The marathon: dietary manipulation to optimize performance.

Despite pronounced involvement of the cardiovascular and respiratory systems during the marathon, the limiting factor for this event revolves around the supply and utilization of intramuscular and extramuscular fuel reserves. The single most consistently observed factor contributing to fatigue at work intensities selected by marathon runners is the depletion of muscle's endogenous carbohydrate, glycogen. Dietary manipulations which reduce the rate of muscle glycogen degradation will, therefore, spare this important fuel and delay fatigue. The purpose of this paper will be to review dietary factors which are pertinent to fuel utilization in order to optimize marathon performance.