It’s getting cold in here; please don’t take off all your clothes.
Part 3. Can you acclimate to brace the cold?
Dr Thomas Solomon, PhD. 28th Feb 2020.
In Part 1 I discussed the risks of winter training and in Part 2 I described the approaches you might take to help mitigate the risks of hypothermia. To conclude this series, I will help you learn from Wim Hof, Korean sea-diving women, and marine mammals, to understand whether you can acclimate to the cold.
Reading time ~17-mins (3400-words) or listen to Podcast version here.
Exposing your skin to cold air decreases your sweat rate, heart rate, and breathing rate to prevent body heat loss and conserve energy. Inhalation of cold air constricts the bronchioles in your lungs, which reduces the volume of air you can inhale per minute (tidal volume) and your oxygen consumption rate (VO2). Immersion in cold water causes similar responses but with the added danger of a greater transfer of heat away from your body. These are the reasons, as explained in Part 1, that exercise in the cold generally reduces exercise performance.
Most runners will be exposed to cold conditions at some point. Athletes competing in obstacle course races (OCR) are additionally exposed to multiple and/or prolonged water immersions and full-submersions, either through dunking, wading, or swimming in cold water and/or ice. So, today, I want to help you learn how you might be able to acclimate to such conditions.
There are plenty of anecdotes about individuals who can endure the cold for prolonged periods. Wim Hof has gained recent notoriety for his “cold endurance” feats of standing in ice while wearing just underpants. He has built a mass-following around his “Wim Hof Method” to promote well-being using cyclic hyperventilation followed by breath-holding, cold exposure and meditation. While the original “Hoff” from the 1980s was more at home on a beach, he could withstand the cold of the ocean in just his underpants (well, speedos). Our modern-day Hof, known as “the Iceman”, shares 80s Hoff’s speedo-clad cold resilience and a number of case studies using state-of-the-art methodology to probe his biology have been published. Using hyperventilation to increase sympathetic activation is not unique to the Hof; elevated heart rate is a typical response to it. What is special is the ability to sit in ice for up to around 2-hours, a feat that only a few humans on this planet have achieved. What explains that? Firstly, not many people feel the need to purposefully sit in ice for 2 hours, but the Hof has a large vasoconstriction response to cold in his skin, which retains heat, indicative of habituation to frequent cold exposure. It has also been demonstrated that when the Hof uses cyclic hyperventilation prior to cold exposure, it activates primary control centres for detecting pain/cold stimuli promoting a painkilling-like response. Furthermore, his breathing method activates cortical areas of his brain that are associated with focus during adverse stimuli, like the cold. During cold exposure experiments, the Hof uses forceful respiration (hyperventilation), which imaging studies have shown to increase sympathetic activation and glucose oxidation in vigorously-contracting respiratory muscles, generating heat that dissipates to the lungs and warms circulating blood. During cold “max tests”, the Hof also uses a g-Tummo like breathing practice, which involves isometric muscle contraction combined with meditative visualization of flames, that similarly increases heat production when people are exposed to cold.
Will hyperventilating and breath-holding help me prior to cold exposure?
There is no magic behind using prior hyperventilation to prolong your ability to hold your breath. The cells in your body use fuel and oxygen to produce ATP. This process yields carbon dioxide (CO2). When we hold our breath, our cells continue to use oxygen and our brain senses the accumulating CO2 level in our blood as an increase in acidity (lower pH), which eventually acts as a trigger for you to breathe. Oxygen saturation of blood leaving our lungs is around 99% so hyperventilation prior to a breath-hold does not increase blood oxygen levels. Instead, hyperventilation lowers the level of CO2, reducing acidity, and thereby allowing you to resist the urge to breath for longer. Essentially, hyperventilation gives you the impression that you do not need to breathe by delaying the signal to your brain that tells you to do so. Of course, the longer you hold your breath, the lower oxygen levels in your blood will drop which, if you do not resume breathing, will starve the brain and cause unconsciousness.
Hyperventilating prior to an underwater breath-hold, a practice that has long been employed by free-divers, is dangerous. Yes, it makes it easier to resist the urge to breathe for longer but lowering the safety net of the blood CO2 level can prolong the need to resurface beyond the time at which blood oxygen has dropped below a level that will cause a loss of consciousness. Drowning is not a prudent goal. So, please do not use hyperventilation prior to full body water immersion, and hence, breath-hold, in a race!
Like anyone who does out-of-the-ordinary things, Wim Hof is indeed fun to read about. But, is he some kind of wizard? Nope, just a chap who has acclimated to cold conditions over the years and uses methods to generate heat and feelings of warmth. Will g-Tummo like breathing help you during a race? No. Holding isometric contractions while trying to run is insane. Will visualising flames during running in the cold help warm you up? Who knows; but, unlike real flames, it won’t hurt, so long as you can fully concentrate on the terrain.
What about your brown fat - will that keep you warm?
The fat tissue that sits under your skin and around your visceral organs is called white adipose tissue. It has several functions, including insulative properties that keep you warm at rest and during exercise, but its starring role in your body is to store lipid (fat droplets) that can be released into the blood to be used as fuel. There is also another type of fat called brown adipose tissue, which is a thermogenic type of fat that metabolises fuel to increase body heat. Hibernating animals have plenty of it; small rodents and newborn baby humans are endowed with it, and, more recently, it was discovered that adult humans also have some of it albeit, in small amounts situated mostly in the neck and around the kidneys. Brown adipose tissue is activated by adrenergic stimuli, the two of relevance here being exercise and cold exposure, which both increase adrenaline (epinephrine) levels, activating brown adipose tissue to produce heat. For more info, my good friend, former colleague, and rock star in this field, Dr Camilla Scheele, has written a nice review.
It is difficult to study long-term cold acclimation in humans. Wim Hof’s resilience to cold through his many years of repeated cold exposure has not been followed; instead, a “snapshot” has been taken after years of practice. This would be like measuring a random athlete’s VO2max today and saying, “it is large” but not being able to say how or why it is large because you lack a detailed training log or any informative data to see whether their VO2max has changed over the years. Fortunately, evidence for cold acclimation can be found by studying Korean breath-hold women divers, called haenyeo. Studies show that their body insulation (measured as the rate of skin heat loss relative to the difference between core temperature and skin temperature) was superior to non-divers, even when body fat levels were matched, and that their circulatory countercurrent heat exchange was enhanced, reducing their heat loss. These women are also able to withstand colder water immersion without shivering. Until the late 1970s, the haenyeo had dived for around 2000-years wearing cotton suits. Within 5-years of switching to neoprene wetsuits, which prevent cold stress by reducing body heat loss, the haenyeo had lost their thermoregulatory superiority, indicating that these traditional divers had indeed developed insulative cold acclimation to their daily exposure to cold while diving. So, yes, theoretically you, like the haenyeo are able to acclimate to the cold.
The evidence suggesting that you can acclimate to the cold is compelling yet the physiological adjustments to chronic cold exposure are small, slow to develop, and variable between individuals. Athletes exposing themselves to cold weather may acclimate but my experience is that they find the adaptations to be meagre unless the exposure is rather severe and over many months. However, since some data shows that cold weather athletes have greater exercise economy during cycling at submaximal intensities when riding in cold conditions at 5oC when compared to non-cold acclimated subjects, cold weather training is prudent if your event will be in the cold - “leave no stone unturned”.
Marine mammals, like dolphins, have a very strong dive response and are able to adapt to cold water dives very rapidly and continue to allow oxygen to reach the heart and brain for long durations while being active. Our dive response is comparatively weak and cold water immersion causes a whole bunch of physiological responses that prevent efficient muscular activity in order to keep our “thinkcentre” running smoothly. As Bill Murray once said, “Son of a bitch, I'm sick of these dolphins.” (The Life Aquatic with Steve Zissou). But, just like our flippered-friends, we see a surge in blood lactate levels and hyperventilation upon rising back to the surface after cold water immersion (yes, there is a lot of cool exercise physiology data collected from Dolphins). In many people, the dive response elicits a form of panic. It is important to know that the full dive response only occurs if your face is immersed, so aiming to keep your head out of the water during a race is very sensible.
In 2010, I went diving in Silfra, a glacial melt pool in the heart of Þingvellir National Park in Iceland. On arrival, I donned my drysuit and was given the option of climbing down into the water or cliff diving into it. The latter option sounded cool and all I had read was that the water would be cold; I opted for the jump. When I hit the water, I entered panic mode. The water at Silfra tends to be just around 2 to 3°C, close to freezing - I discovered that just at the moment I broke the surface tension. I will never know how much my spleen contracted but other parts of me definitely contracted to new levels!
Just like my experience in Silfra, cold water immersion during an obstacle race can come as a shock. Full submersion will force a dive response and, when you resurface, you will hyperventilate, finding it hard to catch your breath and possibly even see stars. Knowing when it is coming and staying calm is critical. With the exception of Kevin Costner, we humans have not evolved to be aquatic and are generally not well adapted to cold water. So, the key question is, “Can you train to become cold resilient?”.
What can you do to acclimate to race-day cold water immersion?
The dive response is an autonomic process. Overriding it is essentially impossible. But being aware of the physiological signs will help prepare you for it and anticipating when the cold immersion is coming will help you reduce panic, stay calm and in control, thus minimising wasteful energy expenditure on flapping around. Besides being well-prepared with your physical condition and your nutrition and clothing (see Part 2), resilience to the cold is something both trail runners and obstacle course racers must possess. At the Spartan World Championships in 2018, a swim at the top of the first mountain summit caused chaos. The air temperature was close to zero Celcius and the wind speed was high. It felt cold, really cold. Upon entering the lake, I immediately knew the swim would be an ordeal. Sure enough, it was tough. The constant freezing of one’s skin and musculature could be felt. It was carnage - many were pulled from the race at that point, suffering from hypothermia. During the swim, I remember meeting a certain Spartan Nomad who was in similar shape to me: just about resisting the dark side. We swam together, encouraged each other, and after a few minutes of wishing I was a Dolphin, we had endured and were back into our running. After the race, I remember thinking about how useful cold water preparation had been on my OCR journey.
As I have done when teaching physiology to medical students and exercise science undergrads, there are some simple things you can do to simulate the dive response in the comfort and safety of your own home. To exploit them and help yourself “train” for the cold, developing the following methods using progressive training approaches where the duration and frequency of immersions are gradually-increased over several weeks:
IMPORTANT: If you have cardiovascular disease or asthma, do not proceed, you should consult your doctor first - there is an increased risk of complications following cold water immersion and breath holding, which can trigger cardiac muscle spasm or exercise-induced bronchoconstriction. This is not to be ignored!
Cold water hand immersion.
Repeated, short, daily bouts. Experimental and empirical evidence suggests that this may help you "fumble" through a cold race day by helping you better recovery from an immersion.
Experience the dive response. Empirical evidence suggests this will help you learn to control your breathing upon water immersion. Buy a water spray bottle from a garden centre, fill with cold water. Sit down and maintain a steady breathing rhythm. Spray water directly onto your face (5-10 sprays) and try to maintain steady breathing (you will hyperventilate and feel uncomfortable). Dry your face, rest for 1-2-minutes, repeat.
Cold water face-submersion snorkel breathing.
Train safe - never do alone. Learn to manage your reaction to the dive response. Empirical evidence suggests this will help you learn to control your breathing upon water immersion. Buy a well-fitting snorkel, adjust it so no water may inlet into the facemask. Fill a sink or a bucket with cold water. Sit down in front of the bucket/sink and practise breathing until you are breathing normally through your mouth into the snorkel. Submerge your face into the water and try to maintain a steady breathing rhythm through the snorkel (you will hyperventilate - if you feel uncomfortable, remove your head from the water). Once you feel comfortable with the face submersion, build yourself up to doing repeated and longer bouts.
Cold water shower breathing practice.
Train safe - never do alone. Master your reaction to cold water immersion and practice controlling your breathing. Empirical evidence suggests this will help you learn to control your breathing upon water immersion.
Cold water bathing.
Train safe - never do alone. Jedi-level cold water immersion (no lightsabers needed). Practice your breathing. Empirical evidence suggests this will help you learn to control your breathing upon water immersion. Experimental evidence indicates that this may help you cold acclimate BUT, as will be discussed in a forthcoming article, using cold baths as a “recovery” tool has variable effects on exercise adaptations and performance, so proceed with caution.
All of these approaches can be done in the comfort and safety of your own home. As I stress for some of the exercises above, never do them alone - always have someone with you to monitor.
What might you take home from this series?
No study has examined the effect of cold tolerance training on running performance. Therefore, there is no experimental evidence to support that dedicating large amounts of time to adapting to the cold will win you your race. Yes, investing some time on cold habituating your hands and learning how to deal with your dive response is sensible. This will prepare you for the shock of entering unexpectedly cold water during a race. But, as you continue on your quest to train smart, always focus on the areas where you will definitely make performance gains - training well, eating well, and sleeping well, and, when exposed to the cold, to use appropriate clothing and feeding approaches (as discussed in Part 2). In other words, always ripen the low-hanging fruit before reaching for the unknown.
Until next time, keep training smart!
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About the author:
Thomas Solomon is passionate about relaying scientific information to the masses and helping folks meet their fitness and performance goals. He holds a BSc in Biochemistry and a PhD in Exercise Science and is an ACSM-certified Exercise Physiologist and Personal Trainer, a VDOT-certified Distance running coach, and a Registered Nutritionist. Since 2002, he has conducted biomedical research in exercise and nutrition and has taught and led university courses in biochemistry, molecular medicine, and exercise physiology. His work is published in over 70 peer-reviewed medical journal publications and he has delivered over 50 conference presentations & invited talks at universities and medical societies. Thomas has coached and provided training plans for truck-loads of athletes and regular folk, has competed at the highest level in obstacle course racing, and continues to run, lift, and climb. To stay on top of scientific developments, he participates in journal clubs, peer-reviews grants and journal papers, and invests every Friday in reading what new delights have spawned onto PubMed. In his spare time, Thomas hunts for phenomenal mountain views to capture through the lens, boulder problems to solve, and for new craft beer with the goal of sending his gustatory system into a hullabaloo.