In order to participate in activity we are required to move. How does this movement occur? This movement is the result of muscle contractions. For these to take place the muscle requires a source of energy. Our muscles gain their energy from breakdown of a chemical compound called ADENOSINE TRPHOSPHATE ATP. Our muscles only have a limited supply of ATP so it needs to be constantly re synthesised to allow movement. Our body has adapted 3 energy systems to regenerate ATP. Which energy system the body uses depends on the speed, intensity and length of time of the activity. The three systems are 1.ATP-CP system 2.LACTIC ACID system 3.AEROBIC system

The ATP-PC system supplies energy anaerobically. – This means the energy is supplied without the presence of oxygen. Both these systems are used for quick high intensity activities. As stated earlier we have very limited supplies of ATP in the muscles – when working the supply burns out in around 1 second. As a result the body automatically switches to the ATP-PC system. In this system the chemical compound CREATINE PHOSPHATE CP is used to release energy. However the energy released is not used for muscle contraction but to rebuild the levels of ATP which is used for muscle contraction. The ATP-CP can rebuild your levels of ATP immediately at high speeds. As a result the body uses this systems for intense, explosive activities such as sprinting and throwing. However, like ATP the CP supplies are only limited, so once the CP levels drop fatigue sets in. This usually occurs after about 10 seconds of maximal effort. However, after between 2-5 minutes rest both ATP and CP levels will be restored.

The LACTIC ACID system also supplies energy anaerobically. When the high intensity energy demands last longer than 10 seconds the ATP-CP system can no longer supply the energy. After 10 seconds the CP levels have depleted. As a result the energy for rebuilding the ATP now comes from the Lactic Acid system. This system involves the anaerobic breakdown of GLYCOGEN – this is a form of carbohydrate which is stored on our muscles and liver. We obtain this substance through the foods we eat. When broken down it supplies the energy to rebulid the ATP – it also generates a substance called PYRUVIC ACID. Because there is no oxygen present in the anerobis energy system the Pyruvic Acid is converted into Lactic Acid. This bulid up of Lactic Acid in the muscles is what causes pain and fatigue. Once the exercise has stopped the muscles are flushed of the lactic acid allowing them to recover. This system supplies the energy quickly and is principally used in short term high intensity activities, such as a 400m, 100m swim etc. However, it also comes in to play at the end of aerobic events. Why? The LACTIC ACID system can supply energy for about 1 minute

The AEROBIC system also supplies energy aerobically. When the energy demands of the activity last longer that 1 minute the energy must come form a much longer lasting source. This is when the AEROBIC SYSTEM is used. Similar to the Lactic Acid system, the aerobic system uses the substance glycogen to rebuild the ATP. However during this break down oxygen is present. Due to the presence of oxygen the Pyruvic acid that is formed is not converted into Lactic Acid, but into Carbon Dioxide and Water - therefore the onset of fatigue is delayed. The aerobic system can supply energy over a long period of time, but this happens relatively slowly. As a result the system is mainly used in endurance events such as distance running and cycling etc.