It is used when there is a plentiful supply of oxygen for the muscles to use while working. This system starts to ‘kick-in’ after about 3 minutes and theoretically will go on for ever.
The ADP formed during energy production uses energy from glucose/glycogen (carbohydrates), fat or protein breakdown to reform ATP.
These three energy systems do not provide energy for physical activity – only ATP can do this – they provide energy to restore ADP into ATP.
(anaerobic = without oxygen) These systems produce energy when muscles need to move quickly or forcefully, but do not need to keep going for very long.
If the activity is continued, lactic acid is produced.
After the activity has been finished, the performer needs to have a rest and take in the extra oxygen that is needed.
With continued high intensity exercise, there is a build-up of lactic acid in the working muscles.
If the rate of build-up is greater than the rate of removal then the muscles become fatigued and muscle contraction becomes impaired.
Once exercise has started, the demand for energy increases and the stored supply of ATP is used up in a couple of seconds.
If continued muscular contraction is to take place, ATP has to be reformed from ADP once it has been used up. The body has three systems for doing this, which are collectively known as energy systems – there are two anaerobic and one aerobic system.