BUDAPEST - Hungary's 'Iron Lady' Katinka Hosszu admitted feeling the strain after retaining the women's 400m individual medley title at the World Aquatics Championships on Sunday to complete the IM double on home soil in Budapest.

Hosszu clocked a new championship-record time of 4min, 29.33sec with Spain's Mireia Belmonte taking silver at 2.84sec back and Sydney Pickrem of Canada earning bronze at 3.55.

This is the third straight world championships where Hosszu has won both the 200m and 400m IM title and she is also the world-record holder in both events.

Despite her nickname, Hosszu looked exhausted when she touched the wall and composed herself before celebrating in front of the raucous home crowd at Duna Arena.

She admitted her punishing schedule, racing in the 200m and 400m IMs, 100m and 200M backstroke, the 200m freestyle and 200m butterfly, had taken its toll, but the home support carried her.

"It's been a hard week for me," the 28-year-old admitted after her victory.

"Of course, the Olympics schedule is different - the 400 IM is on the first day there.

"I swam 4.26 in Rio and 4.29 here, I thought that I was in even better shape this year, but because it was on the last day it was difficult to swim a best time.

"In the last 100, I've definitely heard the crowd. They pulled me, I wasn't just swimming for myself I was swimming for everybody here. I knew I would have a really busy schedule and that on the last day, I would have this hard program.

"I was trying to recover between races as much as I could. It was just amazing for me today, I have to take a moment to enjoy the whole experience."

Hosszu said the pressure of performing at home had been an issue - until she won her first gold in Monday's 200m IM final.

"Honestly, coming into the world champs I tried to tell myself I didn't feel pressure and I'm just going to give my best," she said.

"But before the 200IM final, yes, I did feel the pressure. Once I got the gold, though, I felt relief and could enjoy racing here."

Hosszu said she is looking forward to defending her 200m and 400m IM Olympic titles in 2020.

"Tokyo is in my mind, I'm very excited about it," she said.

"Now I feel free, I have all the titles, I have all the records. I just enjoy swimming I really love the sport.

"I do feel the motivation in me to keep going, I'd love to challenge for Tokyo as well."

Belmonte, who finished with three world medals, including gold in the 200m butterfly, described Hosszu as "unbeatable" at home.

"Katinka was very fast right from the start, no surprise that she was unbeatable this time as well, since her performance was stable throughout the entire tournament," said the Spaniard.

Agence France-presse