Cars today are designed with rubberized, plastic bumpers that are spring loaded to reduce the high cost of car repairs. Fender benders that used to cost $3,000 now only leave a $500 paint scratch!  The problem is that @ 2/3rds of accidents are rear-enders, which causes a plastic deformation then spring loads the struck car forward.  Even low impacts create a hyper-extension of the neck... loading into the seatback then the seat rebounds forward.