Even as the country prepares to introduce martial arts as a compulsory school sport, research showing that an average of four children die each year during judo lessons in Japan has alarmed some parents.
Yoshihiro Murakawa is one of those concerned about the government's plan, because he is convinced his 12-year-old nephew died in a reckless judo practice.
The Japan Judo Accident Victims Association, which Murakawa helped create with other families last March, has urged the government to set safety guidelines for judo at school.
"Many factors are involved here," Murakawa said of his nephew Koji's death during judo club training.
"First of all, many judo instructors at Japanese schools are too ignorant about what to do when a serious incident occurs," he told AFP.
Murakawa also criticised some judo club instructors at Japanese schools for neglecting safety measures, such as letting children rest properly.
Koji's mother had asked for special attention to be paid to him when he joined the judo club at a middle school in central Shiga prefecture, because he had an asthma problem.
But one afternoon in July 2009, Koji was still tackling older students and the instructor in the freestyle "randori" training despite being exhausted, Murakawa quoted students as saying.
After a final throw, Koji lost consciousness and fell into a coma before dying a month later, Murakawa said.
At least 110 children were killed in school judo practice over 27 years from 1983, according to research by Ryo Uchida, an assistant professor at Aichi University of Education.
"In judo, the number of cases in which trainees die due to techniques unique to the sport such as throwing is significantly high," said Uchida.
In 2009 and 2010 alone, 13 children have died and the latest case, involving a six-year-old boy, occurred in November, a local newspaper reported.
Parents have been alarmed by the statistics because Japan plans to introduce traditional martial arts, including judo, as a required subject not only for boys but also girls at middle schools from 2012. Middle school pupils are aged between 12 and 15.
Yasuhiko and Keiko Kobayashi, whose youngest son suffered a grave brain injury when he was 15, also questioned whether the government was fully prepared, saying there had been a lack of thorough investigation into the causes of serious judo incidents.
"With so many children dying, there was no single case taken to a court for a criminal charge," the father said. "No one has taken responsibility."
Uchida said judo instructors had failed to take safety measures and assumed "occasional injuries or deaths are unfortunate but cannot be fully prevented."
Judo, which became an official Olympic sport at the 1964 Tokyo Games, has long been seen as a tool for training young Japanese minds and bodies and a major part of military and police training.
Murakawa criticised what he called a "military-like" judo culture which tolerates "beating and kicking" in the name of discipline for young trainees.
"Children, afraid of getting beaten up, must obey the coach and cannot ask for a rest for no matter what," he said.
The head of the French Judo Association, Jean-Luc Rouge, said he had not heard about judo deaths in France, which has the world's largest judoka population of 600,000 -- of which 75 percent are children under 14.
"There are some injuries, of course, because it's a sport. But in France all family members can do judo," Rouge told AFP by telephone.
Some Japanese judo athletes were "like army commandos", he added.
Sports doctor Yuzo Shinbara, who is a member of the medical science panel under the All Japan Judo Federation, rejected the argument that there was a mentality among judo trainers which justified tough initiation practices.
"We in the judo federation feel such an agony to know that children are dying in judo," he said.
The sports association, which recognises 56 grave judo incidents including deaths during six years to 2009, has published its own safety guidelines and is studying the risk of head injuries with medical experts, he said.
The Japanese government, however, has not provided official safety guidelines for judo lessons at schools.
"The government does not have a guideline specific to each sport about risks of injuries or safety measures," said an education ministry official, who noted most judo injuries occur during extra-curricula club activities.
Uchida warned that more children would be exposed to a risk of serious injuries when judo became part of the official curriculum.
"Judo is an inspiring sport and very educative to one's mind," Uchida said. "But schools must have a safety guideline."