Exercise physiology#Metabolic changes

Under provision of energy (including energy metabolism or metabolism) is understood in the physiology of the mobilization, transport and the reduction of high-energy substrates ATP production ( resynthesis ) in the muscle cells of mammals. It is used to perform muscular work. There are different types of energy supply differentiated by energy source ( creatine phosphate, carbohydrates, fats or proteins) and metabolic (aerobic ( oxidative), anaerobic lactacid ( with lactate ) or anaerobically alactacid (without lactate ) ). The associated running with oxygen metabolic processes are described as aerobic, which occur in the mitochondria. The anaerobic metabolism, however, runs from outside the mitochondria in the cytoplasm. If this is done with an increased lactate production, one speaks of a lactaciden energy supply, otherwise alactaciden of metabolism.

4.1 ATP as the basis of the energy metabolism 4.1.1 breakdown of ATP releases energy
4.1.2 ADP

4.2.1 Anaerobic alactacid ( phosphate metabolism)
4.2.2 Anaerobic lactacid

4.3.1 Aerobic glycolysis
4.3.2 Aerobic lipolytic ( Aerobic lipolysis)

Introduction

In order for a muscle contraction can perform work, he needs energy, which comes from the exothermic chemical reactions. This chemical is converted into mechanical energy. The energy requirements of the organism thus increases during physical work. The energy required for muscle contraction is largely provided by hydrolysis ( hydration ) of adenosine triphosphate (ATP ) into adenosine diphosphate ( ADP ) and phosphate (Pi ) are available. The ATP is thus the direct supplier of energy to muscles. However, since its stock is very limited, the muscles must, for example, during physical activity ATP (re) produce, in order to maintain the activity can. The for Reconstruction ( resynthesis ) of ATP energy required is obtained in turn by stepwise oxidation of nutrients sugar (carbohydrates ), fats or fatty acids and proteins ( amino acids). Your are here three fundamentally different mechanisms. There are the anaerobic alactacide energy supply, which anaerobically ( without the aid of oxygen) and alactacid, ie without ( significant ) production of lactic acid ( lactate ) runs. The second Resyntheseweg is the anaerobic lactacide, which even runs anaerobically, but is associated with a lactate production. In contrast, in the aerobic energy supply, energy is released under oxygen consumption.

History

Already in 1841 observed Berzelius and 1877 Du Bois -Reymond, that a close relationship between muscle contraction and metabolism prevails, and showed that the contraction working the muscle cell is connected to a lactate. These observations brought 1914 Parnas and Wagner to the to see the degradation of glycogen of the muscle underlying lactate as an immediate source of energy of contraction work. This statement was supported by the fact that the formation of lactate from glycogen is associated with a release of energy. However, in 1926 the dependence of the contraction process of the lactate were questioned and proved by Clark and Eggleton 1932 that is significantly above the Lactatverwertung beyond lactate formation occurs only at a longer muscle work by the experiments of Hött and Marks. (Since the Lactatverwertung long time was not particularly respected, you went at that time, however, assume that only after prolonged muscular work at all lactate is formed).

After the substance creatine phosphate was discovered in the muscle, a correlation between the creatine phosphate metabolism and contraction processes in the muscle cell was closed as a waste and in the recovery period, a rise of creatine phosphate was observed during the contraction process. While these and other findings gave rise already doubts about the dependence of the contraction process, and the lactate and identify an important role of creatine phosphate, has been clearly refuted by Lunddgaard 1931 Lactattheorie muscle contraction. By means of a suitable test with the aid of a poisoned him muscle with a particular substrate, which prevents lactate, but this contractile and the work was proportional to the breakdown of creatine phosphate, he put the Lactattheorie an irrevocable. In the lactate so that is an anaerobic Resyntheseweg for the creatine phosphate was seen. Furthermore, it was found that under aerobic conditions absent a lactate and held the resynthesis of creatine phosphate by oxidative reactions.

Finally Lohmann discovered in 1931 then the adenosine triphosphate ( ATP). Also the creatine phosphate was provided as an immediate energy source of muscle work in question by this discovery now, as in the following period the ATP a very important role as a coenzyme, regulatory factor was attributed in cell metabolism, energy transfer and immediate source of energy. As has been found, which the high energy content has actually ATP, it is detected as a direct energy source in muscle contraction and formulated by Lohmann the underlying quantitative reactions:

Energy storage

While the high-energy phosphates ATP and creatine phosphate ( KRP) are available within the muscle cell, glycogen, fats and proteins can also be used from other depots. The various energy storage differ significantly in the available amount and the maximum possible energy flow rate.

Adenosine triphosphate ( ATP)

The directly available ATP stores ranging from severe muscular stresses only to provide for about one to two seconds, ie one to three muscle contractions, energy. Even under the condition that the ATP is cleaved to AMP, there is only one in the resting muscle ATP stock of approximately 6 mol / g = 6 mmoles / kg. Now, if you consider the fact that man every day as much ATP consumed, as it corresponds to his body weight, so it's more surprising that ATP, which nevertheless be so important applies for muscle contraction and is the only direct source of energy, just as limited in is the muscle cell present.

Creatine phosphate ( PKR)

Since the present in muscle ATP supply only for one to three muscle contractions sufficient ( about 2 seconds of load time), the body must be continually seek to re-synthesis of ATP as a vital substance. Here the creatine phosphate comes into play, which is an energy-rich chemical compound of creatine (Kr ) and a phosphate group. The present bond between the phosphate and the creatine has a corresponding ATP energy potential. Due to the fast reaction proceeding:

Is resynthesized ATP by cleavage of the phosphate group and its transfer to ADP. In addition, PKR is in about three to four times as large amount (20-30 micromoles / g ) compared with the ATP in the muscle cell stock. The creatine phosphate storage is therefore of great importance for the performance of the skeletal muscles, as it (about 6 s, high Trained Untrained about 12-20 s ) is in strong concentration of work for about 10 seconds in a position to provide the necessary energy. In addition, it is the energy source that the ATP can be resynthesized immediately until then other pathways are activated at a later date.

The creatine phosphate is further seen an important role as an energy gap, resulting in high substrate throughput rates are made possible. It is also clear that the creatine phosphate content depends on the amount and duration of work done. If it comes to extremely high loads, the creatine phosphate storage can be almost completely exhausted and are quickly replenished after the end of exercise. However, should it happen that the replenishment of high-energy phosphates ceases, it will void the contractility of the muscle.

Glucose

In healthy people, the blood contains a certain amount of glucose within a range of concentrations ( see also blood sugar). If this energy is implemented, there will be a continual replacement of the two next mentioned energy sources.

Glycogen

This is a form of glucose, so to speak, " storage-stable form." Glycogen can be used as muscle glycogen in skeletal muscle (1.5 g muscle Glykogen/100 g wet tissue ), and stored in the liver. Liver glycogen ( 75-90 g ) is used to maintain constant blood sugar levels (80-100 mg% ) and thus contributes to maintaining the functioning of the central nervous system ( CNS) in. Since the CNS is dependent on a constant supply of glucose from the blood and even has low glycogen stores, save up to 60% of the votes from the liver to the blood glucose brain metabolism. With prolonged submaximal loads (long-term endurance) the glucose uptake of the muscle from the blood flowing through the liver glycogen and thus plays a significant role. Studies by Coggan (1990 ), that after a 90 -minute exposure to 60% of VO2max, the oxidation of plasma glucose is about one- third of the total carbohydrate oxidation.

In case of strong depletion of glycogen in the liver occurs a drop in blood sugar levels and% can already cause coordinative disturbances at less than 70 mg. Normally, an intensive Glucoseverstoffwechselung to the detriment of the brain metabolism is, however, prevented by protective mechanisms. This reduces the plasma concentration of insulin, which regulates the permeability of glucose through the cell membrane, with decreasing Glykogenvorräten by prolonged muscular work on up to 50 % of the output value from rest. In addition, the liver can at long lasting burdens partially glucose from substrates such as alanine and glycerol re- establish ( gluconeogenesis ).

During intense continuous power ( competition ), the glycogen reserves of the body ranging from about 60 min to 90 min to maintain the glucose replenishment.

Fats

Body fat is present in the subcutaneous adipose tissue ( skin depot ) and in the muscle cell in the form of triglycerides. Triglycerides consist of three fatty acids bonded to glycerol. The free fatty acids ( FFS) can be oxidized in almost all organs. In the muscle cell, it is converted into so-called " C2 - body " acetyl- CoA and introduced into the citric acid cycle. However, the chemical reaction is very slow, so that this form of energy supply with increasing strain provides a decreasing relative proportion of energy provided. With further increasing intensity also their absolute share decreases. The intramuscular triglyceride content is from 0.3 to 0.8 % by volume. The free fatty acids are released upon exposure to water (hydrolysis) of the triglycerides. Lipolysis ( Triglyceridspaltung ) is stimulated by the stress -induced release of catecholamines adrenaline and noradrenaline and on prolonged exposure primarily by growth hormone somatropin. Inhibited it is through the blood lactate concentration. To run Blutlactatwerte 5-8 mmol / l to a significant reduction in plasma levels of fatty acids.

The use of fat oxidation is dependent on various factors such as exercise duration, exercise intensity and intramuscular Glykogenangebot. The fat depots of subcutaneous fat are mainly low and medium intensity and already reduced glycogen used during prolonged stress, mobilization begins only after a 15 to 30 -minute exposure time. The endurance training status plays an important role here, since with increasing power level, the percentage of fatty acid combustion rises to the provision of energy and thus carbohydrate depots are protected.

Blood fats are an intermediate form as an energy source. In addition to the metabolism of glucose, the muscle cells are also able to mobilize energy directly from fat.

Proteins

Energy metabolism

→ See also energy metabolism

The energy required for the resynthesis of ATP can be mobilized in different ways. There are four types of energy supply differentiated by energy source and pathway. Based on the provision of energy forms that occur in the competition in a particular proportional and temporal structure, takes place in the sports science-based training theory, the structural performance derivative of the training areas.

ATP as the basis of the energy metabolism

Breakdown of ATP releases energy

The basis for each muscle contraction the degradation of adenosine triphosphate to adenosine diphosphate ( ADP ) and phosphate (P). The ATP is a high energy compound consisting of adenine with ribose and three phosphates. It is the only energy source that can use the cell directly. The ATP is so important not only allows mechanical work, but also very important energieerfordernde transformations, the activation of the free fatty acids and the preservation of the labile protein structures. Which is important for the muscle contraction reaction of the ATP to the myosin ATPase is:

In another (not typically associated myosin ATPase ) chemical reaction ATP can be degraded to AMP ( adenosine monophosphate ):

However, the latter reaction is a minor role in energy production represents the tension development of the muscle is strongly dependent on the existing ATP content. Humiliations this content lead (from a critical threshold ), first to a limitation of stress development and finally to the inability contraction upon excitation stimuli. Thus, the changes in the ATP content with changes in the potential labor power of a muscle cell are associated. Explore shortening muscles, but which do not work, show no, or only a minor ATP - waste. Verrichtende working muscles, which are also under stress, show a decreased function of this performance ATP levels and a corresponding heat generation. The heat development during muscular work thus goes hand in hand with a change in the level of ATP and can be explained as a consequence of entropy.

ADP

By reducing the damage caused by the myosin ATPase ADP can by a suitable reaction that myokinase (2 mol ADP → 1 mol ATP 1 mol AMP), are obtained under extreme emergency conditions, ATP ( this reaction plays for the energy supply of the muscles normally but no relevant role ). Thus, the major ATP would be directly providable for further contraction work. Inferring the high from myosin ATPase ADP concentrations, and the sensitivity of myokinase to high ADP- mirror, that is, their activity is increased by a high ADP levels, the concentration of ADP is considered as a control variable for the supply of ATP from ADP. Thus, the apparent end product ADP is not a negligible quantity, for his high-energy phosphate bond can be at least theoretically still used.

Anaerobic energy metabolism

Anaerobic alactacid ( phosphate metabolism)

In the anaerobic energy supply alactaciden no oxygen is required and there is no lactic acid. She plays the first few seconds of an athletic stress the crucial role and only lasts for a few seconds or a few maximal muscle contractions ( eg, short sprints, sprints, some forms of strength training ) because the serving as an energy carrier creatine phosphate is present in the muscle cells only in small quantities. The ATP production rate ( more precisely, the resynthesis of ATP from ADP and the energy per unit time) is the anaerobic metabolism alactaciden highest. After the pre-existing ATP supply of the muscles is used up within a few seconds, the more ATP resynthesis occurs in the following 10-30 seconds using the creatine phosphate also readily available.

The energy-yielding anaerobic alactaciden reactions:

Anaerobic lactacid

→ See also lactic acid fermentation

The anaerobic metabolism lactacide does not require oxygen, but leads to the formation of lactic acid (lactate ). He is very fast ( about half the ATP formation rate of anaerobic metabolism alactaziden ), ranging in approximate maximum load (95%) 20 - 40 seconds. Energy is present in the cytosol, glucose is obtained from the ATP via glycolysis. Disadvantage: If increasing performance and maintaining a high Leistungsabforderung the aerobic mechanisms of degradation and recovery of the lactate formed can not prevent a sharp rise in lactate concentration. It finally comes to a sharp rise in lactate, the performance should be discontinued or the intensity can be greatly reduced.

When anaerobic lactaciden energy metabolism by reducing sugar ( glucose) or glycogen is produced ( a storage form of glucose) via chemical reactions lactate and ATP:

This reaction is therefore referred to as glycolysis followed by lactic acid fermentation, which takes place in the sarcoplasm (see Weineck 2006, p 101). As an energy supplier glucose is used ( especially from glycogen ). Intracellular glycogen is energetically favorable, because it must be effected not only via the blood stream. The degradation of 1 mole of glucose to lactate brings 2 mol ATP. If glycogen recovered, bringing the mathematically 3 moles of ATP. The intermediate product, pyruvic acid ( pyruvate ), is converted during the anaerobic lactic acid fermentation to lactate.

However, the formed during the lactic acid fermentation of lactate has on the whole metabolism, both locally and generally, impact as it is transported through the lactate shuttle mechanism in other areas of the body. After maximum loads in muscle lactate levels up to 25 mmol / kg, to find up to 20 mmol / kg in the blood. This is accompanied usually an extreme acidity in the local tissues, and in the arterial blood, which is a acidosis (strongly of reduced pH) connected. By acidosis occurs an enzyme inhibition, which brings about a standstill of the glycolytic metabolism processes. This abort the maximum load is an important protective function for the organism; they prevents excessive acidification of the muscle, which would result in a destruction of intracellular protein structures result.

Aerobic energy metabolism

Aerobic glycolysis

The aerobic glycolytic metabolism uses uses oxygen carbohydrates. He plays in the energy deployments for all charges which will last longer than a minute a part. The energy is obtained by the simplified formula glucose oxygen → carbon dioxide water energy. This path has the following characteristics: it is saved faster than fat metabolism ( ATP production rate is about one-quarter of anaerobic alactaciden metabolism ), the glycogen (the specific form of glucose ) in muscle, must be not only antransportiert and glucose may by carbohydrate-containing drinks are tracked. He uses the energy released in the Weiterverstoffwechselung the high-energy intermediates energy. This is primarily to the sales tax incurred on anaerobic metabolism lactaciden lactate and pyruvate. The sub-processes oxidative decarboxylation, citric acid cycle and respiratory chain do not find, in contrast to the anaerobic metabolic pathways in the cytoplasm instead, but in the mitochondria. The aerobic carbohydrate metabolism has the largest proportion of the muscle work at medium and submaximal intensity. Disadvantage: The body's glycogen reserves are limited to about 60 to 90 minutes continuous load, through long hours of muscle work, the absorption capacity of the intestine for carbohydrates limits the intensity of the performance.

The activated acetic acid ( acetyl -CoA), which is caused by oxidative decarboxylation, by running for the further reduction of the citric acid cycle and the respiratory chain. In this type of energy supply glucose about 32 moles of ATP are produced from 1 mol. If the intracellular glycogen used to reduce arise even 34 mol ATP:

The aerobic breakdown of glucose to about 15 times the amount of ATP can be obtained as in the lactic acid fermentation. However, this high energy yield also has a significant disadvantage. With the help of oxidative combustion Although many moles of ATP are provided, but carried this energy deployment over long reaction chains, which is why it takes a long time, until this energy is available.

Aerobic lipolytic ( Aerobic lipolysis)

→ See also fat burning

The aerobic lipolytic metabolism uses uses oxygen fatty acids. The energy is obtained by the simplified formula fat oxygen → carbon dioxide water energy. The process is also an essential part ( ATP production ) in the mitochondria ( beta-oxidation ), very large endogenous reserves (sufficient for several days of continuous loads ), at low intensity has the largest proportion of the muscle work. Disadvantage: very slow ( ATP formation rate is only about a tenth of anaerobic metabolism alactaciden ).

In addition, in contrast to anaerobic energy production, here in addition to glucose and fats are burned (in the form of free fatty acids = FFS) (lipolysis - 1 mol FFS yields approximately 130 moles of ATP). This reaction sets in endurance exercise after about 20 minutes. Moreover, in cases of emergency or protein serve as an energy source, these two types of energy (FFS and protein ), especially in endurance exercise (low load intensity ) are relevant.

Combination of the forms under real loads

Due to the fact that the contraction rate of the muscle is the slowest in the energy-rich phosphates fastest and the oxidative energy production due to different flow rates is often observed at various stress intensities with different exposure time, a mixed shape of the energy-producing systems. Thus, the intensity of muscle work, so the speed of contraction of the muscle fiber, depending on the potential energy flow rate changes.

It appears, therefore, the great utility of the different flow rates. Shall be achieved, for example high intensities (high energy sales), this is mainly for speed loads the case, higher flow rates must be achieved. Consequently, must be resorted to anaerobically - alactacide (ATP, PKR) as well as on the lactacide energy. If you want to lower labor intensities are covered, such as in long- distance races, inevitably outweigh the aerobic energy supply processes.

Oxygen deficit and EPOC

→ See EPOC and oxygen deficit

Enzyme substrate (biology) Exothermic reaction Chemical energy Jakub Karol Parnas Epinephrine Thermogenesis Pyruvate decarboxylation Excess post-exercise oxygen consumption

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