The 3 different energy systems
There are three energy systems which convert adenosine diphosphate (ADP) back into adenosine triphosphate (ATP) for the body to be able to function, these include; The ATP-PC system also known as creatine phosphate (CP) or the phosphocreatine (PC) system, the lactate or anaerobic glycolysis system also commonly known as the lactic acid system and the third energy system is the aerobic system also known as the oxygen, or oxidative system. Both the ATP-PC and the lactate energy systems are anaerobic systems, where ATP is created without oxygen, whereas the aerobic system uses oxygen to create ATP.
These energy system create ATP in different places within the cell, ATP-PC and the lactate systems create ATP via anaerobic energy production in the fluid of the cells known as the cytoplasm, whereas the aerobic energy production of ATP occurs deeper within the cell in small structures called mitochondria, these mitochondria are known as the ‘powerhouse’ of a cell.
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Each of the three energy systems uses a different macronutrients to convert the ADP back into ATP for energy. The macronutrients which are used to fuel the energy systems are proteins, carbohydrates & fats, these are known as energy substrates. All three energy substrates play an important part in ATP production within each of the three different systems, carbohydrate is catabolised into glucose & fats into fatty acids, these two substrates are the preferred energy sources and used to create ATP when the body is in an aerobic state. Proteins catabolised into amino acids and are used to create phosphocreatine’s which is stored within the muscle for use at a time when needed.
Each of the three different energy systems provides a different amount of ATP and at different speeds; Energy from the ATP-PC system can be accessed quickly as phosphocreatine which is stored within the muscle can rapidly resynthesise ATP from ADP however not much ATP is generated due to low supply of phosphocreatine. Energy from the lactate system can be accessed relatively quickly from glucose in the blood and glycogen stored within the liver and muscle. This re-synthesis of ATP from ADP occurs slower than the ATP-PC system, however generates more ATP due to larger amounts of the glucose and glycogen fuel available. The down side to this energy pathway is that the by-product lactate is produced and after 1-3minutes which reduces the ability to create more ATP and needs to be removed. Energy from the aerobic system is the preferred energy at rest and low intensity as it generates lots of ATP however does this relatively slowly from the fatty acids and glucose in the blood. This process is completed the mitochondria of the cell and continues all the time an individual is alive.