The dominant energy system involved with a long distance runner is the aerobic energy system. This is where the body uses oxygen for the production of ATP (energy). In this system, carbohydrates are used (in the from of glucose) and fats (in the form of free fatty acids) which are mixed with oxygen, to produce the ATP. Protein can also be used, but it hardly ever is. Also the ATP/PC energy system may be used at the very beginning of the race as it gives a burst of energy. This energy system only lasts for up to ten seconds. The Lactic acid system may be used at the sprint finish at the end of the race because it provides a very quick supply of ATP for intense short bursts of activity, usually from 30-60 seconds. As a result lactic acid will accumulate and cause muscle fatigue and...