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I'm looking into the science of cold water swimming from the perspective of a triathlete.

Conventional advice states that after swimming in the cold our peripheral body temperature is low and we should try to prevent this cold blood from flowing into our core.

There are plenty of do's and don'ts on many websites: eg: Do: Take a hot drink, use a blanket. Don't: Take a hot shower as it can cause peripheral vessels to dilate

However, I can't seem to find any information regarding exercising after getting mild hypothermia. eg. is it good to go jogging?

On one hand, jogging would generate body heat to warm us up. But on the other hand, muscle contraction in our legs may encourage more blood flow towards our core. What is the general advice on this issue?

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  • How could you prevent that blood from moving to the core? It's like a minute or something for a round-trip. Nov 11, 2021 at 22:04
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    @DaveNewton hypothermia triggers vasoconstriction, to reduce blood flow in the periphery, but physical activity causes vasodilation, which increases peripheral blood flow. So you can control, to an extent, the amount of blood that flows through the limbs and returns to the trunk. Nov 11, 2021 at 23:58
  • @DavidScarlett ... Severe hypothermia is a different scenario than actively swimming in a cold-water triathlon. I've never seen any research indicating that a cold-water swim followed by the remaining triathlon events is particularly dangerous, but if there are good sources available, I'd like to see them. Nov 12, 2021 at 0:53
  • @DaveNewton Agreed, and I suspect there will only be research on medically-significant hypothermia, which would involve temperature changes far greater than any mild hypothermia experienced after swimming. Nov 12, 2021 at 3:23
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    Are you referring to the phenomenon called "after drop"? That's if you completely stop exercising. As a triathlete, that isn't going to be as much of a factor since you move from T1 onto the bike and keep exercising. Also, if you are in water that is that cold, wear the wetsuit. That keeps heat in quite well, and gives a great flotation bonus. (As a former competitive swimmer, wearing a wetsuit is basically legal cheating :D )
    – JohnP
    Mar 8 at 16:45

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NO! That is, if we're really talking mild hypothermia:

Mild hypothermia – Alert, but mental status may be altered. Shivering present. Not functioning normally. Not able to care for self. Estimated core temperature 32 to 35°C (90 to 95°F).

Here is why:

Individuals should be extracted from the cold environment in the horizontal position whenever possible. Even low-intensity use of peripheral muscles should be avoided, as muscular perfusion and consequently core temperature afterdrop is accelerated by exertion

And:

the hypothermic heart is very sensitive to movement. Rough handling of the patient may precipitate arrhythmias, including ventricular fibrillation.

Even if the odds of this happening may seem low with mild hypothermia, especially in trained individuals, it is deadly when it happens.
In case of hypothermia, get the medical help at the event, and follow their instructions.


[1] https://www.uptodate.com/contents/accidental-hypothermia-in-adults - accessed 18-04-2022

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