In a one hundred metre sprint, the energy expenditure is thirty three kilojoules, or three and one third kilowatts during each second of the run. Eighty-five percent of this energy comes from breaking down ATP and phosphocreatine. This is only the equivalent of the aerobic sugar breakdown brought about by one and a half litres of oxygen, but it is released more quickly than the aerobic processes would allow. The remaining fifteen percent of the energy comes from the aerobic breakdown of the sugar stores. The heart rate will have increased to more than one hundred beats per minute even before the race, in anticipation of the body's demands, but it is only after the race that the aerobic processes will come into play to replenish the cellular energy stores.
Training has a dramatic and very specific effect on the body's musculature and circulation.
Muscles and the muscle cells within each muscle specialise in the performance of specific types of contractions. Some muscles, for example those involved in the maintenance of posture, are designed to perform long lasting contractions, with the minimum of energy consumption. Other muscles on the other hand may only occasionally be called into action, but the action requires very fast movements, such as those required to escape from an attack. These muscles may be extremely effective at providing lightning-fast movement, but will be unable to sustain these movements for very long. Each muscle is made up of a variety of muscle fibres which fall into two main categories.