Researchers first discovered the metabolic switch in 2005, when a team headed by Oklahoma State University's Michael Davis — who has been investigating the metabolic, gastrointestinal, respiratory and blood systems of sled dogs for 10 years — did a controlled study at a professional racing kennel in Alaska. (scientificamerican.com)
Bones suggest that dogs pulled sleds 9000 years ago — implying humans domesticated dogs to put them to work. (science.sciencemag.org)
While Labs certainly weren't bred for sled dog racing, let me ask you this: was a Doberman? (dogingtonpost.com)