Ariarne Titmus says surrendering her 400m freestyle world record to Canadian teenager Summer McIntosh has lit a fire ahead of her Olympic title defence in Paris next year.

Swimming at Canada's national trials for the upcoming world championships in Japan, McIntosh cut 0.32 seconds off the world mark set by Titmus last year.

The 16-year-old then backed it up with a world record in the 400m individual medley on Saturday night.

McIntosh won in 4:25.87 seconds, bettering the old world best time of 4:26.36 set by Katinka Hosszu of Hungary at the 2016 Rio Olympics.

The first person to hold both long-course world records, McIntosh just missed setting a world record in the 200m IM, while she also won gold in the 200m butterfly during a golden week in Toronto.

McIntosh finished fourth behind champion Titmus at the Tokyo Olympics, where the Australian also won gold in the 200m freestyle.

"Certainly having your own world record broken is a tough pill to swallow," Titmus said on Channel Nine.

"But I think you have to look at the good in everything and it's probably a good thing it was broken now.

"It gives me a little bit of fire in the belly."

Titmus said the prospect of taking on McIntosh and American legend Katie Ledecky next year in the Paris Olympics was exciting.

She felt the Toronto youngster had added another level of intrigue.

"I think it's naive to think that the world of swimming is going to stop. It's exciting for our sport. It's exciting for the 400 freestyle," Titmus said.

"I think the match-up between Summer, Katie and I is just going to be as strong as ever in Paris.

"Time is flying. It's only a year and a half away. It's exciting for the sport."