Narrator: This is Science Today. Head injury is not simply a blow to the head - it's rather a violent movement that suddenly stops and causes the brain to move back and forth. According to Dr. David Hovda, director of the UCLA Brain Injury Research Center, this type of injury is usually not as severe as when the head is rotated at the same time it's being moved back and forth.
Hovda: An example is that if you had somebody who was falling and who instinctively was looking in the other direction as they were falling and was rotating their head violently at the same time their head had moved, they can actually have a more severe head injury.
Narrator: That's because the greatest amount of torque occurs in the middle part of the brain where a lot of critical areas are.
Hovda: Parents are often so shocked when they come into the emergency room to see their child - they say, "well they were just on a small bicycle" and they weren't going but two or three miles an hour. How could this be so life threatening? Well, it has to do with physics - how much force the head must endure, not to mention that your moving.
Narrator: For Science Today, I'm Larissa Branin.