At the rear-end collision it is likely to receive a so-called whiplash injury. Restraints are designed to protect the head from it.
Up until the mid-1990s, restraints were passive and their effectiveness depended only on the correct setting. But already in 1997, Saab introduced the first production car equipped with active headrests. The mechanism was simple and reliable – in the front seat backrests lever system was established which under the weight of the head moved forward. Mechanical systems of active head restraints are often called reactive.
Whatever headrests are, passive or active, in most cases, in order to make benefits, they need the right adjustment. Nissan and Infiniti specialists in the case of active head restraints advise to install them so that the middle of the head restraint will be in the same level with the ears. But passive ones, according to experts Euro NCAP, must be configured as follows: headrest should be at the top of the level and the distance from the back of the head – in the range of 40 mm.