My sister and I were in a car accident together. I had a little stiffness and I was sore for a few days. My sister still has severe headaches and neck pain three months later. Why the difference between us?

Doctors and physical therapists wonder the same thing. Researchers are trying to figure it out. The Whiplash Research Unit in Australia may have come clues. They compared patients with mild, moderate, and severe pain from whiplash to subjects who had no injury and no neck problems.

Motion, sensitivity to heat, and psychologic distress were all measured. The researchers found changes in how the nervous system feels the pain and how the muscles react. These changes were present in all whiplash patients. The patients with the most pain were the most sensitive to the changes.

The scientists thought the differences in severity of symptoms might be related to psychologic distress. This study didn't show that at all. More studies are needed to understand how the body processes pain after whiplash.