Beginning in 2012, judo has been selected to be a compulsory course in junior high schools in Japan. However, the number of participants, in particular beginners, who die or are injured in judo is higher than that for other sports. For this reason, there is a fear that there will be a drastic increase in the number of judo-related accidents leading to death or injury in junior high schools. The most serious form of head injury is acute subdural hematoma (ASDH). The purpose of the present study is to compare ASDH occurrence indices and to evaluate the effectiveness of using head protectors. Based on measurements of head acceleration during falling, the Head Injury Criterion (HIC), maximum angular acceleration and angular velocity variation range were calculated. The results indicated that the relative displacement between the brain and skull was most strongly correlated with the angular velocity variation range, which is thus a candidate evaluation index for ASDH. The results also suggest that in order to prevent ASDH, a head protector should be made of shock absorbing materials with a small coefficient of restitution, so as to reduce the rebound velocity of the skull after occipital impact.
