Children have poorly developed fragile and flexible neck muscles. When a forward-facing child's heavy head is thrust forward in a crash, the child suffers an enormous amount of stress on neck. If the spinal cord stretches too far in a crash (a mere 6mm) the child may suffer paralysis or death. The young child's cervical vertebrae are not strong enough to protect the spinal cord adequately when forward-facing in a frontal crash. As an example, an average three-year-olds head weighs on average 2.7kg, which means that in an accident at only 50km/h the head weighs 270 kilos! In the event of an impact using a rear-facing child seat the whole of the child's back takes the impact instead of only where the harness touches the body, consequently protecting the much more vulnerable neck, head and spine. The risk of serious injury or fatality has been shown to be five times less while travelling rear-facing.