Understanding The Claw as a hypothermia indicator

The Claw isn’t a fist. With The Claw, all fine motor control is lost and the fingers spread apart, and the swimmer in unable to close them. Remember I’ve said previously that there were no muscles in the fingers? The tendons contract due to impaired peripheral blood flow and the fingers bend slightly, like a person imitating a cat’s claw-strike.

Donal’s Claw, seen underwater

For those used to cold water, appearance of the Claw is normal, and only experience by the swimmer can track its progression from the initial barely noticeable slight weakness in the little finger, who spreads out ever so slightly from the ring finger, so slight you may not notice it has moved mild to the state at which it indicates immediate water evacuation is required, where are fingers are spread and the best will in the world won’t close them. However The Claw is not a useful external visible indicator for others, only the swimmer can accurately determine both its presence and extent.

Above, after a brief 5 minute swim at Cap Gris Nez in, CS&PF English Channel pilot Paul Foreman shows peripheral vaso-constriction in the hands,as seen by the extensive white, of an non-adapted person.

With worst case Claw, when I am in my most hypothermic state, I am still able to hold a feed bottle. Also, as experience progresses some swimmers, (including me) report the incidence of Claw decreases, but all other hypothermic warning signs are still relevant.

In fact, Extreme Dan Martin had a very interesting comment here on the linked piece above when I wrote it last year, such that is worth putting here as it adds an important piece to the overall cold puzzle:

I spoke to a hand and forearm surgeon on a swim camp in Jersey and she said that it’s due to the nerve running through your elbow. Apparently it’s one of the closest to the skin’s surface (it’s the reason why hitting your ‘funny bone’ hurts/numbs so much). She told me that when the nerve gets cold it jams on and this causes the muscles to contract causing the claw. I think it now being there when it’s very cold is that we’re not in long enough to chill the nerve down as other things pack in first!

This would have to be the Median Ulna Nerve (thanks Ryan!), which passes under the Carpal Tunnel (which when pressed on too much, causes Carpal Tunnel Syndrome).

(I was going to link a video of fingers being articulated by retraction of the tendons in an opened wrist, but decided graphic surgical video content may not be your thing).

I say all this because I think it’s important to be accurate about cold and not rely too closely on formulaic solutions or warnings. Understanding is better than rote.

Where did my Claw go? (loneswimmer.com)

20 thoughts on “Understanding The Claw as a hypothermia indicator

  1. Pingback: Developing a cold threshold scale and index | wildbigswim

  2. Pingback: Ice Mile Dilemmas – III – Black Rain | LoneSwimmer

  3. Robbie, I too am a mature medical student. You can email me to discuss research collaborations if you like – my full name ryanhuckle at gmail etc. (sorry for highjacking the post LS!).


  4. Just to clarify a bit more on the nerves of the hand etc..

    The Ulnar nerve passes by the elbow and innervates the pinky finger sensation/movement and the general finger muscles that allow us to move our fingers together (interossei muscles),

    The first sign of trouble with the Ulnar nerve will be be loosing sensation over your pinky finger, which is exclusively supplied by this nerve (this will be first to go because the nerves supplying are very superficial and exposed to the cold!)

    A little bit further on the muscles will start being affected, resulting in not being able to bring your fingers together (imagine trying to hold a piece of paper between your fingers and keep it there, or when you are OW swimming not being able to bring your fingers back together again after spreading them out).

    If the Ulnar is completely gonzo, after making a fist the 4th and 5th fingers will claw in and stay there (time to reconsider your length of stay in the water!)

    The median nerve is what passes through the carpal tunnel and innervates most of the hand. The key to tell it is affected is in 1st and 2nd fingers. When the 1st and 2nd fingers are no longer bending and you can’t touch your thumb to pinky you know it’s definitely time to quit for sure!

    I’m sure you already know all this by experience but just wanted to give a slightly more anatomical/medical perspective in case you are interested.

    Cheers for all the articles have really enjoyed reading!


      • Glad you liked it. I’ve just got into open water swimming recently and been out pretty much everyday since the nice weather hit (or warm bath swimming as I call it although none of my friends agree!)

        I’m a mature medical student and would love to study the effects of an ice bath on the elbow/hands in acclimatised ow swimmers vs control and monitor all these things to see if there truly is a clear chain of events or any difference between the two


  5. Hi Donal, this was an interesting article related to why your hands claw, but the nerve you’re referring to is the ulna nerve – this looks after open/closing movements of 2 fingers (the little finger and the ring finger), and the function of fanning apart and together ALL fingers. It is also the ‘funny bone’ nerve and it runs in the little notch you can feel on the inside edge of your elbow in line with your little finger. I was interested in the picture you took, as it looks more like Reynaud’s Disease than a normal reaction to the cold.


    • Thanks very much Ryan, I’ve updated the article. One of my kids hasReynaud’s, I remember always having to be careful of how easily he could get really cold when young, yes, the Claw does look like that…


    • I should have known the name of the nerve from last week’s anatomy lecture, but I must have been asleep then! I have heard the effect alluded to as Reynaud’s disease before, but my reaction, and that of a few others that I know, is exactly like that in Donal’s photograph (almost all of the loss of control accounted for by the ring and little fingers). What is the true distinction between Reynaud’s and a normal reaction to cold?


      • Ah sorry for confusion – the fingers of English Channel pilot Paul Foreman look like Reynauds. This is pretty common as far as I know, and there’s a wikipedia page with a good explanation. The other pic of the hand underwater certainly looks like my usual experience of ‘claw hand’ (little finger affected first!)!

        To clarify also, the ulna nerve actually runs through Guyon’s canal which is on the inside of your wrist, but you were correct originally the median nerve does run through the carpal tunnel. Sorry for correcting, just thought you’d like the correct anatomy!


  6. Because I am fat but my hand very thin, I wear neoprene gloves and socks (the rest of me normal swimwear, not wetsuit). Therefore I cannot rely on my fingers to know when to get out. I wear them also because when I get out I want to have feel of my hands (crucial to get out by the ladder and also wear clothes immediately). But now I don’t have a way to know when numbness is more than safe:/


  7. I did a 11 mile swim in 56F water 2 months ago (South Africa), challenging is not the word. Experienced the claw but like you said with experience you can handle all sorts of things. Again just realized the importance of effective mental training. I use a 50/50 mixture of Vaseline and Lanolin (nipple cream), the Lanolin helps the Vaseline to for a layer on your skin and doesn’t come off easily as compared to using Vaseline alone.


  8. Interesting stuff. I get a repetitive strain injury, have it now in fact, in my right arm and I can feel the path of the nerve down my arm and into my fingers and my hand claws like that sometimes. No relevance to swimming at all though 🙂


      • Yeah. It was new to me and can’t remember now who suggested it. But I was saying I suffer with my hands getting cold and that I couldn’t put lots of Vaseline on them because then feeds became tricky and goggles ended up covered in it. They said, put some on your elbows and your hands won’t get as cold. It’s now part of my normal routine… nice layer of Vaseline on the elbows and far less clawing and cold in hands. Couldn’t work out why it was effective but your post gives it a perfect context!!


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