The aim of this study is to verify the influence of the change of the spine configuration on human cervical vertebral motion and on head/neck/torso kinematics under low speed rear-end impacts. Seven healthy human volunteers participated in the experiment. Each subject sat on a seat mounted on a sled that simulated actual car impact acceleration. Impact speeds (4, 6, and 8 km/h), and seat stiffness (rigid and soft) without headrest were selected. During the experiment, the change of the spine configuration and the interface load pressure distribution was recorded. The cervical vertebrae motion was also recorded by 90 f/s cineradiography. The localized straightening of the lumbar spine starts at around 30 ms with the rigid seat. The localized straightening of the thoracic spine reaches the maximum at around 80 ms when the load pressure distribution is at its peak value due to the interaction between the shoulder and the seat back. For the softer seat, the pelvis starts to sink into the seat back and cushion at around 70 ms. As for this seat the load pressure is distributed over a large area, the localized straightening of the middle thoracic spine occurred together with deflection of seat back itself at around 120 ms. The results of the study can help clarify the relationship between the localized straightening of the spine and cervical vertebrae motion with respect to the difference in seat characteristics.
Abstract