How cold weather alters fluid and nutritional requirements during exercise.
Introduction
When one studies the animal kingdom, he finds that humans may be described as warm-weather, tropical animals who neither adapt or tolerate cold weather. As we know, however, humans still must work and exercise in such environments. In order to cycle effectively outdoors in the winter and early spring, you need to know how cold affects you and whether it alters your fluid and nutritional requirements during exercise.
While cycling, your body is generating 8 to 12 times the heat it would while at rest, which is more than enough to maintain your body temperature in the cold. Under most circumstances when you are dressed properly cold weather has little or no effect on your body temperature because your energy production overrides the cold temperatures and wind chill.
Some cyclists who exercise in the cold have higher caloric needs. Scientists have found that this is primarily due to the various cycling conditions encountered and amount and type of clothing and shoes worn. For example, riding a heavier bicycle and the added rolling resistance of riding on trails or in the snow and heavier shoes will increase your energy cost. In addition, there is an increase in energy needs due to the use of heavier shoes and more clothing. Simply adding an additional 100 to 200 grams to each shoe causes a 1 percent increase in oxygen consumption during cycling. While there is no need to significantly increase your caloric intake during cold weather, you may want to consider taking in a small snack before your ride. Once you begin digesting the food this will add some heat to your body by metabolism and help keep you warm.
“Roughly speaking, there are three times when a cyclist in training in the winter should drink: when he is thirsty, when he isn’t thirsty, and in between.”
As in the summer your fluid replacement needs are crucial to your performance while training. While in the summer you lose a tremendous amount of fluids through sweating, in the winter you lose more fluids while breathing cold air, which must be warmed and moistened in your throat and lungs. As you exhale, you lose lots of water, which is why you can see your breath during heavy exercise. The humidity content of cold air is much less than warm air. This is why your throat feels much drier in the winter.
If a person is active under these cold, dry conditions, the amount of moisture lost through respiration increases significantly and must be replaced. It is essential to keep up with this loss, with frequent fluid replacement during the day and while cycling, if possible. In addition, you lose more water through increased urine production in the cold. The medical community calls this phenomena, cold dieresis.
As in the summer, winter dehydration can lead to fatigue, which will affect your ability to train or compete at your optimum. And as in the summer, a decrease in your blood volume caused by sweating and insensible water loss from breathing means less blood flow to your skin and extremities. This will lead to a more rapid cooling of your body and possible increase in susceptibility to hypothermia and/or frostbite.
Fluid temperature is also a concern to many while exercising. A liter of water heated to 130 degrees Fahrenheit, about as warm as you can drink, would provide approximately 18 kcal of heat to an individual. While a liter of water at near freezing would absorb about 35 kcal of energy to heat it up to your normal body temperature. From this you can see that drinking warm water will add very little energy to your body, while drinking cold water can rob your body of calories.
But, there is the thirst quenching aspect of cold water that makes it appealing during exercise. With the adequate heat production that occurs during exercise, the intake of cold water will do you no harm. If you are feeling chilled, it would be best to avoid a further caloric drain, but if the choice is between cold water and no water, drink the cold water. When cycling carry your water under your jacket and close to your body to keep it from getting too cold. A CamelBak drinking system may be advantageous during winter cycling or skiing, since it can be worn under a training jacket.
When you were a kid you were often told not to eat snow due to its cooling effect and that it would give you a sore throat. The same hold true whether you are cross-country skiing or mountain biking in the back country. Snow will leach heat from your body, but once again one must consider how much heat you are producing during exercise and how dehydrated you are from prolonged exercise.
Primarily, the temperature of the snow must be considered, for the snow close to the surface will be as cold as the air temperature, while deeper snow will be as cold as the average temperature of the last few hours. Snow should be used for fluid replacement only if exercising and not fatigued. Snow at a temperature closer to melting point is safer than cold snow with regard to heat loss. In addition, eating very cold snow could freeze the delicate tissue lining the mouth and throat. The old stories are not far from wrong. It may be safer to put some snow into your water bottle, which contains other water, which will cool down the water, and will quench your thirst with minimal heat loss. If the water is kept close to your body it will be warmed to body temperature in a few minutes.
As with summer, use energy drinks that contain carbohydrate because they will do double duty, replacing carbohydrate and fluid. Remember to drink 8 to 12 ounces before your ride and 4 to 8 ounces every 15 to 20 minutes during your ride or ski. Avoid drinks containing caffeine and alcohol because they speed up dehydration by promoting urine production. Alcohol also decreases glucose output by the liver in the cold and speeds heat loss by dilating your skins blood vessels. Roughly speaking, there are three times when a cyclist in training in the winter should drink: when he is thirsty, when he isn’t thirsty, and in between.
Lastly, if you’re prone to exercise-induced asthma cold, dry air can precipitate an attack. A lightweight scarf or ski mask pulled loosely in front of your mouth can help warm incoming air. With proper precautions and hydration winter will not leave you lukewarm about training.