Winter Fuel Tips
You need adequate pre-exercise fuel to generate body heat. Hence, you want to fuel-up before you embark on winter exercises, particularly before you ski, run outside, or embark on any outdoor activity in extreme cold.
Food's overall warming effect is known as thermogenesis (that is, "heat making"). Your body generates about 10 percent more heat after eating than on an empty stomach. Eating not only provides fuel but also increases heat production (warmth).
Aerobic workouts can increase your metabolism by seven to 10 times above the resting level. So if you were to exercise hard for an hour and dissipate no heat, you could cook yourself in the process. In the summer, your body sweats heavily to dissipate this heat. But in the winter, the warmth helps you survive in a cold environment. Exercise is an excellent way to warm up in the winter.
If you become chilled during winter exercise (or even when swimming), you'll likely find yourself searching for food. A drop in body temperature stimulates the appetite and you experience hunger. Your body wants fuel to "stoke the furnace" so it can generate heat.
For safety, you should always carry some source of emergency food (such as an energy bar) with you in case you slip on the ice or experience some incident that leaves you static in a frigid environment. Winter campers, for example, commonly keep a supply of dried fruit, chocolate, or cookies within reach, in case they wake up cold in the middle of the night.
Cold weather itself does not increase energy needs, but you will burn extra calories if your body temperature drops and you start to shiver. Shivering is involuntary muscle tensing that generates heat.
When you first become slightly chilled (such as when watching a football game), you'll find yourself doing an isometric type of muscle tensing that can increase your metabolic rate two to four times.
As you get more chilled, you'll find yourself hopping from foot to foot and jumping around. This is nature's way to get you to generate heat and warm your body.
If you become so cold that you start to shiver, these vigorous muscular contractions generate lots of heat—perhaps 400 calories per hour. Such intense shivering quickly depletes your muscle glycogen stores and drains your energy. This is when you'll be glad you have emergency food with you.
Your body uses a considerable amount of energy to warm and humidify the air you breathe when you exercise in the cold. For example, if you were to burn 600 calories while cross-country skiing for an hour in 0 degrees, you might use about 150 of those calories to warm the inspired air. In summer, you would have dissipated that heat via sweat.
If you wear heavy clothes, you will burn a few more calories carrying the extra weight of skis, boots, heavy parka, snow shoes, etc. The Army allows 10 percent more calories for heavily clad troops who exercise in the cold. If you are a runner, however, the weight of your extra clothing is minimal. Think twice before chowing down.