Three Energy Systems Part II By Scott Canipe
In part II, the three energy systems will explained in greater detail. But before this is done let us summarize what we learned in part I.
The three energy systems:
First of the three energy systems activities used:
Of the three energy systems, ATP-CP is the simplest one and supplies the body with immediate energy. It is part of one of the two anaerobic energy systems (without the presence of oxygen). It utilizes the ATP that is stored in the muscle to generate energy. It is the energy pathway that is used for muscle contractions of high intensity but over short periods of time. This energy reserve is accessible for approximately 0-10 seconds of high intense exercise and then it must be replenished.
The ATP-CP system comprises an interaction between two molecules, ATP and creatine phosphate (CP) within the mitochondria of a cell. The CP molecule releases a large amount of energy when the bonds between its creatine and phosphate molecules are divided. This compound of creatine and phosphate (CP) is very important in this process. It phosphorylates ADP (adds the third phosphate group back) and converts it into ATP using the enzyme called “creatine kinase.” As explained in part I of the three energy systems, this is called “phosphorylation.” ATP is now available to begin the energy cycle again. At this point, the cell's percentage of CP is three to five times higher than that of ATP; hence, CP is the main source of energy.
The ATP-CP pathway is the body's primary immediate source of energy of the three energy systems. Activities which require rapid and immediate energy are heavily dependent on this pathway. After ATP-CP is used up the other two energy systems take over.
CP (creatine phosphate) is synthesized naturally within the body. It comes from amino acids (The liver generates creatine phosphate from amino acids) and dietary intake such as meats or supplementation.
This is the reason why you hear so much about CREATINE KINASE being sold in the supplement marketplace such as GNC and so forth. This supplement aids in the function of the ATP–CP energy pathway.
Note: For very high intense/all out exercises such as sprinting, ATP-CP can only be made available up to about 10 seconds. However, some studies have shown that ATP-CP can also be used as energy up to 60 seconds of a moderate exercise such as casual walking. The illustrates how the timing of the three energy systems are phased in and out depending the intensity of the exercise.
Second of the three energy systems activities used:
Medium duration activities such as sprint swimming, lifting weights like a bodybuilder does, moderate intensity jump roping, and other activities lasting between ten seconds and four minutes are considered to be using the anaerobic lactic glycolysis energy system.When approximately 10 seconds have expired during intense exercise, the CP begins to phase out as energy and glycogen begins to come into effect. At about 45 seconds the muscles are being contracted using glycogen exclusively. This is second energy system.
The lactic acid energy system utilizes glycogen from carbohydrates. This is a two-phase energy system also called glycolysis. Glycolysis is essentially the blood transporting a glucose molecule from carbohydrates into ATP and two molecules of pyruvic acid in the cell. There is a series of complicated steps to accomplish this feat, actually 10 steps that I will not get into here.
As the muscle is being contracted, after approximately 2 minutes, without adequate oxygen reserves, the pyruvic acid is converted into alanine and lactic acid. Some of the lactic acid begins to escape into the bloodstream. However, if the stress of the exercise is continuously strenuous, lactic acid buildup grows. When the bloodstream gets full of lactic acid, the muscles are then unable to contract; fatigue increases and the exercise becomes much more difficult. This is referred to as the lactate threshold. This explains the burning feel as fatigue sets in as a result of the lactic acid buildup (Although lactic acid produces an acidic environment it is NOT a waste byproduct as erroneously believed by many).
Of the three energy systems, the anaerobic lactic glycolysis is largely used during medium intensity exercises
Third of the three energy systems activities used:
The aerobic glycolysis energy system works by supplying oxygen to the muscles. This is the most complex of the three energy systems. It requires the heart, lungs and the whole circulatory system to work.
It also incorporates proteins, carbohydrates, and fats to generate ATP for energy. This last of the three energy system is carried out in three-stages comprised of many complicated steps. It prepares the enzyme Aceytl-CoA, the Krebs cycle of glycolysis and the electron transport chain through these steps resulting in the production of ATP and water molecules.
Depending on the intensity of the exercise will dictate when muscles will begin to use aerobic glycolysis system for energy.
If the exercise is exerted maximally then it could be as early as thirty seconds before this aerobic energy system begins to phase in. If the exercise is continued out moderately, then it typically takes around two minutes and the aerobic energy system activates.
At this point, large amounts of oxygen are supplied from the bloodstream to the muscles for energy. Glycogen is synthesized into ATP in the mitochondria. Water and carbon dioxide are the byproducts of this process that the muscle cells diffused into the bloodstream. This expulsion of the waste products enables the muscles to continue on without fatigue.
The heart and the lungs have to work harder to move the oxygenated blood throughout the body. Aerobic energy allows the muscles to continue to work and contract.
As well as using glycogen for the bases of ATP synthesis, this aerobic energy system can also use fat after glycogen stores have been depleted. This is one of the main reasons that many fitness enthusiasts subscribe to either doing cardio first thing in the morning or after a heavy strength training session to burn body fat.
The reasoning behind this is:
A. First thing in the morning the body has not consumed any food for about eight to twelve hours after sleeping. So therefore, in the morning, glycogen levels are very low and doing cardio at this time can increase the chances of using fat as energy for the exercise session.
B. Immediately after doing heavy strength training ensures that glycogen stores have been lowered substantially or even exhausted. Hence, by doing cardio at this point, some of the energy required will be derived from the fat cells.
The complexity of this system, along with the fact that it relies on the circulatory system to supply oxygen, makes it slower to act than the anaerobic systems. The aerobic glycolysis system kicks into effect during long-term, low-to-moderate-intensity exercises. It can be relied upon for long periods of time making it the primary system used for endurance activities.
(Click here for part I that lays the foundation of the three energy systems.)
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