Why is traditional marine advice to stay still, rather than swim vigorously, if fallen in cold water?
Traditional marine advice says that, if one falls into cold water, it is better to stay still rather than try to swim (unless the shore is so close that you are absolutely able to make it) to extend the survival time because heat loss is greater when swimming than staying still.
However, I have also heard that, in cold water, people need to swim FAST in order to keep warm and prevent hypothermia by generating more body heat, and slowing down means trouble.
These two are contradictory sayings. Is there any scientific research confirming which is true? Does it make a difference if one is a marathon swimmer who is trained to swim 6 hours or more in 15 - 16°C, compared to a swimmer who only swims in warm (>24°C) pools or sea?
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Because swimming takes energy that your body could be using for heat and instead uses it for movement.
The more energy you use in cold water, the more your body cools off. If you cannot climb out of the water, conserve body heat by remaining as still as possible and reducing the amount of your body exposed to the water. Protect your critical heat loss regions: the head, sides, armpits, and groin. Do not swim unless shore, a raft, or an overturned boat is nearby. Swimming accelerates heat loss. Remaining still in the water increases your survival time.
Swimming may give a feeling of warmth but it accelerates muscle cooling. The body may produce more heat when swimming but it is also more quickly lost from the arm and leg muscles. Once these muscles cool, swimming becomes more difficult or impossible.
Note that if you have a life jacket, then the Heat Escape Lessening Position is recommended.
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If you are swimming or vigorously treading water, two things will happen that make you colder:
- significantly increased rate of blood flow out to the moving muscles in the arms and legs, which are long and thin and have a lot of surface area to dump heat
- increased heat transfer from your skin to the water, because a constant flow of new cold water will replace the still water immediately next to the skin which has already been warmed by your body. This will happen anyway but happens faster if you are moving.
My understanding is that whether this is a good or bad thing depends on how cold the water is and how much heat you’re generating. An Olympic swimmer training in a pool might prefer something on the lower end of normal pool range (i.e. still not very cold).
I’m honestly not sure in an open water race whether it’s a performance issue, a comfort issue, a safety issue or just something athletes say to psych themselves to go hard. It could be that when you’re swimming hard, the endorphins numb the perception of cold. There’s a chance these effects are non-linear, and the difference in heat loss between floating/swimming is large, but moderate/fast is smaller, and if the difference in heat generated rose with speed in a non-linear way there could be some speed at which the lines of those graphs cross and speed is favorable. If I find a link I’ll post it. But there may not be a rule of thumb; it may depend on exact water temp, race length, and physiology of the individual.
But an ordinary person in a dangerous survival situation would not want this enhanced cooling.
This post was sourced from https://outdoors.stackexchange.com/a/21542. It is licensed under CC BY-SA 4.0.
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