How swimming in cold water affects muscles

After reading about how so many OW swimmers swim without wetsuits I decided that I needed to toughen up.  Mau took me to his 20C ocean water pool for my first cold water pool training.  Our objective was to do 1-3k; it was really mentally hard as I was constantly looking at my watch and the laps were not increasing fast enough. The first 1k felt ok, but during the 2k the coldness had entered my body; my toes were numb and I couldn’t feel my hands. I was swimming fast because I wanted to get out. After 2k, I decided I needed to warm up and went to the indoor pool. What happened here was very weird; I got into the indoor pool and I had no strength. The water temp was probably 26C so it was significantly warmer than the outdoor pool but it still wasn’t as warm as the pools I usually swim in.  When I started swimming I could not dig down with each stroke and find power. Usually when I am tired, I can find power within tired muscles but I couldn’t feel anything. My arms felt empty. I was also doing 24-25 strokes a lap which is much higher than my average.  I extended the length of my strokes and slowed down my turnover but I couldn’t decrease stroke count. It was completely un-gratifying.  I am convinced that I need to do more cold-water training so my muscles get used to these adverse effects.

The rest of the day I was in a state of exhaustion and in total we had only done 3k. What happened to cause such unfavorable effects on my muscles? I searched Google for “How swimming in cold water effects muscles” but got mostly hypothermia explanations and the water temp was not cold enough be qualify for hypothermia. Mauricio has a theory and I will post it here. But I would love any medical professionals or anyone who might have an idea to chime in.

“What I think is happening is that because of the drastic temperature change, our bodies are led to believe that we are swimming in much warmer water than what it actually is.  Our bodies feel changes in temperature very dramatically when the temperature changes SUDDENLY, and that is what happened today.  So, our bodies adjust as if the water was hot.  So, what do our bodies do if the water is hot (remember, our bodies thought that the water was much hotter than what it actually was)?  They immediately try to cool the system down. The body’s biggest concern is the brain and internal organs, so warm blood flows away from our core to our extremities and skin in order to cool our body (since the body thinks that the water we are swimming in is hotter than our blood’s temperature), leading to less blood in our muscles, muscle relaxation and less oxygen in our muscles –> Less energy.  That’s my bet. “

Categories: Cold Water, Training


7 replies

  1. Great post. This is the kind of experiential content that helps others as you troubleshoot and overcome training challenges. Swimming in cold ocean water is not a sport of the masses because of the ocean factors. It’s an element in elite military, S&R, frogman and survival training around the world, so here’s a pat on the back for every improvement, big or small.

  2. Thanks to Ellathemermaid ( for her response to the question I asked her on cold water training and acclimatization. She has quite a bit of experience with cold water swimming and is training to cross the English Channel next summer. Good luck with the swim, and thanks for your input on this matter. Copying her response as follows: “The tolerating the cold has been an interesting journey for me. I initially started open water swimming in New Zealand and all the swimming there was in wetsuits, and I would think that 16 degrees was freezing. I ditched the wetsuit last Summer, when the water was about 17 / 18 degrees, and just gradually upped the amount of time and distance I spent in the water. I lost a lot of weight (for various reasons) at the start of this year and so struggled badly with the cold. I found it really hard to do even half an hour at 14 degrees. Have put the weight back on over the Summer, which has made a massive difference, and little things like putting Vaseline on your elbows and taking cold showers helps too. Towards the end of the Summer I have continued to swim, as the temperature drops, and learnt what the signs are for different stages of hypothermia, and therefore how far I can push myself. I always have a good crew and other people there to keep an eye out / make sure I am safe. The long distance swim training camp in Cork (lead by Ned Denison) in June was also brilliant for cold water acclimatisation and also learning so much from the inspirational swimmers there. Over the winter I intend to swim at least once a week, to keep my body used to the cold, and will just reduce the time I spend in the water as the temperature drops lower. Enjoy!”

  3. Another good reply by a Dr who sent us his input on this cold water swimming discussion: “Emily admits that she has never trained in a pool at that low temperature, so she doesn’t have a baseline for what her strokes/lap should be in the cold environment. In the situation described, she moved from salt to fresh water (less buoyancy), and probably never fully got warm between the two. Did she stretch before entering the pool, as she normally does before pool training? And finally, the mitochondria, those little subcellular engines that provide the energy for muscle contraction – they burn ATP. There are signals which speed them up or slow them down. Maybe the sequence of very cold exercise – no exercise – followed by somewhat cold exercise without stretching caused low mitochondrial activity. But, all of this is just a guess”

  4. From my brillant Aunt (Diana Kunze, who despite being a Neurosciences Researcher and Professor, has not figured out how to leave a comment on this blog!)

    “I think the exxplanation about diversion of the blood to the skin is probably correct but it involves some central nervous system adaptation occurring to “reset’ the thermostat for temperature control..
    That happens in other parts of the autonomic system- for instance in blood pressure control.
    It is a cool question (I am very interested in how the brain resets its control mechanisms for all kinds of autonomis reflexes). I will look into it some more and get back to you….


  1. Cold Water Swimming « Swimming the Strait of Gibraltar

Leave a Reply

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

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

Google photo

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

Twitter picture

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

Facebook photo

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

Connecting to %s

%d bloggers like this: