Cold water immersion and cold-shock, the first three minutes

I’d hazard a reasonable guess that what puts people off real cold water swimming is not what I write so much about, that is, hypothermia and cold exposure over long periods. Instead I’d postulate that it is the thoughts and fear of the initial cold shock and of the difficulty and pain involved with immersing oneself and the immediate reaction thereafter.

It seems obvious that if you’re not used to long immersion in cold, then the initial pain is all you can relate to, and it becomes the whole story. I say this based on two specific reasons:

  • Conversations seem to indicate almost everyone seems to have an innate and visceral antipathy to the idea of getting into water as cold, or colder than, liquids in their refrigerators.
  • My own reactions (I am after, all my own best test subject).

In human evolution, we have lost much of the defences against cold that other mammals have. We have no immediate protection of either fur or significant fat to protect in case of sudden cold immersion. Instead we have evolved as tool-makers, and provide our own thermal micro-climate in the form of clothing. To go voluntarily into cold water without external protection therefore strips away the defences we have developed, casts us back a hundred thousand years, and we go into an environment against which we cannot win or survive.

Cold water swimmers are time-travellers, returning to a state from our evolutionary past when all modern physical advantages are stripped away, but we can still use the main tool, the primate brain, to understand what is happening.

Cold water, which in sea survival terms is defined as water as high as 25º Celsius, will always eventually make you hypothermic.

Before I get de-railed into another discussion of non-shivering thermogenesis (another day), I’d therefore say that our avoidance of cold immersion is an autonomic subconscious defence mechanism. Fire, heights,  cold, there are all environmental factors that could and would have instantly killed our ancestors, so we evolutionarily selected to be fearful of these dangers.

Along with this seemingly universal response, there are my own reactions as a trained and experienced cold water swimmer. I’ve been swimming in skin through the Irish winter since the winter of 2007/2008, in preparation for the two-way English Channel relay. Not as long as some, longer than others.

On a cold morning, even earlier in the winter, it is still not easy to start. I sometimes faff about for a while, watching the water, chatting to anyone around, fiddling with swim gear, all seem to be a subconscious avoidance mechanism. I finally get changed, and once that is done, I move quickly to the water’s edge. Because bad as it sometimes is to get in, staying out longer will only make it worse. I often find myself in those few seconds prior to immersion, whether at the edge or waist deep, standing on freezing concrete and steel steps, asking myself what the hell I am doing, dreading the immersion. And then unlike the summer, I need a few seconds to settle internally.

I’ve written before about the drop in stress hormone production that was key for me understanding the exposure increases in experienced swimmers. Though I am always a bit apprehensive prior to cold water, let’s set that arbitrarily today at about 8º Celsius, it hasn’t for a long time resulted in increased pre-swim heart rate. There’s no longer any specific strong physical manifestation of pre-cold-swim nervousness. But there remains a certain mental edginess. This is of course attenuated by the invaluable knowledge that comes to all experienced cold water swimmers: It hasn’t killed me before, there’s no reason to believe it will kill me this time. This sounds melodramatic, but it simply means that I have valuable experience, not that I consciously worry if the cold will kill me. However it is a fact that non-swimmers worry about precisely this fact. And if I, as a very experienced cold swimmer carry this nervousness, then it stand to reason that the less experienced you are with cold, the more that immersion shock worries you. I simply understand that immersion in cold water will hurt. It’s simply a fact, regardless of experience.

Back to me, standing there at the Guillamenes. We’ll assume a mid-tide, it’s not important, but it allows me to stand on the new metal platform below the steps. The water is up to my knees.

Stepping into cold water isn’t that bad. Walking down the concrete steps will make the soles of my feet cold. The rest of my feet and lower legs don’t have a high density of thermoreceptors, so there isn’t much cold pain. During deep winter, I’ll take a few slow deep breaths and ensure I feel calm. A last push on of my earplugs and make sure my goggles and cap are correctly in place. Then I splash the water on my face. Once that is done, I am ready and dive out.

The first ten seconds seem the worst (but in not in fact). For a new swimmer to deep water this is very difficult though. For cold water, relative to your experience, but the thermo-receptors suddenly start sending lots of messages to the brain, that are indistinguishable from pain. I’ve discussed thermo-receptors previously so we won’t divert there either.

So we are overwhelmed to some lesser or greater extent by the pain of cold sensations. By thirty seconds into the swim, we enter the most dangerous phase, cold shock. Humans have a mammalian diving reflex, which is an autonomic response to sudden immersion, which causes us to hold our breath, and slows our heart-rate and circulation. However cold water, and for this specific case, studies by Frank Golden identified this as water under 15° Celsius, the mammalian diving reflex is overcome by cold shock. Cold shock doesn’t occur immediately, but from 30 seconds to 3 minutes afterwards.

  • Breathing rate increased from normally around 10 breaths per minute, to 60 breaths per minute.
  • Your usual ability to hold your breath decreases from at least a minute to 10 seconds.
  • Surface blood vessels close down, causing a sudden increase in blood pressure.
  • Most critically, you may inhale or gasp, even if your face is underwater.

All these changes can lead to

  • Hyperventilation from the breathing rate increase, which can cause dizziness and confusion.
  • The increase in blood pressure can cause cardiac arrests or strokes.
  • Sudden inhalation coupled with these, can lead to aspiration of water, and drowning.

If you do not experience a cardiac arrest of stroke, there is still the possibility of swim failure, which can lead to drowning, due to water aspiration, weakness or confusion.

These are all the worst case scenarios, but all real and happen more regularly with boat crews. Regular immersion decreases all these possibilities and symptoms, but does not eliminate them. The Golden studies mentioned above show cold shock can be reduced by 50% after only a week of cold showers. Fitness also decreases the cardiac arrest and stroke possibilities.

If the water is under about 8° Celsius, I feel that real shock only after those first few seconds and it lasts long than at 10° or above. I don’t really fell any above 14°.  My stroke is ragged, and I don’t try to fight it. I deliberately flail and swing my arms. My breathing rate is elevated, I am not bilaterally breathing as I usually do, but breathing every second stroke, to accommodate the hyperventilation. I swim across the Guillamene Cove, 75 metres wide, passing Ballyheigue rock, following the coast. Once I reach 100 metres, outside the cove, I can feel, for me, the worst has passed. For others less trained, the difficult period will last longer. For those with little training at all, having got through this period, they may never reach a state of comfort in the cold, the cold/pain from the facial thermo-receptors remaining strong enough that they must exit the water.

Our fears of cold immersion are based on a visceral knowledge that sudden cold water is dangerous. We usually don’t know why, but the reasons are all sound. The dangers inherent in entering cold water are higher than of hypothermia, more deaths are caused by sudden cold immersion than by hypothermia, but are ameliorated by training and regular exposure.

So swim in cold water. It will make you safer.

Extreme Winter Swimming #1

Extreme Winter Swimming #1 (Photo credit: Andrey 747)

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20 thoughts on “Cold water immersion and cold-shock, the first three minutes

  1. Pingback: Winter Swim | LoneSwimmer

  2. Greetings from Norway .

    The water in the Oslo fjord at this time is at its coldest . 4-5 celsius. I have for a month gradually been increasing my time from 30 sec. I am now at ca 2min getting use to it and loving it, having a loud alarm to make me come up . I am doing the Wim Hof (Iceman) 10 week course extending it with this extreme cold water exposing.

    Living 50 metres from the fjord I feel a certain responsibility In having to use the fjord for this hehe! .

    I have not read all your articles yet, but quite a few of them . I have not seen you mention the breathing technique and complete oxygenation of the body prior to immersion, It is part of the Wim Hof technique.
    I am assuming you are informed about this aspect? 🙂

    I am however wondering what amount of time would be a max for this type of extreme cold(Getting right back into the house and getting warm again mostly) . I talked to one that is doing 15 minutes from Hungary which sounds inhuman heheh!
    Do you have a ca. recommended amount of time that would be max for this kind of temperature ?
    I am adding ca 10 sec every 4-5 days. Could I go faster you think ?

    I dont take my head under, I swim around for a minute or so and then I stand on the bottom for a minute focusing . Should I be moving all the time ? Is not the blood from the extremities mixing more wit my core when I move ?

    Thank you for all the science and experience you are sharing . Big inspiration !

    Happy new year to you !

    Nikolai Winge


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  7. Hi Donal,
    We got 6º here at High Rock in Dublin on the 3rd of November! Brrrrrr.
    At High rock we have a steep ladder and a row of swimmers descending one after the other (like lemmings jumping off a cliff) You just have to keep going, and I always have the butterflies of anticipation and nerves, but I guess its that adrenalin, going feral, back to our natural state that’s the buzz I and we all crave.
    Bring on the winter swimming!


  8. Hi Donal,
    Once again, a really interesting post – and one that I almost whole-heartedly agree with.

    When we are taking new open water swimmers into the lakes, rivers, and sea around North Wales – one of the things we talk to them about is not starting to swim until they’ve got through the “cold shock” phase. By remaining in standing-depth water, if “bad things” start to happen (they feel panicky etc) then they can simply put their feet down.

    Certainly from my experiences on the safety teams for a variety of large mass open water swims, the majority of people that we pull out are in the first few hundred metres – for exactly the problems that you highlight above.

    Clearly, as an experienced open water swimmer, you know your own capabilities and have (over the years) built up your own experience and judgement. I feel that a strong message should be given out to new open water swimmers that the “cold water shock” is a normal part of swimming, and not to be frightened by it – but also (critically) to allow it to pass before they set off into deeper water.

    One of the ways that we get people to prove to themselves (not us) that their breathing is under control and they are physically ready to swim in deeper water is to take a big breath, put their face in the water, and exhale slowly and gently for 8 to 10 seconds – as they would if they were swimming front crawl. If they can do that without a problem – then away they swim.

    Happy swimming. Dan


  9. I didn’t really mind the initial immersion and shock what has stopped me from cold water swimming is the aftershock and shaking. I used to swim in a cold water lido and then cycle to work. The swim was fine but afterwards the shaking would start whilst getting dressed and continue for around 10-15mins during which I would be on the bike creating my own headwind. It got to the stage where I was wearing 5 layers, two of them thermal long sleeve tops plus windproof jacket, and 2 cycling jerseys.

    Liked by 1 person

  10. It’s posts like this one that make Loneswimmer my favourite blog!!! Reminded me of the following which is still very recent.

    Midway through September this year I arrived at the Guillamene, wetsuit ready to go in the car but for reasons unknown it stayed there, opting instead for budgie smugglers. If anyone would have asked me to do this previous to that day I’d have told them ‘cold water yeah you must be dreaming.’ The wetsuit is now reserved for surfing and snorkelling only.

    Learning how best to deal with and lessen the effects of the cold and especially afterdrop, has been at the forefront of this relatively new cold water swimming experience. My first real afterdrop happened when passing through Fiddown on the way back to Piltown I noticed I wasn’t wearing a seatbelt!!! Or recently after a swim at Salthill Galway I checked the price of a hot chocolate which cost €3.50 BUGGER! I thought, as all I had was €2, right I’ll have to settle for a latte! So with a smile I set the €2 down on the counter and with anticipation watched the warm inviting coffee being made. In no time at all the girl behind the counter handed me the coffee and then to my complete surprise hesitated at the €2….??? With a quick upward glance I could see that coffee was right up there with the price of hot chocolat! Oops

    The hot chocolate/latte incident could be forgiven. The car seat belt however was a very dangerous assembly. To me they are both examples of deep survival. An insight to what happens on the subconscious level when the brain is working to override unnecessary patterns of behaviour to keep you alive. If this kind of thing can happen after exiting the water then it surely highlights the dangers of it happening whilst in the water. Yes I was in my car out of the wind and with the heater up full bore but forgot to wear my seatbelt, the very thing that would likely save my life in the event of an accident. The brain was doing its job but the pilot was disengaged not listeneing and unaware.

    So is there an open water example of a seat belt? Donal has a great post on a wristwatch as open water safety device. Perhaps that’s one example, and a bloody good one! I think the best safety harness in cold water though and for that matter any situation is your brain. My mistake that day was lack of knowledge and understanding. My behaviour was impulsive and I was in a hurry, rushing around not thinking trying to find a point of reference. Almost identical to what happens when you panic minus the feeling of dangerous threat. I would argue that the same behaviour in open water would carry with it the consequence of very real panic, worry and anxiety and thus the inability to think and take decisive and corrective action, especially for beginners who will likely already be out of their comfort zone. I wasn’t one with my car I was disconnected I was cold and had a one track mind because I was rushing, I had a serious false sense of security. A dangerous assembly in any environment. A brisk walk and a light jog would have been a much better and safer idea.

    The golden rule number one that I now follow is ’’Be Here Now’’ observe, listen and feel what is happening around you. Learn to recognise what your body is telling you. Become one with the environment, enjoy and respect its shear wonder. And of course avoid impulsive behaviour, do not rush. Sprint the final 100 if you must, but do so with the strength of conviction.


    • Ha, but it’s not Don! There are very real physical limitations, as I’ve shown repeatedly. What is in your head, is the decision to accept these facts and continue to learn and improve anyway.


  11. Hi – I really enjoyed this post. Everything you say about that awful initial immersion period is so true! But if you can just tough that out it gets better and better – I find the first 3 minutes are pretty agonising – and 3 minutes at these low temperatures feels like a very long time. Well written and described!


    • Thanks Iona, honestly, I’m entirely happy with the post, a few too many digressions and it didn’t stick to what I’d aimed at. So I guess that means I’ll have to find another way to write again about it in the future!


  12. Have to say I’m not particularly looking forward to this year’s Christmas Day swim after reading that and being reminded how cold it can be!!!


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