By Chris Gallagher and Hyun Oh

TOKYO (Reuters) - The competition at the London Olympics is already guaranteed to be intense but three Japanese gymnasts may have an extra source of motivation as they vie for gold medals: sibling rivalry.

"When it comes to competing, of course I don't want to lose to the younger two," grinned Kazuhito Tanaka, 27, referring to his sister Rie and brother Yusuke.

"I'd lose my standing as the big brother," he told reporters after a recent training session ahead of the trip to London, where all three siblings will make their Olympics debut.

It is rare for two siblings to become top-tier athletes, three is even rarer. This will be the first time Japan sends three siblings to compete in gymnastics at the Olympics.

For the Tanakas, whose parents were also gymnasts and their father a coach, a common dream and strong work ethic runs in the family, 25-year-old Rie told reporters at a separate practice session.

"The bond we have through hard work is really strong. And since we were little, we all wanted to go to the Olympics," said Rie, who is captain of the Japanese women's team.

Kazuhito was the first to follow in their parents' footsteps and take up the sport as a child. Rie became interested after watching her big brother train, while Yusuke, 22, started because he did not want to be home alone bored.

Despite being such a family of gymnasts, their father went to surprising lengths to keep the sport from becoming too much of a focus in their home life, easing the pressure and helping them learn to appreciate gymnastics on their own.

"Our dad even made a rule that we couldn't talk about gymnastics at home," said Rie, who won her first national title in April.

"It was like being in any other home in that we'd pretty much forget about gymnastics with the conversations we were having," she said.

'RISING TO THE CHALLENGE'

Kazuhito, also a captain, will lead the men in their quest to recapture the team gold, which they won in Athens in 2004 before taking silver in 2008 in Beijing.

He said he took heart from having his brother on the same team, but he puts his focus squarely on the squad once they hit the gymnasium, with everyone on equal footing.

"I try to think of Yusuke more as a team mate than a brother, and I feel a sense of encouragement from no matter who my team mate is," he said.

In the individual categories, the men will be looking to win their first gold medal since 1984, with Kohei Uchimura, who has won three consecutive world all-around titles, seen as a strong contender.

Uchimura came close four years ago, having won silver in the all-around in Beijing.

While the women have won only one medal, Japan's female athletes have enjoyed a recent string of successes, most notably the women's soccer team winning last year's World Cup, and Rie is hoping some of the magic will rub off on her squad.

"We (Japanese women) are strong at rising to the challenge," said Rie, who noted she was more excited than nervous about competing in the Olympics.

"We'll use that strength as a weapon to do our best."

(Editing by Peter Rutherford)