and may not be available for any specific type of exercise. Intense cycling or running can easily consume 600–800 or more kcal per hour. Unless glycogen stores are replenished during exercise, glycogen stores in such an individual will be depleted after less than 2 hours of continuous cycling or 15 miles (24 km) of running. Training and carbohydrate loading can raise these reserves as high as 880 g (3600 kcal), correspondingly raising the potential for uninterrupted exercise. Effects In one study of five male subjects, "reduction in preexercise muscle glycogen from 59.1 to 17.1 µmol × g−1 (n = 3) was associated with a 14% reduction in maximum power output but no change in maximum O2 intake; at any given power output O2 intake, heart rate, and ventilation (VE) were significantly higher, CO2 output (VCO2) was similar, and the respiratory exchange ratio was lower during glycogen depletion compared with control." Avoidance There are several approaches to prevent glycogen depletion: Carbohydrate loading is used to ensure that the initial glycogen levels are maximized, thus prolonging the exercise. This technique amounts to increasing complex carbohydrate intake during the last few days before the event. Consuming food or drinks containing carbohydrates during the exercise. This is an absolute must for very long distances; it is estimated that Tour de France competitors receive up to 50% of their daily caloric intake from on-the-bike supplements. Lowering the intensity of the exercise to the so-called 'fat max' level (aerobic threshold or "AeT") will lower the fraction of the energy that comes from glycogen as well as the amount of energy burned per unit of time. See also Exercise Intolerance Second Wind (exercise phenomenon) McArdle Disease (GSD-V) Metabolic Myopathies References Sports terminology Endurance games