TOKYO (Reuters) - Double Olympic gold medallist Ryoko Tani has slammed Japan's "sloppy technique and weak hearts" for their stunning failure on the judo mats at the London Games.

The 36-year-old Tani, women's 48-kilogram champion at the 2000 and 2004 Olympics, warned that Japan faced a tough slog to get back to the top after Russia's emergence in London, local media reported on Wednesday.

Japan won just one gold in London, Kaori Matsumoto's in the women's 57-kilo division, with the men failing to win a title for the first time since judo became an Olympic sport at the 1964 Tokyo Games.

"Both the men and women's spirit, technique and condition were all over the place," Tani told Japan's Kyodo news agency.

"Either they had the technique but lacked heart or they were in great condition but the technique and heart wasn't there."

Russia, who had failed to win a judo gold at the 2008 Beijing Olympics, won three in London, along with one silver and one bronze.

Japan had been tipped to win at least half of the 14 gold medals in the seven weight categories for men and women. They won four in Beijing in 2008 and eight in Athens in 2004.

"Judoka from other countries went to the Olympics with the goal of winning the gold medal," said Tani. "The way they fixed their sights on that was amazing."

Tani, now a politician, added: "Japan do well in other international competitions but you could see the difference in motivation."

Rule changes introduced in 2009 that banned certain moves were supposed to have been of benefit to Japanese fighters, but they made no difference in London.

"The Russians for example were overpowering," said Tani, glowing in praise of how London's medal-topping judo country had reversed its fortunes in the Japanese martial art.

"I think they rebuilt from zero. They couldn't fight the way they had so they retrained and you saw the result."

The Russians, cheered on by President Vladimir Putin, himself a judo black belt, had not won a gold medal since the collapse of the Soviet Union.

"Unless Japan comes up with a serious plan to improve, (Russia's) level is not one that we can catch up with in two or three years," said Tani.

"Judo is Japan's speciality. We should have the pride to back up the talk. Some intensive technical development is what's needed."

(Reporting by Alastair Himmer; Editing by Patrick Johnston)

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