Atp resynthesis energy systems

The ATP-PC System

So although fat acts as a vast stockpile of fuel, energy release is too slow for very intense activity 5. Carbohydrate Unlike fat, carbohydrate is not stored in peripheral deposits throughout the body. A heavy training session can deplete carbohydrate stores in the muscles and liver, as can a restriction in dietary intake.


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Carbohydrate can release energy much more quickly than fat 5. Protein Protein is used as a source of energy, particularly during prolonged activity, however it must first be broken down into amino acids before then being converted into glucose. As with, fat, protein cannot supply energy at the same rate as carbohydrate. The rate at which is energy is released from the substrates is determined by a number of factors.

For example, if there are large amounts of one type of fuel available, the body may rely more on this source than on others. There are three separate energy systems through which ATP can be produced. A number of factors determine which of these energy systems is chosen, such as exercise intensity for example.

Basic Terminology

PCr is broken down releasing a phosphate and energy, which is then used to rebuild ATP. Combined, the ATP-PCr system can sustain all-out exercise for seconds and it is during this time that the potential rate for power output is at its greatest 1. If activity continues beyond this immediate period, the body must rely on another energy system to produce ATP. Glycolysis literally means the breakdown lysis of glucose and consists of a series of enzymatic reactions. Remember that the carbohydrates we eat supply the body with glucose, which can be stored as glycogen in the muscles or liver for later use.

In fact, oxygen availability has been shown to have little to do with which of the two end products, lactate or pyruvate is produced. Hence the terms aerobic meaning with oxygen and anaerobic meaning without oxygen become a bit misleading 5. As its name would suggest the fast glycolitic system can produce energy at a greater rate than slow glycolysis. However, because the end product of fast glycolysis is lactic acid, it can quickly accumulate and is thought to lead to muscular fatigue 1.


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  • This also coincides with a drop in maximal power output as the immediately available phosphogens, ATP and PCr, begin to run out. By about 30 seconds of sustained activity the majority of energy comes from fast glycolysis 2. At 45 seconds of sustained activity there is a second decline in power output the first decline being after about 10 seconds.

    Activity beyond this point corresponds with a growing reliance on the.

    Slow glycolysis is exactly the same series of reactions as fast glycolysis that metabolise glucose to form two ATPs. Following glycolysis, further ATP can be produced by funnelling acetyl coenzyme A through the. Krebs Cycle The Krebs cycle is a complex series of chemical reactions that continues the oxidization of glucose that was started during glycolysis.

    Acetyl coenzyme A enters the Krebs cycle and is broken down in to carbon dioxide and hydrogen allowing more two more ATPs to be formed. However, the hydrogen produced in the Krebs cycle plus the hydrogen produced during glycolysis, left unchecked would cause cells to become too acidic 2.

    Electron Transport Chain Hydrogen is carried to the electron transport chain, another series of chemical reactions, and here it combines with oxygen to form water thus preventing acidification. This chain, which requires the presence of oxygen, also results in 34 ATPs being formed 2.

    Beta Oxidation Unlike glycolysis, the Krebs cycle and electron transport chain can metabolise fat as well as carbohydrate to produce ATP. Acetyl coenzyme A can now enter the Krebs cycle and from this point on, fat metabolism follows the same path as carbohydrate metabolism 5. Fat Metabolism So to recap, the oxidative system can produce ATP through either fat fatty acids or carbohydrate glucose.

    The key difference is that complete combustion of a fatty acid molecule produces significantly more acetyl coenzyme A and hydrogen and hence ATP compared to a glucose molecule. However, because fatty acids consist of more carbon atoms than glucose, they require more oxygen for their combustion 2. So if your body is to use fat for fuel it must have sufficient oxygen supply to meet the demands of exercise.

    Securing energy for sports performance

    If exercise is intense and the cardiovascular system is unable to supply cells with oxygen quickly enough, carbohydrate must be used to produce ATP. Put another way, if you run out of carbohydrate stores as in long duration events , exercise intensity must reduce as the body switches to fat as its primary source of fuel.

    However, amino acids, the building blocks of protein, can be either converted into glucose or into other intermediates used by the Krebs cycle such as acetyl coenzyme A. The oxidative system as a whole is used primarily during rest and low-intensity exercise. Between the two could be anything: an intense twenty-second activity, one minute of constant force exertion, or a five-minute event with varied intensities of effort. As you can see, there are many expressions of energy output depending on the amount of force required and the length of the activity.

    What then, is the energy source for activities that fall on the continuum at various points? This is the essence of bioenergetics - so many possibilities and so many factors involved. What dictates which one or two is relied upon the most is the effort required. Take home point: ATP must be present for muscles to contract.

    If depleted, it must be replenished if further muscle contraction is to continue. Perform an explosive, one-time movement such as a standing long jump or vertical jump and you exert maximal effort, but guess what? You will not become fatigued from this single exertion. However, jump multiple times and eventually you will become fatigued.


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    • Going all-out for as long as possible will deplete immediate ATP stores, then glycolytic stores. Continuing effort must be fueled by the oxidative system at a lower intensity, all other factors being equal.

      Energy Systems & Exercise | Lactic Acid, Aerobic and Anaerobic

      The most pure aerobic activity that exists is sleeping or lying comatose. It is immediate and functions without oxygen. During the first few seconds of any activity, stored ATP supplies the energy. For a few more seconds beyond that, PC cushions the decline of ATP until there is a shift to another energy system. Examples: a short sprint, lifting a heavy resistance for three repetitions, or pitching a baseball. Now it becomes more complicated as energy demands shift to this system. Dietary carbohydrates supply glucose that circulates in the blood or is stored as glycogen in the muscles and the liver.

      Like the ATP-PC system, oxygen is not required for the actual process of glycolysis but it does play a role with the byproduct of glycolysis: pyruvic acid. It is estimated glycolysis can create energy at approximately 16 calories per minute.

      Here is where it gets interesting. After maximum power declines around 12 seconds, further intense activity up to approximately 30 seconds results in lactic acid accumulation, a decrease in power, and consequent muscle fatigue. Exerting further effort up to approximately 50 seconds results in another drop in power due to the shift in dependence on the oxidative system. Bottom line: it is getting tougher. Example: think of an all-out sprint, to a slower jog, to an eventual walk. That is the progression of the three energy systems when going all-out. Recall the byproduct of glycolysis is pyruvic acid.

      In fast glycolysis, more power can be generated, but pyruvic acid is converted to lactic acid and fatigue ensues quickly. Slow glycolysis is different. Relatively less power is generated, but pyruvic acid is converted to acetyl coenzyme A acA , fed through the oxidative Krebs cycle, more ATP is produced, and fatigued is delayed.

      Thus, extreme fatigue can be avoided but relatively less-intense effort can continue to be expressed in slow glycolysis as compared to fast glycolysis. Examples: any moderately-long runs such as yards, a effort of all-out MMA maneuvers, or a one-minute full-court press - offense display - and another full-court press effort in basketball. Continued effort results in further decline, either via fast glycolysis quick decline or slow glycolysis slower decline. Examples: 6-mile run, low-level manual labor on an eight-hour work shift, or a 3-mile walk. The Krebs cycle is a sequence of chemical reactions that continues to oxidize the glucose that was initiated during glycolysis.

      Remember the acA? Through more chemical reactions in the electron transport chain, hydrogen combines with oxygen, water is produced, and acidity is prevented.