2019 年 85 巻 875 号 p. 19-00059
From worldwide statistical data of whiplash injuries in the rear-end impact accidents, females have been found to be at a higher risk than males and the reason for the same is an ongoing research topic. First, we created finite element model of the head and neck of a 50th %ile Japanese adult female (JAF50) by scaling an existing 50th %ile (JAM50) male model. The activity level of neck muscles before a rear-end impact was determined using the L36 of DOE method, which held a neutral posture of the head with the relaxed muscles under 1G condition. Subsequently, the head and neck behaviors of both the models were validated using the volunteer's rear-end impact test data. Comparing both the results using a new index (S - θmax), which measured the S-shape deformation of the neck during rear-end impacts, the model results were found to have the same trends as that of the volunteer's test data. JAF50 had a higher (S - θmax) value than JAM50, which means that a female neck undergoes larger S-shaped mode than a male. This index value difference between the genders was due to the difference in their muscle forces while maintaining a neutral posture of the head. This difference in the muscle forces, however, was not proportional to only the head mass ratio of the two genders. As a result of the investigation of the underlying reason, the neck muscle force ratio of each gender at the neutral position was roughly related to mass ratio × neck column cross-sectional area ratio × neck length ratio. If the ratio (female to male) of neck circumferences was 3: 4, the female muscle force could be nearly twice less than that of a male. We also estimated the muscle activity for each gender assuming the same (S - θmax) = 15 ° at the rear-end impact of Δ V = 5 km/h. It was found that a female's muscle activity is about twice that of a males for the same rear-end impact conditions.