Total energy expenditure during marathon training and competition is among the highest reported for any endurance activity. 2) Although training intensity for the marathon may vary between 60-125% of maximal physical working capacity, elite runners must run consistently at about 80-90% of VO2max in order to achieve successful competitive performances. 3) Earlier studies demonstrated that carbohydrate was the preferential fuel for endurance exercise, but more recent studies have suggested a greater role for lipids than previously thought. Also, proteins may contribute as much as 5-10% of the total energy to a marathon performance. 4) The preponderance of Type I and IIA skeletal muscle fibers among marathon runners and their significantly improved storage capacity for intramuscular lipids and increased mitochondrial density may account for increased reliance on oxidation of fats.
