1This study aimed to clarify the rotational acceleration of the head of an uke during tai-otoshi, 2 seoi-nage, osoto-gari, and ouchi-gari when safe ukemi is performed. 3Eight judo club members of the National Institute of Technology (mean age, 17.5 ± 1.5 years; 4 mean height, 173.0 ± 4.21 cm; mean weight, 72.4 ± 10.57 kg) were subjects who acted as the 5 ukes. A subject with 8 years of experience in judo and qualified to the second dan (age, 20 years; 6 height, 165.0 cm; weight, 70.0 kg) played the role of throwing the uke. A rotational velocity 7 sensor was used to measure the rotational acceleration in the sagittal plane of the uke's head. 8One-way analysis of variance (Friedman test) was used for the statistical analysis, and when a 9 significant difference was observed, multiple comparison test was performed using the 10 Bonferroni method. The results revealed that of the four throwing techniques, osoto-gari 11 generated maximum rotational acceleration of the uke's head. Furthermore, the maximum 12 rotational acceleration was greater with tai-otoshi than with seoi-nage. Our results suggested that 13 among the four throwing techniques, osoto-gari was most likely to injure the head. 14 15 keywords: judo accident, head injury, rotational acceleration, sagittal plane, throwing technique

The purpose of this study is to clarify the strain distribution within deep brain and influence of brain shape factors on the strain distribution by using three dimensional physical head models during rotational impact. Three different shaped brain models were constructed; actual human brain shape model, no-ventricle model and simplified shape model. Angular acceleration pulse, whose peak of 4500 rad/s 2 with 8 ms pulse duration, was induced to the models. After rotating 60 degree, all models were decelerated with 1500 rad/s 2 peak with 30 ms duration. As for the strain distribution within deep brain inducing actual human brain, strain concentrations were measured at corpus callosum and brain stem. This was due to constraint of cerebrum brain rotational motion by falx and tentorium and hollow shape of ventricle. The maximum principal strain at brainstem in no-ventricle brain model was larger than the actual brain shape model. However the strain distributed near the corpus callosum in no-ventricle brain model was smaller than the actual brain shape model. The strain in the simplified brain shape model was smaller compared with other brain models. Therefore the cerebral ventricle relieved strain at brainstem and increased the strain near the corpus callosum. On the other hands, the sulci has a influences of increasing strain within deep brain.

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