Three years after her shock exit, American gymnast Simone Biles is back on the Olympic scene with gold firmly in her sights.

The 26-year-old will compete in the Artistic gymnastics women's team final on Wednesday at 2:15am AEST and the individual events later in the week.

The four-time Olympic gold medallist made a strong start in the competition, scoring highly during the women's artistic gymnastic qualifications. 

It was a long-anticipated return after the most decorated gymnast in history withdrew from the Tokyo Olympic Games in 2021, citing mental health concerns at the time. 

Later, she revealed it was actually a case of "the twisties" — a serious mental health condition that can be debilitating for gymnasts. 

So what are the twisties and how did Biles recover?

What are the twisties?

The twisties is a dangerous phenomenon that gymnasts experience in which they lose their perception of their body while in the air — which can result in serious injury. 

It can set in when a gymnast is attempting high-level movements, making it difficult to compartmentalise the exact movement they're attempting. 

It's a phenomenon not widely researched but spoken of and experienced by some elite gymnasts. 

While many experience it in their career, it is especially gruelling and dangerous to suffer from during competition. 

US gymnasts Laurie Hernandez and Aleah Finnegan have also spoken of it during their careers. 

What does it feel like to have the twisties?

Essentially, for the gymnast, it feels like their rhythm is off and they are not in control of their body's movement. 

During the Tokyo 2020 games, Biles was trying to perform a "2.5 twist" but ended up doing a "1.5 twist". 

She said she felt "lost in the air".

"I don't think you realise how dangerous this is on a hard/competition surface," she said in 2021. 

"It's honestly petrifying trying to do a skill but not having your mind and body in sync." 

What causes the twisties?