The Three Energy Systems
The Three Energy Systems
The first way the body gets ATP is through the phosphagen system, also known as the ATP-CP system, which uses the ATP stored in the muscles to supply that energy. The body can store enough ATP at any one time to allow for around 3 seconds of full powered exertion (a little more or a little less depending on your physical fitness and various other factors), at which point it will need to look elsewhere.
Fortunately breaking the ATP molecules results in some useful bi products – ADP (andenosinediphosphate) and AMP (andenosine monophosphate) with two and one bonded phosphagen molecules respectively. So if you imagine you have three bonded molecules and they break you will understandably be left with a one and a two, or three single molecules. It’s basic maths… The good news is that using a substance called creatine phosphate (hence the CP!) can then recombine these molecules to make them back into ATP ready to be broken once more for extra energy. The body can store enough creatine for roughly 8-10 seconds of continued exertion, meaning that in total the body can use the phosphagen system for around 13 seconds maximum of continued exertion.That is enough to sprint just over 100 metres. It is thought however that through the use of creatine supplements that this maximum time can be increased marginally.
At this point if exertion continues the body needs to get its ATP from somewhere else and this is when it looks to its stored carbohydrates in the form of glycogen. This represents the shift to what is known as the ‘glycogen lactic acid system’.
This system is a slightly slower and less efficient means of supplying energy, which requires the body to split the glycogen first into glucose and then again into ATP. This unfortunately creates a number of unwanted by-products called metabolites including lactic acid (from which the substance takes its name).This metabolic build-up creates the uncomfortable, mildly painful ‘burning’ sensation we get in our muscles when we push ourselves in the gym. The body can sustain itself using the glycogen lactic acid system for a further one minute and thirty seconds until this build up becomes too much to tolerate. If we continue to try and push ourselves at MHR past this point, it can lead to nausea and even fainting.
It was long believed that lactic acid was actually responsible for this failure and for the burning sensation. However, more recent research has shown us that lactate is not harmful in itself but rather seems to correlate with other factors that fatigue the glycogen lactic acid system. Thus high level athletes can still monitor their build-up of lactate in the blood in order to calculate a ‘lactate inflection point’. With training, it is possible to improve tolerance to metabolites and thus sustain maximum exertion for longer.
Guess what you can use to improve this aspect of your fitness? HIIT!
Both these systems are anaerobic, meaning that for the first one minute and forty-three seconds the body won’t be using oxygen or burning fat.
In order to lose weight then the training must continue past this point and force the body to find its energy elsewhere. This is where the aerobic system comes in, relying on the oxidisation of foodstuffs in our mitochondria. In other words, the body looks to our supplies of glycogen (and so ATP) stored in our cells as fat and then uses the oxygen in our blood to break them down and carry them to our muscles. This is then what leads to fat being burned directly. This forces us to breathe more heavily in order to supply the necessary amount of oxygen and it increase our heartrate further to transport the oxygen to the fat stores and then to bring the energy to our muscles and brain.
The aerobic energy system can actually be used indefinitely and will continue until you completely exhaust all supplies of energy located around the body. During a typical prolonged endurance test, you will find you also breakdown protein for energy and even muscle. This in contrast to high intensity exercises that will use 100% carbohydrates for fuel, purely because they provide the quickest and most accessible source of ATP.