Energy systems
Three systems in the body create ATP energy. These work simultaneously, but the contribution from each depends on the type of exercise, its intensity and duration.
ATP-CP
The sprint system - this provides enough energy for a five- to six-second sprint and doesn't require oxygen (anaerobic). CP (creatine phosphate) is another high-energy molecule where the phosphate can be broken off very quickly, releasing energy; it's used to convert ADP back to ATP. Muscles don't have large stores of CP, so it's used up fast. This is why some athletes use creatine supplements to maximise their muscle stores. ¨
Anaerobic
The high power system - this provides energy for a 90-second power burst. This system is the fast anaerobic (without oxygen) breakdown of glucose for energy, but only provides two molecules of ATP along with a waste product called lactic acid - too much of this causes muscle fatigue.
Aerobic
The endurance system - how long you can keep going depends on how fit you are! This system is the slow aerobic (with oxygen) breakdown of glucose for energy - so keep breathing in that oxygen. It provides a massive 38 molecules of ATP - that's nearly 20 times more than the anaerobic system. The aerobic system can also use fat to produce ATP energy. Endurance training can make the muscles use fat more efficiently - a good reason to improve your endurance fitness.