The 29-year-old, who took gold in the 100m and 200m breaststroke at the 2004 Athens Olympics and retained both titles in Beijing, said he has prepared to improve his form and enjoy the London Olympics.

"I'm feeling good about this pool. I just arrived two days ago, so I feel a little tired," said Kitajima after training. "But I have one week to go so I want to improve my condition," he added.

With a dazzling medals' haul under his belt, Kitajima is seeking to stamp his authority in 100m and 200m breaststroke in London. However, he played down his chances of whopping both of the two titles by saying he will try his "hardest".

Kitajima was the first swimmer in history to claim gold in both the 100m and 200m breaststroke events at successive Olympic Games, becoming the first breaststroke swimmer to win a total of four Olympic gold medals.

The Japanese prodigy set Olympic records in 100m and 200m breaststroke at Beijing Games in 58.91 and 2:07.64, respectively.

After the Beijing Olympics, Kitajima took 10 months off from competition and spent the time coaching children and giving speeches about his athletic career. In March of 2009, amid speculations over his retirement, Kitajima announced he was moving to the United States to study English. While there, he teamed up with Dave Salo, swimming coach at the University of Southern California, and recovered his passion for swimming.

At the Shanghai World Championships last year, Kitajima finished runner-up to Daniel Gyurta of Hungary in the 200m. He was fourth in the 100m which was won by Alexander Dale Oen of Norway.

Kitajima will spearhead the Japanese challenge in the pool at London Olympics. Other top swimmers from Japan include Ryosuke Irie who finished runner-up to American Ryan Lochte in the 200m backstroke in Shanghai, and Takeshi Matsuda who won the 200m butterfly bronze in Beijing and silver at Shanghai World Championships.

In the women's contest, the focus will be on world 50m backstroke silver medallist Aya Terakawa, who will swim in the 100m backstroke and 4X100 medley relay in London.

"I have been trying to make sure that I am in my best form for the competition. I have been trying to start slowly to make sure that I am in peak condition," said Terakawa after training.

The 27-year-old participated in the 2004 Athens Games and finished eighth in the 200m backstroke. She missed the Beijing Olympics. Speaking of her second Olympic tour, she said she was not very stressed out and worried, and had no difficulty coming back.

The swimming events are slated for July 28 to August 4 at London Olympics, with 496 swimmers competing for 34 gold medals including 32 in pool and two in open water.