Introduction Drowning is the third leading cause of accidental death worldwide. Many deaths from immersion in cold water are wrongly attributed to hypothermia. Humans can survive numerous hours in cold water, as seen in open water swimmers who complete endurance swims for many hours at low water temperatures. Previous studies performed on cold-water swimmers have shown distinct physiological differences in those regularly exposed to cold water compared to controls. The aim of this study was to identify whether regular cold water swimmers exhibit physiological adaptation to cold water immersion in static and dynamic conditions.

Method A prospective case-control study, where participants were immersed in cold water (12°C); once during a static immersion and once during a swimming (dynamic) immersion. Six cold water acclimatised (CWAI) participants were matched to six non-cold water acclimatised participants for body fat percentage and gender for both the static and dynamic immersions and mean changed between the two groups compared.

Results CWAI participants show a decreased metabolic rate leading to fall in core temperature during static immersion. In dynamic immersion, deep body temperature is maintained with little increase in metabolic heat production.

Discussion CWAI participants show a hypothermic-type adaptation during static immersion in cold water. In contrast, an insulative-type adaptation is seen during dynamic immersion in the CWAI participants. The onset of shivering is delayed by adaptation to cold water. Insulative adaptation benefits the cold water swimmer as there is little or no increase in metabolic heat production. The swimmer can maintain their core temperature without wasting vital energy.

Conclusion CWAI participants exhibit different types of adaptation depending on the type of immersion experienced.