(NBC News) - Simone Biles knew she was carrying a lot when she walked into the Ariake Gymnastics Centre in Tokyo on Tuesday. As the face of the U.S. Olympic team, she was shouldering her country's gold medal hopes. As the greatest gymnast of all time, she was toting expectations for athletic dominance and repeated brilliance. As an outspoken advocate for female athletes, she was lugging around the pressure to make her fans proud.
Or, as she put it Monday, she was carrying "the weight of the world" on her shoulders. And she was making it look easy. Until it no longer was.
In making the stunning decision to withdraw from the team final competition Tuesday, Biles acknowledged the tremendous pressure she had been facing as the "head star of the Olympics" and said she needed to focus on her mental health.
"We also have to focus on ourselves, because at the end of the day we're human, too," Biles said, according to The Associated Press. "We have to protect our mind and our body, rather than just go out there and do what the world wants us to do."
Biles, a four-time Olympic gold medalist, said she was not in the right state of mind to continue the competition.
"Physically, I feel good," she told Hoda Kotb on NBC's "TODAY" show after she withdrew. "Emotionally, that kind of varies on the time and moment. Coming here to the Olympics and being the head star of the Olympics isn't an easy feat. So we're just trying to take it one day at a time, and we'll see."
Biles' candid admission, which follows Naomi Osaka's decision this year to withdraw from tennis tournaments to protect her mental health, again put a global spotlight on the often taboo subject of mental health in sports.
"I do hope that people can relate and understand it's OK to not be OK; and it's OK to talk about it," she wrote in Time magazine. "There are people that can help, and there is usually light at the end of any tunnel."
Biles said she was inspired by Osaka and would tell others who are struggling to put their own needs first.
"Put mental health first, because if you don't, then you're not going to enjoy your sport and you're not going to succeed as much as you want to," she said. "So it's OK sometimes to even sit out the big competitions to focus on yourself, because it shows how strong of a competitor that you really are, rather than just battle through it."
Olympic athletes are competing under exceedingly unusual circumstances this year. They face more isolation this year with the Games taking place as the world is still in the coronavirus pandemic. And because Tokyo is under a state of emergency, spectators have been barred from most events where the athletes are competing.
"It's been really stressful this Olympic Games," Biles said. "Just as a whole, not having an audience, there are a lot of different variables going into it. It's been a long week. It's been a long Olympic process. It's been a long year. So just a lot of different variables, and I think we're just a little bit too stressed out. We should be out here having fun, and sometimes that's not the case."
After the U.S. team struggled during qualifying rounds, Biles wrote Monday on Instagram that she felt "like I have the weight of the world on my shoulders at times."
"I know I brush it off and make it seem like pressure doesn't affect me but damn sometimes it's hard hahaha! The olympics is no joke!" she wrote. "BUT I'm happy my family was able to be with me virtually🤍 they mean the world to me!"
Dr. Leela R. Magavi, a psychiatrist who has frequently worked with student-athletes and professional athletes, said the societal expectations from fans, the media and others can make athletes feel as though "every single step that they take will be significantly scrutinized, and this kind of pressure is so severe" that they can have trouble even focusing on their day-to-day activities.
Magavi said athletes like Biles, "who have such stature" and are "essentially symbolizing and representing a country," can have so much anticipatory anxiety and face such enormous pressure to be perfect and never falter that "in this way they lose that passion for the game that was the first reason they joined the game in the first place."
Magavi said she commends Biles for prioritizing her mental health needs over "societal expectations."
"It really does take courage and emotional strength," she said.
Biles got an outpouring of support after she withdrew.
Former Team USA gymnast Aly Raisman told "TODAY" that it was important to "think about how much pressure has been on her, and there's only so much that someone can take."
"She's human, and I think sometimes people forget that, and Simone, just like everyone else, is doing the best that she can," she said.
"I also am just thinking about the mental impact that this has to have on Simone," Raisman continued. "It's just so much pressure, and I've been watching how much pressure has been on her in the months leading up to the Games, and it's just devastating. I feel horrible."
At the news conference Tuesday, Biles said she knew she needed to take a step back to "work on my mindfulness" and give her teammates the chance to take over, so as not to hurt their medal chances.
She competed in Team USA's first rotation on the vault but bailed out of her Amanar vault. She completed only 1½ twists on a 2½-twisting Yurchenko vault and then took a stumble on the landing.
"I didn't want to risk the team a medal," she said of her decision to withdraw. "They've worked way too hard for that, so I just decided that those girls need to go in and do the rest of the competition."
Biles, Jordan Chiles, Sunisa Lee and Grace McCallum of Team USA took silver. The Russian Olympic Committee team won gold.
Biles won five medals in Rio de Janeiro in 2016.
Asked about Thursday's individual all-around competition, Biles said, "We're going to take it day by day, and we're just going to see."
A day later, USA Gymnastics confirmed that she was withdrawing from the event.