Tag Archives: Brown fat

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.

Brown Fat

This is a repost with some very slight edits because of a request. I first came across the mentions of Brown Fat in early 2010. The New England Journal of Medicine (NEJM) published the first peer reviewed scientific papers on Brown Adipose Tissue in 2009. The research was undertaken due to the great concerns over growing obesity levels. Should it be possible to easily trigger brown fat growth then overall calorific consumption would increase and help combat weight issues.


“I’ve been doing a bit of reading on some new research papers on body fat (adipose tissue).

Most (almost all) of the fat in our bodies is white fat. Fat stores energy and acts as an insulator. White fat specifically, which could be up to 25% of body weight, does not generate heat.

Until last year, brown fat was only thought to occur in infants because they can’t shiver and that it disappears in adults because we can shiver and don’t need it.

However new research papers in 2009 showed some very good news for OW swimmers (though swimming wasn’t mentioned in the papers).

Most of the initial interest in this seems to be around using brown fat to act as a calorie burner to reduce adult obesity. Pity they didn’t test some OW swimmers who’d be willing to act as serious cold guinea pigs.

Apparently 20 to 80% of adults have some brown fat tissue (and women more than men). This is good news because brown fat, unlike white fat, also acts an energy generating source. It has mitochondria and can generate ATP (adenosine triphosphate*), which is the main source for metabolism, as well as acting as an insulator. (BTW, brown fat cells are only about 50% the size of white fat cells which is more good news).

So that’s good news.
Even better: Guess how you activate the growth of brown fat in the adult human body?

Exposure to cold…Yes , that simple. In case I read, they were able to stimulate it by a few short ( < 30 minutes) periods in a cold-food freezer.

PET scans showed brown fat increases around primarily the neck and upper thorax after exposure to cold for a few hours.

So when one thinks about the old stories of getting acclimated to cold by repeated exposure, it appears this process may have been activated.

(This also finally explains for me how to reconcile the whole 2nd Law of Thermodynamics with energy loss in the human body changing with acclimation, which I always thought bogus. I guess I can pull my open question from Wolfram-Alpha.)

It also explains (along of course with a rare nice sunny warm day) why I could do a fairly comfortable 40 minutes today in 8.3 degree Celsius water when 2 years I was only starting swimming without a suit around this time of year.

All this is my psychopathology. Telling me something will get you no-where, I need to understand. I’m not good at “just accept it”.

*(Ernest Maglicho has a great chapter on the energy system in “Swimming Fastest”).

Story on brown fat

6 Research papers