Gymnast Simone Biles still struggling

US gymnastics superstar Simone Biles said she was still struggling with the "twisties", the mental block that has sidelined her in Tokyo, as her Olympic campaign looked in increasing doubt yesterday.

Biles posted video on Instagram of her landing on her back in training, on cushioned pads, and wrote that she was having problems "literally on every event, which sucks".

The 24-year-old gymnastics great came to Tokyo seeking five gold medals to equal the all-time career record of nine, but withdrew during the women's team competition and also skipped her all-around title defence.

"This was not happening before I left the USA. It randomly started happening after prelims competition the very next morning," Biles posted.

"I seriously cannot comprehend how to twist. Strangest and weirdest feeling... It's honestly petrifying trying to do a skill but not having your mind and body in sync," she added.

Biles said previous bouts of twisties had taken two or more weeks to pass, but there was "honestly no telling (the) time frame".

"Something you have to take day by day, turn by turn," she wrote, warning: "But unfortunately in Olympic routines I do a ton of twists in each event."