When is it Too Cold to Breath Run? (Copy)
When temps get extreme, too much of a good thing becomes a bad thing
NOTE: This Journal entry is publicly available, because the information is too important to paywall.
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This past week has seen historic severe winter weather all across the continental US. A massive polar vortex has unleashed extreme cold air that has created blizzard conditions in southern Gulf coast, a week of temperatures 10 to 25℉ below historical average, and created an emergency blood shortage (please donate!). On one hand, this shouldn’t really be that big of a surprise; January is the coldest time of year for a majority of the country. On the other hand, a series of mild winters the last few years has lulled many of us runners into a state of… not necessarily complacency, but perhaps a bit of a routine where dealing with severe winter weather wasn’t too great of a concern.
Well, now’s the time to be concerned. We’re not going to go into clothing and shoe options, and other such details, as there’s already plenty of great information out there on these topics. What we are going to focus on is the issues involved with exercising in extreme cold temperatures. As Professor Myra Nimmo from the School of Biosciences at the University of Birmingham, UK, states: “To plan for a performance in the cold requires an understanding of the mechanisms underpinning the physiological response.”
And this cuts to the heart — or should we say lungs — of the issue. The Breath Runner Method is all about taking steady, deep inhales of air while running. When does that become a problem? Dr. Michael Kennedy, PhD, of the University of Alberta in Edmonton, Canada, cautioned, “If it’s a really cold day, a high-intensity run or ski could change your life.” And not for the better. Extreme cold causes extreme impacts to the body, and the body reacts with extreme responses.
When we breath in extremely cold, dry air while running, this evaporates the water from the airway epithelium, the surface of our bronchial tubes. As the epithelium dehydrates, it causes changes in airway wall structure and function. This damage triggers a release of histamine, an inflammatory mediator, which causes the smooth muscles of the bronchioles to constrict. This swelling makes it hard to breathe — it’s literally exercise-induced asthma. In a worst-case scenario, this could lead to permanent airway damage. "The inflammatory response is so large that the lungs never recover back to a healthy baseline," according to Dr. Kennedy, "They basically remodel." Additionally, the dehydration of the airways causes the body to respond by increasing mucus release. If the dehydration is severe enough, it can cause the mucus to be thicker, making it harder to clear. This combination of the sinuses and upper airways getting dried out and the smaller lower bronchioles getting inflamed and gummed up with thick mucus is a recipe for disaster.
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But again, the key question is: How cold is too cold for running? The answer is, of course: It depends. How well adapted are you to the cold? How susceptible are you to Exercise-Induced Bronchodilation (EIB; otherwise known as Exercise-Induced Asthma)? How long and how hard are you planning on running? What are you wearing? How old are you?
By and large, running in cold weather has tremendous health benefits. But here we’re not talking about “normal” cold — we’re talking about extreme cold, where health risks start increasing exponentially with every drop in degrees. As the temps plummet, most of the body’s energy is used to maintain core temperature. To conserve heat, blood flow is re-directed away from the skin and extremities towards the chest and abdomen (core). However, we’re running, so a LOT of bloodflow is going to the working muscles in the legs. The higher efforts of running are helping keeping our internal core temperature up. Presumably, we’re dressed appropriately for the weather; our extremities are covered, and therefore we’re good, right? Not necessarily.
If we normally sweat easily, we can quickly saturate even the best high-wicking cold weather running gear. In extreme cold, the sweat can freeze on the outer layer of the clothing, which will reduce our performance. Stay out there long enough in those conditions, and the surface chilling can become a source for hypothermia - the cooling of the body’s core temps. The more our core cools, the worse our run becomes. Dr. Phillip J Wallace of the Environmental Ergonomics Laboratory, Department of Kinesiology at Brock University in Ontario, Canada, states, “Overall, simply cooling the skin impaired endurance capacity, but this impairment is further magnified by core cooling.” In other words, there is an increased risk of frostbite, and potentially hypothermia, if we stay out there too long.
Also, we’re most likely wearing a face mask of some sort. While this will offer protection for our sinuses and upper airways, remember that we’re breathing out a LOT of water vapor with our exhales, and that moisture will freeze on the mask, restricting airflow. Removing the mask makes it easier to breathe, but now we’re again subjecting our upper respiratory system to cold shock, which has been shown both increase the feeling of breathlessness (technical term: dyspnea) and coughing. For those of us who already suffer exercise-induced asthma, this additional stressor can quickly push things into dangerous realms. As the late Professor Kai-Håkon Carlsen, of the University of Oslo in Norway declared, "It is important that athletes at risk are monitored through regular medical control."
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Yeah, but… How Cold is TOO Cold? Unfortunately, it’s not an easy question to answer. Dr. Hannes Gatterer, Ph.D., of the Institute of Mountain Emergency Medicine (Eurac Research) in Italy states, “Despite the obvious requirement for practical recommendations and guidelines to better facilitate training and competition in such cold environments, the current scientific evidence-base is lacking." What IS known — and which should be blatantly obvious — is that the longer one is in extreme cold, the greater the health risks. As explained by Dr. John W Castellani of the Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, and Professor Michael J Tipton of Extreme Environments Laboratory, Department of Sport and Exercise Science, at the University of Portsmouth, UK: “Participants in prolonged, physically demanding cold-weather activities are at risk for a condition called "thermoregulatory fatigue." During cold exposure, Castellani and Tipton explain, “the increased gradient favoring body heat loss to the environment is opposed by physiological responses and clothing and behavioral strategies that conserve body heat stores to defend body temperature. The primary human physiological responses elicited by cold exposure are shivering and peripheral vasoconstriction. Shivering increases thermogenesis and replaces body heat losses, while peripheral vasoconstriction improves thermal insulation of the body and retards the rate of heat loss. A body of scientific literature supports the concept that prolonged and/or repeated cold exposure, fatigue induced by sustained physical exertion, or both together, can impair the shivering and vasoconstrictor responses to cold,” which creates thermoregulatory fatigue. As our body loses its ability to maintain central thermoregulatory control, we face an increased susceptibility to hypothermia.
This phenomenon has been termed “Hiker’s hypothermia”, which is basically the polar opposite (pun intended) of the “Boiled Frog” analogy. The increased strain of the extreme temperatures coupled with the already high level of stress induced by running can conspire to impair our ability to accurately judge the level of danger we are subjecting ourselves to. And it doesn’t have to take a long time for this to happen when the temps are low enough. Jiansong Wu, Dean of the School of Emergency Management & Safety Engineering in Beijing, China, notes, “The high physiological strain at the very beginning moment of cold exposure can significantly affect the ability to make correct judgment and action." In other words, don’t be a hero. There’s very few of us out there who are truly adapted to running in sub-zero ℉. And even for those who are, Dr. Castellani notes, “The few studies that have been done suggest that aerobic performance is degraded in cold environments.”
Specific to the Breath Runner Method, there’s important paradoxes about exercising in the cold of which we must be aware. Not the least of which is: it’s easier to go harder, and that’s not always a good thing. As Dr. Oleg V. Grishin, of the Research Institute for Physiology in Russia states, "Under cold conditions the decrease of energy expenditure is the natural phenomenon." The less energy expended, the more available to do the work! But it’s exactly this phenomena that can lead to trouble.
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Thomas J. Doubt, of the Naval Medical Research Institute’s Hyperbaric Environmental Adaptation Program in Bethesda, MD, cautions, "Ventilation is substantially increased upon initial exposure to cold, and a relative hyperventilation may persist throughout exercise." So even though we feel like it’s easier, our body - especially our respiratory system, is in over-drive. With prolonged exercise, he notes, “ventilation may return to values comparable to exercise in warmer conditions. The oxygen demand of exercise is generally higher in the cold, but the difference between warm and cold environments becomes less as workload increases. Heart rate is often, but not always, lower during exercise in the cold.” Sounds OK, right? Ready to boil that frog yet? Think about it, and again, we’re talking about extreme cold — it feels relatively easier to run in the cold from an exertion standpoint, but we’re also using a greater amount of oxygen to do the work, which requires a higher breathing rate, which is subjecting our respiratory system to greater stress.
Linda Eklund of the Division of Medicine at Umeå University in Sweden discovered, “Elite cross-country skiers are regularly exposed to cold, dry air and have a high prevalence of asthma compared to the Swedish population. Heavy exercise during cold air exposure at -15°C/5°F induced signs of an airway constriction to a similar extent as rest in the same environment. However, biochemical signs of airway epithelial stress, cytokine responses, and symptoms from the lower airways were more pronounced after the exercise trial." In other research, she concluded that healthy individuals performing short-duration moderate- and hard-intensity exercise in sub-zero temperatures responded with lung function changes and an increased airway permeability (structural changes of the airway wall which result in its thickening from scar tissue, airway hyper-responsiveness (AHR), and potentially a progressive irreversible loss of lung function).
Dr. Eike Marek of the Institute for Prevention and Occupational Medicine at the Ruhr University Bochum has found that athletes who exercise in extremely cold air have “changes in the lung epithelial cells caused by inhalation of cold and dry air." His research found that the water vapor of exhaled breath in extreme cold air conditions contains a number of chemical markers, including hydrogen peroxide, which is described as an indicator of airways inflammation. “The concentration and release of hydrogen peroxide increased after exercise in cold air, [which] points to an increase in inflammatory and oxidative stress.” Researchers from Beckett University and Trinity University, both in Leeds, UK, found that in cold temperatures, oxygen requirements for exercise was significantly higher than in warm conditions. This increased oxygen demand at the same exercise intensity ultimately leads to an earlier onset of fatigue, and possible early cessation of exercise. This could seriously heighten the risk of hypothermia if we’re out running in the trails, getting good and sweaty, and then find we have to start walking. It doesn’t even need to be extreme cold for this to be an issue. Core body temperatures as low as 33.3°C/92℉ have been observed in 18.3°C/65℉ conditions.
So the danger is: very cold air makes it easier for us to go harder, because the need to keep the body’s core temperature up over-rides our uncomfortability of being in the cold. But in extreme cold, high efforts which require deep breathing to power the muscles may cause damage to the respiratory system. Your lungs won’t freeze, but push it hard enough, and they’ll never be the same. Dr R J Shephard, Professor Emeritus of Applied Physiology at the University of Toronto, Canada cautions, “An increase in the intensity of physical activity may be counter-productive because of increased respiratory heat loss, increased air or water movement over the body surface, and a pumping of air or water beneath the clothing. Shivering can generate heat at a rate of 10 to 15 kJ/min, but it impairs skilled performance, while the resultant glycogen usage hastens the onset of fatigue and mental confusion.”
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There’s other aspects to extreme cold to which we must acknowledge. Dr. Gordon Giesbrecht, also known as ‘Professor Popsicle’, who runs the Laboratory for Exercise and Environmental Medicine at the University of Manitoba, Canada, cautions, "Cold exposure also elicits an increase in pulmonary vascular resistance." In other words, it’s not just our respiratory system that’s working harder. Our heart is under increased strain. Dr. Tiina Ikäheimo of the Center For Environmental and Respiratory Health Research at the University of Oulu, Finland, found that exercising in extreme cold often "augments cardiac workload in persons with coronary artery disease more" than it does in relatively benign temperatures. Dr. Alan Ruddock, Ph.D., Associate Professor of Sport Physiology and Performance at Sheffield Hallam University, UK, wrote the chapter on Physiology and Risk Management of Cold Exposure in the book Extreme Sports Medicine. He minces no words: “Declining body temperatures are associated with reduced dexterity, shivering, poor muscle co-ordination and force production, amnesia and cardiovascular strain that might challenge human survival let alone performance.” When’s the last time you had a cardiac stress test done?
Running in extreme cold AND at altitude compound the risks. Researchers at the Sport Mountain and Health Research Centre, University of Verona, Italy found that when compared to single stress exposure, exercise performance and physiological and perceptual variables undergo additive or synergistic effects when cold and hypoxia are combined. Once again, the more extreme the circumstances, the risk factors don’t multiply — they increase exponentially.
Age is yet another factor that can’t be dismissed. Dr. Liron Sinvani, M.D., an associate professor of medicine at the Donald and Barbara Zucker School of Medicine at Hofstra/Northwell in Hempstead, NY notes, as we age, most people tend to lose muscle, a condition known as sarcopenia. Muscle density provides insulation and generates heat. Older adults are also more likely to have thinner skin, making it easier for heat to escape, as well as decreased blood flow in the skin. “All of these things culminate in a reduced ability to regulate their body heat,” putting them at greater risk for danger in cold weather, Dr. Sinvani explains. Of course, if we stick to a well-balanced run training program which includes strength and conditioning exercises, we can help reduce our risks. As researcher Juhani Smolander of the ORTON Research Institute in Helsinki, Finland, found, while enhanced aerobic fitness may not give additional protection against core cooling in the elderly, it did seem to attenuate older subjects' heightened blood pressure response to cold."
Another aspect of extreme cold that not many runners think about: what happens to our sneakers? Researchers at the Department of Physical Medicine and Rehabilitation at the Mayo Clinic Sports Medicine Center in Rochester, MN found that the colder it gets, the more significant the reduction of shock attenuation in most commonly used running shoes. Their conclusions are fairly blunt: “These findings have important clinical implications for individuals training in extreme weather environments, particularly those with a history of lower limb overuse injuries.”
Again, and this can’t be stressed enough — You Do You. There are a whole host of known benefits to running in cold weather. But when the temperatures start to get extreme — it’s generally acknowledged that temperatures below -15°C/5°F qualify as extreme — it’s time to start questioning one’s rational for running in those conditions. As I often tell my Age Group athletes, if your mortgage isn’t dependent on the results of your next race, chances are you’re better off doing something a bit less strenuous.
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