How to not get cold, what to wear and how – winter swimrun is around the corner!

Next week the much dreaded Hellas Frostbite Swimrun race takes place, a winter swimrun in Stockholm, Sweden. We know for a fact that the organizers have prepared for the worst. If the ice will be to thick to break, they will saw their way through and create an ice channel for the racers to swim in.

Brrr. It doesnt get much colder than this. 

To prepare for the race, have a look at our guide below, on what to think of when doing a cold swimrun race.

/The WoS Team

Shoes 2015OtilloRace

Today we talk with our WoS expert Nic. Nic is a PhD student in public health sciences at Karolinska Institutet, also working as an expert investigator at the Public Health Agency of Sweden, the national government authority with responsibility for public health issues.

Hi Nic and thanks for taking the time to talk to us at WoS. You are a swimrunner with vast experience, having done your fair share of races and adventures in difficult and cold conditions?

Nic: Hi and thanks for having me. Yes, I started swimrunning already in 2008 when preparing for my first ÖtillÖ race in 2009. We have a house along the ÖtillÖ route so I’ve spent my upbringing running on these islands and I’ve been windsurfing the area for many years, so I know my way around.

Nice, given your expert opinion, what should a swimrunner think about before hitting the cold water.

Nic: Well, it’s important to understand the basics behind why you get cold. As long as your body temperature fall short of 37 degrees Celsius it’s in a constant state of negative heat transfer, losing moisture through either sweating, insensible perspiration or respiration. If maintained over time this can lead to dehydration and make the body more susceptible to hypothermia and other cold injuries.

Water conducts heat away from the body up to 25 times faster than air, and adding the wind-chill factor to this, your heat loss will become even greater. When wearing a wetsuite you are protected from the wind-chill and the high loss of heat in the water, but you sweat more which could lead to higher heat loss when swimming if your wetsuit is not a 100 % fit allowing fresh cold water in. To sum up: You basically lose body heat from low outside temperature, rain, sweat, water and wind.

What happens when the body loses heat?

NIC: The body shuts down systematically starting with fingers and toes, undergoing a physiological amputation of the extremities to protect vital organs.

bodyloosing heat

There are 4 zones on the body which are better at releasing heat than the rest, the crotch, armpits, neck and head.

So, what should a swimrunner wear?

Nic: Most swimrunners prefer not to add any extra insulation, but for some races it could be smart to do so. If you’re a thin person with low body fat %, have an effective metabolism, a low-level of fitness or fuel store capacity, you might want to add an extra layer or two, especially if you’re doing a longer race meaning low energy levels towards the end. It happens from time to time that people quit races because of being too cold in the final stages. Having a neoprene cap and gloves available in your equipment could be a good idea, or lots of Vaseline to protect the exposed areas around the head and neck.

But shouldn’t you wear anything underneath and if so, what?

Nic: This is a tricky question. I would say it completely depends on the type of race you are doing, and when in the season. But to start off. If you are going to keep the wetsuit on for the entire race, I would say it doesn’t really matter what type of material you wear underneath, just as long as it feels comfortable and doesn’t give you any chafing. You will get sweaty and most likely wet when swimming, and since the wetsuit doesn’t allow for air to circulate  and release heat, having a material that ‘breathes’ away the redundant heat won’t help you at all.

layer breatability

Now if you on the other hand plan to cab-down during the race, then it’s another matter. During these moments you will have the possibility to release redundant heat why you should choose a material that does this well. Both polyester and wool will do this for you where the difference between the two is that wool also keeps you a bit warmer than polyester. Here I would go for a regular t-shirt layer and boxers, or perhaps knee-long boxers. I would choose a two-piece so I can take of the t-shirt if necessary.

So, the combination of a wetsuit and functional clothing is a bit tricky?

Nic: Following the logic of how the body protects itself and where it disposes of heat, the current available wetsuits would have to be re-constructed to allow for maximal ‘during-the-race’ adaptation. As it is now, the swimrunner don’t have that many options to stay warm, apart from having a hundred fit wetsuit and protective clothes underneath, hoping for the best during the race.

Because when you pass a certain point of losing body heat, you won’t be able to make up for it unless you quit the race completely. And on the other hand, if you need to release heat, you basically have the option to cab-down or take the suit off, and swim with it slightly open to allow water in and cool off this way. Both very basic and rough options and not the fine-tuning we are used to with e.g. general running or hiking clothes.

To be most effective in reducing excessive heat a wetsuit should be possible to ventilate around the neck, around the armpits and the crotch or that you have the ability to adjust the water intake during the swim, just enough to keep you levelled. Adding zippers to the heat zones mentioned above, like with traditional outdoor clothing, would be optional, but that would most likely also impede on the flexibility of the wetsuit. But, here the industry has lots of potential to develop the ultimate swimrun wetsuit that can ventilate while running and swimming.

So all in all and to sum-up, having an extra layer can be good for longer colder races if you’re a person with a low % of body fat who usually get cold easily?

Nic: Well that’s the basic idea and the best way as always is to get out there and make a trial swimrun to get to know your body and gear. Pay attention that not all wetsuits are equally thick making them keep or lose heat differently in the water and that they really close shut around the neck, other than this just try your way through and also with the eventual clothing you want to have underneath.

And when racing, what I usually do before entering a longer running segment is to give the wetsuit a thorough rinse by opening up around the neck with my hands and take in plenty of cold water. Doing this 2-3 times helps cool off the body quickly before starting to run. If you are uncertain, buying a full suit is always the better option since you can cut your way through at your own convenience.

Okay Nic, thanks for the help. Good luck with your swimrun this year, any last thoughs?.

Nic: No problem and thanks, and yes, we must not forget about the energy levels since they are an important part of this subject, a post for the future!


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