The food we eat, in the form of carbohydrates, fats and proteins, is used as fuel for reactions in the body that make us 'alive'. To utilise these fuels for muscle action, the body converts them to a common 'energy currency', called adenosine tri-phosphate (ATP). There are essentially two mechanisms for producing ATP, the aerobic and anaerobic pathways. 'Aerobic' means literally with oxygen, while 'anaerobic' means without oxygen.
For low intensity activities, for example sleeping, working and jogging, and more intense however sustained activities such as marathon running, the ATP required for muscle contraction is produced primarily by the aerobic pathway. The rate that ATP is supplied by the aerobic processes is relatively slow, and therefore the rate of work output is also slow. The by-products of aerobic metabolism are carbon dioxide, which is exhaled by normal respiration, and water. As long as there is a continual supply of fuel (eg. fats and carbohydrates stored in the body) and oxygen, aerobic activities can continue for long periods.
For more explosive movements, such as sprinting or jumping, ATP is required at a faster rate. This ATP can be supplied by anaerobic pathways. There are two pathways by which the body produces energy anaerobically. The muscle can use stores of ATP, or a similar compound called phosphocreatine, already present in the muscles. ATP can also be produced via the lactate anaerobic system, so called as lactic acid is produced as a by-product. The anaerobic processes cannot continue indefinitely as the stores of ATP or phosphocreatine become depleted, and lactic acid accumulates within the muscles and causes muscle pain and fatigue.
During exercise, both aerobic and anaerobic systems work concurrently, however the proportion of ATP supplied from each process varies according to the intensity and duration of exercise. For example, 100m sprinters will use predominantly the anaerobic system, an 800 meter runner both anaerobic and aerobic sources, while the long distance runner will derive most of their energy via aerobic processes.
Anaerobic - ATP-CP
This system uses creatine phosphate (CP) and has a very rapid rate of ATP production. The creatine phosphate is used to reconstitute ATP after it’s broken down to release its energy. The total amount of CP and ATP stored in muscles is small, so there is limited energy available for muscular contraction. It is, however, instantaneously available and is essential at the onset of activity, as well as during short-term high-intensity activities lasting about 1 to 30 seconds in duration, such as sprinting, weight-lifting or throwing a ball.
Anerobic - Lactic Acid
Anaerobic glycolysis does not require oxygen and uses the energy contained in glucose for the formation of ATP. This pathway occurs within the cytoplasm and breaks glucose down into a simpler component called pyruvate. As an intermediate pathway between the phosphagen and aerobic system, anaerobic glycolysis can produce ATP quite rapidly for use during activities requiring large bursts of energy over somewhat longer periods of time (30 seconds to three minutes max, or during endurance activities prior to steady state being achieved).
Aerobic
This pathway requires oxygen to produce ATP, because carbohydrates and fats are only burned in the presence of oxygen. This pathway occurs in the mitochondria of the cell and is used for activities requiring sustained energy production. Aerobic glycolysis has a slow rate of ATP production and is predominantly utilized during longer-duration, lower-intensity activities after the phosphagen and anaerobic systems have fatigued.
It is important to remember that all three of these systems contribute to the energy needs of the body during physical activity. These systems do not work independently of each other, but rather dominate at different times, depending on the duration and the intensity of the activity.
In groups you must create the following about one of the energy systems. You can use the computers available to research but by the end of the lesson you should have completed your presentation:
- A diagram that explains how the energy is created
- 5 Facts about the system
- A brief explanation of how it works (one paragraph)
- Sports/Activities that the system works with
