There are three separate energy systems required involve in physical activities. Different sports may require the development of one of these systems or all three. With knowledge of these different energy systems this enables training

A second source of energy is Anaerobic System. Also known as lactic acid system or glycolytic. Here muscle glycogen is used as fuel initially, but blood glucose and liver glycogen can be drawn upon to produce ATP (But not many ATP molecules are produced only 2 per glucose molecule). This system requires a series of chemical reaction to occur and produces lactic acid as a breakdown product. It lasts longer, up to a few minutes, but lactic acid build up in muscle inhibits efficient contraction and causes the familiar "burning" feeling in a near exhausted muscle. Interval training, short near maximal bursts initiates this system, and trains your body to tolerate lactic acid build-up and to develop this mechanism. This system is used in a sprint in cycling and may be used for intense periods in a game like rugby. A problem with the lactic acid system is that the lactic acid needs to be removed and metabolized by the body, procedures which both consume energy. Thus endurance athletes should avoid using this system except perhaps at the very end of an event.

These three systems operate together depending on the effort required, the body using the aerobic system primarily and saving anaerobic power for sudden bursts. An endurance athlete should avoid using anaerobic system because lactic acid may interfere with muscles action. The point at which lactic acid become debilitating is called the anaerobic threshold (AT), and can be measured to monitor changes in an individuals fitness. The other way of measuring the aerobic system is to measure V02 max., the amount of oxygen your body utilizes at a maximal sustainable effort. Depending on the sport involved, one or all of these systems may be used. Some sports may concentrate on one system, and actively avoid using the other, typically the aerobic endurance athlete avoiding the lactic acid system. Other sports may require more flexible energy sources, a racing cyclist needs an excellent aerobic base, but needs to be able to sprint briefly and repeatedly using the anaerobic system. For this individual the training should mimic this and utilize "interval" techniques. Again, sports involving primarily strength or a sudden effort may require strength and speed training of the muscles involved. This develops the anaerobic systems primarily. At the end of the day however, all of this can be summed up by the word "specific". To be successful you training must be "specific", and mimic the sport in which you wish to succeed. Training that is not "specific" and develops inappropriate energy systems may be actually detrimental to performance in your chosen sport.