By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Note: This article is part 1 of a two-part series on outdoor winter sports, physiology and exercise clothing.
Outdoor recreational and competitive winter sports such as alpine and Nordic skiing, ice skating, snowshoeing, backpacking, snowmobiling, and ice climbing are commonly performed in extremely cold weather. Cold temperatures, however, have a profound influence over many body functions, and this effect is further magnified by high wind speeds.
If you’re skiing or skating into the wind, for instance, the wind chill factor increases in direct proportion to your travel velocity. Whenever possible, cold-weather endurance events should begin with participants facing into the wind and returning with the wind at their backs to avoid the unnecessary exposure of sweat-soaked clothing to icy wind.
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The Body Reacts to Cold Environments by Producing and Conserving More Heat
Exposure to a cold, windy environment prompts two major physiological responses – heat production through increased shivering and heat conservation by the constriction of blood vessels in the skin. The brain’s temperature-regulating center in the hypothalamus orchestrates these adjustments by activating the sympathetic nervous system to maintain the body’s internal temperature as close to 98.6 degrees Fahrenheit (37 degrees Celsius) as possible.
Shivering (uncontrolled, non-rhythmic skeletal muscle contraction and relaxation) has the potential to increase the body’s metabolic rate three to five times above normal during both rest and sub-maximal exercise. A considerable increase in heat production maintains your thermal balance, but it can be extremely fatiguing and distracting during winter sports that require a high degree of coordination and concentration.
Shivering generally involves the neck, abdomen, and chest muscles before it spreads to the hands and feet. The constriction of skin blood vessels decreases the flow of warm internal blood to the body’s surface, reducing the heat loss caused by being in a cold environment.
By contrast, surface blood vessels dilate in hot, humid environments. These blood vessels carry blood and internal heat to the peripheral areas of the body, causing the skin to become red, sweaty, and flushed. Peripheral vasoconstriction in cold weather generally elevates blood pressure but it often does not noticeably affect the heart rate.
Superficial vessels of the head are important to maintaining oxygen supply to the brain, but they are generally not involved in the constrictive response created by a cold environment. About 10% of the body’s heat, however, is lost through the head in cold weather. As a result, it is wise wear a suitable head covering during winter sports.
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Frostbite and Hypothermia
Extremely cold, windy environments can cause dangerous injuries such as frostbite (body tissue freezing) and hypothermia (body temperature reduction). The early signs of frostbite include tingling and numbness in the earlobes, fingers, and toes.
The extremities are most susceptible to frostbite because they have very little metabolically active tissue and depend heavily on the flow of hot blood from the body’s core. A drop in skin temperature below 22 degrees Fahrenheit can freeze tissue in less than one minute; that frozen tissue may cause permanent circulatory damage and even gangrene.
The victims of frostbite are often unaware of its danger due to the blocking of sensory nerve activity by the cold. Medical care for advanced frostbite involves a slow, controlled warming of affected areas in a clinical setting.
It is also important to not walk on frostbitten toes. Walking can cause additional damage, which can lead to amputation.
In addition, prolonged exposure to cold temperatures inhibits the body’s central nervous system function leading to hypothermia, a drop in the body’s core temperature below 95 degrees Fahrenheit. This potentially fatal condition is marked by a reduction in metabolic rate and the inability to shiver.
Someone suffering from hypothermia may have abnormal heartbeats, weakness and mental confusion. Eventually, that person may become drowsy, collapse and fall into a coma.
During winter weather, wearing wet clothing, standing in place watching winter sports or exercising is risky because it can lead to hypothermia. Hypothermia is occasionally seen after participants reach the finish line of Nordic ski races, as the rate of their heat loss remains high while the rate of heat production suddenly decreases.
Avoiding a dangerous post-exercise drop in body temperature can be prevented in several ways, such as:
- Immediately donning additional clothing
- Seeking the warmth of a building or vehicle
- Drinking warm fluids
Alcoholic drinks should be avoided in situations where you are outdoors for long periods of time (such as during winter sports). The ethanol in alcoholic drinks overrides and disrupts the body’s temperature regulation by dilating surface blood vessels, causing more hypothermia and making you numb to cold weather’s effects.
Effects of cold weather on the body during exercise depends on the severity of the low temperature, wind speed and exercise intensity. During low- and moderate-intensity exertion in extreme cold, the exercise-related increase in metabolic heat production is often too small to offset the body’s heat loss in a cold environment. As a result, shivering and reductions in nerve conduction velocities may cause you to crash into a few extra gates during a slalom race or reduce your shooting accuracy during the biathlon.
Preventing Cold Air from Affecting the Throat and Lungs
Cold air is also detrimental to athletic performance in winter sports. It causes throat irritation and aggravate pre-existing conditions such as asthma. Some people also experience chest pain (angina) due to breathing cold air, which could also explain why seemingly healthy persons occasionally experience heart attacks while shoveling snow on cold winter mornings.
Considerable water loss from the ventilatory tract also occurs in cold weather. Breathing cold, low-humidity air, for example, increases the inevitable dehydration during prolonged exercise. When inhaled air is warmed in the upper bronchi of the lungs, humidification occurs at the expense of moisture from the respiratory passages.
To avoid dryness in the mouth and burning in the throat as the result of inhaling cold air, wear a scarf or surgical-mask type protector that covers your nose and mouth, which will trap water in your exhaled air. It will warm and moisten the next breath of inhaled air, preventing unnecessary dehydration.
Several Factors Affect How People React to Cold Environments
There are several factors that influence people’s response to exercise in cold and windy weather:
1. Fitness level – Cold-weather conditioning generally increases the body’s cold tolerance by more quickly increasing metabolic heat production and skin temperature. To maintain body temperature in a cold environment, you must work at it. The more fit you are, the more work you will be able to do and the longer your exercise duration will be.
2. Percentage of body fat – People with a high amount of body fat tolerate cold weather during rest and low-intensity exercise better than others, because their larger subcutaneous fat level provides more resistance to heat loss. Studies of deep ocean divers show that their body temperature decreases much more rapidly in lean individuals during cold-water immersion due primarily to a lack of insulation.
Women generally have greater skinfold thicknesses than men, but when body fat percentages are equal, there are no gender differences in cold tolerance.
3. Acclimatization – Humans possess much less capability to adapt to prolonged exposure to cold than heat or altitude. However, repeated exposure to hands and feet to cold environments leads to enhanced blood flow when these extremities are repeatedly subjected to cold stress.
Cold-acclimatized persons also have higher circulating levels of hormones such as epinephrine, norepinephrine, thyroxine and cortisol to further increase the body’s heat generation. The military has evaluated servicemembers’ ability to tolerate cold by examining physiological changes that occur while sleeping in a cold environment.
4. Clothing – Dressing for cold weather should focus on providing just enough insulation to maintain the body’s temperature at about 99.5-101 degrees Fahrenheit. As the same time, winter garments should not cause the wearer to sweat excessively; a controlled increase in body temperature remains important for optimal metabolic efficiency. Winter clothing should be selected to maintain comfort during the entire duration of winter sports events.
Wearing multiple layers of lightweight clothing insulates the body by trapping warm air between the layers of clothing. Ideally, the innermost layer should be a polypropylene or cotton fishnet material to wick moisture away from the skin. Down or wool provide excellent insulation and are thus often selected as middle layer material.
The outer shell of winter clothing – such as a coat or jacket – should be both water- and wind- resistant. These garments should have zippers that can be opened or closed when needed to provide cooling as the body heats up or heating as the body cools down. Proper head covering is a must, as well as earmuffs, gloves, mittens or thick socks over ears, fingers, and toes.
Participants in outdoor winter sports most often overdress rather than underdress; they tend to overestimate the extent to which exercise produces metabolic heat. It’s important to dress properly for winter sports as a spectator or athlete; the exposure of skin to cold temperatures and high winds after overdressing can cause a rapid thermal drain and more quickly bring on hypothermia or frostbite.
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