Understanding Whiplash -- Four Phases of Injury

Rear-end car accidents are the leading cause of whiplash injuries. Because of how common these crashes are, researchers have worked extensively to better understand exactly how whiplash occurs. This research not only helps improve treatment approaches, but also guides the design of safer vehicles to reduce injury risk.

When a rear-end collision happens, the head and neck go through four rapid phases of motion: retraction, extension, rebound, and protraction.

Retraction Phase
Immediately after impact, the seat back pushes the upper body forward while the head initially lags behind. This creates a motion similar to tucking the chin. During this moment, the neck briefly forms an S-shaped curve—where the upper part of the neck bends forward and the lower part bends backward. Maximum retraction often occurs just as the head contacts the headrest (depending on its position). Researchers believe that this sudden difference in motion between the upper and lower parts of the neck may create a rapid pressure increase within the spinal canal, contributing to injury.

Extension Phase
Following retraction, the head moves backward into extension—similar to looking up toward the ceiling. This places the entire cervical spine into backward bending. If the headrest is missing, positioned too low, or too far behind the head, the neck can extend excessively, increasing the risk of hyperextension injury.

Rebound Phase
After reaching peak extension, the head quickly reverses direction and moves forward. This rebound motion generates some of the highest forces measured in whiplash research. During this phase, the neck is vulnerable to strong compression and forward-bending stresses.

Protraction Phase
In the final phase, the torso is restrained by the seatbelt while the head continues moving forward briefly. This creates another rapid change in motion, forcing the neck into flexion (forward bending). Similar to earlier phases, this sudden movement can generate increased pressure within the spinal canal.

Importantly, this entire sequence happens incredibly fast—within about 50 to 80 milliseconds. That’s three to four times faster than the brain can process visual information and activate the neck muscles to brace for impact. In other words, the body simply cannot react quickly enough to prevent the motion once the crash begins.

Because of this, proper positioning before a collision is critical. Experts recommend adjusting the headrest so the top of it is level with the top of your head and keeping it within two inches (about five centimeters) of the back of your head. The seatback should be reclined slightly—between 100 and 110 degrees—to reduce the chance of the body sliding upward during impact. And of course, always wear your seatbelt.

If you are involved in a rear-end collision, clinical guidelines consistently recognize chiropractic care as a safe, conservative, and effective option for reducing pain and improving function after whiplash injuries.

This article is based on content originally published by Chiro-Trust.org.  It has been adapted for use on this website with permission.