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“While genetics play a significant role, so too, does experience, for running (and especially running long distances) has a high metabolic cost. The dogs’ muscles must be strong, but most of all, they must be efficient. The ability to run fast and consistently for long periods of time depends on the body’s ability to provide adequate energy to working muscles and to efficiently remove waste products such as carbon dioxide and lactic acid. In both humans and dogs, only about a quarter of the energy from the breakdown of fats and carbohydrates in food is converted into mechanical energy; the rest is dissipated as heat. The primary focus of training for a race—for both humans and canines—is teaching the body to get better at converting available energy from glucose, carbohydrates, fats, and proteins into energy. This can only really be achieved through regular exercise”
― Lee Morgan, Four Thousand Paws: Caring for the Dogs of the Iditarod: A Veterinarian's Story