How much time should you take between sets? Understanding ATP
What is ATP?
ATP (adenosine triphosphate) is one of the three main energy systems used during exercise. The other two are glycolysis and aerobic metabolism. During exercise, the body uses oxygen to produce energy from carbohydrates or fats stored in the muscles. These fuels are broken down into carbon dioxide and water molecules, which then become usable by your cells for fuel.
The body’s primary source of energy comes from glucose, which it stores in the liver and muscle cells. Glucose is converted into glycogen when not needed.
Glycogen is broken down into glucose when needed. When your muscles need energy, they break down glycogen to release its stored sugar as a form of energy called ATP (Adenosine Triphosphate).
ATP is an organic molecule made up of three atoms: adenine, cytosine and guanine. Adenosine is a phosphate group attached to another atom.
ATP can be produced through several pathways; however, the most common pathway involves using phosphocreatine as a starting material. Phosphocreatine consists of two molecules of creatine bound together with four molecules of nitrogen.
A phosphate group is transferred from phosphocreatine (PCr) to adenosine, creating ADP (adenosine diphosphate). This reaction is reversed when ATP needs to be broken down.
More energy is yielded compared to glycolysis. Also, it does not produce lactic acid.
The body uses ATP for immediate available energy that drives muscle contractions. ATP eventually breaks down to ADP and phosphate.
The body uses another enzyme called ATPase to regenerate ATP from ADP and phosphate groups. This process occurs during short intervals of exercise of low to moderate intensity (anaerobic exercise).
ATP can be produced in high amounts that rapidly breakdown and regenerate from the starting material during periods of intense activity lasting up to about 10 seconds (anaerobic exercise). This process is known as creatine phosphate (CP).
After about 10 seconds of intense activity, the body must then rely on the aerobic system to produce energy. This process involves the use of oxygen in which pyruvate is broken down in the mitochondria and produces ATP (aerobic exercise).
How is ATP Used?
ATP is used during short bursts of exercise lasting up to about 10 seconds (anaerobic exercise). The body then relies on the aerobic system to produce energy during periods of exercise lasting longer than about 10 seconds and up to about 2 hours (aerobic exercise).
Muscles can also run out of ATP quickly, especially if it is not properly regenerated. This is why you should take a break after an intense activity lasting up to about 10 seconds.
The muscles need time to refill their supply of ATP and CP.
The body breaks down sugars, fats and proteins to produce ATP. The breakdown of these substances produces metabolic waste and intermediates known as carbon dioxide, water and ammonia.
As the intensity of exercise increases, so does the concentration and amount of metabolic waste and intermediates produced. A person will then develop acidosis, a condition in which blood pH decreases due to an increase in blood acidity.
Muscles can run out of oxygen quickly under great exertion. The body’s cells need a constant supply of oxygen to produce ATP and other substances necessary for cell growth, maintenance and repair.
The process of respiration involves an exchange of gases between the air we breathe and our blood.
Respiration takes place in the lungs where blood gets oxygen from the atmosphere and loses carbon dioxide. The process occurs by way of blood vessels known as alveoli that are supplied by air sacs called lungs.
The oxygenated blood flows from the lungs through blood vessels at the bottom of our feet and rises up to the heart. The heart pumps oxygenated blood through arteries to cells all over the body.
ATP is required for muscular contraction, including the squeezing motion of the gut that moves food through the digestive tract. Muscles also contract in other areas of the body such as the heart (cardiac muscle) and blood vessels (visceral muscle).
The body can produce ATP anaerobically and aerobically. During short bursts of exercise lasting up to about 10 seconds, the body produces ATP anaerobically.
The body then relies on the aerobic system to produce energy during periods of exercise lasting longer than about 10 seconds and up to about 2 hours.
ATP stores are quickly depleted during intense muscular contractions. ATP must be produced during muscular contraction to maintain a steady supply of energy for cells.
ATP also stores regenerate during relaxation when energy is not required. ATP cannot be stored in the body, therefore it must be continuously produced to meet energy demands. ATP can be regenerated by breaking down sugars (glycolysis), fats (Krebs cycle) and proteins (cellular enzymes). If the demand for energy exceeds the ability of the body to produce ATP, then fatigue sets in.
ATP provides cells with quick bursts of energy. ATP is constantly being produced and used up in our bodies.
The short, high-energy phosphate bond in ATP provides the power for muscular movement. Muscles rely on stored ATP for energy. Once the phosphate bond is broken, energy is released and this results in muscular movement.
The aerobic and anaerobic energy systems function independently of each other. Both systems are always functioning even at rest.
The intensity of exercise determines which system is primarily engaged under normal circumstances. As exercise intensity increases, so does the demand for energy. This increase in energy demand stimulates the body to enhance its ability to meet that demand. This enhancement is in the form of more mitochondria and more capillaries to deliver oxygen.
The anaerobic energy pathway produces only a little ATP over a short period of time, but does it very quickly. The aerobic pathway takes a little longer to produce a lot of ATP.
The intensity of exercise determines which system is the primary source of ATP production. The rate of energy production also affects the relative contribution of each system to total energy production. For example, during long distance running, aerobic energy pathway contributes a larger portion of the total energy produced than it does during short bursts of activity.
Glycolysis is the breaking down of glucose (sugar) molecule in order to extract potential energy that can be used to produce ATP. It takes place in the cytoplasm of cells rather than in the mitochondria and is independent of oxygen.
It produces a small amount of ATP over a short period of time, but is a very quick source of energy that can be used to meet an energy demand that requires a quick increase in ATP. It also produces lactic acid as a waste by-product. Lactic acid causes muscles to become fatigued or sore after exercise.
Glycolysis occurs in the cytoplasm rather than the mitochondria. Glucose is consumed without the use of oxygen.
Instead, ATP is generated by the conversion of glucose into pyruvate by a series of enzyme-catalyzed reactions. Pyruvate then enters a chain of additional reactions that result in its eventual conversion into acetyl coenzyme A (acetyl CoA). Acetyl CoA enters the Krebs cycle. Two molecules of pyruvate are converted into two acetyl CoA in each turn of the cycle. The pyruvate is not stored but is combined with the next available molecule of acetyl CoA, forming citric acid. The Krebs cycle (or citric acid cycle) takes place in the matrix of mitochondria and is an aerobic process that requires oxygen to produce ATP.
The rate of glycolysis is influenced by all types of stimuli that affect the activity of the various enzymes involved. For example, when muscles are exercised, the number of enzyme molecules increases in order to speed up the rate of ATP production.
The increase in the number of enzyme molecules can be accomplished without a significant lag time since they are not produced de novo from protein building blocks in cells but rather are made as needed by modifying existing proteins.
Lactic acid is a three-carbon molecule produced during oxidation of glucose, the last step in the glycolysis process. It is the cause of muscle fatigue.
The reason it causes fatigue is not well understood, but it is thought to inhibit the activity of the enzyme that catalyzes the final step of glycolysis.
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