Structure, physiology and biochemistry of muscles. Biochemistry of muscle activity Biochemistry of muscle activity and training
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Introduction
1. Skeletal muscles, muscle proteins and biochemical processes in muscles
2. Biochemical changes in the body of martial arts athletes
4. The problem of recovery in sports
5. Features of metabolic states in humans during muscle activity
6. Biochemical control in martial arts
Conclusion
Bibliography
Introduction
The role of biochemistry in modern sports practice is increasingly increasing. Without knowledge of the biochemistry of muscle activity, mechanisms of metabolic regulation when performing physical exercise It is impossible to effectively manage the training process and its further rationalization. Knowledge of biochemistry is necessary to assess the level of fitness of an athlete, identify overloads and overexertion, and for the correct organization of a diet. One of the most important tasks of biochemistry is to find effective ways to control metabolism, based on deep knowledge of chemical transformations, since the state of metabolism determines normality and pathology. The growth and development of a living organism, its ability to withstand external influences and actively adapt to new conditions of existence depend on the nature and speed of metabolic processes.
The study of adaptive changes in metabolism allows us to better understand the characteristics of the body’s adaptation to physical activity and find effective means and methods for increasing physical performance.
In combat sports, the problem of physical fitness has always been considered one of the most important, determining the level of sports achievements.
The usual approach for determining training methods is based on empirical laws that formally describe the phenomena of sports training.
However, physical qualities themselves cannot exist on their own. They appear as a result of the central nervous system controlling muscles that contract and waste metabolic energy.
The theoretical approach requires constructing a model of the athlete’s body, taking into account the achievements of world sports biology. To control adaptation processes in certain cells of the organs of the human body, it is necessary to know how the organ is structured, the mechanisms of its functioning, and the factors that ensure the target direction of adaptation processes.
1. Skeletal muscles, muscle proteins and biochemical processes in muscles
Skeletal muscles contain a large amount of non-protein substances that easily pass from crushed muscles into an aqueous solution after protein precipitation. ATP is a direct source of energy not only for various physiological functions (muscle contractions, nervous activity, transmission of nervous excitation, secretion processes, etc.), but also for plastic processes occurring in the body (construction and renewal of tissue proteins, biological syntheses). There is constant competition between these two aspects of life - the energy supply of physiological functions and the energy supply of plastic processes. It is extremely difficult to give certain standard norms for the biochemical changes that occur in an athlete’s body when practicing one or another sport. Even when performing individual exercises in their pure form (athletics running, skating, skiing), the course of metabolic processes can differ significantly among different athletes depending on the type of their nervous activity, environmental influences, etc. Skeletal muscle contains 75-80 % water and 20-25% dry matter. 85% of the dry residue is proteins; the remaining 15% is made up of various nitrogen-containing and nitrogen-free extractives, phosphorus compounds, lipoids and mineral salts. Muscle proteins. Sarcoplasmic proteins make up up to 30% of all muscle proteins.
Muscle fibril proteins make up about 40% of all muscle proteins. The proteins of muscle fibrils include primarily two major proteins - myosin and actin. Myosin is a globulin-type protein with a molecular weight of about 420,000. It contains a lot of glutamic acid, lysine and leucine. In addition, along with other amino acids, it contains cysteine, and therefore has free groups - SH. Myosin is located in muscle fibrils in thick filaments of “disc A”, and not chaotically, but strictly ordered. Myosin molecules have a filamentous (fibrillar) structure. According to Huxley, their length is about 1500 A, thickness is about 20 A. They have a thickening at one end (40 A). These ends of its molecules are directed in both directions from the “M zone” and form club-shaped thickenings of the processes of thick filaments. Myosin is an essential component of the contractile complex and at the same time has enzymatic (adenosine triphosphatase) activity, catalyzing the breakdown of adenosine triphosphoric acid (ATP) into ADP and orthophosphate. Actin has a much smaller molecular weight than myosin (75,000) and can exist in two forms - globular (G-actin) and fibrillar (F-actin), capable of transforming into each other. The molecules of the first have a round shape; the second molecule, which is a polymer (a combination of several molecules) of G-actin, is filamentous. G-actin has low viscosity, F-actin has high viscosity. The transition of one form of actin to another is facilitated by many ions, in particular K+ and Mg++. During muscle activity, G-actin transforms into F-actin. The latter easily combines with myosin, forming a complex called actomyosin and is a contractile substrate of the muscle, capable of producing mechanical work. In muscle fibrils, actin is located in thin filaments of the “J disk”, extending into the upper and lower thirds of the “A disk”, where actin is connected to myosin through contacts between the processes of thin and thick filaments. In addition to myosin and actin, some other proteins were also found in myofibrils, in particular the water-soluble protein tropomyosin, which is especially abundant in smooth muscles and in the muscles of embryos. The fibrils also contain other water-soluble proteins that have enzymatic activity” (adenylic acid deaminase, etc.). The proteins of mitochondria and ribosomes are mainly enzyme proteins. In particular, mitochondria contain enzymes of aerobic oxidation and respiratory phosphorylation, and ribosomes contain protein-bound rRNA. Proteins of muscle fiber nuclei are nucleoproteins containing deoxyribonucleic acids in their molecules.
Proteins of the muscle fiber stroma, making up about 20% of all muscle proteins. From stromal proteins, named by A.Ya. Danilevsky myostromins, built the sarcolemma and, apparently, “Z disks” connecting thin actin filaments to the sarcolemma. It is possible that myostromins are contained along with actin in thin filaments of “J disks”. ATP is a direct source of energy not only for various physiological functions (muscle contractions, nervous activity, transmission of nervous excitation, secretion processes, etc.), but also for plastic processes occurring in the body (construction and renewal of tissue proteins, biological syntheses). There is constant competition between these two aspects of life - the energy supply of physiological functions and the energy supply of plastic processes. An increase in specific functional activity is always accompanied by an increase in ATP consumption and, consequently, a decrease in the possibility of using it for biological syntheses. As is known, in the tissues of the body, including in the muscles, their proteins are constantly being renewed, but the processes of breakdown and synthesis are strictly balanced and the level of protein content remains constant. During muscle activity, protein renewal is inhibited, and the more, the more the ATP content in the muscles decreases. Consequently, during exercise of maximum and submaximal intensity, when ATP resynthesis occurs predominantly anaerobically and least completely, protein renewal will be inhibited more significantly than during work of average and moderate intensity, when energetically highly efficient processes of respiratory phosphorylation predominate. Inhibition of protein renewal is a consequence of a lack of ATP, which is necessary both for the breakdown process and (in particular) for the process of their synthesis. Therefore, during intense muscle activity, the balance between the breakdown and synthesis of proteins is disrupted, with the former predominant over the latter. The protein content in the muscle decreases slightly, and the content of polypeptides and nitrogen-containing substances of non-protein nature increases. Some of these substances, as well as some low-molecular proteins, leave the muscles into the blood, where the content of protein and non-protein nitrogen increases accordingly. In this case, protein may also appear in the urine. All these changes are especially significant during high-intensity strength exercises. With intense muscular activity, the formation of ammonia also increases as a result of deamination of a portion of adenosine monophosphoric acid that does not have time to be resynthesized into ATP, as well as due to the cleavage of ammonia from glutamine, which is enhanced under the influence of an increased content of inorganic phosphates in the muscles, activating the enzyme glutaminase. The ammonia content in muscles and blood increases. Elimination of the resulting ammonia can occur mainly in two ways: the binding of ammonia with glutamic acid to form glutamine or the formation of urea. However, both of these processes require the participation of ATP and therefore (due to a decrease in its content) experience difficulties during intense muscle activity. During muscular activity of medium and moderate intensity, when ATP resynthesis occurs due to respiratory phosphorylation, the elimination of ammonia is significantly enhanced. Its content in the blood and tissues decreases, and the formation of glutamine and urea increases. Due to the lack of ATP during muscular activity of maximum and submaximal intensity, a number of other biological syntheses are also hampered. In particular, the synthesis of acetylcholine in motor nerve endings, which negatively affects the transmission of nervous excitation to the muscles.
2. Biochemical changes in the body of martial artists
The energy needs of the body (working muscles) are satisfied, as is known, in two main ways - anaerobic and aerobic. The ratio of these two pathways of energy production varies in different exercises. When performing any exercise, all three energy systems practically operate: anaerobic phosphagen (alactate) and lactic acid (glycolytic) and aerobic (oxygen, oxidative) “Zones” of their action partially overlap. Therefore, it is difficult to isolate the “net” contribution of each of the energy systems, especially when operating for a relatively short maximum duration. In this regard, “neighboring” systems in terms of energy power (area of action) are often combined into pairs, phosphagen with lactacid, lactacid with oxygen. The system whose energy contribution is greater is indicated first. According to the relative load on the anaerobic and aerobic energy systems, all exercises can be divided into anaerobic and aerobic. The first - with a predominance of the anaerobic, the second - the aerobic component of energy production. The leading quality when performing anaerobic exercises is power (speed-strength capabilities), when performing aerobic exercises - endurance. The ratio of different energy production systems largely determines the nature and degree of changes in the activity of various physiological systems that ensure the performance of different exercises.
There are three groups of anaerobic exercises: - maximum anaerobic power (anaerobic power); - near maximum anaerobic power; - submaximal anaerobic power (anaerobic-aerobic power). Exercises of maximum anaerobic power (anaerobic power) are exercises with an almost exclusively anaerobic method of supplying energy to working muscles: the anaerobic component in the total energy production ranges from 90 to 100%. It is provided mainly by the phosphagen energy system (ATP + CP) with some participation of the lactic acid (glycolytic) system. The record maximum anaerobic power developed by outstanding athletes during sprinting reaches 120 kcal/min. The possible maximum duration of such exercises is a few seconds. Strengthening the activity of vegetative systems occurs gradually during work. Due to the short duration of anaerobic exercises, during their execution the functions of blood circulation and respiration do not have time to reach their possible maximum. During a maximal anaerobic exercise, the athlete either does not breathe at all or only manages to complete a few breathing cycles. Accordingly, the “average” pulmonary ventilation does not exceed 20-30% of the maximum. Heart rate increases even before the start (up to 140-150 beats/min) and continues to rise during the exercise, reaching its highest value immediately after the finish - 80-90% of the maximum (160-180 beats/min).
Since the energy basis of these exercises is anaerobic processes, strengthening the activity of the cardio-respiratory (oxygen transport) system has practically no significance for the energy supply of the exercise itself. The concentration of lactate in the blood during work changes very little, although in working muscles it can reach 10 mmol/kg or even more at the end of work. The lactate concentration in the blood continues to increase for several minutes after stopping work and reaches a maximum of 5-8 mmol/l. Before performing anaerobic exercise, the concentration of glucose in the blood increases slightly. Before and as a result of their implementation, the concentration of catecholamines (adrenaline and norepinephrine) and growth hormone in the blood increases very significantly, but the concentration of insulin decreases slightly; glucagon and cortisol concentrations do not change noticeably. The leading physiological systems and mechanisms that determine sports results in these exercises are the central nervous regulation of muscle activity (coordination of movements with the manifestation of great muscle power), the functional properties of the neuromuscular system (speed-strength), the capacity and power of the phosphagen energy system of working muscles.
Exercises near maximum anaerobic power (mixed anaerobic power) are exercises with predominantly anaerobic energy supply to working muscles. The anaerobic component in the total energy production is 75-85% - partly due to the phosphagen and, to a greater extent, due to the lactic acid (glycolytic) energy systems. The possible maximum duration of such exercises for outstanding athletes ranges from 20 to 50 seconds. To provide energy for these exercises, a significant increase in the activity of the oxygen transport system already plays a certain energetic role, and the greater the longer the exercise.
During the exercise, pulmonary ventilation rapidly increases, so that by the end of the exercise, which lasts about 1 minute, it can reach 50-60% of the maximum working ventilation for a given athlete (60-80 l/min). The concentration of lactate in the blood after exercise is very high - up to 15 mmol/l in qualified athletes. The accumulation of lactate in the blood is associated with a very high rate of its formation in working muscles (as a result of intense anaerobic glycolysis). The concentration of glucose in the blood is slightly increased compared to resting conditions (up to 100-120 mg%). Hormonal changes in the blood are similar to those that occur during maximum anaerobic power exercise.
The leading physiological systems and mechanisms that determine athletic performance in exercises near maximum anaerobic power are the same as in the exercises of the previous group, and, in addition, the power of the lactic acid (glycolytic) energy system of the working muscles. Exercises of submaximal anaerobic power (anaerobic-aerobic power) are exercises with a predominance of the anaerobic component of energy supply to working muscles. In the total energy production of the body, it reaches 60-70% and is provided mainly by the lactic acid (glycolytic) energy system. In the energy supply of these exercises, a significant share belongs to oxygen (oxidative, aerobic) energy system. The possible maximum duration of competitive exercises for outstanding athletes is from 1 to 2 minutes. The power and maximum duration of these exercises are such that in the process of their implementation the performance indicators. The oxygen transport system (heart rate, cardiac output, PV, O2 consumption rate) may be close to or even reach the maximum values for a given athlete. The longer the exercise, the higher these indicators are at the finish line and the greater the proportion of aerobic energy production during the exercise. After these exercises, a very high lactate concentration is recorded in the working muscles and blood - up to 20-25 mmol/l. Thus, the training and competitive activity of martial arts athletes takes place at about the maximum load of the athletes’ muscles. At the same time, the energy processes occurring in the body are characterized by the fact that, due to the short duration of anaerobic exercises, during their execution the functions of blood circulation and respiration do not have time to reach the possible maximum. During a maximal anaerobic exercise, the athlete either does not breathe at all or only manages to complete a few breathing cycles. Accordingly, the “average” pulmonary ventilation does not exceed 20-30% of the maximum.
A person performs physical exercise and expends energy using the neuromuscular system. The neuromuscular system is a collection of motor units. Each motor unit includes a motor neuron, an axon, and a set of muscle fibers. The amount of MU remains unchanged in humans. The amount of MV in a muscle is possible and can be changed during training, but no more than 5%. Therefore, this factor in the growth of muscle functionality has no practical significance. Inside the CF, hyperplasia (increase in the number of elements) of many organelles occurs: myofibrils, mitochondria, sarcoplasmic reticulum (SRR), glycogen globules, myoglobin, ribosomes, DNA, etc. The number of capillaries serving the CF also changes. The myofibril is a specialized organelle of the muscle fiber (cell). It has approximately equal cross-section in all animals. Consists of sarcomeres connected in series, each of which includes actin and myosin filaments. Bridges can form between the actin and myosin filaments, and with the expenditure of energy contained in ATP, the bridges can rotate, i.e. myofibril contraction, muscle fiber contraction, muscle contraction. Bridges are formed in the presence of calcium ions and ATP molecules in the sarcoplasm. An increase in the number of myofibrils in a muscle fiber leads to an increase in its strength, contraction speed and size. Along with the growth of myofibrils, other organelles serving the myofibrils also grow, for example, the sarcoplasmic reticulum. The sarcoplasmic reticulum is a network of internal membranes that forms vesicles, tubules, and cisterns. In the MV, the SPR forms cisterns; calcium ions (Ca) accumulate in these cisterns. It is assumed that glycolytic enzymes are attached to the SPR membranes, therefore, when the access of oxygen is stopped, significant swelling of the channels occurs. This phenomenon is associated with the accumulation of hydrogen ions (H), which cause partial destruction (denaturation) of protein structures and the addition of water to the radicals of protein molecules. For the mechanism of muscle contraction, the rate of pumping out Ca from the sarcoplasm is of fundamental importance, since this ensures the process of muscle relaxation. Sodium, potassium and calcium pumps are built into the SPR membranes, so it can be assumed that an increase in the surface of the SPR membranes in relation to the mass of myofibrils should lead to an increase in the rate of MV relaxation.
Consequently, an increase in the maximum rate or speed of muscle relaxation (the time interval from the end of the electrical activation of the muscle until the mechanical tension in it drops to zero) should indicate a relative increase in the membranes of the SPR. Maintaining the maximum pace is ensured by reserves in the MV of ATP, KrF, the mass of myofibrillar mitochondria, the mass of sarcoplasmic mitochondria, the mass of glycolytic enzymes and the buffer capacity of the contents of muscle fiber and blood.
All these factors influence the process of energy supply to muscle contraction, however, the ability to maintain maximum tempo should depend primarily on the mitochondria of the SPR. By increasing the amount of oxidative MV or, in other words, the aerobic capacity of the muscle, the duration of the exercise at maximum power increases. This is due to the fact that maintaining the concentration of CrF during glycolysis leads to acidification of the MV, inhibition of ATP consumption processes due to the competition of H ions with Ca ions at the active centers of myosin heads. Therefore, the process of maintaining the concentration of CrF, with the predominance of aerobic processes in the muscle, becomes more and more effective as the exercise is performed. It is also important that mitochondria actively absorb hydrogen ions, therefore, when performing short-term extreme exercise (10-30 s), their role is more limited to buffering cell acidification. Thus, adaptation to muscular work is carried out through the work of each cell of the athlete, based on energy metabolism during the life of the cell. The basis of this process is the consumption of ATP during the interaction of hydrogen and calcium ions.
Increasing the entertainment value of fights involves a significant increase in the activity of the fight with a simultaneous increase in the number of technical actions performed. Taking this into account, a real problem arises related to the fact that with increased intensity of a competitive match against the background of progressive physical fatigue, temporary automation of the athlete’s motor skill will occur.
In sports practice, this usually manifests itself in the second half of a competitive match held with high intensity. In this case (especially if the athlete does not have a very high level of special endurance), significant changes in blood pH are observed (below 7.0 conventional units), which indicates an extremely unfavorable reaction of the athlete to work of such intensity. It is known that, for example, a stable disruption of the rhythmic structure of a wrestler’s motor skill when performing a backbend throw begins with the level of physical fatigue at blood pH values below 7.2 arb. units
In this regard, there are two possible ways to increase the stability of the motor skills of martial artists: a) raise the level of special endurance to such an extent that they can carry out a fight of any intensity without pronounced physical fatigue (the reaction to the load should not lead to acidotic shifts below pH values equal to 7.2 conventional units); b) ensure stable manifestation of motor skills in any extreme situations physical activity at blood pH values reaching 6.9 arb. units Within the first direction, a fairly large number of special research, which determined the real ways and prospects for solving the problem of accelerated training of special endurance in martial arts athletes. On the second problem, there are no real, practically significant developments to date.
4. The problem of recovery in sports
One of the most important conditions for intensifying the training process and further increasing sports performance is the widespread and systematic use of restorative means. Rational recovery is of particular importance during extreme and near-maximum physical and mental stress - obligatory satellites of training and competitions in modern sports. Obviously, the use of a system of restorative means makes it necessary to clearly classify the processes of restoration in conditions of sports activity.
The specificity of recovery changes, determined by the nature of sports activity, the volume and intensity of training and competitive loads, and the general regime, determines specific measures aimed at restoring performance. N.I. Volkov identifies the following types of recovery in athletes: current (observation during work), urgent (following the end of the load) and delayed (for many hours after completion of work), as well as after chronic overexertion (the so-called stress recovery). It should be noted that the listed reactions are carried out against the background of periodic recovery due to energy consumption under normal living conditions.
Its character is largely determined by the functional state of the body. A clear understanding of the dynamics of recovery processes in conditions of sports activity is necessary for organizing the rational use of recovery means. Thus, functional changes that develop in the process of ongoing recovery are aimed at providing increased energy requirements of the body, at compensating for the increased consumption of biological energy in the process of muscle activity. Metabolic transformations occupy a central place in the restoration of energy costs.
The ratio of the body's energy expenditure and its restoration during work makes it possible to divide physical activity into 3 ranges: 1) loads at which aerobic support for work is sufficient; 2) loads in which, along with aerobic support of work, anaerobic energy sources are used, but the limit of increasing the supply of oxygen to the working muscles has not yet been exceeded; 3) loads at which energy needs exceed the capabilities of current recovery, which is accompanied by rapidly developing fatigue. In certain sports, to assess the effectiveness of rehabilitation measures, it is advisable to analyze various indicators of the neuromuscular system and use psychological tests. The use in practice of working with high-class athletes of in-depth examinations using an extensive set of tools and methods allows us to evaluate the effectiveness of previous rehabilitation measures and determine the tactics of subsequent ones. Recovery testing requires staged examinations carried out in weekly or monthly training cycles. The frequency of these examinations and research methods are determined by the doctor and coach depending on the type of sport, the nature of the loads of a given training period, the restorative means used and the individual characteristics of the athlete.
5 . Features of metabolic states in humans during muscular activity
The state of metabolism in the human body is characterized by a large number of variables. In conditions of intense muscular activity, the most important factor on which the metabolic state of the body depends is the application in the field of energy metabolism. To quantify metabolic states in humans during muscular work, it is proposed to use three types of criteria: a) power criteria, reflecting the rate of energy conversion in aerobic and anaerobic processes; b) capacity criteria characterizing the body’s energy reserves or the total volume of metabolic changes that occurred during work; c) efficiency criteria that determine the extent to which the energy of aerobic and anaerobic processes is used when performing muscular work. Changes in exercise power and duration have different effects on aerobic and anaerobic metabolism. Such indicators of the power and capacity of the aerobic process, such as the size of pulmonary ventilation, the level of oxygen consumption, and oxygen intake during work, systematically increase with the duration of exercise at each selected power value. These indicators increase noticeably with increasing intensity of work in all time intervals of the exercise. Indicators of maximum accumulation of lactic acid in the blood and total oxygen debt, which characterize the capacity of anaerobic energy sources, change little when performing exercises of moderate power, but increase noticeably with increasing duration of work in more intense exercises.
It is interesting to note that at the lowest power of exercise, where the content of lactic acid in the blood remains at a constant level of about 50-60 mg, it is practically impossible to detect the lactate fraction of the oxygen debt; There is no excess release of carbon dioxide associated with the destruction of blood bicarbonates during the accumulation of lactic acid. It can be assumed that the noted level of accumulation of lactic acid in the blood does not yet exceed those threshold values, above which stimulation of oxidative processes associated with the elimination of lactate oxygen debt is observed. Indicators of aerobic metabolism after a short lag period (about 1 minute) associated with training show a systemic increase with increasing exercise time.
During the running-in period, there is a pronounced increase in anaerobic reactions leading to the formation of lactic acid. An increase in exercise power is accompanied by a proportional increase in aerobic processes. An increase in the intensity of aerobic processes with increasing power was established only in exercises whose duration exceeds 0.5 minutes. When performing intense short-term exercises, a decrease in aerobic metabolism is observed. An increase in the size of the total oxygen debt due to the formation of the lactate fraction and the appearance of excess carbon dioxide release is detected only in those exercises, the power and duration of which are sufficient to accumulate lactic acid over 50-60 mg%. When performing exercises of low power, changes in the indicators of aerobic and anaerobic processes show the opposite direction; with increasing power, changes in these processes change to unidirectional.
In the dynamics of indicators of the rate of oxygen consumption and “excess” carbon dioxide release during exercise, a phase shift is detected; during the recovery period after the end of work, synchronization of shifts in these indicators occurs. Changes in oxygen consumption and lactic acid levels in the blood with increasing recovery time after intense exercise clearly show phase differences. The problem of fatigue in the biochemistry of sports is one of the most difficult and still far from being solved. In its most general form, fatigue can be defined as a state of the body that occurs as a result of prolonged or strenuous activity and is characterized by a decrease in performance. Subjectively, it is perceived by a person as a feeling of local fatigue or general fatigue. Long-term studies make it possible to divide the biochemical factors that limit performance into three groups associated with each other.
These are, firstly, biochemical changes in the central nervous system, caused both by the process of motor excitation itself and by proprioceptive impulses from the periphery. Secondly, these are biochemical changes in skeletal muscles and myocardium, caused by their work and trophic changes in the nervous system. Thirdly, these are biochemical changes in the internal environment of the body, depending both on the processes occurring in the muscles and on the influence of the nervous system. Common features of fatigue are an imbalance of phosphate macroergs in the muscles and brain, as well as a decrease in ATPase activity and phosphorylation coefficient in muscles. However, fatigue associated with work of high intensity and long duration also has some specific features. In addition, biochemical changes during fatigue caused by short-term muscular activity are characterized by a significantly greater gradient than during muscular activity of moderate intensity, but the duration is close to the limit. It should be emphasized that a sharp decrease in the body’s carbohydrate reserves, although of great importance, does not play a decisive role in limiting performance. The most important factor limiting performance is the level of ATP both in the muscles themselves and in the central nervous system.
At the same time, one cannot ignore biochemical changes in other organs, in particular in the myocardium. With intense short-term work, the level of glycogen and creatine phosphate in it does not change, but the activity of oxidative enzymes increases. When working for a long time, there may be a decrease in both the level of glycogen and creatine phosphate, as well as enzymatic activity. This is accompanied by ECG changes indicating dystrophic processes, most often in the left ventricle and less often in the atria. Thus, fatigue is characterized by profound biochemical changes both in the central nervous system and in the periphery, primarily in the muscles. Moreover, the degree of biochemical changes in the latter can be changed with increased performance caused by the effect on the central nervous system. I.M. wrote about the central nervous nature of fatigue back in 1903. Sechenov. Since that time, data on the role of central inhibition in the mechanism of fatigue have been growing. The presence of diffuse inhibition during fatigue caused by prolonged muscle activity cannot be doubted. It develops in the central nervous system and develops in it through the interaction of the center and the periphery with the leading role of the former. Fatigue is a consequence of changes caused in the body by intense or prolonged activity, and a protective reaction that prevents the transition across the line of functional and biochemical disorders that are dangerous to the body and threaten its existence.
Disorders of protein and nucleic acid metabolism in the nervous system also play a certain role in the mechanism of fatigue. At long run or swimming with a load, causing significant fatigue, a decrease in RNA levels is observed in motor neurons, while during prolonged but not tiring work it does not change or increases. Since chemistry and, in particular, the activity of muscle enzymes are regulated by the trophic influences of the nervous system, it can be assumed that changes in the chemical status of nerve cells during the development of protective inhibition caused by fatigue lead to changes in trophic centrifugal impulses, leading to disturbances in the regulation of muscle chemistry.
These trophic influences are apparently carried out through the movement of biologically active substances along the axoplasm of efferent fibers, described by P. Weiss. In particular, a protein substance was isolated from peripheral nerves, which is a specific inhibitor of hexokinase, similar to the inhibitor of this enzyme secreted by the anterior pituitary gland. Thus, fatigue develops through the interaction of central and peripheral mechanisms with the leading and integrating importance of the former. It is associated both with changes in nerve cells and with reflex and humoral influences from the periphery. Biochemical changes during fatigue can be generalized, accompanied by general changes in the internal environment of the body and disturbances in the regulation and coordination of various physiological functions (during prolonged physical activity involving significant muscle mass). These changes can also be of a more local nature, not accompanied by significant general changes, but limited only to working muscles and the corresponding groups of nerve cells and centers (during short-term work of maximum intensity or long-term work of a limited number of muscles).
Fatigue (and especially the feeling of tiredness) is a protective reaction that protects the body from excessive degrees of functional exhaustion that are life-threatening. At the same time, it trains physiological and biochemical compensatory mechanisms, creating the prerequisites for recovery processes and further increasing the functionality and performance of the body. During rest after muscular work, normal ratios of biological compounds are restored both in the muscles and in the body as a whole. If during muscular work catabolic processes necessary for energy supply dominate, then during rest anabolic processes predominate. Anabolic processes require energy expenditure in the form of ATP, therefore the most pronounced changes are found in the area of energy metabolism, since during the rest period ATP is constantly being spent, and, therefore, ATP reserves must be restored. Anabolic processes during the rest period are due to catabolic processes that occurred during work. During rest, ATP, creatine phosphate, glycogen, phospholipids, and muscle proteins are resynthesized, the body's water-electrolyte balance returns to normal, and damaged cellular structures are restored. Depending on the general direction of biochemical changes in the body and the time required for separation processes, two types of recovery processes are distinguished - urgent and abandoned recovery. Urgent recovery lasts from 30 to 90 minutes after work. During the period of urgent recovery, the products of anaerobic decomposition accumulated during work, primarily lactic acid and oxygen debt, are eliminated. After finishing work, oxygen consumption continues to be elevated compared to the resting state. This excess oxygen consumption is called oxygen debt. The oxygen debt is always greater than the oxygen deficit, and the higher the intensity and duration of work, the more significant this difference is.
During rest, the consumption of ATP for muscle contractions stops and the ATP content in mitochondria increases in the first seconds, which indicates the transition of mitochondria to an active state. The ATP concentration increases, increasing the pre-working level. The activity of oxidative enzymes also increases. But the activity of glycogen phosphorylase decreases sharply. Lactic acid, as we already know, is the end product of the breakdown of glucose under anaerobic conditions. At the initial moment of rest, when increased oxygen consumption remains, the supply of oxygen to the oxidative systems of the muscles increases. In addition to lactic acid, other metabolites accumulated during work are also subject to oxidation: succinic acid, glucose; and at later stages of recovery, fatty acids. Lag recovery lasts long after the job is finished. First of all, it affects the processes of synthesis of structures used up during muscle work, as well as the restoration of ionic and hormonal balance in the body. During the recovery period, glycogen reserves accumulate in the muscles and liver; these recovery processes occur within 12-48 hours. Lactic acid entering the blood enters the liver cells, where glucose synthesis first occurs, and glucose is the direct building material for glycogen synthetase, which catalyzes glycogen synthesis. The process of glycogen resynthesis is phasic in nature, which is based on the phenomenon of supercompensation. Supercompensation (overrecovery) is the excess of the reserves of energy substances during the rest period to the working level. Supercompensation is a passable phenomenon. The glycogen content, which has decreased after work, increases during rest not only to the initial level, but also to a higher level. Then there is a decrease to the initial (to working) level and even a little lower, and then there is a wave-like return to the original level.
The duration of the supercompensation phase depends on the duration of the work and the depth of the biochemical changes it causes in the body. Powerful short-term work causes a rapid onset and rapid completion of the supercompensation phase: when intramuscular glycogen reserves are restored, the supercompensation phase is detected after 3-4 hours and ends after 12 hours. After prolonged work of moderate power, supercompensation of glycogen occurs after 12 hours and ends between 48 and 72 hours after the end of work. The law of supercompensation is valid for all biological compounds and structures that are, to one degree or another, consumed or disrupted during muscle activity and are resynthesized during rest. These include: creatine phosphate, structural and enzymatic proteins, phospholipids, cellular orgonella (mitochondria, lysosomes). After the resynthesis of the body's energy reserves, the processes of resynthesis of phospholipids and proteins are significantly enhanced, especially after heavy strength work, which is accompanied by their significant breakdown. Restoration of the level of structural and enzymatic proteins occurs within 12-72 hours. When performing work that involves loss of water, reserves of water and mineral salts should be replenished during the recovery period. The main source of mineral salts is food.
6 . Biochemical control in martial arts
During intense muscular activity, large amounts of lactic and pyruvic acids are formed in the muscles, which diffuse into the blood and can cause metabolic acidosis of the body, which leads to muscle fatigue and is accompanied by muscle pain, dizziness, and nausea. Such metabolic changes are associated with the depletion of the body's buffer reserves. Since the state of the body's buffer systems is important in the manifestation of high physical performance, CBS indicators are used in sports diagnostics. The CBS indicators, which are normally relatively constant, include: - blood pH (7.35-7.45); - pCO2 - partial pressure of carbon dioxide (H2CO3 + CO2) in the blood (35 - 45 mm Hg); - 5B - standard blood plasma bicarbonate HSOd, which when the blood is completely saturated with oxygen is 22-26 meq/l; - BB - buffer bases of whole blood or plasma (43 - 53 meq/l) - an indicator of the capacity of the entire buffer system of blood or plasma; - L/86 - normal buffer bases of whole blood at physiological values of pH and CO2 of alveolar air; - BE - excess base, or alkaline reserve (from - 2.4 to +2.3 meq/l) - an indicator of excess or deficiency of buffer. CBS indicators reflect not only changes in the blood buffer systems, but also the state of the respiratory and excretory systems of the body. The state of acid-base balance (ABC) in the body is characterized by a constant blood pH (7.34-7.36).
An inverse correlation has been established between the dynamics of lactate content in the blood and changes in blood pH. By changing the ABS indicators during muscle activity, it is possible to monitor the body’s response to physical activity and the growth of the athlete’s fitness, since with the biochemical control of the ABS, one of these indicators can be determined. The active reaction of urine (pH) is directly dependent on the acid-base state of the body. With metabolic acidosis, urine acidity increases to pH 5, and with metabolic alkalosis it decreases to pH 7. Table. Figure 3 shows the direction of changes in urine pH values in relation to indicators of the acid-base state of plasma. Thus, wrestling as a sport is characterized by high intensity of muscle activity. In this regard, it is important to control the exchange of acids in the athlete’s body. The most informative indicator of ACS is the value of BE - alkaline reserve, which increases with increasing qualifications of athletes, especially those specializing in speed-strength sports.
Conclusion
In conclusion, we can say that the training and competitive activity of martial artists takes place at about the maximum load of the athletes’ muscles. At the same time, the energy processes occurring in the body are characterized by the fact that, due to the short duration of anaerobic exercises, during their execution the functions of blood circulation and respiration do not have time to reach the possible maximum. During a maximal anaerobic exercise, the athlete either does not breathe at all or only manages to complete a few breathing cycles. Accordingly, the “average” pulmonary ventilation does not exceed 20-30% of the maximum. Fatigue in the competitive and training activities of martial arts athletes occurs due to near maximum load on the muscles during the entire period of the fight.
As a result, the pH level in the blood increases, the athlete’s reaction and his resistance to attacks from the enemy worsen. To reduce fatigue, it is recommended to use glycolytic anaerobic loads in the training process. The trace process created by the dominant focus can be quite persistent and inert, which makes it possible to maintain excitation even when the source of irritation is removed.
After the end of muscular work, a recovery, or post-working, period begins. It is characterized by the degree of change in body functions and the time required to restore them to the original level. Studying the recovery period is necessary to assess the severity of a particular job, determine its compliance with the body’s capabilities and determine the duration of the necessary rest. The biochemical basis of the motor skills of martial artists is directly related to the manifestation of strength abilities, which include dynamic, explosive, and isometric strength. Adaptation to muscular work is carried out through the work of each cell of the athlete, based on energy metabolism during the life of the cell. The basis of this process is the consumption of ATP during the interaction of hydrogen and calcium ions. Martial arts, as a sport, are characterized by high intensity muscle activity. In this regard, it is important to control the exchange of acids in the athlete’s body. The most informative indicator of ACS is the value of BE - alkaline reserve, which increases with increasing qualifications of athletes, especially those specializing in speed-strength sports.
Bibliography
1. Volkov N.I. Biochemistry of muscle activity. - M.: Olympic sport, 2001.
2. Volkov N.I., Oleynikov V.I. Bioenergy of sports. - M: Soviet Sport, 2011.
3. Maksimov D.V., Seluyanov V.N., Tabakov S.E. Physical training of martial artists. - M: TVT Division, 2011.
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Muscular system and its functions
contractions, general overview of skeletal muscles)
There are two types of muscles: smooth(involuntary) and striated(arbitrary). Smooth muscles are located in the walls of blood vessels and some internal organs. They constrict or dilate blood vessels, move food along the gastrointestinal tract, and contract the walls of the bladder. Striated muscles are all skeletal muscles that provide a variety of body movements. The striated muscles also include the cardiac muscle, which automatically ensures the rhythmic functioning of the heart throughout life. The basis of muscles is proteins, making up 80–85% of muscle tissue (excluding water). The main property of muscle tissue is contractility, it is provided by contractile muscle proteins - actin and myosin.
Muscle tissue is very complex. A muscle has a fibrous structure, each fiber is a muscle in miniature, the combination of these fibers forms the muscle as a whole. muscle fiber, in turn, consists of myofibrils Each myofibril is divided into alternating light and dark areas. Dark areas - protofibrils consist of long chains of molecules myosin, light ones are formed by thinner protein threads actina. When the muscle is in an uncontracted (relaxed) state, the actin and myosin filaments are only partially advanced relative to each other, with each myosin filament being opposed and surrounded by several actin filaments. Deeper advancement relative to each other causes shortening (contraction) of the myofibrils of individual muscle fibers and the entire muscle as a whole (Fig. 2.3).
Numerous nerve fibers approach and depart from the muscle (reflex arc principle) (Fig. 2.4). Motor (efferent) nerve fibers transmit impulses from the brain and spinal cord, bringing the muscles into working condition; sensory fibers transmit impulses in the opposite direction, informing the central nervous system about muscle activity. Through sympathetic nerve fibers, metabolic processes in the muscles are regulated, whereby their activity adapts to changed working conditions and to various muscle loads. Each muscle is penetrated by an extensive network of capillaries, through which substances necessary for the functioning of the muscles enter and metabolic products are eliminated.
Skeletal muscles. Skeletal muscles are part of the structure of the musculoskeletal system, are attached to the bones of the skeleton and, when contracted, move individual parts of the skeleton and levers. They are involved in maintaining the position of the body and its parts in space, provide movements when walking, running, chewing, swallowing, breathing, etc., while generating heat. Skeletal muscles have the ability to be excited under the influence of nerve impulses. Excitation is carried out to contractile structures (myofibrils), which, contracting, perform a certain motor act - movement or tension.
Rice. 2.3. Schematic representation of the muscle.
Muscle (L) consists of muscle fibers (B), each of them is made of myofibrils (IN). Myofibril (G) composed of thick and thin myofilaments (D). The figure shows one sarcomere, bounded on both sides by lines: 1 - isotropic disk, 2 - anisotropic disk, 3 - area with less anisotropy. Transverse media of multifibril (4), giving an idea of the hexagonal distribution of thick and thin multifilaments
Rice. 2.4. Diagram of the simplest reflex arc:
1 - afferent (sensitive) neuron, 2 - spinal node, 3 - interneuron, 4 .- gray matter of the spinal cord, 5 - efferent (motor) neuron, 6 - motor nerve ending in muscles; 7 - sensory nerve ending in the skin
Recall that all skeletal muscle consists of striated muscles. In humans, there are about 600 of them and most of them are paired. Their weight makes up 35-40% of the total body weight of an adult. Skeletal muscles are covered on the outside with a dense connective tissue membrane. Each muscle has an active part (muscle body) and a passive part (tendon). Muscles are divided into long, short And wide.
Muscles whose action is directed in the opposite direction are called antagonists unidirectional - synergists. The same muscles in different situations can act in one and another capacity. In humans, spindle-shaped and ribbon-shaped are more common. Fusiform muscles located and function in the area of long bone formations of the limbs, they can have two bellies (digastric muscles) and several heads (biceps, triceps, quadriceps muscles). Ribbon muscles have different widths and usually participate in the corset formation of the walls of the body. Muscles with a feathery structure, having a large physiological diameter due to large quantity short muscle structures, much stronger than those muscles in which the course of the fibers has a rectilinear (longitudinal) arrangement. The former are called strong muscles that perform small-amplitude movements, the latter are called dexterous muscles that participate in movements with a large amplitude. According to the functional purpose and direction of movement in the joints, muscles are distinguished flexors And extensors, adductors And abducens, sphincters(compressive) and expanders.
Muscle strength determined by the weight of the load that it can lift to a certain height (or is able to hold at maximum excitation) without changing its length. The strength of a muscle depends on the sum of the forces of the muscle fibers and their contractility; on the number of muscle fibers in the muscle and the number of functional units, simultaneously excited when tension develops; from initial muscle length(pre-stretched muscle develops greater strength); from conditions of interaction with skeletal bones.
Contractility muscle is characterized by its absolute force, those. force per 1 cm 2 cross-section of muscle fibers. To calculate this indicator, muscle strength is divided by area its physiological diameter(i.e. the sum of the areas of all muscle fibers that make up the muscle). For example: the average person has the strength (per 1 cm 2 of muscle cross-section) of the gastrocnemius muscle. - 6.24; neck extensors - 9.0; triceps brachii muscle - 16.8 kg.
The central nervous system regulates the force of muscle contraction by changing the number of functional units simultaneously involved in contraction, as well as the frequency of impulses sent to them. The increase in pulse frequency leads to an increase in voltage.
Muscle work. During the process of muscle contraction, potential chemical energy is converted into potential mechanical energy of tension and kinetic energy of movement. There is a distinction between internal and external work. Internal work is associated with friction in the muscle fiber during its contraction. External work manifests itself when moving one’s own body, load, or individual parts of the body (dynamic work) in space. It is characterized by the efficiency factor (efficiency) of the muscular system, i.e. the ratio of the work performed to the total energy expenditure (for human muscles the efficiency is 15-20%; for physically developed, trained people this figure is slightly higher).
With static efforts (without movement), we can talk not about work as such from the point of view of physics, but about work, which should be assessed by the physiological energy costs of the body.
Muscle as an organ. In general, muscle as an organ is a complex structural formation that performs certain functions and consists of 72-80% water and 16-20% dense matter. Muscle fibers consist of myofibrils with cell nuclei, ribosomes, mitochondria, sarcoplasmic reticulum, sensitive nerve formations - proprioceptors and other functional elements that provide protein synthesis, oxidative phosphorylation and resynthesis of adenosine triphosphoric acid, transport of substances within the muscle cell, etc. during the functioning of muscle fibers. An important structural and functional formation of a muscle is a motor, or neuromotor, unit, consisting of one motor neuron and the muscle fibers innervated by it. There are small, medium and large motor units depending on the number of muscle fibers involved in the act of contraction.
A system of connective tissue layers and membranes connects muscle fibers into a single working system, which, with the help of tendons, transmits the traction that occurs during muscle contraction to the bones of the skeleton.
The entire muscle is penetrated by a branched network of blood vessels and lymphatic branches. suckers. Red muscle fibers have a denser network of blood vessels than white. They have a large supply of glycogen and lipids, are characterized by significant tonic activity, the ability to endure prolonged stress and perform prolonged dynamic work. Each red fiber has more mitochondria than white ones - energy generators and suppliers, surrounded by 3-5 capillaries, and this creates conditions for more intense blood supply to the red fibers and a high level of metabolic processes.
White muscle fibers have myofibrils that are thicker and stronger than the myofibrils of red fibers; they contract quickly, but are not capable of prolonged tension. White matter mitochondria have only one capillary. Most muscles contain red and white fibers in varying proportions. There are also muscle fibers tonic(capable of local excitation without its spread); phase,.capable of responding to a spreading wave of excitation with both contraction and relaxation; transitional, combining both properties.
Muscle pump- a physiological concept associated with muscle function and its effect on its own blood supply. Its principal action is manifested as follows: during contraction of skeletal muscles, the influx of arterial blood to them slows down and its outflow through the veins accelerates; during the period of relaxation, venous outflow decreases, and arterial inflow reaches its maximum. The exchange of substances between blood and tissue fluid occurs through the capillary wall.
Rice. 2.5. Schematic representation of the processes occurring in
synapse upon excitation:
1 - synaptic vesicles, 2 - presynaptic membrane, 3 - mediator, 4 - post-synaptic membrane, 5 - synaptic cleft
Mechanisms of muscle Muscle functions are regulated by various reductions departments of the central nervous system (CNS), which largely determine the nature of their versatile activity
(phases of movement, tonic tension, etc.). Receptors The motor apparatus gives rise to afferent fibers of the motor analyzer, which make up 30-50% of the fibers of mixed (afferent-efferent) nerves heading to the spinal cord. Muscle contraction Causes impulses that are the source of muscle sensation - kinesthesia.
The transfer of excitation from nerve fiber to muscle fiber occurs through neuromuscular junction(Fig. 2.5), which consists of two membranes separated by a slit - presynaptic (nerve origin) and postsynaptic (muscle origin). When exposed to a nerve impulse, quanta of acetylcholine are released, which leads to the appearance of an electrical potential that can excite the muscle fiber. The speed of nerve impulse transmission through a synapse is thousands of times less than in a nerve fiber. It conducts excitation only in the direction of the muscle. Normally, up to 150 impulses can pass through the mammalian neuromuscular junction in one second. With fatigue (or pathology), the mobility of neuromuscular endings decreases, and the nature of impulses may change.
Chemistry and energy of muscle contraction. Contraction and tension of the muscle is carried out due to the energy released during chemical transformations that occur when entering the
muscle with a nerve impulse or applying direct irritation to it. Chemical transformations in muscle occur as in the presence of oxygen(under aerobic conditions) and in his absence(under anaerobic conditions).
Cleavage and resynthesis of adenosine triphosphoric acid (ATP). The primary source of energy for muscle contraction is the breakdown of ATP (found in the cell membrane, reticulum and myosin filaments) into adenosine diphosphoric acid (ADP) and phosphoric acids. In this case, 10,000 cal are released from each gram molecule of ATP:
ATP = ADP + H3PO4 + 10,000 cal.
During further transformations, ADP is dephosphorylated to adenylic acid. The breakdown of ATP is stimulated by the protein enzyme actomyosin (adenosine triphosphatase). It is not active at rest; it is activated when the muscle fiber is excited. In turn, ATP acts on myosin filaments, increasing their extensibility. Actomyosin activity increases under the influence of Ca ions, which, at rest, are located in the sarcoplasmic reticulum.
ATP reserves in muscle are insignificant and, to maintain their activity, continuous ATP resynthesis is necessary. It occurs due to the energy obtained from the breakdown of creatine phosphate (CrP) into creatine (Cr) and phosphoric acid (anaerobic phase). With the help of enzymes, the phosphate group from KrP is quickly transferred to ADP (within thousandths of a second). In this case, for each mole of CrP, 46 kJ are released:
Thus, the final process that provides all the energy expenditure of the muscle is the oxidation process. Meanwhile, long-term muscle activity is possible only if there is a sufficient supply of oxygen to it, since The content of substances capable of releasing energy gradually decreases under anaerobic conditions. In addition, lactic acid accumulates; a shift in the reaction to the acidic side disrupts enzymatic reactions and can lead to inhibition and disorganization of metabolism and a decrease in muscle performance. Similar conditions arise in the human body during work of maximum, submaximal and high intensity (power), for example, when running short and medium distances. Due to the developed hypoxia (lack of oxygen), ATP is not completely restored, a so-called oxygen debt arises and lactic acid accumulates.
Aerobic resynthesis of ATP(synonyms: oxidative phosphorylation, tissue respiration) - 20 times more effective than anaerobic energy generation. The part of lactic acid accumulated during anaerobic activity and in the process of long-term work is oxidized to carbon dioxide and water (1/4-1/6 of it), the resulting energy is used to restore the remaining parts of lactic acid into glucose and glycogen, while ensuring the resynthesis of ATP and KrF. The energy of oxidative processes is also used for the resynthesis of carbohydrates necessary for the muscle for its immediate activity.
In general, carbohydrates provide the greatest amount of energy for muscle work. For example, during the aerobic oxidation of glucose, 38 ATP molecules are formed (for comparison: during the anaerobic breakdown of carbohydrate, only 2 ATP molecules are formed).
Aerobic pathway deployment time ATP formation is 3-4 minutes (for trained people - up to 1 minute), the maximum power is 350-450 cal/min/kg, the time to maintain maximum power is tens of minutes. If at rest the rate of aerobic resynthesis of ATP is low, then during physical activity its power becomes maximum and at the same time the aerobic pathway can work for hours. It is also highly economical: during this process there is a deep decomposition of the starting substances to the final products CO2 and NaO. In addition, the aerobic pathway of ATP resynthesis is distinguished by its versatility in the use of substrates: all organic substances of the body are oxidized (amino acids, proteins, carbohydrates, fatty acids, ketone bodies, etc.).
However, the aerobic method of ATP resynthesis also has disadvantages: 1) it requires the consumption of oxygen, the delivery of which to muscle tissue is ensured by the respiratory and cardiovascular systems, which is naturally associated with their tension; 2) any factors affecting the state and properties of mitochondrial membranes disrupt the formation of ATP; 3) the development of aerobic ATP formation is long in time and low in power.
Muscular activity carried out in most sports cannot be fully ensured by the aerobic process of ATP re-synthesis, and the body is forced to additionally include anaerobic methods of ATP formation, which have a shorter deployment time and a greater maximum power of the process (i.e. the largest amount of ATP, "formed per unit time) - 1 mole of ATP corresponds to 7.3 cal, or 40 J (1 cal == 4.19 J).
Returning to the anaerobic processes of energy formation, it should be clarified that they occur in at least two types of reactions: 1. Creatine phosphokinase - when CrP is cleaved, the phosphorus groups from which are transferred to ADP, thereby resynthesizing ATP. But the reserves of creatine phosphate in the muscles are small and this causes a rapid (within 2-4 s) extinction of this type of reaction. 2. Glycolytic(glycolysis) - develops more slowly, within 2-3 minutes of intensive work. Glycolysis begins with the phosphorylation of muscle glycogen reserves and blood glucose. The energy of this process is enough for several minutes of hard work. At this stage, the first stage of glycogen phosphorylation is completed and preparation for the oxidative process occurs. Then comes the second stage of the glycolytic reaction - dehydrogenation and the third - the reduction of ADP to ATP. The glycolytic reaction ends with the formation of two molecules of lactic acid, after which respiratory processes unfold (at 3-5 minutes of work), when lactic acid (lactate), formed during anaerobic reactions, begins to oxidize.
Biochemical indicators for assessing the creatine phosphate anaerobic pathway of ATP resynthesis are the creatinine coefficient and alactic (without lactic acid) oxygen debt. Creatinine ratio- is the excretion of creatinine in urine per day per 1 kg of body weight. In men, creatinine excretion ranges from 18-32 mg/day x kg, and in women - 10-25 mg/day x kg. There is a relationship between the content of creatine phosphate and the formation of creatinine. linear relationship. Therefore, using the creatinine coefficient, the potential capabilities of this ATP resynthesis pathway can be assessed.
Biochemical changes in the body caused by the accumulation of lactic acid as a result of glycolysis. If at rest before the onset of cervical activity lactate concentration in the blood is 1-2 mmol/l, then after intense, short-term exercise for 2-3 minutes this value can reach 18-20 mmol/l. Another indicator reflecting the accumulation of lactic acid in the blood is blood count(pH): at rest 7.36, after exercise decreases to 7.0 or more. The accumulation of lactate in the blood determines its alkaline reserve - alkaline components of all blood buffer systems.
The end of intense muscle activity is accompanied by a decrease in oxygen consumption - initially sharply, then more gradually. In this regard, they highlight two components of oxygen debt: fast (alactate) and slow (lactate). Lactate - this is the amount of oxygen that is used after finishing work to eliminate lactic acid: a smaller part is oxidized to J-bO and COa, the larger part is converted into glycogen. This transformation requires a significant amount of ATP, which is formed aerobically due to oxygen, which constitutes lactate debt. Lactate metabolism occurs in liver and myocardial cells.
The amount of oxygen required to fully ensure the work performed is called oxygen demand. For example, in a 400 m race, the oxygen demand is approximately 27 liters. The time to run the distance at the world record level is about 40 seconds. Studies have shown that during this time the athlete absorbs 3-4 liters of 02. Therefore, 24 liters is total oxygen debt(about 90% of oxygen demand), which is eliminated after the race.
In the 100 m race, the oxygen debt can reach up to 96% of the demand. In the 800 m run, the share of anaerobic reactions decreases slightly - to 77%, in the 10,000 m run - to 10%, i.e. the predominant part of energy is supplied through respiratory (aerobic) reactions.
The mechanism of muscle relaxation. As soon as nerve impulses stop entering the muscle fiber, Ca2 ions, under the action of the so-called calcium pump, due to the energy of ATP, go into the cisterns of the sarcoplasmic reticulum and their concentration in the sarcoplasm decreases to the initial level. This causes changes in the conformation of troponin, which, by fixing tropomyosin in a certain area of actin filaments, makes it impossible for the formation of cross bridges between thick and thin filaments. Due to the elastic forces that arise during muscle contraction in the collagen threads surrounding the muscle fiber, it returns to its original state upon relaxation. Thus, the process of muscle relaxation, or relaxation, as well as the process of muscle contraction, is carried out using the energy of ATP hydrolysis.
During muscle activity, the processes of contraction and relaxation alternately occur in the muscles and, therefore, the speed-strength qualities of the muscles equally depend on the speed of muscle contraction and on the ability of the muscles to relax.
Brief characteristics of smooth muscle fibers. Smooth muscle fibers lack myofibrils. Thin filaments (actin) are connected to the sarcolemma, thick filaments (myosin) are located inside the muscle cells. Smooth muscle fibers also lack cisterns with Ca ions. Under the influence of a nerve impulse, Ca ions slowly enter the sarcoplasm from the extracellular fluid and also slowly leave after the nerve impulses stop arriving. Therefore, smooth muscle fibers contract slowly and relax slowly.
General overview of skeletal human muscles. Muscles of the trunk(Fig. 2.6 and 2.7) include the muscles of the chest, back and abdomen. The muscles of the chest are involved in the movements of the upper limbs, and also provide voluntary and involuntary respiratory movements. The respiratory muscles of the chest are called the external and internal intercostal muscles. The respiratory muscles also include the diaphragm. The back muscles consist of superficial and deep muscles. Superficial ones provide some movements of the upper limbs, head and neck. The deep (“rectifiers of the trunk”) are attached to the spinous processes of the vertebrae and stretch along the spine. The back muscles are involved in maintaining the vertical position of the body; with strong tension (contraction), they cause the body to bend backward. The abdominal muscles maintain pressure inside the abdominal cavity (abdominals), participate in some body movements (bending the torso forward, bending and turning to the sides), and during the breathing process.
Muscles of the head and neck - mimic, chewing and moving the head and neck. Facial muscles are attached at one end to the bone, at the other to the skin of the face, some can begin and end in the skin. Facial muscles provide movements of the facial skin, reflect various mental states of a person, accompany speech and are important in communication. When the chewing muscles contract, they cause the lower jaw to move forward and to the sides. The neck muscles are involved in head movements. The posterior group of muscles, including the muscles of the back of the head, with tonic (from the word “tone”) contraction holds the head in an upright position.
Rice. 2.6. Muscles of the anterior half of the body (according to Sylvanovich):
1 - temporal muscle, 2 - masseter muscle, 3 - sternocleidomastoid muscle, 4 - pectoralis major muscle, 5 - middle scalene muscle, b - external oblique muscle of the abdomen, 7 - vastus medialis, 8 - vastus lateralis, 9 - rectus femoris muscle, 10 - sartorius, 11 - tender muscle 12 - internal oblique abdominal muscle, 13 - rectus abdominis muscle, 14 - biceps brachii muscle, 15 ~ external intercostal muscles, 16 - orbicularis oris muscle, 17 - orbicularis oculi muscle, 18 - frontalis muscle
Muscles of the upper limbs provide movement of the shoulder girdle, shoulder, forearm and move the hand and fingers. The main antagonist muscles are the biceps (flexor) and triceps (extensor) muscles of the shoulder. The movements of the upper limb and, above all, the hand are extremely diverse. This is due to the fact that the hand serves as a human organ of labor.
Rice. 2.7. Muscles of the posterior half of the body (according to Sylvanovich):
1 - rhomboid muscle, 2 - rectifier torso, 3 - deep muscles of the gluteal muscle, 4 - biceps femoris muscle, 5 - calf muscle, 6 - Achilles tendon, 7 - gluteus maximus muscle, 8 - latissimus skipae muscle, 9 - deltoid, 10 - trapezius muscle
Muscles of the lower extremities provide movement of the hip, lower leg and foot. The thigh muscles play an important role in maintaining an upright body position, but in humans they are more developed than in other vertebrates. The muscles that carry out movements of the lower leg are located on the thigh (for example, the quadriceps muscle, the function of which is to extend the lower leg at the knee joint; the antagonist of this muscle is the biceps femoris muscle). The foot and toes are driven by muscles located in the lower leg and foot. Flexion of the toes is carried out by contraction of the muscles located on the sole, and extension by the muscles of the anterior surface of the leg and foot. Many muscles of the thigh, leg and foot are involved in maintaining the human body in an upright position.
Muscular activity - contraction and relaxation occur with the obligatory use of energy, which is released during the hydrolysis of ATP ATP + H 2 0 ADP + H 3 P0 4 + energy at rest, the concentration of ATP in muscles is about 5 mmol/l and, accordingly, 1 mmol of ATP corresponds to physiological conditions approximately 12 cal or 50 J (1 cal = 4.18 J)
Muscle mass in an adult is about 40% of body weight. In athletes building muscle, muscle mass can reach 60% or more of body weight. The muscles of an adult at rest consume about 10% of the total oxygen entering the body. During intense work, muscle oxygen consumption can increase to 90% of the total oxygen consumed.
Energy sources for aerobic resynthesis of ATP are carbohydrates, fats and amino acids, the breakdown of which is completed by the Krebs cycle. The Krebs cycle is the final stage of catabolism, during which acetyl coenzyme A is oxidized to CO2 and H20. During this process, 4 pairs of hydrogen atoms are removed from acids (isocitric, α-ketoglutaric, succinic and malic acid) and therefore 12 ATP molecules are formed from the oxidation of one molecule of acetyl coenzyme A.
ANAEROBIC PATHWAYS OF ATP RESINTHESIS Anaerobic pathways of ATP resynthesis (Creatine phosphate, glycolytic) are additional methods of ATP formation in cases where the main pathway for ATP production - aerobic - cannot provide muscle activity with the necessary amount of energy. This happens in the first minutes of any work, when tissue respiration has not yet fully developed, as well as when performing high-power physical activity.
Glycolytic pathway of ATP resynthesis This resynthesis pathway, like Creatine phosphate, belongs to the anaerobic methods of ATP formation. The source of energy necessary for ATP resynthesis in this case is muscle glycogen, the concentration of which in the sarcoplasm ranges from 0.2-3%. During the anaerobic breakdown of glycogen, the terminal glucose residues in the form of glucose-1-phosphate are alternately cleaved from its molecule under the influence of the enzyme phosphorylase. Next, glucose-1-phosphate molecules through a series of successive stages (there are 10 in total) are converted into lactic acid (lactate)
Adenylate kinase (myokinase) reaction Adenylate kinase (or myokinase) reaction occurs in muscle cells under conditions of significant accumulation of ADP in them, which is usually observed with the onset of fatigue. The adenylate kinase reaction is accelerated by the enzyme adenylate kinase (myokinase), which is located in the sarcoplasm of myocytes. During this reaction, one ADP molecule transfers its phosphate group to another ADP, resulting in the formation of ATP and AMP: ADP + ADP ATP + AMP
Work in the maximum power zone Continue for s. The main source of ATP under these conditions is creatine phosphate. Only at the end of the work is the creatine phosphate reaction replaced by glycolysis. Examples of physical exercises performed in the maximum power zone include sprinting, long and high jumps, some gymnastic exercises, and lifting weights.
Work in the submaximal power zone Duration up to 5 minutes. The leading mechanism of ATP resynthesis is glycolytic. At the beginning of work, until glycolysis has reached its maximum speed, the formation of ATP occurs due to creatine phosphate, and at the end of work, glycolysis begins to be replaced by tissue respiration. Work in the submaximal power zone is characterized by the highest oxygen debt - up to 20 liters. Examples of exercise in this power zone include middle distance running, sprint swimming, track cycling, and sprint speed skating.
Work in a high power zone Duration up to 30 minutes. Work in this zone is characterized by approximately equal contributions from glycolysis and tissue respiration. The creatine phosphate pathway for ATP resynthesis functions only at the very beginning of work, and therefore its share in the total energy supply of this work is small. Examples of exercises in this power zone include the 5,000 m race, distance skating, cross-country skiing, and middle- and long-distance swimming.
Operation in a moderate power zone Continues for more than 30 minutes. Energy supply to muscle activity occurs predominantly aerobically. An example of such power is marathon running, track and field cross-country, race walking, road cycling, and long-distance cross-country skiing.
Useful Information In the International System of Units (SI), the basic unit of energy is the joule (J) and the unit of power is the watt (W). 1 joule (J) = 0.24 calories (cal). 1 kilojoule (kJ) = 1000 J. 1 calorie (cal) = 4.184 J. 1 kilocalorie (kcal) = 1000 cal = 4184 J. 1 watt (W) = 1 J-s"1 = 0.24 cal-s -1. 1 kilowatt (kW) = 1000 W. 1 kg-m-s"1 = 9.8 W. 1 horsepower (hp) = 735 watts. To express the power of ATP resynthesis pathways in J/min-kg, it is necessary to multiply the value of this criterion in cal/min-kg by 4.18, and to obtain the power value in W/kg, multiply by 0.07.
WITHmuscle fiber structure and contraction.
Muscle contraction in a living system is a mechanochemical process. Modern science considers it the most perfect form of biological mobility. Biological objects “developed” the contraction of muscle fiber as a way to move in space (which significantly expanded their life capabilities).
Muscle contraction is preceded by a tension phase, which is the result of work carried out by converting chemical energy into mechanical energy directly and with good efficiency (30-50%). The accumulation of potential energy in the tension phase brings the muscle into a state of possible, but not yet realized, contraction.
Animals and humans have (and humans believe that they have already been well studied) two main types of muscles: striated and smooth. Striated muscles or skeletal are attached to bones (except for striated fibers of the cardiac muscle, which differ from skeletal muscles in composition). Smooth muscles support the tissues of internal organs and skin and form the muscles of the walls of blood vessels, as well as the intestines.
In the biochemistry of sports they study skeletal muscles, “specifically responsible” for sports results.
A muscle (as a macro formation belonging to a macro object) consists of individual muscle fibers(micro formations). There are thousands of them in a muscle; accordingly, muscle effort is an integral value that sums up the contractions of many individual fibers. There are three types of muscle fibers: white fast-twitch , intermediate And red slow-twitch. Types of fibers differ in the mechanism of their energy supply and are controlled by different motor neurons. Muscle types differ in the ratio of fiber types.
A separate muscle fiber - a thread-like acellular formation - simplast. The symplast “does not look like a cell”: it has a highly elongated shape with a length of 0.1 to 2-3 cm, in the sartorius muscle up to 12 cm, and a thickness of 0.01 to 0.2 mm. The symplast is surrounded by a shell - sarcolemma, to the surface of which the endings of several motor nerves approach. Sarcolemma is a two-layer lipoprotein membrane (10 nm thick) reinforced by a network of collagen fibers. When they relax after contraction, they return the symplast to its original shape (Fig. 4).
Rice. 4. Individual muscle fiber.
On the outer surface of the sarcolemma-membrane, an electrical membrane potential is always maintained, even at rest it is equal to 90-100 mV. The presence of potential is a necessary condition for controlling muscle fiber (like a car battery). The potential is created due to the active (meaning with the expenditure of energy - ATP) transfer of substances through the membrane and its selective permeability (according to the principle - “whoever I want, I’ll let him in or let him out”). Therefore, inside the simplast, some ions and molecules accumulate in higher concentrations than outside.
The sarcolemma is well permeable to K + ions - they accumulate inside, and Na + ions are removed outside. Accordingly, the concentration of Na + ions in the intercellular fluid is greater than the concentration of K + ions inside the symplast. A pH shift to the acidic side (during the formation of lactic acid, for example) increases the permeability of the sarcolemma for high-molecular substances (fatty acids, proteins, polysaccharides), which normally do not pass through it. Low molecular weight substances (glucose, lactic and pyruvic acids, ketone bodies, amino acids, short peptides) easily pass (diffuse) through the membrane.
Internal contents of simplast – sarcoplasm– This is a colloidal protein structure (the consistency resembles jelly). In a suspended state, it contains glycogen inclusions, fat droplets, and various subcellular particles are “built in”: nuclei, mitochondria, myofibrils, ribosomes and others.
Contractile “mechanism” inside the symplast – myofibrils. These are thin (Ø 1 - 2 microns) muscle filaments, long - almost equal to the length of the muscle fiber. It has been established that in the symplasts of untrained muscles, the myofibrils are not located in an orderly manner, along the symplast, but with scatter and deviations, and in trained ones, the myofibrils are oriented along the longitudinal axis and are also grouped into bundles, like in ropes. (When spinning artificial and synthetic fibers, the macromolecules of the polymer are not initially located strictly along the fiber and, like athletes, they are “persistently trained” - oriented correctly - along the axis of the fibers, by repeated rewinding: see the long workshops at ZIV and Khimvolokno).
Under a light microscope, it can be observed that the myofibrils are indeed “striated.” They alternate light and dark areas - disks. Dark rims A (anisotropic) proteins contain more than light discs I (isotropic). Light discs crossed by membranes Z (telophragms) and a section of myofibril between two Z - called membranes sarcomere. The myofibril consists of 1000 – 1200 sarcomeres (Fig. 5).
The contraction of a muscle fiber as a whole consists of individual contractions sarcomeres. Contracting each separately, the sarcomeres together create an integral force and perform mechanical work to contract the muscle.
The length of the sarcomere varies from 1.8 µm at rest to 1.5 µm during moderate and up to 1 µm during full contraction. The disks of sarcomeres, dark and light, contain protofibrils (myofilaments) - protein thread-like structures. They are found in two types: thick (Ø – 11 – 14 nm, length – 1500 nm) and thin (Ø – 4 – 6 nm, length – 1000 nm).
Rice. 5. Myofibril area.
Light wheels ( I ) consist only of thin protofibrils, and dark disks ( A ) – from protofibrils of two types: thin, fastened together by a membrane, and thick, concentrated in a separate zone ( H ).
When the sarcomere contracts, the length of the dark disk ( A ) does not change, and the length of the light disk ( I ) decreases as thin protofibrils (light disks) move into the spaces between thick ones (dark disks). On the surface of protofibrils there are special outgrowths - adhesions (about 3 nm thick). In the “working position” they form an engagement (cross bridges) between thick and thin threads of protofibrils (Fig. 6). When contracting Z -membranes rest against the ends of thick protofibrils, and thin protofibrils can even wrap around thick ones. During supercontraction, the ends of the thin filaments in the center of the sarcomere are curled, and the ends of the thick protofibrils are crushed.
Rice. 6. Formation of adhesions between actin and myosin.
Energy supply to muscle fibers is carried out using sarcoplasmic reticulum(aka - sarcoplasmic reticulum) – systems of longitudinal and transverse tubes, membranes, bubbles, compartments.
In the sarcoplasmic reticulum, various biochemical processes occur in an organized and controlled manner; the network covers everything together and each myofibril separately. The reticulum includes ribosomes, they carry out the synthesis of proteins, and mitochondria - “cellular energy stations” (as defined in the school textbook). Actually mitochondria embedded between myofibrils, which creates optimal conditions for energy supply to the process of muscle contraction. It has been established that in trained muscles the number of mitochondria is greater than in the same untrained muscles.
Chemical composition of muscles.
Water with leaves 70 - 80% of the muscle weight.
Squirrels. Proteins account for from 17 to 21% of muscle weight: approximately 40% of all muscle proteins are concentrated in myofibrils, 30% in sarcoplasm, 14% in mitochondria, 15% in sarcolemma, the rest in nuclei and other cellular organelles.
Muscle tissue contains enzymatic myogenic proteins groups, myoalbumin– reserve protein (its content gradually decreases with age), red protein myoglobin– chromoprotein (it is called muscle hemoglobin, it binds more oxygen than blood hemoglobin), and also globulins, myofibrillar proteins. More than half of the myofibrillar proteins are myosin, about a quarter - actin, the rest is tropomyosin, troponin, α- and β-actinins, enzymes creatine phosphokinase, deaminase and others. Muscle tissue contains nuclearsquirrels– nucleoproteins, mitochondrial proteins. In proteins stroma, entwining muscle tissue - the main part - collagen And elastin sarcolemmas, as well as myostromins (associated with Z -membranes).
Inpre-soluble nitrogen compounds. Human skeletal muscles contain various water-soluble nitrogen compounds: ATP, from 0.25 to 0.4%, creatine phosphate (CrP)– from 0.4 to 1% (with training, its amount increases), their breakdown products are ADP, AMP, creatine. In addition, muscles contain a dipeptide carnosine, about 0.1 - 0.3%, involved in restoring muscle performance during fatigue; carnitine, responsible for the transport of fatty acids across cell membranes; amino acids, and among them glutamine predominates (does this explain the use of monosodium glutamate, read the composition of seasonings, to give food the taste of meat); purine bases, urea and ammonia. Skeletal muscle also contains about 1.5% phosphatides, which participate in tissue respiration.
Nitrogen-free connections. Muscles contain carbohydrates, glycogen and its metabolic products, as well as fats, cholesterol, ketone bodies, and mineral salts. Depending on the diet and the degree of training, the amount of glycogen varies from 0.2 to 3%, while training increases the mass of free glycogen. Storage fats accumulate in muscles during endurance training. Protein-bound fat makes up approximately 1%, and muscle fiber membranes can contain up to 0.2% cholesterol.
Minerals. Minerals in muscle tissue make up approximately 1 - 1.5% of muscle weight; these are mainly potassium, sodium, calcium, and magnesium salts. Mineral ions such as K + , Na + , Mg 2+ , Ca 2+ , Cl - , HP0 4 ~ play a vital role in the biochemical processes during muscle contraction (they are included in “sports” supplements and mineral water).
Biochemistry of muscle proteins.
The main contractile protein of muscles is myosin refers to fibrillar proteins (Molecular weight about 470,000). An important feature of myosin is the ability to form complexes with ATP and ADP molecules (which allows you to “take” energy from ATP), and with the protein actin (which makes it possible to maintain contraction).
The myosin molecule has a negative charge and specifically interacts with Ca ++ and Mg ++ ions. Myosin, in the presence of Ca++ ions, accelerates the hydrolysis of ATP, and thus exhibits enzymatic adenosine triphosphate activity:
myosin-ATP+H2O → myosin + ADP + H3PO4 + work(energy 40 kJ/mol)
The myosin protein is formed by two identical, long polypeptide α-chains, twisted like a double helix, Fig. 7. Under the action of proteolytic enzymes, the myosin molecule breaks into two parts. One of its parts is capable of binding to actin through adhesions, forming actomyosin. This part is responsible for adenosine triphosphatase activity, which depends on the pH of the environment, the optimum is pH 6.0 - 9.5, as well as the concentration of KCl. The actomyosin complex disintegrates in the presence of ATP, but in the absence of free ATP it is stable. The second part of the myosin molecule also consists of two twisted helices; due to an electrostatic charge, they bind the myosin molecules into protofibrils.
Rice. 7. Structure of actomyosin.
The second most important contractile protein is actin(Fig. 7). It can exist in three forms: monomeric (globular), dimeric (globular) and polymeric (fibrillar). Monomeric globular actin, when its polypeptide chains are tightly packed into a compact spherical structure, is associated with ATP. By splitting ATP, actin monomers - A, form dimers, including ADP: A - ADP - A. Polymeric fibrillar actin is a double helix consisting of dimers, Fig. 7.
Globular actin transforms into fibrillar actin in the presence of K + and Mg ++ ions, and fibrillar actin predominates in living muscles.
Myofibrils contain a significant amount of protein tropomyosin, which consists of two α-helical polypeptide chains. In resting muscles, it forms a complex with actin and blocks its active centers, since actin is able to bind to Ca ++ ions, which remove this blockade.
At the molecular level, thick and thin protofibrils of the sarcomere interact electrostatically, since they have special areas - outgrowths and protrusions - where a charge is formed. In the A-disk region, thick protofibrils are built from a bundle of longitudinally oriented myosin molecules, thin protofibrils are arranged radially around thick ones, forming a structure similar to a multi-strand cable. In the central M-band of thick protofibrils, myosin molecules are connected by their “tails”, and their protruding “heads” - outgrowths are directed in different directions and are located along regular spiral lines. In fact, opposite them in the fibrillar actin spirals at a certain distance from each other, monomeric actin globules are also protruding. Each protrusion has active center, due to which the formation of adhesions with myosin is possible. Z-membranes of sarcomeres (like alternating pedestals) hold thin protofibrils together.
Biochemistry of contraction and relaxation.
The cyclic biochemical reactions that occur in the muscle during contraction ensure the repeated formation and destruction of adhesions between the “heads” - the outgrowths of the myosin molecules of thick protofibrils and the protrusions - the active centers of thin protofibrils. The work of forming adhesions and moving the actin filament along the myosin filament requires both precise control and significant energy expenditure. In reality, at the moment of fiber contraction, about 300 adhesions are formed per minute in each active center - protrusion.
As we noted earlier, only ATP energy can be directly converted into mechanical work of muscle contraction. ATP hydrolyzed by the enzymatic center of myosin forms a complex with the entire myosin protein. In the ATP-myosin complex, myosin, saturated with energy, changes its structure, and with it the external “dimensions” and, in this way, performs mechanical work to shorten the growth of the myosin filament.
In resting muscle, myosin is still bound to ATP, but through Mg++ ions without hydrolytic cleavage of ATP. The formation of adhesions between myosin and actin at rest is prevented by the complex of tropomyosin with troponin, which blocks the active centers of actin. The blockade is maintained and ATP is not broken down while Ca++ ions are bound. When a nerve impulse arrives at a muscle fiber, it is released pulse transmitter– neurohormone acetylcholine. Na+ ions neutralize the negative charge on the inner surface of the sarcolemma and depolarize it. In this case, Ca++ ions are released and bind to troponin. In turn, troponin loses its charge, causing the active centers - the protrusions of actin filaments - to be unblocked and adhesions between actin and myosin arise (since the electrostatic repulsion of thin and thick protofibrils has already been removed). Now, in the presence of Ca ++, ATP interacts with the center of enzymatic activity of myosin and is cleaved, and the energy of the transforming complex is used to reduce the adhesion. The chain of molecular events described above is similar to an electric current recharging a microcapacitor; its electrical energy is immediately converted into mechanical work on the spot and needs to be recharged again (if you want to move on).
After the rupture of the adhesive, ATP is not cleaved, but again forms an enzyme-substrate complex with myosin:
M–A + ATP -----> M – ATP + A or
M–ADP–A + ATP ----> M–ATP + A + ADP
If at this moment a new nerve impulse arrives, then the “recharging” reactions are repeated; if the next impulse does not arrive, the muscle relaxes. The return of a contracted muscle upon relaxation to its original state is ensured by the elastic forces of proteins in the muscle stroma. Putting forward modern hypotheses of muscle contraction, scientists suggest that at the moment of contraction, actin filaments slide along myosin filaments, and their shortening is also possible due to changes in the spatial structure of contractile proteins (changes in the shape of the helix).
At rest, ATP has a plasticizing effect: by combining with myosin, it prevents the formation of its adhesions with actin. By breaking down during muscle contraction, ATP provides energy for the process of shortening the adhesions, as well as the work of the “calcium pump” - the supply of Ca ++ ions. The breakdown of ATP in muscle occurs at a very high rate: up to 10 micromoles per 1 g of muscle per minute. Since the total reserves of ATP in the muscle are small (they may only be enough for 0.5-1 sec of work at maximum power), to ensure normal muscle activity, ATP must be restored at the same rate at which it is broken down.
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