To minimise the load applied to an occupant's neck in a rear impact, it's essential to minimise the extent to which the head moves relative to the chest. An effective method is to quickly hold the head in position so it's not thrown rearward. Active head restraints help achieve this.
During normal driving, the active head restraints are positioned as far forward as possible without detracting from comfort.
If the vehicle is hit from behind, the force with which the occupant presses into the seatback is instantaneously used to move the headrest forward. The head restraint's forward movement prevents excessive rearward inclination of the neck, so it greatly mitigates the load applied to the neck.
To prevent the head restraint from moving forward and causing discomfort during normal driving, the forces applied to the seatback were analysed during a rear impact and during normal driving, and the results were reflected in the active head restraints design.
As a result, the head restraints are optimally positioned to mitigate neck injuries without marring comfort during normal vehicle operation.