Get ready for world records.

Ian Thorpe showed he could challenge some of his own world marks at this month's national swimming titles in Sydney when he set a personal best time over 50 metres on Sunday night.

Thorpe's time of 23.51s in the sprint saw him finish third behind fellow Sydney swimmer David Carter at the ACT Open Championships.

It demonstrated his sharpness even as he tunes for the longer events he dominates and will contest at the nationals - which double as world championship trials - starting in Sydney on March 22.

Asked whether he expected to break world records in Sydney, Thorpe, who holds the world marks in the 200, 400 and 800m freestyle, was typically modest but certainly not ruling it out.

"I hope to swim well," said Thorpe.

"I don't know if that means I'll break world records but I hope to be swimming at my best so I guess it's possible."

He announced at the weekend that he would chase seven titles at the world championships in July, adding the 200 metres individual medley to his schedule.

Even though Thorpe slowed down in the freestyle leg of the 200IM at the ACT Open, he about three seconds off the Australian and Commonwealth 200m IM record with his time of two minutes, 03.60 seconds.

It was more than four seconds ahead of second placed Commonwealth Games 200m IM gold medallist Justin Norris.

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