ABSTRACT
Fatigue is an inevitable accompaniment of prolonged strenuous exercise, but the nature of the fatigue process will be influenced by many factors. The most important of these is undoubtedly the intensity of the exercise in relation to the capacity of the individual, and the most effective way to delay the onset of fatigue and improve performance is by training. The primary cause of fatigue in exercise lasting more than 1 h but not more than 4–5 h is usually the depletion of the body's carbohydrate reserves. This time scale covers most ball games such as football, hockey and tennis, and also individual events such as marathon running. Systematic training results in many adaptations to the cardiovascular system and to the muscles, allowing them to increase the extent to which they can use the relatively unlimited fat stores as a fuel and thus spare the rather small amounts of carbohydrate which are stored in the liver and in the muscles. Where the availability of carbohydrate fuel limits exercise, this will result in an improved performance.
