The report, entitled "I Was Hit So Many Times I Can't Count: Abuse of Child Athletes in Japan", and released in the week the Tokyo 2020 Olympic Games had been due to begin, documents how some athletes committed suicide after suffering abuse.

Depression, physical disabilities and lifelong trauma were also uncovered in the report, which includes testimony from athletes competing in more than 50 sports.

More than 800 former child athletes, including Olympians and Paralympians, took part in a survey for the report, conducted between March and June.

The results have raised serious questions for the Olympic and Paralympic host nation and Japanese sport.

The report details Japan's history of corporal punishment in sport – known as taibatsu in Japanese – and child abuse in sports training throughout Japanese schools, federations and elite sports.

Japanese athletes reported abuses including being punched in the face, being kicked, being beaten with objects like bats or bamboo kendo sticks, being deprived of water, being choked, being whipped with whistles or racquets and being sexually abused and harassed.

Human Rights Watch called for Japan to take "decisive action" in response to the report.

"Participation in sport should provide children with the joy of play, and with an opportunity for physical and mental development and growth," the report states. 

"In Japan, however, violence and abuse are too often a part of the child athlete's experience. 

"As a result, sport has been a cause of pain, fear and distress for far too many Japanese children.

"Athletes interviewed by Human Rights Watch described a culture of impunity for abusive coaches. 

"Of recent child athlete interviewees who experienced abuse, all but one reported that there were no known consequences for the coach."

Cases of abuse in Japanese sport had previously been uncovered, including in judo in the build-up to the 2012 Olympic Games in London, where former women's team head coach Ryuji Sonoda was forced to resign after 15 female athletes alleged he had committed violence and harassment against them.

In the same year, a 17-year-old high school basketball player in Osaka committed suicide as a result of abuse.

The report documents suicides in other sports including volleyball and table tennis.

Japan had introduced reforms aimed at removing taibatsu from sport during its bid to host the 2020 Olympics and Paralympics.

But Human Rights Watch found that these reforms are optional "guidelines" instead of rules, that progress has been "uneven and unmonitored" and that there is no mandatory reporting of abuse complaints or statistics.

"We show in our report that the reforms that were made in 2013 are not mandatory and have not been implemented," Human Rights Watch director of global initiatives Minky Worden told German public broadcaster Deutsche Welle.

"So long as the sports federations have a choice whether to devote resources to staff who could take complaints, and so long as sports and schools protect abusive coaches and move them around, children will not be safe."

Tokyo is due to host the postponed Olympic and Paralympic Games in 2021.

"We acknowledge the Human Rights Watch report entitled “I Was Hit So Many Times I Can’t Count” Abuse of Child Athletes in Japan,'" the International Olympic Committee (IOC) said in a statement.

"Harassment and abuse is unfortunately part of society and also occurs within sport. 

"The IOC stands together with all athletes, everywhere, to state that abuse of any kind is contrary to the values of Olympism, which calls for respect for everyone in sport. All members of society are equal in their right to respect and dignity, just as all athletes have the right to a safe sporting environment – one that is fair, equitable and free from all forms of harassment and abuse.

"The IOC places the safety and wellbeing of athletes as a priority and is committed to leading and supporting the Olympic Movement in the implementation of measures to protect the athletes from any form of abuse. 

"The IOC Safeguarding team is in regular contact with National Olympic Committees (NOCs), including the Japanese Olympic Committee, to offer advice and support, including highlighting the available IOC initiatives - such as the IOC Athlete Safeguarding Toolkit; Safe Sport educational tools and materials, and initiatives to protect athletes at the Olympic Games and Youth Olympic Games. 

"All the initiatives available to assist NOCs and International Federations to safeguard athletes can be found on Olympic.org/Safe Sport and Athlete365."

The full report is available here.