Kinematic and electromyographic response to whiplash loading in low-velocity whiplash impacts--a review.

Whiplash injury is a common injury, with a substantial health and economic burden. For five decades, researchers have been striving to discover the mechanisms of acute whiplash injury to develop methods of prevention through automobile design, and to develop treatment approaches. While earlier experiments with animals, cadavers, and military volunteers have provided some useful insights, it is only in recent years that research has progressed to reveal how neck muscles respond to collisions, particularly how they bear the burden of the forces of collision and how impact direction affects the neck muscle response which may determine the mechanism of injury. Initial volunteer experiments tended to focus on impact velocities (specifically differences in target and bullet vehicle velocities) and head acceleration, but gradually the focus has shifted to understanding the pattern of spinal segment motion and muscle contraction in response to the perturbation. An approach has been devised using sled impacts with healthy volunteers to elucidate in more detail various head kinematics and cervical muscle responses in low-velocity whiplash-type impacts. This approach involves the use of four levels of very-low to low velocity impacts to describe the kinematics of the head and the EMG response of cervical muscles in response to acceleration, but avoids any discernible risk of injury. This allows researchers to determine the cervical muscle response under many different scenarios, including varying direction of impact, awareness of impending impact, and others, without subjecting volunteers to any discernible risk. An initial series of results of impacts from eight directions is presented here, and these reveal that the cervical response to whiplash-type impacts is modified by impact awareness, muscles studied, and direction of impact. This will hopefully improve the understanding of the human response to low-velocity whiplash impacts.