Participants:

KEY POINTS

INTRODUCTION

The seasonal changes that bring colder weather do not stop athletes from training and competing. Our eclectic panel of experts rely on their clinical and research expertise to discuss concerns that are novel to this environment, and provide suggestions for preparing and protecting athletes for exercise in cold weather.

1. What are the physiological and psychological responses to cold exposure that coaches and athletic trainers should keep in mind?

Burruss: Temperature discrimination may be the first comfort factor we learn to deal with after birth, i.e., we need to seek warmth. Conversely, being cold or the need to seek shelter is a primal need and it is natural for an athlete to find working in the cold unpleasant. The typical psychological response even for professional athletes is, ?I can handle this.? Athletes rarely exposed to the cold are unfamiliar with what they can tolerate and how their performance might be affected. The opportunity to practice in the cold helps athletes know what they can tolerate, how it will affect them, and how to prepare. The concept of being comfortable with clothing, for example, goes beyond that of simple fit. It includes the confidence of knowing that what you are wearing will protect you from the elements, that you can perform in the clothing, and that you can easily deal with any clothing adjustments if environmental conditions change, such as when entering the locker room during pre-game and at half time.

Castellani: Hypothermia, which is a decrease in body core temperature, occurs when the rate of heat loss exceeds that of heat production. Heat is produced by our basal metabolism, by diet-induced thermogenesis, and by muscular contraction. By far, muscular exercise has the greatest potential to increase heat production, by as much as 10 to 20 times that generated at rest. In the cold, heat is lost primarily through radiation and convection. Physiologically, there are two responses to minimize hypo-thermia. The first is an increase in shivering thermogenesis (i.e, an increase in metabolic heat production caused by involuntary muscle contraction). Decreases in core temperature and skin temperature both play a role in this response. The other physiological response to the cold is peripheral vasoconstriction, a decrease in blood flow to the skin. These two responses help conserve body heat by two mechanisms, 1) increasing heat produced (shivering) and 2) decreasing heat loss to the environment (vasoconstriction). Other changes that occur during exercise in the cold include small changes in heart rate and ventilation. Ventilation is slightly higher in the cold at low exercise intensities but this difference is abolished as the exercise intensity increases. What is more important to the athlete is that cold air is usually associated with dry air, thus there is an increase in respiratory water loss during cold-air exercise, emphasizing the important role of maintaining fluid consumption.

Snyder: Accompanying the physiological responses described by Dr. Castellani is the potential for fatigue and a decrease in physical performance. With vasoconstriction and other blood flow alterations, circulating levels of free fatty acids could be reduced, carbohydrate utilization will be increased, as will lactic acid production as the exercising muscle has a reduced amount of blood and thus oxygen available to it. Because the main metabolic fuel for shivering is carbohydrate, shivering during non-exercise periods may promote carbohydrate depletion. As fatigue occurs during prolonged exercise and exercise intensity is reduced, heat production will also be reduced. If carbohydrate use occurs to such an extent that hypoglycemia results, then the rate of shivering will be further reduced. Core temperature will drop and hypothermia can occur. As skeletal muscle cools, its maximum strength, muscular endurance, and aerobic capacity are all reduced. The cardiopulmonary system is also affected by exercising in the cold, as ventilation rate will increase and peripheral blood flow is reduced.

Rundell: Cold weather endurance athletes such as cross-country skiers, or runners who live and train in a cold environment, typically deplete glycogen stores and dehydrate during prolonged workouts are especially at risk. It is important to remember that cold weather also depresses thirst, so athletes need to begin the workout well hydrated. Consumption of about 250 ml of a carbohydrate/electrolyte solution every 15-20 minutes during the exercise bout will help. Recent research by Seifert et al. (1998) demonstrated that ad-lib water ingestion by elite cross-country skiers was inadequate to minimize the disruption in fluid balance during 90 minutes of low intensity ski training. This implies that the athlete must make a deliberate, conscious effort to drink fluids, preferably a carbohydrate/electrolyte beverage, on a regular schedule during the workout. The increased lactate production during submaximal exercise mentioned by Dr. Snyder is also a consequence of exercising in the cold. Submaximal oxygen consumption may also be increased, not so much due to the cold per se, but because of poorer work economy stemming from impaired muscle coordination, increased pre-shivering muscle tone, or the added oxygen cost and glycogen use during shivering.

2. Can acclimatization occur with training in the cold?

Rundell: Acclimatization to the cold, although not as extensive as acclimatization to hot weather, does occur. Acclimatized individuals exhibit a down regulation of the mean skin temperature at which shivering begins. Another unique adaptation to cold weather exercise is increased intermittent peripheral vasodilation, referred to as cold-induced vasodilation, which functions to keep extremities warm.

Castellani: The physiological changes that occur with cold acclimatization are interesting but there really is no practical value for the athlete to try to acclimatize to the cold. There are no studies to date that have examined acclimatization in athletes exercising outdoors over a winter season and whether there is a performance or thermoregulatory benefit to this. The reported acclimatization patterns include: 1) increased shivering (only seen in 1-2 studies); 2) habituation, which is characterized by blunted shivering and cutaneous vasoconstriction (thus increasing the potential for a greater reduction in body temperature). Habituation can be induced by exposure to conditions that cool the body surface but do not change the core temperature; and 3) insulative acclimation (greater fall in skin temperature ? greater vasoconstriction, associated with lower core temperatures during cold exposure) is associated with repeated reductions in core temperature.

Snyder: Some data suggest that chronic cold exposure will increase subcutaneous body fat to enhance insulation. However, these findings are derived from cross-sectional studies; thus, population differences, not acclimatization or habituation, might explain the observation.

3. What are the physical risks of cold exposure to athletes? How can the dangers be minimized?

Castellani: The most important risks to athletes are hypothermia and peripheral cold injuries, such as frostnip and frostbite. Peripheral cold injuries are caused by the freezing of tissue. The ambient conditions for this type of exposure are often severe, i.e., low ambient temperatures and increased wind velocity. There is little risk of frostbite above a windchill of -29°C (-20?F). Below this, the risk increases but only on exposed skin. The best precaution is to cover as much of the periphery as possible (gloves, mittens, face protection), lotions can be used to cover facial features, and use of common sense is perhaps the most important preventative. If the weather is very severe, training time has to be curtailed. Hypothermia can occur even when exercise is performed at a moderate rate, but the ambient conditions are both wet and cold. The reasons are that once clothing is wet, it loses its insulative properties, and water is an excellent heat conductor, 25 times greater than air. The most important thing an athlete can do to prevent hypothermia is to dress in rain gear if the conditions are wet, dress in layers to allow sweat to evaporate (and even potentially avoid hyperthermia), and restrict time spent outdoors following exercise. It is wise to take a buddy along, especially when running or skiing for long distances off the beaten track. It is also critical for the long-distance athlete to maintain plasma glucose levels because hypoglycemia impairs shivering. Plasma glucose can become very low during long exercise sessions, so the ingestion of carbohydrate is important. With proper precautions, people can safely exercise outdoors at very low temperatures (-10?F or lower) with little risk of hypothermia.

Rundell: Even though the risk is small during exercise, hypothermia is of great concern because it has the potential to be fatal. Anyone exercising in the cold should be aware of the symptoms: ataxia (incoordination), drowsiness, blurred vision, numbness, and decreased shivering. In addition to inadequate clothing, dampness, dehydration, and other nutrition factors, the state of physical condition, caffeine use (caffeine may produce peripheral vasodilation), and extreme cold and/or wind can accentuate heat loss. Cold-weather exercise may also increase the risk of accidental injury due to impaired motor control. A good example of this type of injury involves the alpine ski racer who has a 2-hour training session running gates, then cools down during the ride up chair lift, and doesn?t replenish fluid and carbohydrate during the training session. Consequently, by the end of the session, the athlete may be glycogen depleted and dehydrated, a combination that will result in compromised motor control, a recipe for a serious crash. Male cross-country skiers and cyclists training in cold weather have an additional area of the anatomy that is susceptible to frostbite. This ?groin area? injury, which incidentally is quite common among neophyte cold-weather cyclists and skiers, can be easily prevented by the use of commercially available gortex/fleece paneled briefs. An important precaution against any type of frostbite is simply an awareness of wind chill, including that generated by the athlete?s locomotion and limb movement. For example, the wind chill generated by a cyclist traveling at 20 mph at 10 ?F would be ~4-fold greater than a runner traveling at 5 mph. In this case, the runner would be at minimal risk of frostbite, while the cyclist would be at higher risk.

Burruss: Common sense tells us that things freeze in cold weather and unprotected exposure to the cold can result in frost bite. Additionally, the perception of being ?tight,? i.e., losing flexibility, is magnified in the cold for that very reason. Dehydration is also a risk. Athletes often think that they do not need to hydrate because it is cold. They may not have as much sweat on their body surfaces as in hot environments, but they ?blow off? a fair amount of fluid through their rapid breathing. Additional factors can increase the risk of hypothermia. It is well known that alcohol consumption, which promotes peripheral vasodilatation and accentuates heat loss, and smoking, which decreases oxygen carrying capacity of the blood, can compound cold injury to the extremities. While these aren?t threats in serious athletes, alcohol consumption or smoking can come into play during recreational sports and leisure-time physical activities in the cold.

4. How important is hydration during exercise in the cold?

Snyder: Extremely important. Due to the very dry environment that generally accompanies cold weather, significant body fluid is lost. Unlike in a hot environment, when visible sweat drips off the body, in a cold/dry environment sweat can evaporate so quickly that the athlete does not have a clear picture of how quickly fluid loss accumulates. As Mr. Burruss noted, much more fluid is lost in the expired air. A confounding problem is that when peripheral vasoconstriction occurs along with dehydration, blood flow is reduced. This reduced oxygen and nutrient supply to skin could increase the risk of frostbite.

Castellani: Hyperthermia and hypohydration in an athlete who is exercising very strenuously and for a shorter duration is more of a problem than hypothermia. Most athletes, when exercising in a cold environment, are not really being cold stressed, per se. Usually, their metabolic heat production is so high that, if they are clothed properly, they are more likely to be sweating and losing body fluids. Loss of body fluids at this point can cause the same problems as when exercising in a hot environment, i.e., a decrease in exercise performance, an increased cardiovascular strain, and an increase in core body temperature. Problems often occur when the athlete stops exercise and decreases metabolic heat production. If the ambient conditions outside are severe and the athlete is exposed for a long time and the clothes are wet from sweat and/or rain, body heat loss can be accelerated, and hypothermia becomes a real risk.

Rundell: Exercise in the cold certainly presents a unique set of circumstances. On one hand, cold temperature stimulates peripheral vasoconstriction, which may in turn lead to increased diuresis due to increased central venous pressure. However, increased metabolic heat from exercise stimulates peripheral vasodilation and sweat production. Both impact hydration status, which among other effects, increases the susceptibility to cold-weather injury because of a reduced skin blood flow in dehydrated individuals. Previous research (Ekblom and Berg, 1994) has demonstrated that cross-country skiers may lose up to 3% of their body weight during a race. In a recent study, skiers who drank water ad lib during 90 minutes of easy ski training lost~2% body weight. When the skiers maintained a schedule of fluid feedings during the 90-minute ski, weight loss represented only about 0.6% of body weight. Moreover, subjects who supplemented with a carbohydrate-electrolyte solution maintained significantly better fluid balance as evidenced by the attenuated reduction in plasma osmolality and reduced fluid loss due to urine production.

Burruss: I have seen athletes neglect replenishing fluids in the cold and consequently suffer the same ill effects as they would in the heat. Marked dehydration causes decreased blood volume and increases susceptibility to cold injury. It is important to educate athletes about hydration in cold, even cool weather. In very cold environments it might be beneficial to provide a tepid, or a warmed fluid replacement. We have used ?hot? fluids on the sideline and in the locker room to supplement our hydration. This strategy might provide psychological benefits as well.

5. Are any athletic injuries more prevalent during cold-weather exercise?

Burruss: It?s not clear whether cold weather gives rise to certain injuries on the field. Most obvious are the potential danger of exposed tissue freezing and the risk of an athlete not maintaining flexibility that resuls in strain injuries. In the case of football, the frozen playing surface poses an issue. The lack of footing (traction) leads to slipping and possible collisions with the frozen surface (contusions). Experimenting with footwear and cleat length can reduce these threats.

Rundell: An overlooked problem of cold weather exposure is exercise-induced bronchospasm (EIB). EIB is often coupled with asthma, and is sometimes referred to as exercise-induced asthma. We have found a 3-fold higher incidence of EIB among elite cold weather athletes over their warm weather counterparts. EIB exhibits a myriad of symptoms, including labored breathing, dyspnea, chest tightness, excess mucus, and post (or during) exercise cough or wheeze, and performance variability that can be related to environmental conditions. These symptoms are often seasonal and are most severe during exercise in a cold, dry environment. If undiagnosed and untreated, EIB can produce decrements in pulmonary function that dramatically affect the ability to exercise in the cold. The vast majority of athletes we?ve identified as EIB positive were totally unaware of their symptoms. Many thought that the post-race hack was something that went with the turf or was a response of having worked harder than usual. About 50% of EIB-diagnosed athletes may be ?refractory,? which is defined as exhibiting one-half the severity of original bronchospasm within 30 min to 2 hours after initial bout of EIB. Using this knowledge, some athletes can manage EIB non-pharmacologically by incorporating a warm-up of sufficient intensity as to trigger the response 30 min prior to competition. For those EIB-diagnosed athletes not fortunate enough to be refractory, pharmacological intervention may be warranted, but the specific medication must not be a restricted substance. A call to the Olympic Drug Reference Line will clarify this. Many of our symptomatic athletes are also chronically exposed to bad air: the waxing rooms for the nordic skier, epoxy/resin vapors in boat repair areas of the slalom paddler, and the high nitrogen dioxide content found in ice areas may contribute to EIB. Avoiding or minimizing exposure to such areas could help.

Snyder: Because EIB is induced when fluid is lost from the mucous layer of the respiratory tract during mouth breathing, facemasks help reduce the fluid loss. A facemask will present a microenvironment of warm/moist air to be rebreathed. During the last Winter Olympics in Nagano, many skaters wore facemasks not only during the warm-up and cool-down sessions, but also during the competition.

6. What practical steps should coaches and athletes take when preparing for training and competition in the cold?

Castellani: The training approach for the coach and athlete really should not change for the cold. It is still important that the athlete maintains good hydration and eats primarily carbohydrates. Studies have shown that more glycogen is depleted when exercising lightly at 9?C (48?F) compared to 21?C (70?F). However when the exercise intensity increases, there is no difference in glycogen utilization between ambient temperature conditions. But it is still important for the athlete and coach to understand that carbohydrate is the most important fuel whether it is cold or not, and the training table should reflect this. The most practical steps both the athlete and coach can take is to ensure that the athlete is comfortable exercising in the cold environment. If the conditions are wet and cold (the most dangerous combination), clothing should be worn to keep the athlete as dry as possible without causing a buildup of sweat inside the garment. Coaches and athletes should also remember that if the conditions are such that the athlete is shivering, then training may not be up to standard since shivering (an involuntary muscle contraction) may cause a loss of fine motor control. Shivering may also increase the effort needed to perform exercise since agonist and antagonist muscle groups are both contracting and opposing each other.

Burruss: Include training time in the cold, to acquire the psychologically adjustment of, ?I can handle this.? Also, pay attention to the unending evolution in technology for athletic clothing. Clothing must be practical as to allow functional flexibility, not to just participate in the game, but to allow flexibility exercises on the sideline. Simple measures can help maintain body heat. Gloves, particularly the golf style, are important in dress preparations. The synthetic head gators are helpful and can provide a thin layer to breathe through and buffer that cold blast of fresh air heading to the lungs. Thin, synthetic sock liners are available, and if not, a plastic ice bag can suffice. A thin dry sock should be worn under the plastic bag; a second, thicker sock covers the bag. The sock may need to be changed periodically, such as at half time to insure a dry layer against the skin. Tight athletic shoes can constrict blood flow to the feet, so adjustments in tightness will prove beneficial. Neoprene support wraps have some benefit, but can prove constrictive. Large sideline heating units are practical but are not without danger. Anyone who has been around the gas-fired space heaters has a story about melted clothing or shoes. Heated benches are effective, but lack the safety features that distances the heating unit from direct contact.

Snyder: During exercise training and competition in the cold, an athlete and coach need to protect against: 1) fatigue and frost-bite through the use of proper clothing; and 2) fatigue and dehydration through the use of food and fluid intake (including carbohydrate consumption during and after an exercise bout). Because winter sports are often broken into shifts, a couple of specific tips include consuming at least 300 kcals of high carbohydrate foods in the first two hours after exercise, to begin the glycogen resynthesis process. This helps ensure that sufficient glycogen stores are available for subsequent bouts of exercise, during the afternoon or evening runs or races. Also, athletes should begin their workouts well hydrated and consume about 1 liter of fluid per hour (about 250 ml, or 8 ounces, every 15 min).

Rundell: It is most important to understand that wind chill may be a big factor, even on calm days, if the mode of exercise entails moving at a moderate to high speed. Prolonged periods of non-exercise within the workout, such as technique discussions between coach and athlete should be avoided, since the athlete will lose heat quite rapidly.

SUGGESTED READINGS

Askew, E.W. (1998). Nutrition and performance in hot, cold, and high altitude environments. In: I. Wolinsky (ed.) Nutrition in Exercise and Sport. Boca Raton: CRC Press, pp 597-619

Ekblom, B. and U. Bergh (1994). Physiology and nutrition for cross-country skiing. In: D.R. Lamb, H.G. Knuttgen, R. Murray (eds.) Perspectives in Exercise Science and Sports Medicine. vol 7, Carmel: Cooper Publishing Group, pp. 373-400.

Freund, B.J. and M.N. Sawka (1995). Influence of cold stress on human fluid balance. In: B.M. Marriott (ed.) Nutrient Requirements for Work in Cold and High Altitude Environments. Washington, D.C: National Academy of Sciences. pp. 161-180.

Jacobs, I., L. Martineau, and A.L. Vallerand (1994). Thermoregulatory thermogenesis in humans during cold stress. In: J.O. Holloszy (ed.) Exercise and Sport Sciences Reviews. vol 22, Baltimore: Williams and Wilkins, pp 221-250.

Murray, R. (1995). Fluid needs in hot and cold environments. Int J Sport Nutr. 5:S62-S73. O?Brien, C., A.J. Young, and M.N.

Sawka (1998). Hypohydration and thermoregulation in cold air. J. Appl. Physiol. 84:185-189. Patton, J.F. and J.A.

Vogel (1984). Effects of acute cold exposure on submaximal endurance performance. Med. Sci. Sports Exerc. 16:494-497. Seifert, J., M. Leutkemeier, A.

White, and L.Mino (1998). The physiological effects of beverage ingestion during cross-country ski training in elite collegiate skiers. Canadian J. Appl. Physiol. 23:66-73.

Snyder, A. (1994). Physiology and nutrition for skating. In: D.R. Lamb, H.G. Knuttgen, R. Murray (eds.) Perspectives in Exercise Science and Sports Medicine. vol 7, Carmel: Cooper Publishing Group, pp. 181-220.

Young, A.J. (1988). Human adaptation to cold. In: K.B. Pandolph, M.N. Sawka, R.R. Gonzalez (eds.) Human Performance Physiology and Environmental Medicine at Terrestrial Extremes. Indianapolis: Benchmark Press, Inc. pp. 401-434.

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