synonymMuscle glycogen(muscle glycogen) generally refers to muscle glycogen
Muscle glycogen is the storage form of sugar in muscle. When a large amount of blood sugar is consumed during strenuous exercise, muscle glycogen is decomposed for energy supply. Muscle glycogen cannot be directly decomposed into glucose. It must first be decomposed into lactic acid, and then transported to the liver through bloodliverConvert toHepatic glycogen、glucose。
Muscle glycogen is one of two ways of storing sugar in human body.
Oxidative enzymolysis
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Due to the lack of an enzyme (no glucose 6-phosphatePhosphatase）Muscle glycogen cannot be directly decomposed into glucose. It must first be decomposed to produce lactic acid, which is circulated to the liver through the blood, and then converted intoHepatoseOriginal or synthetic glucose.
In many biological mechanisms such as animals, plants and microorganisms, the anaerobic decomposition of sugar almost follows the same process.Muscle glycogenicZymolysisFunction, that is, muscle glycogen undergoes a series ofEnzymatic reactionFinally, it is converted into lactic acid.The muscle glycogen in muscle tissue is first decomposed by combining with phosphorylation, and then passes through hexose phosphateTriosePhosphate ester, pyruvic acid and a series of intermediate products finally produce lactic acid.
Fermentative process
oneGlycogenstayphosphorylaseUnder the action ofRestore EndAnd combines with 1 molecule of phosphoric acid to produce glucose-1-phosphate
2. Glucose-1-phosphate (G-1P)Mutase(mutase) to glucose-6-phosphate
3. Glucose-6-phosphate (G-6P) can enterGlycolysisperhapsAerobic oxidation of sugarOxidative energy supply is carried out during the process (of course, it can also participate in other metabolic processes of sugar), and the latter process is exactly the same as the metabolic path of glucose
4. The shortened sugar chain can continue the above reaction（Phosphorylation--Isomerization -- entering glycolysis or aerobic oxidation for energy supply)
Note: Muscle glycogen is directly oxidized in muscle. It is not hydrolyzed and re oxidized, and the oxidation here does not mean that onlyoxidation reaction And nothing elseReaction typeOnly two steps in the whole process are true redox reactions.
Total reaction formula
1/n（C6H5O5）n+H2O→2CH3CHOHCOOH
Glycogen lactic acid
Muscle glycogenicZymolysisFunction is a way for carbohydrate to supply energy to tissues.When the body suddenly needs a lot of energy and the oxygen supply is insufficient (such as during strenuous exercise), glycogen fermentation temporarily meets the need of energy consumption.Under aerobic conditions, the glycolysis of glycogen in tissues is inhibited, and aerobic oxidation is the main way of glucose metabolism.
Motor correlation
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Factors affecting reserves
The storage of muscle glycogen in human skeletal muscle is about 10-15 g/kg wet muscle.Influencing factors:
1. Muscle part:
2. Type of muscle fiber: It is generally believed that the glycogen content in fast contracting muscle fibers is slightly higher than that in slow contracting muscle fibers.
3. Sports training level: long-term endurance training can double glycogen reserves.
4. Diet: Muscles with normal glycogen content are less sensitive to dietary sugar.Only when the muscle glycogen is exhausted through exercise in advance, can the muscle glycogen reserves increase significantly after high sugar diet.
The consumption rate of muscle glycogen was the highest.However, due to the rapid increase of muscle lactic acidGlycolysisTherefore, when the exercise reaches exhaustion, the muscle glycogen consumption is less than half of the original reserves.
2. When exercising for a long time at 65% - 85% of the maximum oxygen uptake intensity (sub maximum or sub maximum intensity)
Exercise timeIt can last for 45-200 minutes, the utilization rate of inositogen is quite high, and the consumption of glycogen is the largest.The change of the utilization speed of inositogen with exercise time can be divided into three phases:
At the initial stage of exercise, due to the stimulation of muscle contractionadrenalineRelease and local oxygen reserve decrease, muscle glycogen decomposes rapidly, and glycolysis is the main process of energy supply metabolism at this time.
In the second stage, with the extension of exercise time, the circulatory system adapts to the exercise load, and the glycogen decomposition rate decreases, maintaining a steady stateAerobic metabolism。The glycogen decomposition rate at this stageExercise intensityChanges, such as 25%, 54% and 78% of exercise intensityMaximum oxygen uptakeThe corresponding glycogen decomposition rates were 0.3, 0.8 and 1.5 mmol · kg wet muscle - 1 · min - 1, respectively.
In the final stage, along withGlycogenAnd its reserves are relatively reduced,Decomposition rateIt also decreased significantly. The compensatory measure for muscle is to improve blood sugar absorption and fat utilization.
3. When exercising at 30% maximum oxygen uptake intensity (low intensity)
Intramuscular mainly consists ofFatty acid oxidationFor energy supply, muscle glycogen is seldom used.
（2） Training level
When people with high training level perform quantitative submaximal load exercise, the ratio of fatty acid oxidation energy supply is higher, and the corresponding rate of muscle glycogen use is slower.Therefore, during exercise, it can enhance the oxidation of fatty acids for energy supply and play a saving role in the utilization of muscle glycogen.During the high-intensity submaximal exercise, the muscle glycogen decomposition rate is relatively faster than that of non trainers, which ensures a larger power output during exercise.
（3） Type of muscle fiber
Muscle fibers are divided intoRed muscle fiber(Type I fiber)White muscle fiber(Type II fiber).Endurance training can improve the ability of muscle fiber to oxidize sugar and fatty acid.Below 70%Maximum oxygen uptakeDuring intensive long-term exercise, type I muscle fibersGlycogenThe decrease is the most, which proves that this kind of muscle fiber is most suitable for medium and low intensity exercise.During 75% - 90% maximal oxygen uptake intensity exerciseExercise intensityType ⅱ a muscle fibers were recruited first, and then type ⅱ b muscle fibers were recruited.At the maximum intensity of muscle contraction, type IIb muscle fibers were almost all recruited, and muscle glycogen was rapidly decomposed, with the largest decline.
（4） , Diet
The consumption of muscle glycogen can be reduced by eating sugar 30 minutes before or during exercise.
Elevated plasma before exercisefree fatty acidsIt can increase the proportion of oxidized fatty acids in muscle during exercise and slow down the utilization rate of muscle glycogen.
（5） Influence of ambient temperature
Exercise in hot days increases the energy supply of muscle glycogen decomposition, while in cold days, the body uses more fat for energy supply.
（6） Influence of low oxygen partial pressure
When exercising in the plateau with low oxygen partial pressure, insufficient oxygen supply will increase the proportion of glycolysis and energy supply, accelerate the consumption of muscle glycogen, and significantly increase the production of lactic acid.When oxygen supply becomes the main limiting factor of metabolism, the glucose oxidation ratio is used to metabolize and synthesize the same amount of ATPFatty acid oxidationThe oxygen consumption is less, so;At the beginning of altitude training, the utilization of muscle glycogen increased during exercise.
In the long term (45-200 minutes) high-intensity exercise, muscle glycogen reserves before exercise determine the time to reach exercise exhaustion, which directly affects endurance training and competitionAthletic ability。
The reasons for muscle glycogen consumption in submaximal intensity exercise leading to exercise fatigue are:
(1) Glycogen is separated in muscle cells. When the glycogen in the exercise muscle is exhausted, it is difficult to be supplemented from the non exercise muscle.
(2) Those with low muscle glycogen content should absorb more blood sugar for energy when completing the same load exercise, which may causeHypoglycemia, Impactcentral nervous systemEnergy supply.
(3) Muscle glycogen is a metabolic primer for lipid oxidative energy supply. Sugar deficiency will affect the ability of lipid oxidative energy supply and energy supply.
(4) The storage of muscle glycogen is insufficient, and the proportion of fatty acid energy supply increases, so thatAthletic abilityDown.
When the storage of muscle glycogen is too low, the production of lactic acid is inhibited and reducedAnaerobic metabolismAbility.
In a word, muscle glycogen reserves are necessary energy for endurance exercise and extreme exercise.Try to increase the storage of creatine in the body and reduce the utilization of glycogen during exerciserateIt is particularly important to speed up the recovery of glycogen after exercise and achieve excessive recovery for the improvement of endurance sports ability.
Exercise fatigue
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Due to the decomposition and energy supply of muscle glycogen, some drinks are alkaline.The muscle glycogen storage in the muscle is about 300 grams. If it can be fully converted into energy, the hind foot can play a basketball game.The energy released by inositolysis can be divided into two ways: anaerobic decomposition and aerobic decomposition.Anaerobic decomposition is achieved byoxidaseThe muscle glycogen decomposes into lactic acid and releases energy;Aerobic decomposition refers to the decomposition of muscle glycogen intocarbon dioxideAnd water, producing a lot of energy at the same time.The biggest advantage of the anaerobic decomposition of muscle glycogen to supply energy is that it does not need oxygen to participate in the release of energy, so that the human body can exercise in anaerobic conditions for a short time (snorkeling), or for a long time and very intense exercise (such as running in the middle).Lactic acid, the product of anaerobic decomposition of muscle glycogen, first accumulates in muscle and then gradually releases into blood, which significantly reduces the pH of muscle plasma and blood.The decrease of pH in muscle can inhibit the anaerobic decomposition process of muscle glycogen, and at the same time prevent nerve from transmitting excitation to muscle;The decrease of pH in blood will affect the stability of the internal environment for cell survival, which will lead to the decline of the working ability of many organs such as brain, heart, kidney, etc.The combination of these factors makes the muscle unable to maintain its originalExercise intensity, and even had to stop exercising, which is the phenomenon of fatigue. In the 1990s, some scientists called lactic acid "fatigue element".
The lactic acid accumulated in muscles is mainly discharged into the blood, which depends on the inherent variety of bloodBuffer material(sodium bicarbonate, etc.) neutralize it into salt and weak acid, and then discharge the generated weak acid and other substances out of the body through the joint cooperation of the kidney and lung, so as to maintaininternal environmentIs stable.Under normal circumstances, this stability mechanism of the human body is enough to cope withAcids"Invasion", but in the case of strenuous exercise,Blood lactic acidIt can suddenly increase from 9% mg to 15% mg at rest to 200% mg to 250% mg (middle distance running). At this time, the buffer stored in the blood rapidly decreases (some people study it to reduce by 60%), and this set of stability mechanism will also "fade away".In order to increase the anti fatigue ability of athletes, some physiologists let 1500 meter runners take it before runningsodium bicarbonateAs a result, the average running speed of more than ten athletes increased by 3.1 seconds.Therefore, take it before exerciseAlkaline substanceHematogenicBuffer capacityIt can better fight against fatigue caused by lactic acid, thus improving sports performance.This is the reason why some drinks contain some alkaline substances[1]。
There are two ways of liver glycogen synthesis.1. Direct pathway: glucose (G) is activated to UDPG through G-6-P, G-1-PGlycogenSynthase can synthesize glycogen, while muscle glycogen can only be synthesized in this way.Three carbon pathway2. Indirect way: glucose is first decomposed into lactic acid and pyruvate when replenishing and restoring liver glycogen reserves after starvationTricarbonAnd then enter the liver to generate glucose.Hepatic glycogen inGlycogen phosphorylaseUnder the action, direct phosphoric acid is hydrolyzed into G-1-P, which is converted into G-6-P, which is decomposed into free glucose under the action of liver glucose 6 phosphatase.
Muscle glycogen synthesis has only a direct way. Due to the lack of glucose 6-phosphatase in muscle, muscle glycogen decomposition cannot directly form sugar. It can enter the glycolysis path after forming G-6-P, or be oxidized to decompose, or be recycled by lactic acid after generating lactic acid.
blood sugar
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When blood glucose flows through various tissues with blood, some of it is converted into glycogen storage in various tissues, and muscle glycogen is the most.Muscle contains 1-2% of muscle glycogen. Although its ratio is smaller than that of liver, its total amount is far greater than that of liver glycogen.Therefore, muscle is the most important tissue for glycogen storage.Muscle glycogen can only be generated from glucose and cannot be directly decomposed into blood sugar[2]。
