Leon Marchand's life changed drastically after winning four gold medals a year ago at the Paris Olympics. He was a national hero and had to adjust — particularly when he was at home in France.

"I have to plan things," Marchand explained Saturday. "I can't just go on my own to the city and just go get bread."

"I know how to say 'no' better," he added. "It gets a lot more peaceful when I travel out of France."

After swimming under the tutelage of Bob Bowman at the University of Texas at Austin, Marchand is back and will head the field at the swimming world championships — the biggest meet since the Paris Olympics.

It's also the stepping stone for many toward the 2028 Los Angeles Olympics, with races in the pool which started Sunday and will run through Aug 3.

Marchand, Canada's Summer McIntosh and Katie Ledecky of the US were the stars in Paris. They'll be the swimmers to watch in Singapore, joined by a host of Olympians and younger swimmers who hope to be in Los Angeles in three years time.

The youngest in the field is 12-year-old Yu Zidi of China, who could be a medal contender in her three races, with times at the national championships in May that have shocked global swimming almost as much as the age at which she is posting them.

Yu, who turns 13 in October, clocked a blistering 2 minutes and 10.63 seconds in the women's 200m individual medley, the fastest time in history at that age. She then romped to victory in the 400m medley in 4:35.53, which would have been enough for fourth place at last summer's Olympics.

Marchand will swim only the 200m and 400m individual medleys and some team relays, opting out of his other Olympic gold-medal events — the 200m butterfly and 200m breaststroke.

"This is a transition year for me, so I wanted to have a lighter schedule than usual," Marchand said. "I'm really excited to do less than usual, you know, just to see how far I can go, how fast I can go."

Marchand will be after the 200m IM record set in 2011 by American Ryan Lochte — 1:54.00. He'll also try to break his own 400m IM record (4:02.50) set at the 2023 worlds in Fukuoka, Japan.

He credits Bowman — famous for coaching Michael Phelps to 23 Olympic gold medals — for pushing him in Texas. Bowman tutors an international cast of swimmers that this fall will also include McIntosh.

"He knows how to be calm in every situation," Marchand said of Bowman. "He also has a lot of experience on the biggest stage, so I trust him fully."

Without the stress of two extra races, Marchand is ready to make more history.

"Of course I want to break all the records," he said. "I don't know when that's going to happen."

Many are expecting it to be in Singapore.

AGENCIES VIA XINHUA