Nutrition for Cold Weather Exercise
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Nutrition for Cold Weather Exercise |
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Cross-country skiing, bicycling, hiking, and trail running can all expose the athlete to cold conditions. The energy requirements for activities in a cold environment are similar to those for activities in a temperate environment, provided that adequate clothing is worn and allowances are made for the increased weight of the clothing and condition of terrain. For example, heavy clothing can increase energy expenditure by restricting movement and the energy expenditure for walking on snow is about twice that of walking over a hard surface at the same speed.
At the beginning of these activities, athletes can usually exercise at a rate that generates enough heat to maintain their body temperature. However, prolonged exercise causes depletion of the athlete’s energy reserves (muscle glycogen and blood glucose) and subsequent fatigue.
Cold exposure reduces fat utilization and increases muscle glycogen utilization. Prolonged exercise generally increases the mobilization and oxidation of free fatty acids via the release of epinephrine and norepinephrine into the vascular system. Although cold exposure also triggers a marked elevation in catacholamine secretion, free fatty acid levels increase substantially less than during prolonged exercise in warm weather. The vasoconstriction of the vessels supplying the skin and subcutaneous tissues reduces the blood flow to the subcutaneous tissue (the major storage site for lipids), thereby decreasing fat utilization.
The more rapid rate of muscle glycogen depletion that occurs during cold exposure contributes to fatigue. As the athlete’s exercise intensity and muscular activity decrease, the production of body heat gradually falls. The subsequent development of hypothermia causes the individual to become even more fatigued and less capable of generating body heat through exercise – an ultimately dangerous situation. Shivering is the major method of heat production when the athlete can’t exercise hard enough to keep warm. Shivering causes a four to five-fold elevation in the resting rate of heat production but offers only limited protection against hypothermia compared to exercise. Blood glucose plays an important role in cold tolerance and exercise endurance. Hypoglycemia and fasting both suppress shivering and significantly lower rectal temperature.
Providing a palatable high-carbohydrate diet of sufficient calories is the major challenge of cold-weather nutrition. A high-carbohydrate meal before exercise and carbohydrate feedings during exercise both help to maintain the athlete’s energy reserves. This enables the athlete to generate adequate body heat and reduces the risk of hypothermia during cold weather exercise.
The importance of providing high-carbohydrate foods that are palatable, easily carried, and easily eaten in cold weather cannot be over-emphasized. A high-carbohydrate sports bar or beverage won’t do the athlete any good if the product tastes terrible or is too frozen to eat or drink.
The athlete should consume a high-carbohydrate meal (1 to 4 grams of carbohydrate per kg) one to four hours before exercise. This helps to restore liver glycogen. If the athlete’s muscle glycogen stores are also low, the meal can help to increase them as well when eaten several hours before exercise.
The athlete should consume 30 to 60 grams of carbohydrate per hour to maintain blood glucose levels during cold weather exercise. Carbohydrate feedings provide glucose for the muscles when they are running low on glycogen. Thus, carbohydrate utilization, energy production, and heat production can continue at high rates and cold tolerance is enhanced.
Replenishment of muscle glycogen stores following exercise will also assure the availability of this fuel for shivering thermogenesis and help the body resist hypothermia on the next day of cold weather training. Based on the time spent exercising, the athlete should consume 7 to 10 grams of carbohydrate per kg daily.
The effect of dehydration upon performance in cold weather has not been adequately researched. However, dehydration will probably impair performance and physiological function in cold weather when the athlete exercises hard and wears heavy clothing. When heat production is high and heat loss is impeded by clothing, the harmful effects of dehydration are likely to be similar to those seen in warm environments.
Dehydration can predispose the athlete to an increased risk of frostbite due to decreased skin blood flow. It is easy for athletes to underestimate their fluid needs during cold weather exercise. During such exercise, the athlete should follow the ACSM position stand guidelines for fluid replacement and drink at least 5 ounces every 20 minutes.
1) Askew, EW. Nutrition and performance under adverse environmental conditions. In:
Nutrition in Exercise and Sport, ed. JF Hickson and I Wolinsky, CRC Press Inc., 1989.
2) Wilmore, JH and DL Costill. Thermal regulation and exercise. In: Physiology of Sport
and Exercise, Human Kinetics, 1994.
3) Murray, R. Fluid needs in hot and cold environments. International Journal of Sports Nutrition 5: (suppl) S62-S73, 1995.
Ellen Coleman,
RD, MA, MPH
ellen@cruciblefitness.com
