Extreme cold adaptation in humans, part 1.

It’s spring. We’re in the sea more or want to be, stretching out swimming times or wanting to. It’s probably more appropriate to talk about cold now than during the winter, because we are coming into the most difficult time of year for distance swimmers.

In the winter many stop sea swimming or switch to wetsuits. Those of us who keep swimming skin through the winter do it for the challenge, and only think about relatively short exposure times.

This is following a discussion on USMS time back. American swimmer Mike N_ (Hi Mike!), who  engaged in a fantastic Open Water swimming holiday around Britain and Ireland…in January (crazy man)… directed me to a great paper on extreme cold adaptation in humans.

At various monthly meetings with Eilís for both of my Channel visits, and much to the annoyance of others swimmers wondering when I’d ever shut up (remember the recent introversion points), and going back further to my early days open water swimming, I kept coming up against one question no-one could really answer for me.

All things being equal, especially body size and insulation, why can one person stay longer in cold water than another?

Everyone prevaricates and says “experience”. I say why? They say “mentality”. Why? “Personal strategy”. Explains nothing really.

(Personal strategy is what I could call something like “I tell myself it’s warm“).

These were insufficient answers for me. Yep, geek. I wanted to know. Had the answer been something reasonable I would have forgotten about it. And remember, long swims in cold water, with that personality I mentioned the other day? Well, it’s hard to think about girls in bikinis on your tenth cold lap of Sandycove.

Here was my thinking: Think of a human as a “blackbody”. A blackbody is a physical method of simplifying calculation problems. Instead of dealing with a complex shape like the human body, think of it as a sphere. (It’s where physicist jokes about spheroid chickens in a vacuum*  come from. Those are funny jokes by the way, just in case you are wondering).

So treat two people who are roughly the same size and weight as a sphere. Their surface area is the same so surface area to volume ratio is the same.

Let’s say they have around the same fat percentage. And that the water temperature is the same.

So we have similar figures which should all give a measurement of heat loss: The amount of heat loss of a sphere is directly proportional to surface to volume ratio (large bodies lose heat more slowly than small bodies. It’s why polar bears and some sea swimmers are big).

The rate will also be directly proportional to the temperature difference between the medium and the body. Heat loss will be mediated by insulation properties (fat).

Now setting aside the fact that there is little research that I could find in this area (but not none) predicting heat loss in humans (I even logged a question into the Wolfram Alpha forums), we have a hypothesis: heat loss in water is directly related to a short list of physical factors.

Here’s another way of looking at the same problem with which you’ll be more familiar. New or For Sale houses now in Ireland require a new Energy Rating. That figure gives how well the house performs from a heat loss point of view. If you combine this figure with the number of Degree Days (number of days in Ireland which the temperature is below 15.5C when you want the internal heat to be 18C) you can come up with an equivalent estimate for heating costs over a year, regardless of house shape.

But we can see that the issue of duration in cold water is not answered by treating people as a black-body radiation problem.

(If it was possible, I probably would have an answer to my Wolfram Alpha question, and we would have simple swimmer charts which say if you weigh W, have X body fat percentage, then your exposure duration in X degrees of water would be Y time.)

Something therefore must have been missing from my visualisation. Computer or calculation models are derived by coming up a certain set of basic principles, inputting some real world measurements, and seeing if the output mirrors the real world.

What did I not consider?

An answer is in the next post on this subject.

*A farmer noticed that his chickens were sick, and called in a biologist, a chemist, and a physicist to help diagnose the problem. The biologist observed the chickens, concluding,I can tell you there’s something wrong with your chickens, but I don’t know what’s causing it.” The chemist took fluid samples from the chickens back to his lab, and returned saying, “I can tell you what’s infecting your chickens, but I don’t know how they got it.” Meanwhile, the physicist had been sitting on the floor, scribbling madly on several notebooks worth of paper. Suddenly, he jumped up, exclaiming, “I have the answer, but it only works for spherical chickens in a vacuum.

Go to Part 2 of Extreme Cold Adaptation in Humans.


6 thoughts on “Extreme cold adaptation in humans, part 1.

  1. Great article – thank you. I’ve commented before on your site and am very grateful for the well researched and written articles. I live in Vancouver, Canada and your articles have been integral in helping me navigate from shorter to longer distances in the ocean, especially when I was swimming alone.

    I am now part of an informal club of open water swimmers, and a couple of us have decided to try to swim through the winter without a wetsuit. In my personal experience temperature can get down to around 6 or 7 degrees in the winter here. Right now the water temp is still relatively high – it was around 12 degrees a couple of days ago – but I am only managing around 30 minutes immersion so far.

    We would like to try and extend the time by a couple of minutes every week, paying close attention to how our bodies react and spending the final several minutes close to shore, swimming parallel to the beach to allow for an easy exit strategy. I am very interested in any other techniques to adapt to cold water safely.

    So do you ever put on a wetsuit? And do the wetsuited Sandycove swimmers wear socks and gloves? The loss in technique I have experienced while wearing socks and gloves has been very distasteful to me, but I am also not excited about the idea of all my long swims over the winter being in a pool.

    Thank you once again!


    • Hey Roberta, yes I remember you and thanks again. It’s 11.6C here so we’re pretty similar. What you’re planning is the best idea, I can’t think of anything else, just try to make sure you plan your requirements for post-swim before you swim, because you’ll find you make mistakes and forget basic things when you are really cold. Experience is the best guide.

      No, the only time I’ve worn a wetsuit in year is to go surfing, since without constant swimming I’d get too cold too quickly and I’m pretty much returned from surfing anyway. It get to about 6C normally here also, might get down to under 5C briefly. I just have shorter swims during the worst of it in February and March.

      I can think of two experienced Sandycove distance swimmers who now wear gloves, but I haven’t spoken with them about it.

      Keep dropping by!


  2. Pingback: cold acclimatisation « musings of an aquatic ape

  3. Interesting comment tonight have a look at this clip and see the reaction of some celebs to water that is 2C. Interestingly look at the reaction of the rugby player on the left who uses these baths regulary, what the clip doesn’t show is how confortable he is getting out once the game is over.

    BTW in relation to your post: my guess is its down to metabolism and circulation i.e. by practising this through repeasted exposures your body adapts by generating its own heat and can reach the extremities easier. Similar to being able to spend longer time sitting in a sauna the more you use it.



What do you think?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.