Have you ever had a morning where you just did not have the energy to go out for your five-mile run? What if you woke up in New York City and had to run to Miami? That is the distance Alaskan Huskies run every year at the annual Iditarod sled dog race. How these amazing canine athletes accomplish this feat is interesting to scientists because it provides insight into how human performance can be maintained in challenging conditions.
Muscles get energy to exercise from glucose (sugar) and fats stored in the body. Muscles use oxygen from the air to transform the two into energy. Scientists originally assumed that the Alaskan Huskies used fat to sustain long periods of exercise. Huskies are fed a diet rich in fat, and the body stores fat in greater quantities than glucose. However, a recent study found that the dogs actually used glucose to sustain exercise and that the glucose was made from a part of fat called glycerol. The dogs took advantage of their fat stores, but they used the fat stores to make glucose.
Why go through the trouble of turning a part of fat into glucose rather than using fat as is? That answer is not entirely clear yet, but one possibility is that the dogs typically run the Iditarod at an average of 10 miles per hour, or six-minute miles, while pulling a sled. Muscles prefer glucose to fuel intense exercise because they can get more energy out of it for every molecule of oxygen breathed in. Sustaining such high speeds while pulling a load may require the use of glucose over fat. This is not to say that fat is not important for the dogs. As mentioned, the dogs use the fat, just not directly, and fat is good fuel during rest periods and recovery between running.
The Alaskan Huskies were bred to perform these amazing endurance feats, but we don’t know yet if human muscles can invoke the same rate of fat-to-glucose conversion processes to fuel exercise of such long distance. However, humans performing at such high speeds for prolonged periods would most likely need to do this same type of conversion.
Next time you’re not up for your morning run, channel your inner sled dog: Five miles really isn’t that bad.
Benjamin Miller, PhD, is an associate professor in the Department of Health and Exercise Science at Colorado State University. He co-directs the Translational Research in Aging and Chronic Disease (TRACD) Laboratory with Karyn Hamilton, PhD.