Shannon Rowbury was spent, physically and emotionally. It had happened again.

Four years after being angry and disappointed at finishing behind a flock of runners linked to performance-enhancing substances in the 1,500-meter finals at the London Olympics, Rowbury was again crushed.

She'd just finished fourth in the finals of the same event at the Rio Olympics, losing out on a medal to teammate Jenny Simpson. Simpson's furious last-lap kick had nipped her for the bronze by .52 of a second.

Rowbury was happy for Simpson. She watched as her friend and rival celebrated and held the American flag aloft on the track. She looked at the top two finishers and couldn't help but feel frustrated. Rowbury was in no mood to talk. That night, she retreated from the track and declined to speak to the media.

She'd gone into the race with high hopes and good results in what would turn out to be the best year of her career. But her Olympic experience had again turned sour.

"The only thing I felt after the race was just devastation that what I felt was such an unfair situation in London seemed to be happening again in Rio," says Rowbury. "What do you say to that?"

Rowbury, 32, a three-time Olympian, has had some time to reflect and appreciate what she did in 2016. She won a U.S. 3,000-meter title, set an American record in the 5,000 meters, was fourth in the Olympics and won the Wanamaker Mile at the Millrose Games in New York for a second straight year.

On Saturday, she'll go for a third straight Wanamaker win and hopes to set a record in the process. As focused as she is on starting this year with a bang, she's also determined to speak out about athletes who cheat. From lessons learned at London and Rio, Rowbury says it's her responsibility to promote clean competition. "Too many athletes who compete the right way have been cheated," she says.

It was too painful to speak about in the aftermath of last summer's Games, but she's eager now. "It's still something that hurt me deeply and I think, like London, it will always be something that is still a bit painful to recall," she says.

Rowbury is a fifth-generation San Franciscan, but she'll feel right at home Saturday in the Armory, an imposing castle-like structure built more than 100 years ago in Manhattan and home of the Millrose Games. Two straight victories in the mile at the nation's most prestigious indoor track and field meet will do that. "I love the energy of the indoor stadium and the Armory," she says. "There's just so much history."

In the 1,500 meters at the London Games, six of the top nine finishers have been linked to performance-enhancing drug use, including four that finished ahead of Rowbury. Gabriel Bouys/AFP/GettyImages

Her victory last year in 4:24.39 set the stage for her fine year. Now she's targeting the American indoor record of 4:20.5 set by Mary Slaney in 1982. Rowbury's indoor best is 4:22. "I feel I've done the work and the preparation," Rowbury says. "If things come together well on Saturday, I have a chance."

But aside from the atmosphere and her success in the Wanamaker Mile, there's another reason Rowbury feels so much at home in New York: the New York Road Runners -- the organization that puts on the Millrose Games, the New York City Marathon and the Fifth Avenue Mile, among others -- takes a hard, anti-drug stance in line with her own.

"We have a mandate that we don't invite any athlete that has had any drug history in their past," says Ray Flynn, race director of the Millrose Games. "We want to keep our meet free of any athlete that really has a violation."

It's in keeping with New York Road Runners' Run Clean initiative that tries to ensure athletes compete in what it calls a "healthy and clean environment." NYRR tests elite athletes after they perform, has a pre-race testing program for its marathon and will soon test top runners at some of its non-professional events.

That all gives Rowbury a feeling of confidence that the playing field isn't tilted against her at the Millrose Games or Fifth Avenue Mile, which she's won twice. She hasn't always had that confidence elsewhere. "As I've competed over the years and as I've realized what a plague doping is on our sport, I've spoken out against it and tried to advocate for clean sport myself," she says. Rowbury's passion for policing cheaters was born from the pain of her 2012 London experience. She finished sixth in the 1,500 meters, a race that's been labeled one of the dirtiest in Olympic history. Six of the top nine finishers have been linked to performance-enhancing drug use, including four that finished ahead of Rowbury.

Winner Asli Cakir Alptekin of Turkey was stripped of her gold medal. Silver medalist Gamze Bulut of Turkey failed a drug test in 2016. Tatyana Tomashova of Russia finished fourth after serving a two-year ban starting in 2008. Fifth-place finisher Abeba Aregawi of Ethiopia tested positive for a banned substance in 2016. Natallia Kareiva of Belarus (seventh) and Ekaterina Kostetskaya of Russia (ninth) were banned in 2014.

Among athletes never linked to banned substances in that race, Rowbury was second. But, that's not how the race was judged.

Rowbury went into the event with suspicions but felt powerless to challenge other runners, even after the race. However, Lisa Dobriskey of Great Britain who finished 10th, immediately lashed out that night, telling reporters, "I don't believe I'm competing on a level playing field."

Dobriskey said she wasn't going to point a finger at specific athletes but said, "People will be caught eventually, I think. Fingers crossed, anyway."

Eventually, Dobriskey was proven right and Rowbury's suspicions were validated. "It's a bit mind-blowing to think that half of the field shouldn't have been there to begin with," says Rowbury.

The experience prompted Rowbury in the years following to be more vocal about drug users. "Women's middle distance, especially my event, the 1,500, seems to be especially prone to attract cheaters," she says. "I'm not actually sure why, but there's been such a high percentage of the women who compete in my event that have cheated, to try to get ahead."

Four years later at Rio, she and others again questioned the results. The coach for silver medalist Genzebe Dibaba had been arrested in the months before for administering and distributing banned substances. Winner Faith Kipyegon ran for Kenya, whose track and field manager was sent home and arrested after being accused of violating anti-doping rules. Laura Muir of Great Britain, when asked after the race if the results could be trusted, said, "I have my doubts, let me say that."

Rowbury believed she had been cheated again, though she had no proof. "To finish fourth, in another situation where, 10 years from now, I don't know if they'll also be saying that this race also had women in front of me that shouldn't have been there, that's a really tough pill to swallow," she says.

Plus, like all elite runners, Rowbury dreams of winning an Olympic medal. She'll be 35 for the 2020 Olympics in Tokyo, so her window of opportunity is getting smaller. That exacerbates the pain from London and Rio. "It's challenging," she says. "There's an expiration date on every athlete."

She plans to compete for a berth in the 2020 Games and has the range to run in the 5,000 meters, if she believes that gives her a better chance. For now, though, she's focused on Saturday's mile, grateful for a level playing field.

Like Rowbury, Canada's Charles Philibert-Thiboutot, an Olympian at Rio in the 1,500 meters, is grateful for that aspect of the Millrose. He said he was naïve about drug use until he started competing internationally and found himself going head-to-head with athletes linked to drugs in some way. "It's almost like a slap in the face, you know," says Philibert-Thiboutot, who will run in the men's Wanamaker Mile for the first time. "It's like, 'Wow, this is a reality now.' When you race against the best in the world you cannot expect everyone to be clean. There's some meets where the organizers, I don't think they could care less about who's served a doping ban or not."

Rowbury says it's important to stay positive and avoid bitterness. She'll continue to speak out, but she knows she can only control what she does. "It's challenging to come to terms with the fact people would rather cheat others than play fair," she says, "and I'll never understand that."