Leg exercise and core cooling in an insulated immersion suit under severe environmental conditions

This study was conducted to examine whether the greater rate of heat production through intermittent leg exercise would offset an elevated rate of heat loss and thereby decrease the rate of core cooling during immersion in severe conditions when wearing an insulated immersion suit.

On two separate days, seven male subjects were immersed in 2 degrees C water with air temperature of -2 degreesC, wind speed of 5 m x s(-1), and waves of 30-40 cm high. Subjects wore wool underwear, flight suits, and neoprene immersion suits. They were immersed for 180 min while remaining passive (NonEx) or performing moderate leg exercise for 5 min every 20 min (LegEx). Metabolism, rectal and skin temperatures, and skin heat flux were measured. Subjective evaluation of thermal and physical comfort was obtained.

After 180 min core cooling was less in LegEx (0.3 degrees C) compared to NonEx (0.9 degrees C). This was attributed to a 31% increase in total heat production, but there was only a 21% increase in total heat loss when performing leg exercise compared to lying still. Leg exercise also improved thermal and physical comfort.

The results suggest that wearing an insulated immersion suit under extreme environmental conditions and 5 min of leg exercise every 20 min might improve heat balance, resulting in a net heat gain (10%) compared to lying still in the water. As a result, shivering intensity is reduced, core cooling rate, and thermal and physical comfort is improved. This procedure potentially provides a practically significant survival advantage at sea and also under severe conditions.