This study enhances the existing database of human subject test exposures with an emphasis on electromyographic activity before, during, and after low speed rear impact. Ten nominal 16 km/h closing speed car-to-car impacts were conducted using instrumented male and female subjects aged 22-54 years, with struck vehicle velocity changes of up to 10 km/h. Two head restraint conditions were studied. One condition was a standard seat integrated head restraint. For the second condition the integrated head restraint was modified by adding 2 padding inches to the existing head restraint. No injuries were sustained by any occupant. In all cases, the subjects exhibited pre-impact muscle activity commensurate with that of a relaxed commensurate with that of a relaxed seated posture. Initial muscle activity typically occurred during the initial impact phase as the occupant's cervical spine was extending. Full muscle tension likely did not develop until the cervical spine was flexing. Initial muscle activity was consistent with being triggered by lumbar spine acceleration, and occurred approximately 90-120 milliseconds after onset of lumbar spine acceleration. No significant differences were noted between muscle response times for the two head restraint conditions. Decreases in rearward head displacement, cervical spine extension, and head acceleration were found for the modified head restraint.
Abstract