The feat came despite the flaring of a back injury for the 2016 Olympic 100m freestyle champion, who claimed silver in the event at the Tokyo Games of 2021.

Chalmers has been mixing his swim training with working as a landscape labourer on Queensland's Sunshine Coast.

On Friday two weeks ago, he took a day off to rest for the trials.

"I just spent the day laying on the couch, which my body is clearly not used to," Chalmers said.

"It got pretty stiff and then the Saturday morning, I tried to do a dive and it just all spasmed and locked up.

"I saw physios and doctors and the best thing I could do was to get four cortisones in my lower back and try to get moving again.

"I am just grateful to be here racing and be back on the mend.

"I know that I can get it right in six weeks' time (for the Olympics).

"I have put on a pretty brave face to be able to get through but it has definitely been quite challenging."

Chalmers, who suffers bulging discs and a degenerative spine, has now had 10 cortisone injections in his back during his swim career.

Almost five years ago, he had a second round of heart surgery to correct a condition called supraventricular tachycardia - in layman's terms, his heart sometimes beat irregularly fast.

Chalmers has also had shoulder surgeries and suffered various other injuries, as well as mental health battles.

"The good thing is that mentally and emotionally I'm in a very, very good spot," the 25-year-old said.

"I'm able to rise above the adversity and the challenges that have been thrown at me.

"And that's only because it has happened so many times throughout my career that I have had to rise above something.

"So mentally it hasn't been too bad. It's more just the physical physical pain."

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