cold acclimatisation*


02/12/2011 by Carl Reynolds

don't let your pants freeze

I’m not swimming today, so thought I’d share what I’ve been gleaning from sources various about cold water acclimatisation. In a nutshell then –

1. as your skin gets cold it forms an insulative layer to protect your core. And reduces heat loss, as heat moves more quickly between different temperatures. In other words, the closer your skin temperature to the water temperature, the less heat you lose from your core.

2. the core stays warmer than the outside…for some time. According to what I’ve read a rectal thermometer will confirm this, but I have not experimented.

3. fat helps to insulate.

4. brown fat may or may not expand from its vestigial remains and generate some heat.

5. you lose heat from the outside of your body slightly differently. Extremities, like fingers, have less fat and lose heat quicker. Putting hats on reduces heat loss through your head, but does not account for the major part of your heat retention – despite the mythology that most heat is lost through the head. See here for a taster.

5. swimming regularly in cold water changes your ability to generate heat and maintain heat. In scientific terms you adapt your thermogenesis response.

6. you improve your body’s ability to only need to shiver at a lower temperature.

7. in freezing water you’ll stay alive for up to 30 minutes, but will probably drown before ten minutes is up, as you lose control of your limbs.

8. women seem to get out of cold water sooner than men…because they are smarter (generally).

For the science I looked at various on-line journals including International Journal of Sports Medicine (1987 Oct8(5):325-6), European Journal of Physiology, Experimental Physiology (2000, 85.3:321-326), Dr Jolie Bookspan (, The Lancet (1999, Vol354, Issue9191, p1733) and an excellent series of articles about cold water acclimatisation and habituation on Lone Swimmer. Which also references other scientific sources.

A comment on an earlier post also suggested that you extract more water from your blood, hence the oft observed need for cold water swimmers to pee more. But I’ve yet to find the science on this.

*disclaimer…I am not a scientist, so am open to correction, as I may have misinterpreted what I have read.


22 thoughts on “cold acclimatisation*

  1. LoneSwimmer says:

    Thanks for the shoutout Carl. I put a lot of work into those and I was disappointed by the lack of response! Do you want the meta analysis paper I referenced, I’m pretty sure you’ll enjoy it? I’ll be looking up your references also.

    • The meta analysis would be great – thanks. I also came across some research about cold shock response. It suggested that you lose it after a month of immersing yourself in cold water a few times a week, but it then stays (i.e. not getting it) for up to six months afterwards – even if you don’t swim. I can’t remember exactly where I found it, but do remember that it was a study for the military.

      • LoneSwimmer says:

        I remember reading the same thing. It might even be in the meta. During the winter I only get to the sea once a week, and I seem to retain it ok. I don’t think I have your email, so email me at donal256buckley at gmail?

  2. Ian says:

    Carl, an excellent post. Despite a general understanding of the body’s reaction to cold water, I don’t feel I know enough detail, so it’s good to know that someone is trying to sift through the research. I look forward to more debate in the lido cafe

  3. pip says:

    I sure we can investigate this subject further
    I will find a rectal thermometer from somewhere (probably ebay & listed as used or faulty)
    And bring it to the lido on Sunday Carl you just bring yourself along.

    I have no research to back this up but in evolutionary terms I believe we are all, already adapted to withstand these temperatures.
    Unfortunately on an individual basis we have become acclimatised to modern living and our lasy metabolisms fail to cope.
    If we spent a lifetime having to live in say 0 to 1 degrees we would probably note have an adverse reaction at say -2

    I truly believe there is little or no benefit from a neoprene hat excepting psychologically
    And therefore if you believe it does not help you do not need one

  4. Patricia Sener says:

    I don’t know that I agree with all of this….hands and feet get cold not because they have less fat, but because your body is bringing the warm blood to the core and letting your extremities take a hit to keep you alive. When you cease exposure to the cold water, the process reverses, hence what is known as “afterdrop”, the core temperature drops in your bodies attempt to revive the extremities. Afterdrop happens minutes after you get out of the water, and why it is good to get somewhere warm fast, or suffer more intensified reaction. When I first started cold water training, my core would actually feel like it was on fire (I called it the fuzzy sweater effect). Now my body seems more intelligent in it’s reaction, and I don’t have the fuzzy swear effect any longer. I miss it, but I’m able to stay in a lot longer….

    • Patricia – thanks for disagreeing! Good to have the extra input. Afterdrop is something we talk about at the club without calling it such. We figure that a shower is no good, as it moves the cold from the extremities to the core quicker and it’s far better to snuggle up in a sauna, where you can take heat into the middle too. Seems to work – we get most of our fainters from those who take a hot shower after a cold swim; those who go in the sauna first don’t.

  5. Patricia Sener says:

    Oh, and I swam a double crossing of the Beagle Channel in 2010, hence challenging your notion that women are smarter than men:)

  6. The best text on this topic is by Mike Tipton & Frank Golden – called Essentials of Sea Survival. I very highly recommend it.

    Several chapters on how the human body cools in water, and also a discussion on “afterdrop” and the myths around it. Current science seems to indicate that afterdrop is a phenomena restricted only to the lower intestine – and hence rectal thermometer site. The theory is that this is because this area of the body is heated more my conduction, and as the body will restrict blood-flow to the digestive system in times of physiological stress, this reading is not representative of the true core temperature.

    By taking temperature reading from arteries, you see much less of an “afterdrop” effect. The body aggressively protects the core body temperature. and whether you are re-heating via a shower or a sauna, I would suggest the likelihood of fainting is the same.

    The reason why you see more fainters in the showers is probably because they are stood up, in contrast to the sauna users who will be sitting or even lying down.

    I realise this post was a while ago, and you may have done some testing – but I would be reasonably confident in guessing that with your rectal thermometer, you didn’t find anybody who was hypothermic… they will have stopped swimming long before then. It takes *hours* for a human to become hypothermic, even in iced water. Have a search on youtube for “cold water boot camp” there are loads of great videos – based on solid scientific evidence.


  7. Carl about the fluid loss: as I understand it there’s a single principle involved which is concerned with the way your kidneys regulate blood pressure.
    When you swim, your body is under higher pressure (hydrostatic pressure) than in air even near the surface.
    Also, as you become cold your peripheral blood vessels constrict in order to preserve warmth at the core.
    Both of these events reduce the space in which your blood is circulating, so your kidneys detect a rise in BP. They adjust this by excreting fluid as urine. When you’re becoming hypothermic the mechanism is called ‘cold diuresis’. That might also account for feeling faint in the shower after a swim, as your peripheral blood vessels deconstrict and your BP falls in consequence.
    Also, people do like a nice wee in an effort to warm their surroundings…I guess this tactic is frowned upon in the Lido.

  8. […] has abated, I felt cold, but not desperate to leave the water. I know from previous reading (see cold acclimatisation), that below the immediate layer of outer skin, my core was going to stay warm for some time. But I […]

  9. mauprieto says:

    Hi Carl. Interesting. Question from a cold water novice like me. One thing that people do when swimming in cold waters is sprinting and exerting ourselves to the max, thinking that we will keep warm that way. Thinking further about this, I realize that when we sprint, we are burning energy and heat faster, so sprinting should be counterproductive if what we want is to keep our core warm and swim longer in cold water. So, when swimming in cold water, it should be better to try to swim nice and easy, control our breathing and try to have our muscles relaxed. Is this the case? Should I try to swim relaxed or sprint to start improving my cold water endurance for longer distances? Thx for any light you or anybody around can shed on this!

    • My suggestion – is little and often. Then extend your range as you find it easier. Start relaxed to stretch out the muscles, then up your pace if you feel the need to.

      For myself, relaxed all through is better. It’s partly a physical thing – cold water contracts muscles, so I take it easy to start, but feel no need to be speedy. I save speed for training and the odd race.

      And it’s partly a mental thing. I think, “Yes I am cold, but I’m not dying or going to die anytime soon.” I have found that I relax into the cold. I know I’m in trouble if I cannot touch my fingertips to my thumb tip. For others there will be a different physical sign. So I separate what is going on with my body from a fantasy of what is going on! And endure the cold. And occasionally enjoy it. Be careful and daring!

  10. […] My suggestion – is little and often. Then extend your range as you find it easier. Build it up gradually and not try to push your body too much too son.  Carl Reynolds, Cold Acclimatization […]

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