The present study aims to investigate the relationship between observational and kinematic evaluation of the head injury risk during the breakfall motion for osoto-gari. Forty-seven participants (26 experienced judoka with black belt and 21 beginners) volunteered to participate in the study. We first developed three-dimensional animated movies of the breakfall motion and instructed the participants to evaluate the head injury risk of the motion using a 10-point Likert scale. The peak head extension momentum was also calculated from the biomechanical model. Pearson’s product coefficients were used to elucidate the relationships between the subjective score and the biomechanical parameters in the each group. The present study demonstrated that the observational evaluation of head injury risk in breakfall was significantly correlated to the peak head-neck extension momentum in the group of experienced judoka (r = - 0.39, P =0.048), but not in the group of beginners (r = 0.04, P = 0.57). The current result suggests that the even experienced judo practitioners may not be sufficiently developed to recognize the risk of head injury by observing the breakfall motion; therefore, regardless of judo experience, teachers may need to be educated about head injury prevention to teach judo safely in a school setting.

This study aimed to clarify individual differences in the amount of physical activity and differences between units in physical education classes in junior high school girls. The participants were 42 girls in the second grade of junior high school and 43 in the third grade. The step counts and exercise intensity achieved in classes involving long distance running, kendo, basketball, volleyball, mat movement, and dance were recorded. We conducted the Bartlett’s test and a test of equidistribution of the two groups in order to compare the individual differences in the amount of physical activity between units. Findings revealed that dance, volleyball, and basketball had significantly higher individual differences in step counts as compared to the other units, and mat movement and long distance running had significantly smaller individual differences in the same. Individual differences in exercise intensity were significantly larger in dance, basketball, kendo, and long distance running, and they were significantly smaller in mat movement. A one-way analysis of variance and multiple comparison test to clarify the differences between the units of exercise in terms of the exercise intensity and step count revealed that long distance running involved significantly more intensity than the other units did. Further, the exercise intensity of long distance running and basketball was significantly higher than that of mat movement and kendo. The present study revealed that physical education classes for junior high school girls involve individual differences in the amount of physical activity based on the unit, and that some units do not elicit the optimal amount of physical activity.

In this study, we revealed the reliability of stability in a standing posture on an unstable tilt board that moves in all directions. 50 middle-aged and older people, consisting of 19 men (60.3±9.9 years) and 31 women (58.5±8.4 years). The subjects had their stability in a standing posture on an unstable tilt board for 20 seconds measured three times. We evaluated for the following four variables: all-direction stability index, all-direction average displacement, all-direction angle-change area, and total angle variation index. As a result, all of the evaluation variables except all-direction angle-change area for males showed a higher ICC in the second and third trials (men: 0.74-0.81, women: 0.73-0.79) than that in the first and second trials (men: 0.59-0.75, women: 0.69-0.77). Two-way ANOVA showed all of the evaluation variables were better for women than for men (p<0.05). Significant main effects were observed between the all-direction stability index and all-direction average displacement, and better for the third trial than the first trial (p<0.05). The number of trials in which the effect of practice appears was different between the evaluation variables, but the good reliability was ensured in the second and third trials for all of the evaluation variables. Therefore, it is suggested that the measurement method with the first trial as the practice trial and the second and third trial as the present trial was useful.