Tag Archives: claw

The relevance of shivering in open water swimming

- Apologies to those email subscribers who saw this earlier in the week and are seeing it now again.

For this post, let’s take all the usual pre-swim and first three minutes stuff for granted.

You’re in the water. The water is cold. And you are cold. We start there.


The water is about 10° degrees and you’ve been in for say 30 minutes (without a wetsuit). I’m picking 10° Celsius for a very specific reason, that most people will agree it’s either cool or cold, but many people will still start to stretch out their swimming times at that temperature. So 10°C and 30 minutes is a compromise. It may require colder water and longer times for some, and shorter times and warmer water for others.

The day is overcast and a little breezy. Therefore you are receiving no external heat input from the sun or the ambient temperature.

Donal's Claw
Donal’s Claw

You have The Claw and can no longer touch your little finger to your index finger. You still have 500 metres to get back to your exit point and you feel you need to warm up. So you swim harder. You metabolise more ATP, some of which provides the energy to propel your arms and legs faster, and some goes to produce excess heat, which helps warms you slightly. But your limbs are really cold and it can’t warm you enough.

Brown Fat distribution
Brown Fat distribution

Luckily , you’ve been swimming in cold water regularly and you have built-up some brown fat (Brown Adipose Tissue, aka BAT)  on your shoulders and lower back. BAT doesn’t develop all over like ordinary fat but in those specific parts of the body. You don’t realise it, but the brown fat has also been burning calories specifically to provide heat for you, as unlike ordinary white fat, BAT is metabolically active. Ordinary white fat provides energy by being an ATP store and of course it also insulates. But BAT along with some insulation, burns ATP to produce heat, the blood flows through the BAT and warms up. This is known as NST, Non-shivering Thermogenesis. NST is not sudden, it starts when you are exposed to cold and the BAT is insulating and protecting you immediately, and also providing heat.

BAT ubduced denergizationMaybe you’ve forgotten your watch, or made a distance mis-calculation or the tide is stronger than you realised, and result is the exit is still 1000 metres away. And while the BAT is useful it also consumes your energy reserves more quickly.

A kilometre is a long way when you are really cold. Now you can no longer touch your little finger to your index finger. Your fingers are fully spread. You can’t swim at the same rate you were and start to slow down. And then you get a little shudder. And then another. And then you are shivering in the water.

Shivering is the body’s last attempt to warm itself. Like with any exercise, like with all your swimming, not just at speed, your body is burning more ATP again in a desperate attempt to warm you up. Like all your metabolic processes this is an ancient evolutionary step, from the eons  before we had mastered clothes and heat, even before we’d shed our fur, cold nights on the African plains. And here are, us stupid swimming apes, voluntarily shedding our learned advantages and protections and stepping into a lethal environment where we no longer have a natural protection. And all we have left to protect us from death by hypothermia is a desperate last little biological process. A biological process that evolved … FOR LAND. Not for water where direct conduction of heat away from the body is 30 times the convection heat-loss rate of air. This isn’t the normal shivering we experience during Afterdrop, because then it is helpful for rewarming.

In water, shivering is dangerous and accelerates remaining energy and heat loss.

Shivering will not heat you in water. It will not protect you. Every experienced open water swimmer will tell you, that once shivering in the water develops you are in real danger. (And that’s excluding the fact that you were already in danger merely by being in the cold water to begin). This on our scale, where cold water itself is low down.

If shivering starts, get out of the water.

If you have started shivering you should have already been out of the water. If it happens when you are in the water, you need to get out immediately. If you are crew and your swimmer starts shivering forget about stroke counts or cognitive tests or anything else, and pull them out immediately.

Cold water swimming ability comes from experience. It’s not a talent. It is a skill. Skills can be learned. Part of the skill is developing the knowledge and experience to avoid swimming until you start shivering while still in the water. The learning process for some people (like myself) is facilitated by knowledge.


Where did my Claw go?

Cold, my favourite subject. With so many ways to talk about it.

Every year I note changes in my adaptation and responses. The fun in this, is that I can treat myself like a long-term experiment and see what happens, it makes the cold swimming even more interesting, adds more personal value to it. My main criteria is that for the last five years I’ve never been out of the sea longer than two weeks. The hypothesis therefore (and import of that) is that I never lose my hardening, the ability to swim in cold water. (It wouldn’t even be that long if I lived a bit closer to the sea).  Last year I noticed a huge change in initial cold response to very cold water, where my cold shock largely disappeared with reduction in gasping and heart rate increase and pre-cold tension.

So this year, as we are within weeks of the normal coldest sea temperatures of the year, what I’ve observed is how one of the best recognised symptoms of cold for cold waters swimmers, the Claw, is now longer appearing during the times I am currently swimming. I have extended my cold swimming times from last year and at forty plus minutes in six degrees Celsius, my fingers are still closed and my hand is under control.

Above, we see again peripheral vaso-constriction in the hands, where there is no blood flow in the fingers. As often mentioned before, peripheral vaso-constriction is the body’s response to cold, where blood flow is concentrated in the core to retain essential body heat for survival. In more cold-adapted swimmers (and others) peripheral vaso-constriction seems to occur even more quickly.

Therefore I have to admit, I don’t really understand why my hand isn’t Clawing recently. I’ve certainly been getting cold. So for now I just put it down to another adaptation and if anyone has any thoughts on this I’d love to hear them. It does help to understand also that there no muscles in the fingers. Yes, no muscles, your fingers are operated by muscles running through the Carpal Canal  or Tunnel, which connect via tendons to the bones. It’s the flexion of the muscles in your wrist and forearm pulling on the tendons that moves the fingers, but there are no actual muscles in your fingers so the fingers get cold easily, as there is therefore less blood flow.

I am NOT saying my Claw is gone altogether, just for these shorter, colder times. I have no doubt that longer swims in warmer waters, doing two hours in ten or eleven degrees will see the return of the Claw, as deep winter is not the problem for us, but spring, when temperatures are slightly elevated but swim times must be much longer.

Edit: I should explain: As muscles get colder they contract. This is what pulls the tendons in the fingers apart. The swimmer’s ability to pull is compromised. It affects also the arms and legs so the whole stroke becomes shorter and less effective.

I should also add, the extent of the Claw is determined by your ability to close or touch fingers. A mini Claw will leave you unable to close your small and ring fingers, a full Claw will mean you are unable to touch your thumb and small finger. Unless you have a lot of cold water experience and safety cover, you should not be swimming with full Claw.