Here's why performance anxiety before an Olympic event may not be a bad thing Experts say elite athletes can use nerves to help performance.

 -- Just moments before Mikaela Shiffrin, the world’s top-ranked women’s skier, clipped into her bindings today for the first run in her attempt to defend her Olympic gold medal in the slalom, she vomited.

It was a dramatic physical reaction to the nerves that plague athletes at all levels of competition, but not so rare for Shiffrin. She has been open about the battle she is waging against those nerves with the help of sports psychologists.

In a TV interview between races today, Shiffrin suggested she might have caught a virus, but later acknowledged it was “just nerves again.”

Sports psychologists say extreme performance anxiety like Shiffrin’s is more common than many people think among elite athletes.

What is performance anxiety?

“Performance anxiety is when the mind and the body says, ‘OK, it’s here, whatever we’ve done to prepare, there’s nothing else we can do now aside from try to be successful,” Dr. Neal Bowes, a former professional soccer player and sports psychologist who has prepared Olympians for the games, told ABC News. “And it’s more common than you think.” Think of it as the common “fight or flight” reaction.

Amy Baltzell, who competed in the 1992 Barcelona Games as a rower and is now the president of the Association of Applied Sports Psychology (AASP), agrees. “Most athletes feel performance anxiety and as you get better and the results get more uncertain, that anxiety goes up,” Baltzell said.

Shiffrin makes her nerves work for her

What’s more uncommon is becoming physically ill as Shiffrin does, but from observing her perform and also talk about her struggles with nerves, Bowes -- who has never treated Shiffrin -- believes that although it’s clearly not great for her body, she has found a way to use it as a mental tool that tells her she is ready to compete.

“She’s found a way to believe that getting ill is OK and fairly normal for her,” Bowes said. So when she gets sick, Bowes believes Shiffrin is able to tell herself, “This is normal for me, it’s happened, which means I can now go and ski well.”

“She seems to be able to quickly process the fact that she’s gotten ill, accept as a sign she’s ready to perform and go out and compete,” he added.

What can athletes do to control their nerves?

Sports psychologists have different approaches for how they approach such anxiety among athletes, but all have the same goal.

“You want the butterflies to fly, but we work to get them in formation and have them work for you, not against you,” said Kristen Dieffenbach, an executive board member with AASP and psychologist who has treated a wide range of athletes across disciplines and ages.

Baltzell teaches athletes how to tolerate their anxiety and shift their attention back to the task at hand through mindfulness -- it’s a way to turn “fight or flight” into “fight, flight or compete.”

“I have my athletes visualize themselves performing the part of their performance they most need to prepare for and feel the positive emotions that go with executing that part well,” Baltzell said. “It can be quite helpful for athletes struggling with anxiety.”

Dieffenbach focuses on “controlling the controllables” -- helping athletes figure out their optimal pattern for warming up and preparing for a day of competition.

Bowes recommends visualization and breathing exercises and tells athletes who struggle with nerves to be selective with what they eat.

Another chance at gold

After becoming ill, Shiffrin placed off the podium in fourth place Friday in the slalom. She said she was “disappointed,” adding “it just wasn’t there today to ski the aggressive way I need to be worthy of a medal.”

Vomiting before the race may not have been the main cause for her finish, though. Shiffrin said, “It’s hard to put the blame on any one thing. There’s a lot of things that come together to make it.”

Despite her struggles with nerves, Shiffrin already has that gold medal in the giant slalom in these games and will have another chance to snag more hardware next week in the downhill.