This has to be the worst week for one of the country's premier sports

A 15-strong group of judokas complained to the Japanese Olympic Committee (JOC) in December that they had been subjected to physical punishment by the team's head coach.

The group, which included athletes who took part in the London Olympics, says head coach Ryuji Sonoda (right) routinely abused them, slapping them in the face and hitting them with thick wooden swords, like those used in the Japanese martial art of kendo.

They also complained that some were forced to compete in matches while injured, reports said.

All Japan Judo Federation (AJJF) head Koshi Onozawa said the federation had admonished Sonoda and other coaches, who had admitted several of the allegations.

"We received information that Mr Sonoda, the head coach of the female national team, might have been physically bullying athletes," Onozawa told a news conference.

"Our executive office took this seriously and questioned both him and athletes, discovering the charges were largely true."

Japan's women returned from London with one gold, one silver and one bronze medal in judo, well below their haul from the 2008 Beijing Games.