Seat belt and airbag expert witnesses at Technology Associates describe “whiplash” injuries:
Unfortunately, the effects of whiplash are often downplayed, and its sufferer thought to be malingering, on the grounds that injury isn’t visible. In addition, experiments have shown that the forces to the neck during whiplash are not much greater then those occurring during normal activities (e.g. “plopping down into a seat”, “hopping onto a step”, and even “sneezing”). However, unlike whiplash, normal events do not take a person by surprise, so one can instinctively brace the neck muscles in anticipation, and control the force transmitted to the cervical soft tissues. With whiplash, the force to the neck is violent and sudden, and is not filtered through the neck musculature. Hence, those with thinner or weakened necks (i.e. women and those who have had prior neck injury) are more prone to the effects of whiplash, which can occur from an impact to the car as low as 3G’s.
A problem facing investigators of a whiplash case is that the impact velocity of the striking (rear) car is typically not known with certainty, and this value is needed for determining resulting forces. A conservative estimate of the speed can be surmised by using the damage threshold of the cars’ bumpers (because whiplash injury is caused by low speed impacts involving no (or minimal) damage to the bumpers; hence most of the shock is transmitted to the passengers’ necks). Testing has shown the damage threshold of bumpers of many cars to be about 5 mph; thus lash forces to the neck based on a maximum 5 mph impact velocity to the struck car. However, most crash testing involves the car impacting a rigid barrier, which does not yield in any way, rather than a relatively flexible bumper of another car. Hence, the crash testing can be more severe than an actual impact with another car, and can, in fact, be equivalent to the car’s being struck with another car at up to twice the velocity used for the barrier test.