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Magic metabolism switch

Posted by Gale Bernhardt Apr 7, 2009

Each year I watch the Iditarod sled dog race in Alaska that goes from Anchorage to Nome. I’m attracted to the endurance of the dogs as well as the mushers. Most dog owners will tell you that they can “read” their dog(s). They know when the dogs feel good and when they don’t.


I suspect it was the instinct of top mushers, surveying how the dogs were running and how they acted, that helped them decide to run the dogs longer than common knowledge thought was possible. It was common knowledge that sled dogs needed to be run six hours, rested six hours and repeat this cycle until the end of the race. Running in this six-on and six-off pattern is what mushers thought would produce the fastest overall team, strong to the end.


In recent years, mushers ran the dogs for up to 14 hours at a time and those teams were winning the event. How can this be?


A column in the March 2009 issue of National Geographic pointed to research done by a group of scientists at Oklahoma State University that found that after racing for a few hours, sled dog metabolism seems to “flip a magic switch”. This metabolism switch allows them to burn a huge number of calories (12,000 per day) from a fat-laden diet without depleting muscle fat or glycogen stores. In fact, researchers found that muscle glycogen stores increased during prolonged exercise.


Is this metabolism switch unique to dogs?

In particular, huskies and malamutes?

Is there a metabolism switch like this in humans?

What were Dean Karnazes’s muscle glycogen stores doing while he ran 50 marathons in 50 days last year?

Are we all individually limited by our body, or is it our mind?



McKenzie, EC, et al, “Assessment of alterations in triglyceride and glycogen concentrations in muscle tissue of Alaskan sled dogs during repetitive prolonged exercise”, Am J Vet Res.,  2008 Aug;69(8):1097-103.

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