Just like dogs, humans warm air so rapidly in their mouths and noses that cold air does no damage within. Cold takes its toll in other ways. Muscles become less efficient, giving off more heat then they do in warmer temperatures. An athlete's oxygen consumption also goes up in the cold as his or her body burns food to release energy. Case said those exercising in Alaska during winter should expect a slight decrease in endurance, a drop in body core temperature, muscles that contract at a slower rate and a lower heart rate when compared to summer exercise.
Winter activities have a higher energy cost than the same exercise in the summer.
Walking on snow takes three times the energy of walking on a treadmill, Case said. Moving on snow takes a lot more food, too. Racers on the 100-mile Alaska course consumed an average of 73 calories per mile. Competitors in two races of the same distance in Hawaii and Australia averaged 17 and 14 calories per mile, respectively. The Alaska racers love high fat items, such as cheese and peanut butter.