In Sled Dogs’ Secret to Peak Soldier Performance, Noah Shachtman looks at Oklahoma State veterinarian Michael Davis‘s “absurd idea” — shared by the folks at Darpa, who have been funding all kinds of research into maximizing human performance — to study how the Iditarod sled dogs of Alaska manage to run for more than a thousand miles straight. in order to get our own troops running around war zones at peak efficiency for “days on end without stopping.” The New York Times explains:
When humans engage in highly strenuous exercise day after day, they start to metabolize the body’s reserves, depleting glycogen and fat stores. When cells run out of energy, a result is fatigue, and exercise grinds to a halt until those sources are replenished.Dogs are different, in particular the sled dogs that run the annual Iditarod Trail Sled Dog Race in Alaska. This is a grueling 1,100-mile race, and studies show that the dogs somehow change their metabolism during the race.
Dr. Michael S. Davis, an associate professor of veterinary physiology at Oklahoma State University and an animal exercise researcher, said: “Before the race, the dogs’ metabolic makeup is similar to humans. Then suddenly they throw a switch — we don’t know what it is yet — that reverses all of that. In a 24-hour period, they go back to the same type of metabolic baseline you see in resting subjects. But it’s while they are running 100 miles a day.”
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In fact, sled dogs in long-distance racing typically burn 240 calories a pound per day for one to two weeks nonstop. The average Tour de France cyclist burns 100 calories a pound of weight daily, researchers say.How the dogs maintain such a high level of caloric burn for an extended period without tapping into their reserves of fat and glycogen (and thus grinding to a halt like the rest of us) is what makes them “magical,” Davis says.
The energy comes from somewhere, so they’re burning carbs, protein, and/or fat; the question is how much of each? Human endurance athletes typically eat a high-carb diet — although that may be changing — and “carb load” before a race. They then “hit the wall” when they run out of glycogen, a carbohydrate stored in the muscles and liver. The body can store only so much glycogen.
We need carbs for anaerobic respiration, which we use for sprinting, but we can also use carbs aerobically for long, slow, endurance challenges. Fat makes a better aerobic fuel though, because (a) it’s more calorie-dense, and (b) we can store a lot of it. At roughly 100 calories per mile, a 175-pound runner can theoretically go 35 miles on one pound of fat.