These are held together by high energy bonds, which when broken, produce energy.
During exercise, energy is needed at a faster pace – muscles contract more frequently, the heart beats faster, etc. ATP is made up of one molecule of adenosine and three phosphates.
This system allows the body to work in a steady state – the muscles work below maximal effort and keep this going for a long period of time.
Carbon dioxide and water are produced as by-products.
It takes some time for oxygen to get into the blood and then to working muscles.
The lactic acid system of energy production is used when oxygen is not available and when stores of creatine phosphate run out (after approximately 10 seconds).
The ADP uses energy formed from the breakdown of carbohydrates (glycogen or glucose) to produce ATP. As lactic acid accumulates in the muscle, muscular contraction becomes more difficult.
ATP → ADP P energy (for movement) Carbohydrate → lactic acid energy (to resynthesize ATP) ADP P energy → ATP This energy system does not last long and will sustain energy production for intense activities that last up to 3 minutes.
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.