Sled dog lessons in the Iditarod

Dogs are often called “man’s best friend”, and with good reason. Consider, for example, that they never interrupt us when we talk, that they are always happy to see us when we arrive home, and that they comfort us when we are lovesick. Ever since dogs were domesticated 15,000 years ago, they have worked and lived alongside humans, which some believe may explain this special bond. Each of the 400 breeds and varieties is unique, but only one stands out as the ultra-athlete canine: racing sled dogs.

The racing sled dogs are best known for their “mushing” each march during the Iditarod Trail Sled Dog Race, the longest sled race in the world. They are the top ultra-endurance competitors, covering 1,100 miles from Anchorage to Nome, Alaska, sometimes in just nine days. It’s unclear how they can continue to operate, despite heavy snowstorms, temperatures as low as -40°F and winds of up to 60 mph. No other animal comes close to the physiological attributes of these dogs.

Dr. Michael Davis has focused on the mysteries of this breed for over a decade. The professor from the Center for Veterinary Health Sciences at Oklahoma State University will discuss his recent findings entitled “Metabolic Strategies for Sustained Endurance Exercise: Lessons from the Iditarod.” His presentation is part of the American Physiological Society (APS) conference, The Integrative Biology of Exercise V, to be held September 24-27, 2008 in Hilton Head, SC.

How do they do? The exercise physiology of sled dogs

The physiological knowledge that Davis and his colleagues have uncovered so far is vast. Among their findings are:

Rapid adaptation to exercise and endurance—The most striking characteristic of these dogs is their ability to adapt quickly to intense, sustained exercise within 24 to 48 hours. Conditioned dogs exhibit most of the metabolic changes found in human endurance athletes during their first day of exercise, including depletion of muscle energy stores, increased stress hormones , evidence of cellular damage (such as proteins, lipids, and DNA), and oxidative stress. However, with consecutive days of exercise at the same intensity, these changes are reversed. Within four days of the start of exercise, the dogs’ metabolic profile returned to what it was before the start of the race, despite their sustained and intense exercise. When human ultra-athletes become fatigued, they stay that way until a recovery period that can take an entire day.

Huge aerobic capacity—Racing sled dogs have tremendous aerobic capacity. While untrained sled dogs have an average aerobic capacity of 175 ml/kg/min VO2 max (ratio of oxygen volume to body weight per minute), the aerobic capacity of fully conditioned sled dogs is estimated to be around the double (300 ml/kg/min).

Using a high-fat diet for exercise—During racing periods, sled dogs can burn up to 12,000 kilocalories per day (kcal/day). This means that a 55 pound sled dog will consume the equivalent of 24 McDonald’s Big Macs to fuel its run on any given day. A portion of the hound’s high-fat diet is converted to energy in the liver and used as fuel in the early stages of exercise. Preliminary data suggest that this process is a desirable trait intended to effectively support exercise in runners. It’s worth noting that humans would need 72 Big Macs to fuel the power they need to put in a day’s run, assuming their bodies can absorb and process all the fat in the beef.

Next steps

The mechanisms that make these four-legged athletes top performers are still unknown. Dr. Davis hypothesizes that this may involve the regulation of extremely thin membranes in muscle fibers and changes in the cells responsible for the body’s energy production. “They are unique athletes. What we learn from them will undoubtedly tell us a lot about human performance.

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Bette C. Alvarado