Biomechanical response of the head, neck and torso to direct impact on the back of male and female volunteers.

Low-severity impact at T1, T6, and L1 to the back of volunteers were applied using a newly developed thrust piston with pneumatically charged cylinder (simulated whiplash loading device) in order to simulate the whiplash motions during such impacts. Seven male and two female volunteers were subjected. The average age of the volunteers was 25 years old. The impact of 100-400 N with duration of 50-100 ms was applied to the back of these volunteers. The three impact locations for each volunteer were: 1) the close area of the first thoracic vertebra (T1), 2) the close area of the six thoracic vertebra (T6), and 3) the close area of the first lumbar spine (L1). The test results for human volunteers were compared with the cadaver tests reported in the past. For T1, T6, and L1 impacts, the lower cervical spine showed an initial flexion during early stages of impact. The neck axial force appeared to be in tension in the early stages within 50 ms for T1 and T6 impacts. On the other hand, the neck axial compression force in the early stages became remarkable for L1 impact. Due to the neck muscle tension, the neck moment was observed to be getting small which eventually resulted to a minimal movement of the head. However, the neck axial compression force was not affected due to the muscle tension. It can be argued that the neck muscle tension did not influence the movement of the spine. For T1 and T6 impacts, the neck shear force increased while the change in the neck axial compression force was negligible due to the increase in the impact load level. The head rotational angle and the localized motion of cervical spine for female were bigger than that of male using the same impact load level. It is confirmed that it is necessary to take into account the motion of the spine and/or spine flexibility in evaluating the cause of cervical injuries during low speed rear-end impacts. Furthermore, with this experiment, the difference in the loading condition at the back caused by different impact positions to the spine and the impact load levels could be understood more. This study thus recommends that a new design in the dummy spinal structure must be made in order to obtain an accurate prediction of minor neck injury occurrence. For the covering abstract see E135170.