ABSTRACT
In most sports the limitation to performance is the premature onset of fatigue. Training improves performance in a number of ways and not least, of course, through improvements in skill and greater experience. However, training delays the premature onset of fatigue and this in itself contributes to a significant improvement in performance. Fatigue is not a single phenomenon but the end result of a number of events within the closely coupled chain of reactions which follow the conscious decision to exercise. Inability to maintain a prescribed work task or level of exercise is a common expression of fatigue. The failure of metabolism to provide sufficient energy at the rate required by working muscles, to cover their energy demands, is the most common underlying mechanism for fatigue during dynamic physical activity. This ‘energy crisis’ in working muscles has different aetiologies as one might expect when one considers the range of physical activities which fall under the general heading of ‘Sport’. In order to develop a broad picture of the metabolic support, and of course failure, underlying the performance of dynamic physical activity it is helpful to divide these activities into two general categories, namely the ‘multiple sprint’ sports and the ‘endurance sports’ (Williams, 1987). During participation in the multiple sprint sports, fatigue is associated with the accumulation of the end products of metabolism whereas during endurance sports, fatigue is associated with the depletion of the limited stores of carbohydrate in skeletal muscles. Of course many sports involve an unpredictable mixture of sprint and endurance activities and so localizing the cause of fatigue presents the sports scientist with a more complex set of problems. Therefore, the aim of this introductory chapter is to provide the reader with an overview of some of the metabolic responses to exercise, focusing, where appropriate, on mechanisms which attempt to explain the fatigue process and also on metabolic methods of assessing adaptations to training.
