Simone Biles pushes her limits by doing the 'unimaginable'

The 24-year-old American has won every all-around competition she has entered since 2013

Simone Biles is gunning for more Olympic gold in Tokyo.

Olympic all-around champion Simone Biles said the gymnast she most wants to beat in Tokyo is herself and that she is excited about trying things that were once "unimaginable".

The 24-year-old American has won a record 25 world championship medals, including 19 golds, and has won every all-around competition she has entered since 2013.

She won four gold medals, and a bronze, at the Rio Games five years ago and is a white-hot favourite to add to that tally in Tokyo.

"I'm trying to be better than I was at the last meet, so I'm trying to beat myself," Biles told NBC television.

"And so now I'm doing things that were unimaginable to the sport, and even for myself, and it's honestly crazy but I'm really excited because I feel like I've pushed my limits."

Earlier this year Biles became the first woman to land a Yurchenko double-pike vault in competition.

One of the alternate gymnasts on the US women's team tested positive for the coronavirus on Monday and another alternate was determined to be a close contact, USA Gymnastics said, but the rest of the team was continuing to prepare for the Games.

The Tokyo gymnastics competition gets underway on July 24 with the men's qualification round, and the women's competition starts a day later.