Heat production during cold water immersion: the role of shivering and exercise in the development of hypothermia.

Immersed in cold water, the body loses heat to the external environment. Heat production rises in order to compensate for heat loss by shivering or exercise. The aim of this study was to determine whether heat production is more successfully maintained over a long period of time by physical activity than by shivering when a human being is wearing an insulated survival suit and is immersed in cold water, and whether increased insulation of those parts of the suit exposed to water improves protection against heat loss with all-around standard insulation of the suit. Nine men participated in four series of experiments each lasting six hours. They were immersed in water at 3.6 degrees C and wore survival suits. One series of trials was made at rest, one series with periods of work, one series at rest where the insulation on the back was increased by 10 mm, and one series at rest with a survival suit featuring a new type of insulation. The results showed that periods of work give better chances of survival than continuous heat production by shivering in a well insulated suit. Furthermore, an extra layer of insulation in the back region significantly improved the thermal status of the subjects. When both rectal and skin temperature change at the same time in the same direction, there is a stronger influence on thermoregulation than when rectal temperature alone changes.