Endurance performance is dependent on the coordinated responses of the cardiovascular and respiratory systems, muscle metabolism, mechanical efficiency, and thermoregulation. A number of reviews have focused on one, or several, aspects of these responses (1,7,18). Yet, one central tenet of optimizing endurance performance revolves around the efficient aerobic transformation of metabolic substrate into mechanical power output, with delayed depletion of the glycogen reserves (1,10). Thus, it is important to have an efficient oxygen transport system and a metabolic system that supplies appropriate substrates to the mitochondria for oxidative metabolism with minimal concurrent glycolysis, a concept called “tight coupling” of oxidative metabolism (14).