What is the energy cost of falling into cold water?

At ”Enjoy the cold 2014” at Ny-Ålesund we challenge the participants to test themself in different ways in different situations. One of the days we tested survival suits in cold water (2 degrees Celsius). In addition to that Henning Kaspersen from the Norwegian school of winter warfare wanted to demonstrate for us how it is to fall into such cold water in regular outdoor clothing.

We tested his resting metabolism (resting oxygen uptake) and his maximal metabolism (maximal oxygen uptake) in order to compare the metabolic response of laying into the water for some time.

His maximal oxygen uptake was 49 ml/kg/min and resting oxygen uptake 4 ml/kg/min. Standing by the water just before jumping into the water his oxygen uptake was 7 ml/kg/min followed by 13 ml/kg/min after being 1 minute in the water. The increase in oxygen uptake while staying in the water is due to the need of heat production in order to keep a normal body temperature. This “heating process” requires oxygen.

After 10 minutes in the cold water the oxygen uptake was again 7 ml/kg/min. How is that possible? Henning stayed completely still in the water and the water inside his clothes got warmed-up by heat production and less oxygen is needed to produce heat in such conditions. Every time he moved his arms or feet oxygen uptake increased because the “warm water” became exchanged with cold water that cools down his body temperature whereupon the body responds with increased heat production. After 20 minutes in the water the oxygen uptake was 15 ml/kg/min reflecting that the isolation of the clothing’s was substantially reduced making his body continuously exposed to cold water that send the signal to the body to start to produce heat.

After 20 minutes we took him out of the water – he was not able to get up him self. He did not want to go out and he thinks that he could have stayed 20 more minutes but in a less “comfortable” way than the first 20 minutes. 15 minutes (inside) after getting up from the 2 degrees Celsius water we had him to stand completely still. He was shivering a lot and his oxygen uptake was 30 ml/kg/min – just to produce heat to increase his body temperature! 

The good thing for Henning is that he is fit and therefore had an “oxygen capacity buffer” that enabled him to relatively quickly produce the heat necessary to increase the body temperature back to normal. If he had a maximal oxygen uptake lower than 30 ml/kg/min he could have had a problem! So fitness may be important also for surviving in cold water….

 

Ulrik Wisløff, Professor and head of CERG