Years ago, studies indicated that the human body can take a lot more punishment than previously assumed. For example, in 1942 DeHaven documented that people can survive falls of from 50 feet to 150 feet if the forces of those falls can be distributed over a broad enough surface and long enough time. Later, Staph, while wearing a four-point shoulder harness, rode a rocket sled and withstood without permanent damage a deceleration from 632 mph to 1 mph in only 1.4 seconds.

Head injuries are the most dangerous type of injury resulting from impacts. It has been noted that there are significant differences in skull fractures between men and women and that the thickness of skin and other soft tissue has an influence on fracture levels.About 300,000 individuals survive a head injury serious enough to result in one or more days of hospitalization. Head injury accounts for 12 percent of all injury hospitalizations. Although the majority of these injuries are minor, the long-term consequences related to severe head injury are substantial.

Less is known about the residual effects of minor head injuries, although there is increasing evidence to suggest that they are associated with a multitude of physical symptoms such as persistent headaches, as well as with significant psychosocial and behavioral problems and difficulty in performing one's job.

Motor-vehicle crashes (including motorcycle, bicycle and pedestrian) constitute the leading cause of head injury in the United States. They account for one-third to one-half of all head injuries. Falls are the second leading cause of head injury, accounting for an additional 20 percent to 30 percent of all injured persons.

When a head injury happens, some key questions can help differentiate a mild head injury from a more significant one that should be seen by a physician immediately.

If the answer to any of the following questions is yes, the injured person should undergo a thorough neurologic and physical examination either in the physician's office or in the hospital emergency department within an hour of the injury.

- Did the victim lose consciousness, even momentarily?

- Is the victim complaining of headache, nausea or vomiting? Usually these symptoms indicate an increase in intracranial pressure.

- Is he or she unable to move one side of the body, one arm or one leg? Is there any noticeable facial distortion?

- Did the victim have a seizure after the injury?

- Is there any blood or fluid leaking from the nose or ears? Are the eyes swollen shut with black eyes or a bruise behind the ear?

- Is there any question of child abuse?

- How did the injury happen? Trauma from an auto accident or a long fall (as down a flight of stairs) necessitates immediate physician evaluation.

Any injured victim who is less than completely normal neurologically should be hospitalized for 24 hours of observation. Those with a skull fracture or open skull wound should also be admitted.