CNN  — 

You can learn a lot about a subculture by the slang it develops. Gymnastics has a lot of slang around fear: the twisties, headcasing, mental block, bailing, balking.

Gymnastics is obviously physically demanding with a high injury rate. But it is extremely difficult psychologically as well. Many of the skills could kill you. When Kevin Durant’s foot was off by an inch in Game 7 of the NBA’s Eastern Conference semifinals, his shot was worth two points instead of three, and the Brooklyn Nets lost in overtime. When Riley McCusker’s foot was off by an inch on her beam dismount at the 2017 American Cup, she slammed backward onto her neck and then rolled over it.

For every perfect, floaty flip performed in competition, there are thousands done in practice, many of them ending with scrapes, crashes, and haunting near-misses.

When Simone Biles scratched most of the Olympic team final, she said it was not because of a physical injury, but her mental health. This doesn’t mean she felt sad, or didn’t have her heart in it to compete. It means that her psychological state put her at significant physical risk. If her brain wouldn’t play along with what her body knows how to do, she could be seriously injured.

Vault was the first event for the US and Russia in the team finals. Biles was supposed to compete an Amanar, a backward flipping vault with 2.5 twists. The Amanar has taken out a lot of knees, but Biles has been competing the vault spectacularly since she was a 16-year-old with braces in 2013. But in warmups, she bailed out of it, doing just one 1.5 twists out of a vault that got pretty high in the air. In the competition, it was worse: 1.5 twists again, but with less height, forcing a deep step out of it.

A Yurchenko with 1.5 twists is worth much less than an Amanar, so Biles scored just a 13.766. The US was a point behind Russia after vault, which is usually where the Americans secure a large lead. This made the possibility of winning gold very low, no matter how well Biles’s teammates rallied.

Biles pulled out of the rest of the team competition. “I just don’t trust myself as much as I used to,” Biles told reporters in Tokyo. “I’m a little bit more nervous when I do gymnastics. I feel like I’m also not having as much fun.”

Biles later also withdrew from the individual all-around competition, again saying she wanted to focus on her mental health.

USA Gymnastics said it supported her decision “wholeheartedly,” adding in its statement that Biles would be assessed every day.

Biles trains on the uneven bars ahead of the Tokyo 2020 Olympic Games on Thursday, July 22.

A case of the ‘twisties’

She said in morning practice that she had a little bit of the twisties. The twisties are a mysterious phenomenon – suddenly a gymnast is no longer able to do a twisting skill she’s done thousands of times before. Your body just won’t cooperate, your brain loses track of where you are in the air. You find out where the ground is when you slam into it.

I was a competitive gymnast for 10 years, though a mediocre one. I quit when I acquired 7 inches in height and an attitude problem, on top of an extant paralyzing fear and total lack of flexibility. Since then, I’ve followed gymnastics obsessively, and covered it occasionally. And in March, I came down with the twisties myself when I dragged a CNN crew to an open gym class in Dallas and threw sad, little back full twists into a foam pit.

Swiss gymnast Giulia Steingruber got the twisties in 2014. “When I wanted to twist, especially on vault … I had no feeling where I am. I was really scared,” Steingruber said in a 2016 documentary. “It was quite tough for me, because I didn’t understand why it came, and I couldn’t stop it. It was just strange for me, and it was horrible. The feeling was really horrible.”

She had to relearn it, starting with a simple half twist on floor. “I started to learn the twist again like a small child.” In 2016, she won an Olympic bronze medal on vault.

Flipping and twisting at the same time can be extremely disorienting – you can’t just watch where you are with your eyes. You have to feel it. This is proprioception, a sense of where your body is in space and what it’s doing.

In gymnastics, this is called “air sense.” And Biles is famous for how good hers is. “She’s always had incredible air sense, which is what you need in this sport,” her former coach Aimee Boorman told Houstonia magazine in 2015. “She doesn’t crash very frequently. Other kids, you’ll just see them splat, or get lost in the air. That doesn’t happen with her.”

Her natural talent is why her missed vault is so stunning. But her decision to scratch makes a lot of sense. When the twisties set in, it’s hard to know when they’ll go away. But Biles’s decision to protect herself marks a shift from the old way gymnastics worked in the US.