Below are links to some articles which should prove to be of interest.
The first three concern themselves with some serious health and safety issues which (the articles say) are taking place in some martial arts classes in Japanese schools.
The forth and last one highlights some excellent research carried by academics in the UK regarding the way karate-ka manage to generate their massive punching power:
http://martialartsteachers.com/108-school-judo-class-deaths-charges-silence/
http://www.abs-cbnnews.com/sports/01/02/11/judo-deaths-alarm-japanese-parents
http://news.sky.com/story/972555/brains-not-brawn-give-karate-experts-punch