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 How The Body Uses Energy
Adenosine triphosphate (ATP) is the direct energy source for movement, and your body has different systems to make ATP. The amount of ATP a system makes available determines the amount of energy you can get from that system. Also, the rate at which a system makes ATP available determines the rate at which you can get energy from the system.
Using ATP for energy means breaking off a phosphate group to release the energy. The reaction releases energy and yields ADP(Adenosine Di-Phosphate) plus a phosphate group. The reaction can be reversed, but it needs added energy to do so. The energy systems used for movement (from slowest to fastest) are aerobic lipolysis, aerobic glycolysis, anaerobic glycolysis, and stored adenosine triphosphate coupled with creatine phosphate (ATP/CP). Also, the energy systems that make the most ATP available are the ones that do it the slowest. So, the body is constantly in a state of compromise. Also, the body starts with the slowest system and incrementally adds the faster ones as needed. Aerobic Lipolysis
Aerobic lipolysis burns fat using the Krebs cycle. Stored fat is the body's largest reserve of energy and it makes the largest amount of ATP available. So, even an extremely lean person usually has enough stored fat calories to walk over 100 miles. Aerobic Lipolysis is also the slowest producer of ATP. So, it is most useful for low-energy activities such as slow jogging, walking, breathing, talking, etc. It is the primary energy source used to recycle ADP back into ATP and to recycle spent fuel back into glucose between sets of intense exercise. Also, the body always uses aerobic lipolysis and then adds faster systems as needed.
Aerobic Glycolysis
Aerobic glycolysis is the second largest producer of usable energy in the body. It produces less ATP than aerobic lipolysis but produces it much faster. Aerobic glycolysis works together with aerobic lipolysis to provide energy during exercise. But if the person runs out of usable glycogen, aerobic glycolysis stops. This is what happens when an endurance athlete "hits the wall". It results in lower energy output and extreme fatigue.
Aerobic glycolysis begins by breaking down glucose into pyruvate to produce some ATP, after which the pyruvate is oxidized in the Krebs cycle to produce even more ATP. Also, aerobic glycolysis is useful for moderate rates of energy output for moderate periods such as in running a 4 mile race. Anaerobic Glycolysis
Anaerobic glycolysis is not limited by oxygen uptake and produces ATP at about 100 times as fast as aerobic glycolysis. It produces much less ATP per molecule of glucose and is therefore much less efficient.
It begins with the breaking down of glucose into pyruvate to produce ATP. After that, if energy is needed at a faster rate, much of the pyruvate undergoes fermentation. This will produce ATP without the need for oxygen. One of the end products of anaerobic glycolysis is lactic acid which causes a burning sensation in the muscles and inhibits further glycolysis. This inhibition of further glycolysis reduces the energy output during exercise. This happens when you workout a muscle until you feel it burning. During rest, the lactic acid eventually goes from the muscles into the blood and to the liver where it is converted back to pyruvate and then back into glucose in a process called gluconeogenesis via the Cori Cycle. This process demands energy, so the body uses aerobic lipolysis to power it. Adenosine Triphosphate/Creatine Phosphate (ATP/CP)
Stored ATP reserves are the quickest ways to have ATP available for movement. However, the extremely high rates of energy output are offset by the short supply which lasts only seconds.
In many cases, creatine phosphate (CP) will donate a phosphate group to adenosine diphosphate (ADP) to change it back into adenosine triphosphate (ATP). This increases the amount of ATP available after which the creatine becomes creatinine, which is excreted in the urine. Creatine phosphate is created in the body from amino acids and a phosphate group. However, Creatine that is consumed in either natural form (i.e. beef or salmon) or in supplemental form, gets converted into creatine phosphate when it enters the body, which in turn increases the energy output available via the ATP/CP system. The combination of these energy systems obviously has roots in the survival of our ancestors. But understanding them can help us to maximize the benefits that we get from physical exercise. The body always uses aerobic lipolysis and then adds the other energy systems as needed. Each added energy system acts as a booster to assist the slower energy systems. Other articles |
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