances you can find half a picogram. I don’t even know what that is. A gazillion? I honestly don’t know what it is.”

American sprinter English Gardner, a 2016 Olympic gold medalist in the 4X100 relay, said she religiously reads labels on everything from snacks to hair products. And she still worries a banned substance could find its way into her body.

“It is a fear of mine,” Gardner said. “It’s super unfortunate with [Houlihan’s] case. As an athlete, I feel for her. You never want something like that to come up, especially so close to a big meet like this.”

It has happened, sometimes in ways that stretch credulity. In 2018, 90-year-old cyclist Carl Grove set a record in the Masters’ age 90-94 division, which triggered a drug test. Grove tested positive for trenbolone, a steroid cattle farmers use in producing beef. It turned out Grove had eaten beef the night before his race. Grove’s record was stricken from the books, but he was cleared after further lab tests and because he had taken a test that came back clean the night before.

Long jumper Jarrion Lawson, the 2017 world championships silver medalist, received a four-year ban for a positive trenbolone test. In March 2020, after he had served 19 months, he won an appeal after CAS found the source was beef he had eaten for lunch the day before the test.

This past September, middle-distance runner Brenda Martinez, 33, tested positive for hydrochlorothiazide (HCTZ), a banned substance classified as a masking agent. Martinez pleaded her innocence to the USADA and sent the agency a medication she had been prescribed by a doctor. When the USADA analyzed the medication at a lab, tests showed it was contaminated with HCTZ. She was absolved.

Houlihan’s case, at the start of a marquee event, is a development viewed by many within the sport as an inevitability. For years, USADA Chief Travis Tygart has warned of innocent athletes being punished as cheaters for trace amounts of drugs they did not knowingly ingest.

“In our press releases, our meetings with athletes and sport leaders over the past several years, we’ve brought this issue up and have been advocating to WADA and really asking the question: How many innocent athletes is this system going to sacrifice before we change the rules?” said Tygart, who did not address Houlihan’s case specifically.

In May, partially promoted by Martinez’s case and after several years of USADA advocacy, WADA altered its rules. For eight substances, WADA raised the threshold necessary to trigger an automatic violation. When illegal substances are picked up, they still are reported and tagged for further investigation.

But even tweaking the system to protect innocent athletes presents scientific challenges. For some drugs, WADA upped the threshold to 100 parts per billion.

“To that I would say, now we’re starting to approach the concept, but where’s the science behind it?” Catlin said.

Catlin laid out a hypothetical. Athlete A is found to have traces of a banned substance in his urine at 110 parts per billion. Athlete B has the same substance but at 90 parts per billion. The difference is vanishingly thin, but one athlete would be flagged and the other would not.

“I’m supposed to look at the guy with 110 and say you’re guilty and look at the guy at 90 and say you’re fine,” Catlin said. “I have a hard time doing that.”

The issue points a spotlight on the governing bodies that handle the cases. WADA, CAS and the International Olympic Committee (IOC) are supposed to operate independently from one another, but the number of people who serve in more than one of the organizations leads to perceptions that they lack independence. USADA pushed for a now-ongoing reform process to make the bodies independent.

“You have to remove sport promoters from the anti-doping enforcement side,” Tygart said. “As long as IOC members still run and sit atop WADA and CAS, at a minimum the perception causes athletes to lose trust in the system. It ought to be fully independent, and we’ve been very clear about that for 20-plus years.”

John Coates, the president of CAS, is also the IOC’s vice president and the longtime head of Australia’s national Olympic governing body. German lawyer Ulrich Haas, one of three members on the CAS arbitration panel for Houlihan’s case, wrote the WADA code, is overseeing WADA’s governance reform process and has spoken at WADA functions.

The intersection of WADA and CAS raises many issues, including whether decisions are made in the pursuit of winning a case or justice for the athlete.

Dionne Koller, a sports law professor at the University of Baltimore who sits on USADA’s Anti-Doping Review Board, analogized the system to an NCAA football program’s athletic training staff. A team doctor may be independent, but on some level he knows to keep his job he needs to satisfy the coach, which may lead to him pushing players back to the field.

“There are people who can check the legal boxes for being independent in terms of a chain of reporting, but if they want to continue their access with powerful entities, they are incentivized to keep those entities happy,” Koller said. “In law, we would call this the appearance of impropriety, and we’d avoid it. In the Olympics, it’s just the way business is done.”

As for the athletes, the common currency of the innocent and the guilty is denial. Houlihan’s food truck meal may have been contaminated, but how could she prove that is the only way a steroid could have entered her body? How can governing bodies protect faultless athletes while not granting leniency to a cheater who claims she ate contaminated beef?

Advanced drug-testing technology doesn’t answer any of those questions; it just raises more cases that pose them. The answers, then, must come from people who are presented black-and-white data with which to negotiate contentiously gray terrain.

“The challenge that you face is not with these specific people involved or the motivations of them as much as the fact that you simply have people involved,” Catlin said. “When you have people involved, people can evaluate a set of facts and come to different conclusions. I don’t think it’s the CAS system, per se, that’s flawed. It’s just that human beings are involved in evaluating and making those decisions, and we are by nature flawed.”