Having beaten her nemesis Katie Ledecky over the distance in the Olympic final, the Tasmanian swimming star added the American's world record on an emotional night at the Australian championships in Adelaide.

The Launceston-born 21-year-old was inside the world record time throughout, holding on to clock 3:56.40 - 0.06 seconds inside the mark Ledecky set at the Rio Olympics six years ago.

Titmus said her extrovert coach Dean Boxall had instilled her relaxed return after she left her maiden Olympics with two golds, one silver and one bronze medal.

"The biggest thing since the Olympics was Dean said to me 'you now have this freedom, the pressure's off your back' and I've just loved swimming the past six months," she said.

"Coming here with no pressure other than the pressure I put on myself - which is still pretty high - is fun."

Having contested the individual 200, 400 and 800m freestyle races in Tokyo, Titmus opted for the 100, 200 and 400m at nationals.

She set a personal best in the 100m and won the 200m in a time just 0.22 outside her own Commonwealth and Australian records.

"It's been strange having the 100 and 200, I've just been doing light swimming and waiting to go so it's probably the biggest taper I've done, and maybe I should keep doing that," she said on Amazon Prime Video.

"I thoroughly enjoyed my break and came back and took it very slow in the beginning and never thought that this meet I'd be swimming faster than Olympic trials and Olympic Games.

"But I guess if you keep surprising yourself it keeps the sport interesting."

The results qualify Titmus for world championships and Commonwealth Games but she has said she will only contest the latter.