Human metabolic response to exercise

The energy necessary to support prolonged submaximal exercise is provided by the aerobic metabolism of carbohydrate and fatty acids. Carbohydrate is stored as glycogen, a polymer of glucose, in the liver and in the skeletal muscles, whereas the fatty acids used by working muscles are mainly derived from triglycerides stored in white adipose tissue cells. The relative contributions of carbohydrate and fatty acids to muscle metabolism depend on the relative exercise intensity. The relative exercise intensity is defined as the oxygen cost of the exercise (V0₂) expressed as a percentage of the individual's maximum oxygen uptake (% V0₂ max). At exercise intensities which represent a large % V0₂ max for an individual, muscle glycogen is the main contributor to muscle metabolism. Fatigue is associated with the depletion of the limited intramuscular glycogen stores. When a carbohydrate-rich diet is consumed during recovery after exercise, the muscle glycogen stores are increased above theirpre-exercise concentrations. Thus an exercise and diet regime has been developed to exploit the glycogen supercompensa-tion phenomenon and so increase endurance capacity.