Shivering has long been recognized as a natural way of helping a chilled body warm up, but it does the job slowly -- about one degree Celsius (1.8 degrees Fahrenheit) an hour, according to Canadian physiologist Gordon Giesbrecht. In a hospital there are many faster, more effective ways to reheat a cold body.

Giesbrecht and his colleagues have done research on how best to warm people when high-tech solutions are not available.

Many people believe the best way to rewarm someone who is badly chilled is to put them in a warm room and pack them with hot water bottles. A booklet published by the National Institute on Aging suggests that the rescuer and cold victim remove their clothes and lie down next to each other, thereby transferring body heat.

Giesbrecht believes all these techniques are effective. But they also found that internal body temperature rose faster when the victim was allowed to shiver in an emergency rescue bag or a dry sleeping bag.

According to Giesbrecht, it's more effective to put the chilled person into an emergency rescue bag or a sleeping bag and let him or her shiver. "I cover my subjects up and they warmed at three times the rate anybody else ever reported with shivering," he said.