Hypertrophy and muscle atrophy is a problem of hypodynamia. Muscle hypertrophy

Since the strength of a muscle depends on its diameter, an increase in it is accompanied by an increase in the strength of a given muscle. An increase in muscle diameter as a result physical training called working muscle hypertrophy (from the Greek "tro-phos" - nutrition). Muscle fibers, which are highly specialized differentiated cells, apparently are not capable of cell division with the formation of new fibers. In any case, if the division of muscle cells does take place, then only in special cases and in a very small amount. Working muscle hypertrophy occurs almost or exclusively due to the thickening (increase in volume) of existing muscle fibers... In case of significant thickening of muscle fibers, their longitudinal mechanical splitting is possible with the formation of "daughter" fibers with a common tendon. During strength training, the number of longitudinally cleaved fibers increases.

Two extreme types of working hypertrophy of muscle fibers can be distinguished - sarcoplasmic and myofibrillar. Sarcoplasmic working hypertrophy is a thickening of muscle fibers due to a predominant increase in the volume of sarcoplasm, i.e., their non-contractile part. Hypertrophy of this type occurs due to an increase in the content of non-contractile (in particular, mitochondrial) proteins and metabolic reserves of muscle fibers: glycogen, nitrogen-free substances, creatine phosphate, myoglobin, etc. A significant increase in the number of capillaries as a result of training can also cause some muscle thickening.

The most susceptible to sarcoplasmic hypertrophy are apparently slow (I) and fast oxidative (II-A) fibers. Working hypertrophy of this type has little effect on the growth of muscle strength, but it significantly increases the ability to work continuously, that is, increases their endurance.

Myofibrillar working hypertrophy is associated with an increase in the number and volume of myofibrils, that is, the actual contractile apparatus of muscle fibers. This increases the packing density of myofibrils in the muscle fiber. This working hypertrophy of muscle fibers leads to a significant increase in muscle MS. The absolute strength of the muscle also significantly increases, and with working hypertrophy of the first type, it either does not change at all, or even slightly decreases. Apparently, fast (II-B) muscle fibers are most prone to myofibrillar hypertrophy.

In real situations, muscle fiber hypertrophy is a combination of the two named types with a predominance of one of them. The predominant development of one or another type of working hypertrophy is determined by the nature muscle training... Long dynamic exercises, developing endurance, with a relatively small force load on the muscles, mainly cause working hypertrophy of the first type .. Exercises with high muscle tension (more than 70% of the MPS of the trained muscle groups), on the contrary, contribute to the development of working hypertrophy, mainly of the second type.

At the heart of working hypertrophy is intense synthesis and reduced degradation muscle proteins... Accordingly, the concentration of DNA and RNA in the hypertrophied muscle is higher than in the normal one. Increased creatine content in the contracting muscle can stimulate increased synthesis of actin and myosin and thus contribute to the development of working hypertrophy of muscle fibers.

Highly important role in the regulation of the volume of muscle mass, in particular in the development of muscle hypertrophy, androgens (male sex hormones) play. In men, they are produced by the gonads (testes) and in the adrenal cortex, and in women, only in the adrenal cortex. Accordingly, men have more androgens in their bodies than women. The role of androgens in increasing muscle mass is manifested in the following.

Age-related development of muscle mass goes hand in hand with an increase in the production of androgenic hormones. The first noticeable thickening of muscle fibers is observed at 6-7 years of age, when the formation of androgens increases. With the onset of puberty (at the age of 11-15). an intensive increase in muscle mass in boys begins, which continues after puberty. In girls, muscle development generally ends with puberty. The growth of muscle strength at school age has a corresponding character.

Even after the correction of strength indicators with body size, strength indicators in adult women are lower than in men (for more details, see 1X.2). At the same time, if in women, as a result of certain diseases, the secretion of androgens by the adrenal glands increases, then muscle mass increases intensively, a well-developed muscle relief, muscle strength increases.

In experiments on animals, it was found that the introduction of preparations of androgenic hormones (anabolic steroids) causes a significant intensification of the synthesis of muscle proteins, as a result of which the mass of the trained muscles increases and, as a result, their strength. At the same time, the development of working hypertrophy skeletal muscle can occur without the participation of androgenic and other hormones (growth hormone, insulin and thyroid hormones).

Strength training, like other types of training, does not appear to alter the muscle balance of the two main types of muscle fibers - fast and slow. At the same time, it is able to change the ratio of two types of fast fibers, increasing the percentage of fast glycolytic (BG) and, accordingly, decreasing the percentage of fast oxidative-glycolytic (BOG) fibers (Table 7). At the same time, as a result of strength training, the degree of hypertrophy of fast muscle fibers is significantly greater than 5 slow oxidative (MO) fibers, while endurance training leads to hypertrophy, primarily of slow fibers. These differences show that the degree of working hypertrophy of the muscle fiber depends both on the measure of its use in the "training process, and on its ability to hypertrophy."

Strength training is associated with a relatively small number of repetitive maximal or near-maximal muscle contractions, in which both fast and slow muscle fibers are involved. However, even a small number of repetitions is sufficient for the development of working hypertrophy of fast fibers, which indicates their greater predisposition to the development of working hypertrophy (compared with slow fibers). A high percentage of fast fibers in muscles is an important prerequisite for a significant increase in muscle strength when directed strength training... Therefore, people with a high percentage of fast fibers in their muscles have a higher potential for strength and power development.

Endurance training is associated with a large number of repetitive muscle contractions of relatively low strength, which are mainly provided by the activity of slow muscle fibers. Therefore, a more pronounced working hypertrophy of slow muscle fibers in this type of training is understandable in comparison with hypertrophy of fast fibers, especially fast glycolytic ones (see Table 7).

Table 7. Composition of the quadriceps femoris muscle (outer head) and cross-sectional area different types muscle fibers in athletes of various specializations and non-athletes (F. Prince, et al., 1976)

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Muscle hypertrophy and atrophy

Systematic intensive muscle work leads to an increase in muscle mass. This phenomenon is called working muscle hypertrophy. At the heart of hypertrophy is an increase in the mass of protoplasm of muscle fibers, leading to their thickening. This increases the content of proteins and glycogen, as well as substances that deliver energy used in muscle contraction - adenosine triphosphate and creatine phosphate.

Apparently, in this regard, the strength and speed of contraction of the hypertrophied muscle is higher than that of the non-hypertrophied one.

The increase in muscle mass in trained people, in whom many muscles are hypertrophied, leads to the fact that the body musculature can be 50% of the body weight (instead of the usual 35-40%).

Hypertrophy develops if a person daily for a long time performs muscular work that requires a lot of stress (power load). Muscular work performed without much effort, even if it lasts a very long time, does not lead to muscle hypertrophy.

The opposite of working hypertrophy is muscle atrophy from inactivity. It develops in all cases when the muscle for some reason loses the ability to do its normal work. This happens, for example, with prolonged immobilization of a limb in a plaster cast, with a long stay of the patient in bed, with cutting a tendon, as a result of which the muscle ceases to work against the load, etc.

With atrophy, the diameter of the muscle fibers and the content in them contractile proteins, glycogen, ATP and other substances important for contractile activity drop sharply.

With the resumption of normal muscle function, the atrophy gradually disappears.

A special type of muscle atrophy is observed with muscle denervation, that is, after cutting its motor nerve.

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Muscle fatigue

Fatigue is a temporary decrease in the performance of a cell, organ or the whole organism, which occurs as a result of work and disappears after rest.

If an isolated muscle, to which a small load is suspended, is irritated for a long time with rhythmic electrical stimuli, then the amplitude of its contractions gradually decreases to zero. The recorded contraction is called the fatigue curve.

Along with a change in the amplitude of contractions during fatigue, the latent period of contraction increases and the period of muscle relaxation is lengthened. However, all these changes do not occur immediately after the start of work, but after some time, during which there is an increase in the amplitude of single muscle contractions. This period is called the activation period. With further prolonged irritation, muscle fiber fatigue develops.

A decrease in the performance of an isolated muscle during prolonged irritation is due to two main reasons. The first of them is that during contraction, metabolic products (phosphoric, lactic acids, etc.) accumulate in the muscle, which have a depressing effect on the performance of muscle fibers. Some of these products, as well as potassium ions, diffuse out of the fibers into the pericellular space and have a depressing effect on the ability of the excitable membrane to generate action potentials. If an isolated muscle, placed in a small volume of Ringer's fluid, is irritated for a long time to the point of complete fatigue, then it is enough just to change the solution that washes it in order to restore muscle contractions.

Another reason for the development of fatigue in an isolated muscle is the gradual

shchenie in it energy reserves. With prolonged work of an isolated muscle, a sharp decrease in glycogen stores occurs, as a result of which the processes of resynthesis of ATP and creatine phosphate, which are necessary for contraction, are disrupted.

It should be emphasized that fatigue of an isolated skeletal muscle during direct stimulation is a laboratory phenomenon. Under natural conditions, fatigue of the motor apparatus during prolonged work develops more complexly and depends on a large number of factors. This is due, firstly, to the fact that in the body, the muscle is continuously supplied with blood and, therefore, receives with it a certain amount nutrients(glucose, amino acids) and is released from metabolic products that disrupt the normal functioning of muscle fibers. Secondly, in the whole organism, fatigue depends not only on the processes in the muscle, but also on the processes developing in the nervous system, participating in the control of motor activity. So, for example, fatigue is accompanied by discoordination of movements, excitation of many muscles that are not involved in the performance of work.

I.M.Sechenov (1903) showed that the restoration of the working capacity of the tired muscles of a person's hand after prolonged work on lifting a load is accelerated if, during the rest period, work is performed with the other hand. Temporary restoration of the working capacity of the muscles of the tired arm can be achieved with other types of physical activity, for example, when the muscles are working lower limbs... In contrast to simple rest, such rest was called active by I.M.Sechenov. He viewed these facts as evidence that fatigue develops primarily in the nerve centers.

Experiments with suggestion can serve as convincing evidence of the role of nerve centers in the development of fatigue. So, being in a state of hypnosis, the subject can lift a heavy weight for a long time, if he is convinced that there is a light basket in his hand. On the contrary, when the subject is suggested that he has been given a heavy weight, fatigue develops rapidly when the light basket is lifted. At the same time, changes in pulse, respiration and gas exchange are not in accordance with the real work carried out by a person, but with the one that is suggested to him.

When identifying the causes of fatigue of the motor apparatus as applied to the whole organism, at present, two types of motor activity are often distinguished: local, when a relatively small number of muscles are active, and general, when most of the muscles of the body are involved in work. In the first case, among the causes of fatigue, peripheral factors, that is, processes in the muscle itself, come first;

in the second, central factors and inadequacy of autonomic support of movements (respiration, blood circulation) acquire leading importance. Exploring the mechanisms of fatigue great attention paid in the physiology of work and sports.

Ergography. To study muscle fatigue in humans in laboratory conditions, they use ergographs - devices for recording a mechanogram during movements rhythmically performed by a group of muscles. This record allows you to determine the amount of work performed.

An example of such a simple device is the Mosso ergograph, which records the movement of a loaded finger. Bending and unbending the finger with a fixed position of the hand, the subject raises and lowers the weight suspended from the finger in a certain, preset rhythm (for example, in the rhythm of the metronome beats).

There are ergographs that reproduce certain working movements of a person. So, bicycle ergographs (bicycle ergometers) are widely used. A person rotates the pedals of the device with his feet at a different, predetermined resistance to this movement. Special sensors allow registering movement parameters and the amount of work performed. At the same time, you can record the indicators of respiration, blood circulation, ECG. Bicycle ergographs are widely used in medicine to determine the functional capabilities of the human body.

The shape of the ergogram and the amount of work performed by a person before the onset of fatigue vary from person to person and even from one and the same person under different conditions. In this respect, the ergograms recorded by Mosso on himself before and after receiving the test from students are indicative. These ergograms indicate a sharp decrease in working capacity after intense mental work (Fig. 39).

Working muscle hypertrophy and atrophy from inactivity

Systematic intensive muscle work contributes to an increase in muscle mass. This phenomenon is called working muscle hypertrophy. At the heart of hypertrophy is an increase in the mass of the cytoplasm of muscle fibers and the number of myofibrils contained in them, which leads to an increase in the diameter of each fiber. At the same time, the synthesis of nucleic acids and proteins is activated in the muscle and the content of substances that deliver energy used in muscle contraction increases - adenosine triphosphate and creatine phosphate, as well as glycogen. As a result, the strength and speed of contraction of the hypertrophied muscle increases.

An increase in the number of myofibrils in hypertrophy is facilitated mainly by static work, which requires a lot of stress (power load). Even short-term exercises carried out daily under conditions of the isometric mode are sufficient to increase the number of myofibrils. Dynamic muscular work done with little effort does not cause muscle hypertrophy.

In trained people, in whom many muscles are hypertrophied, the musculature can be up to 50% of body weight (instead of 35-40% in the norm).

The opposite of working hypertrophy is muscle atrophy from inactivity. It develops in all cases when the muscle for some reason does not perform normal work for a long time. This is observed, for example, when a limb is immobilized in a plaster cast, a patient remains in bed for a long time, a tendon is cut, as a result of which the muscle stops performing work, etc.

With atrophy, the diameter of the muscle fibers and the content of contractile proteins, glycogen, ATP and other substances important for contractile activity in them decrease. After the resumption of normal muscle function, the atrophy gradually disappears.

A special type of muscle atrophy is observed with muscle denervation, that is, after the loss of its connection with the nervous system, for example, when its motor nerve is cut. This type of atrophy is discussed below.

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Work hypertrophy and atrophy from inactivity

Systematic intensive muscle work leads to an increase in muscle mass. This phenomenon is called working muscle hypertrophy. Working muscle hypertrophy occurs in part due to longitudinal splitting, but mainly due to thickening (increasing the diameter) of the muscle fibers.

There are two main types of working muscle fiber hypertrophy. The first type - sarcoplasmic - thickening of muscle fibers due to a predominant increase in the volume of sarcoplasm, that is, the non-contractile part of muscle fibers. This type of hypertrophy leads to an increase in the metabolic reserves of the muscle: glycogen, nitrogen-free substances, creatine phosphate, myoglobin, etc. A significant increase in the number of capillaries as a result of training can also cause muscle thickening to some extent. The first type of working hypertrophy has little effect on the growth of muscle strength, but it significantly increases their ability to work for a long time, that is, endurance.

The second type of working hypertrophy - myofibrillar - is associated with an increase in the volume of myofibrils, that is, the actual contractile apparatus of muscle fibers. In this case, the muscle diameter may not increase very significantly, since the density of the packing of myofibrils in the muscle fiber mainly increases. The second type of work hypertrophy leads to significant increases in maximum muscle strength. The absolute strength of the muscle also significantly increases, while in the first type of working hypertrophy, it either does not change at all, or even slightly decreases.

The predominant development of the first or second type of working hypertrophy is determined by the nature of muscle training. Probably, long-term dynamic exercises with a relatively low load cause working hypertrophy, mainly of the first type (a predominant increase in the volume of sarcoplasm, rather than myofibrils). Isometric exercises using large muscle tension(more than 2/3 of the maximum voluntary strength of the trainees muscle groups), on the contrary, contribute to the development of working hypertrophy of the second type (myofibrillar hypertrophy).

At the heart of working hypertrophy is the intensive synthesis of muscle proteins, DNA and RNA. Hormones - androgens - play a very important role in the regulation of muscle mass.

In trained people, in whom many muscles are hypertrophied, the musculature can be up to 50% of body weight (instead of 35-40% in the norm).

With atrophy, the diameter of muscle fibers and the content of contractile proteins, glycogen, ATP and other substances important for contractile activity in them decrease. After the resumption of normal work, muscle atrophy gradually disappears.

O One of the universal adaptive and compensatory processes in the body is hypertrophy. In its most general form, this term denotes an increase in the size of an organ associated with the growth of its specific tissue. At the same time, the functional capabilities of the organ are increased, due to which it is able to more efficiently perform its inherent work. For example, skeletal muscle hypertrophy, which develops during sports by increasing its physiological diameter, increases the force with which this muscle is able to contract. Such working (physiological) hypertrophy can be observed in almost all organs of the human body.

R Before hypertrophy, hyperplasia was opposed - an increase in an organ due to an increase in the number of its constituent cellular elements (without increasing their size). However, at present, it is generally accepted in general pathology that "the phenomenon of hypertrophy as an increase in something homogeneous, whole, in principle, cannot exist at all and that the increase in any structure of the body ultimately lies only in the hyperplasia of its smaller structures" (D . S. Sarkisov and others). This means that hypertrophy of the same skeletal muscle is the result of an increase in the number of sarcomeres, mitochondria, ribosomes, and other ultrastructural elements. Under these conditions, not only the number of active functioning units of an organ or tissue increases, but also an intensification of their work is possible, depending on the requirements presented.

V conditions of pathology, hypertrophy has the same purpose as in the norm. However, in pathology, the hypertrophic process most often develops more intensively, and at the same time, the energy demand of an enlarged organ cannot always be provided with a sufficient blood supply. As a result, areas with a relatively reduced oxygen supply can form in a hypertrophied organ and, as a consequence, necrosis of individual cells can develop with their subsequent replacement with connective tissue. Obviously, in these cases, the effectiveness of organ hypertrophy will begin to decline.

At diseases leading to a decrease in organ function (for example, with heart disease), hypertrophy develops, referred to as compensatory ( rice. 4). It usually maintains the impaired function for a long time at a normal or close to it level, helps to prolong the patient's life. At the same time, over time, the functional capabilities of the hypertrophied tissue of the organ are depleted, and its functional insufficiency develops with all the ensuing consequences. Modern surgery is already on early stages This process is making more and more successful attempts to replace the diseased organ with a healthy one. The problem of organ transplantation, as already mentioned (see Section 4.1), is complicated by the activity of the immune system, which contributes to the rejection of a foreign biological object. At surgical treatment of certain diseases develops the so-called substitutional, or vicarious, hypertrophy. It is observed when one of the paired organs is removed (for example, kidney, lung, etc.). In these cases, the surviving organ takes on the function of the remote; its size increases, its functional ability grows. Vicarious hypertrophy is also found in congenital underdevelopment of one of the paired organs ( rice. 5). Hypertrophy of some endocrine glands can be accompanied by such a pronounced hyperfunction that they begin to "work" in a pathological mode that is harmful to the body. This is the case, for example, in patients with Graves' disease.

A trophy is a process of changes in cells and tissues, the opposite of that which occurs during hypertrophy. A decrease in the functional activity of tissue (for example, the muscles of a limb, on which gypsum is applied in connection with a bone fracture) leads to a decrease in the number of structural elements of cells, their partial destruction. The size of the organ or tissue is reduced.

F physiological hypertrophy and atrophy are, as a rule, reversible processes. After eliminating the causes that caused them, the sizes of organs and tissues are normalized.

D Istrophy refers to structural changes in cells caused by metabolic disorders in the tissue or the cells themselves. Specific reasons for the development of dystrophic processes are disorders of trophism (nutrition) associated with the activity of both cellular and extracellular nutritional mechanisms. The well-known Soviet morphologist VV Serov identifies the following reasons: 1) energy deficiency and disorders of enzymatic processes in the cell; 2) hypoxia; 3) disorders of neuro-endocrine regulation of trophism. The first two of them can take place in case of irrationally structured training work with athletes. In particular, dystrophic processes in athletes are associated with overvoltage caused by excessive physical exertion (A.G. Dembo).

D Istrophies are an extremely broad class of cellular damage. They can be general and local. In connection with metabolic disorders, protein, fat, carbohydrate and mineral forms of dystrophies are isolated. Each of these forms is subdivided into particular forms. So, protein dystrophies include granular dystrophy, hyalinosis, amyloidosis, etc. Each of these forms is characterized by specific structural changes and dysfunctions of cells, tissues and organs.

The amplitude of the tetanic contraction of the muscle exceeds the height of its single contraction. G. Helmholtz (1847) called this process superposition, that is, overlapping contractions, assuming that the effect of two consecutive stimuli is equal to the algebraic sum of single contractions.

However, these data did not correspond to reality. NOT. Vvedensky (1886) conducted an experiment by irritating the muscle fiber with a threshold stimulus, contraction occurred, further irritation with subthreshold stimuli maintained the amplitude of contraction at the initial level. N.E. Vvedensky explained this by the fact that during contraction, the muscle is in a state of increased excitability. Therefore, the amplitude of the second rhythmic contraction becomes greater than that of a single contraction.

At present, the dependence of the amplitude of tetanic contractions on the phase of excitability in which the stimulus falls has been established. This is established by superimposing all three curves: the PD curve, the Verworn curve, and the single contraction curve. So, the shortening of the muscle fiber begins after reaching the peak of depolarization, the middle of the shortening phase coincides with increased excitability in the exaltation phase, and, therefore, the stimulus acting in this phase will lead to a stronger contraction.

It is believed that the increase in the force of contractions under the action of rhythmic stimuli is based on an increase in the concentration of calcium inside the cell, which allows the reaction of interaction between actin and myosin and the generation of muscle force by transverse bridges for a sufficiently long time.
Muscle fatigue. Causes of isolated muscle fatigue, neuromuscular drug, fatigue in vivo

Fatigue is called a temporary decrease in the performance of a cell, organ or the whole organism, which occurs as a result of work and disappears after rest.

If an isolated muscle, to which a load is suspended, is irritated for a long time with rhythmic electrical stimuli, then the amplitude of its contractions gradually decreases until it reaches zero. The curve obtained in this way is called the fatigue curve.

Along with a change in the amplitude of contraction during fatigue, the latent period of contraction increases and the thresholds of irritation and chronaxia increase, that is, excitability decreases. These changes do not occur immediately after work, but after some time, during which there is an increase in the amplitude of single muscle contractions. This period is called the activation period. With further prolonged irritation, muscle fiber fatigue develops.

A decrease in the performance of a muscle isolated from the body during prolonged irritation is due to two main reasons: the first of them is that during contractions, metabolic products (in particular, lactic, phosphoric acids, etc.) accumulate in the muscle, which have a depressing effect on muscle performance. Some of these products, as well as potassium ions, diffuse out of the fibers into the pericellular space and have a depressing effect on the ability of the excitable membrane to generate action potentials.

If an isolated muscle, placed in Ringer's solution, is brought to complete fatigue by prolonged irritation, then it is enough just to change the fluid that washes it in order to restore muscle contractions.

Another reason for the development of fatigue in an isolated muscle is the gradual depletion of energy reserves in it. With prolonged work of an isolated muscle, a sharp decrease in glycogen stores occurs, as a result of which the processes of resynthesis of ATP and creatine phosphate, which are necessary for contraction, are disrupted.

The fatigue of the neuromuscular drug is due to the following reasons. With prolonged irritation of the nerve, the violation of neuromuscular transmission develops long before the muscle, and even more so the nerve, due to fatigue, loses its ability to conduct excitation. This is explained by the fact that in the nerve endings with prolonged stimulation, the supply of the "harvested" mediator decreases. Therefore, the portions of acetylcholine released in synapses in response to each impulse decrease and postsynaptic potentials decrease to subthreshold values.

Along with this, with prolonged irritation of the nerve, there is a gradual decrease in the sensitivity of the postsynaptic membrane of the muscle fiber to acetylcholine. As a result, the potential value of the end plate decreases. When their amplitude falls below a certain critical level, the emergence of action potentials in the muscle fiber stops. For these reasons, synapses fatigue faster than nerve fibers and muscles.

It should be noted that nerve fibers are relatively fatigued. For the first time N.E. Vvedensky showed that a nerve in an air atmosphere retains the ability to conduct excitations even with many hours of continuous stimulation (about 8 hours).

Relative fatigue the nerve partly depends on the fact that the nerve spends relatively little energy when it is excited. Thanks to this, the processes of resynthesis in the nerve are able to cover its relatively low costs during excitation, even if this excitation lasts for many hours.

It should be noted that fatigue of an isolated skeletal muscle during direct stimulation is a laboratory phenomenon. Under natural conditions, fatigue of the motor apparatus during prolonged work develops more difficult and depends on a larger number of factors.

1. In the body, the muscle is continuously supplied with blood, and, therefore, receives with it a certain amount of nutrients (glucose, amino acids) and is released from metabolic products that disrupt the normal functioning of muscle fibers.

2. In the whole organism, fatigue depends not only on the processes in the muscle, but also on the processes developing in the nervous system, participating in the control of motor activity.

So, for example, fatigue is accompanied by discoordination of movements, excitation of many muscles that are not involved in the performance of work.
Active rest and its mechanism. (I.M.Sechenov,

Orbeli-Ginetsinsky phenomenon)

When identifying the causes of fatigue of the locomotor system as applied to the whole organism, at present, two types are often distinguished. motor activity: local, when a relatively small number of muscles are active, and general, when most of the muscles of the body are involved in the work. In the first case, among the causes of fatigue, peripheral factors, that is, processes in the muscle itself, come first; in the second, central factors (nervous system) and insufficiency of autonomic support of movements (respiration, blood circulation) acquire leading importance.

For the first time I.M. Sechenov (1903) showed that the restoration of the working capacity of the tired muscles of a person's hand after prolonged work on lifting a load is sharply accelerated if, during the rest period, work is done with the other hand. Temporary restoration of the working capacity of the muscles of the tired arm can be achieved with other types of physical activity, for example, during work different muscles lower limbs. In contrast to simple rest, such rest was named by I.M. Sechenov active... Sechenov viewed these facts as proof that fatigue primarily develops in the nerve centers.

Experiments with suggestion serve as convincing proof of the role of changes in the state of nerve centers in the development of fatigue in the whole organism. So, the subject can lift a heavy weight for a long time, if he is convinced that there is a light basket in his hand. On the contrary, if the subject, who is lifting a light basket, is convinced that he has been given a heavy weight, then fatigue develops quickly. At the same time, the change in pulse, respiration and gas exchange is not in accordance with the real work carried out by a person, but with the one that is suggested to him (V.M. Vasilevsky, D.I.Shatenstein).

The Orbeli-Ginetsinsky phenomenon was discovered in 1923. In experiments on a neuromuscular preparation, motor fibers were irritated by an electrostimulator. Isolated muscle responded by contraction to each of the rhythmically repetitive stimuli, and a typical curve was recorded on the kymograph tape muscle contraction... With fatigue, the amplitude of the curve decreased. After stimulation of the sympathetic nerves, an increase in the amplitude of muscle contractions occurred, and a new wave of increased activity was noted on the kymogram. Later, the phenomenon was confirmed in mammalian muscles under conditions of normal blood supply.

L.A. Orbeli put forward the idea of \ u200b \ u200bthe universal adaptive-trophic function of the sympathetic nervous system regulating the functional properties of all organs and tissues, setting them to the optimal level for the given conditions. This regulation is not limited to smooth muscles and glands, it covers all links of the reflex arc - receptors, the central nervous system, nerve conductors and skeletal muscles.

The Orbeli-Ginetsinsky phenomenon is based on the activation of the sympathetic nervous system. Further studies made it possible to reveal the generality of the influence of the sympathetic nervous system and the reticular formation of the brain on the restoration of muscle performance.
Work hypertrophy and atrophy from inactivity

Systematic intensive muscle work leads to an increase in muscle mass. This phenomenon is called working muscle hypertrophy. Working muscle hypertrophy occurs in part due to longitudinal splitting, but mainly due to thickening (increasing the diameter) of the muscle fibers.

There are two main types of working muscle fiber hypertrophy. The first type is sarcoplasmic- thickening of muscle fibers due to a predominant increase in the volume of sarcoplasm, that is, the non-contractile part of muscle fibers. This type of hypertrophy leads to an increase in the metabolic reserves of the muscle: glycogen, nitrogen-free substances, creatine phosphate, myoglobin, etc. A significant increase in the number of capillaries as a result of training can also cause muscle thickening to some extent. The first type of working hypertrophy has little effect on the growth of muscle strength, but it significantly increases their ability to work for a long time, that is, endurance.

The second type of working hypertrophy is myofibrillar- associated with an increase in the volume of myofibrils, that is, the actual contractile apparatus of muscle fibers. In this case, the muscle diameter may not increase very significantly, since the density of the packing of myofibrils in the muscle fiber mainly increases. The second type of work hypertrophy leads to significant increases in maximum muscle strength. The absolute strength of the muscle also significantly increases, while in the first type of working hypertrophy, it either does not change at all, or even slightly decreases.

The predominant development of the first or second type of working hypertrophy is determined by the nature of muscle training. Probably, long-term dynamic exercises with a relatively low load cause working hypertrophy, mainly of the first type (a predominant increase in the volume of sarcoplasm, rather than myofibrils). Isometric exercises with the use of large muscle tensions (more than 2/3 of the maximum voluntary strength of the trained muscle groups), on the contrary, contribute to the development of working hypertrophy of the second type (myofibrillar hypertrophy).

At the heart of working hypertrophy is the intensive synthesis of muscle proteins, DNA and RNA. Hormones play a very important role in the regulation of muscle mass - androgens.

In trained people, in whom many muscles are hypertrophied, the musculature can be up to 50% of body weight (instead of 35-40% in the norm).

The opposite of working hypertrophy is muscle atrophy from inactivity... It develops in all cases when the muscle for some reason does not perform normal work for a long time. This is observed, for example, when a limb is immobilized in a plaster cast, a patient remains in bed for a long time, a tendon is cut, as a result of which the muscle stops performing work.

Features of the physiology of excitable tissues in children
Features of the physiology of nerves

Conductivity a newborn child is two times lower than that of an adult, and the rate of excitation conduction is about 50% of that in adults. Conducting excitation along nerve fibers is poorly isolated.

In the process of growing up, nerve fibers are myelinated, the diameter of the axial cylinder and the fiber as a whole increases, and the thicker the fiber becomes, the lower the longitudinal resistance to ion current. This leads to the fact that the speed of AP propagation increases. In children, it reaches the parameters of an adult by the age of 5-9 years for various nerve fibers. So, the anterior spinal roots mature by 2-5 years of age, and the posterior spinal roots by 5-9 years.

Excitability the nerve fibers of a newborn are significantly lower than that of an adult. A characteristic of this is chronaxia, the magnitude of which is several times higher; resting potential, which is significantly lower in children. The low resting potential is due to the fact that the cell membrane has a high ionic permeability and ionic currents are constantly leaking. This leads to a decrease in the transmembrane ion difference (concentration gradient) and leads to the formation of a low amplitude of the action potential in combination with its longer duration and the absence of reversion.

In the process of growth, the membrane permeability decreases and the membrane potential reaches that of an adult. Accordingly, the amplitude of the action potential also increases, the speed of the AP conduction increases, since at a high amplitude it is easier to excite the adjacent section of the fiber.

In a fetus and a child in the first years of life, the pulp fibers are poorly myelinated and the channels for sodium and potassium are evenly spaced. In ontogenesis, the fiber is myelinated, ion channels are concentrated in the interceptions of Ranvier, the distance between the interceptions increases. This characterizes the structural maturity of the pulp fibers. In fleshy fibers, the distribution of ion channels remains uniform.

Lability neonatal nerve fibers are also low. In older children, it increases due to a decrease in the duration of the refractory period and an increase in the speed of arousal.

Features of muscle physiology

In humans, the number of fibers in a muscle is established 4-5 months after birth and then practically does not change throughout life. At birth, their thickness is about 1/5 of the thickness of fibers in adults. The diameter of muscle fibers can vary significantly with exercise.
Excitability the muscles of the newborn are very low. This is indicated by high chronaxia and a large depolarization threshold.

In a newborn, the MP of myocytes is -20-40 mV. The transmembrane difference between K + and Na + ions is not high. Therefore, the value of AP is also small. In addition, the duration of the phases of absolute and relative refractoriness is noted.

In the process of growth, the membrane permeability decreases, the operation of ion pumps improves, and the MP and DP increase.

Lability children are lower than in adults due to the long duration of refractory phases. with age, there is a shortening of the phases of absolute and relative refractoriness and, as a consequence, an increase in the speed of arousal and an increase in the speed of movements.

Conductivity. The rate of PD conduction is low in newborns and increases with age. This is caused by an increase in the thickness of the muscle fiber and an increase in the amplitude of the action potential, since the resistance to ion current decreases and excitation develops faster in the adjacent section of the membrane.

Contractility. Single contractions of the muscles of the newborn are slowed down - both the shortening phase and the relaxation phase - and are characterized by a long contraction time. In the muscles of the child, metabolic products accumulate faster and, therefore, tetanus has a gentle beginning and gradual relaxation, like the tetanus of a tired muscle. Muscles respond with tonic contraction to stimuli of any frequency and contract without pessimal inhibition as much as the stimulus acts. This is due to insufficient maturity of myoneural synapses.

In newborns, there is no division of muscles into fast and slow, but from the first days of life, a child begins to gradually differentiate, which is characteristic of adults.

Elasticity the muscles of a newborn are higher than that of an adult and decreases with age. And the elasticity and strength, on the contrary, increase.

Throughout his life, a person experiences various physical exercise... It can be both professional strength exercises, and simply accompanying loads that are found in various life situations.

With physical exertion, the muscles that are involved in the work process increase. This happens due to an increase in the fibers that make up the muscle. may be the entire length of the muscle, or may be shorter. Muscle fiber consists of a large number of contractile elements - myofibrils. Inside each element are even smaller elements - actin and myosin myofiaments. And due to these elements, muscle contraction occurs.

With regular weight lifting, muscle fibers increase, and this will be muscle hypertrophy.

Muscle hypertrophy - an increase due to the "growth" of muscle fibers.

Most often, muscle hypertrophy is present in athletes involved in bodybuilding. As this sport aims to improve your body with the help of power loads, high-calorie nutrition and the use of various anabolic drugs. As a result, a pronounced muscle relief is formed on the body, that is, muscle hypertrophy occurs.

Processes in muscles during exercise

The basis of the structure of the human body is protein, it is present in all its tissues. Therefore, changes in muscle tissue depend on the synthesis and catabolism of protein in the tissue.

With constant physical exertion, skeletal muscle hypertrophy occurs. When the body experiences stress, the content of the corresponding muscles increases.However, as scientifically established, during physical influences on the body, protein synthesis is suspended, and catabolism is activated in the first minutes of the recovery process. Thus, muscle hypertrophy occurs due to the activation of protein synthesis, and not due to a decrease in the intensity of protein breakdown at a constant level of protein synthesis intensity.

Skeletal muscle hypertrophy

Human muscle tissue performs motor functions, and it forms skeletal muscles. The main task performed by skeletal muscles is contractility, which occurs due to a change in the length of the muscle when it is exposed to nerve impulses. Using their muscles, a person can "wiggle". Each muscle performs "its" specific action, it can only work in one specific direction when acting on the joint. To ensure movement of the joint around its axis, a pair of muscles are involved, present on both sides of the joint.

Determines the number and thickness of fibers that are present in a given muscle. They constitute the anatomical diameter of the muscle (the cross-sectional area of the muscle, made perpendicular to its length).

There is also such an indicator as the physiological diameter (cross section of the muscle, perpendicular to its fibers).

The size of the physiological diameter affects the strength of the muscle. The larger the physiological diameter, the great strength will be inherent in the muscle.

During physical exertion, the diameter of the muscle increases, this is called working muscle hypertrophy.

Working muscle hypertrophy is present when there is an increase in muscle fiber volume. With a strong thickening of the fibers, splitting into several new fibers with a common tendon can occur. Work hypertrophy occurs in healthy people with enhanced function of a tissue or organ of a person. For example, this is hypertrophy of human skeletal muscles.

Causes of muscle hypertrophy

Muscle hypertrophy, in most cases, is caused by regular exercise. However, the amount of calories consumed also affects the increase in muscle mass. If you don't have enough calories, you won't be able to achieve a lot of muscle volume.

Accompanying the achievement of the required muscle volume, that is, there is muscle hypertrophy, reasons based on the following principles:

A constant load is required on all types of muscles, the volume of which needs to be increased.
The load time is selected individually. Don't stick to standards. It is necessary to practice as much as the body allows, but not to complete exhaustion.
Do not cause exhaustion of the nervous system, work with concentration, calmly and judiciously.
On initial stages muscle pain may appear, but this should not be a pretext for stopping the exercise.

There should also be a complete and balanced diet, plenty of drink to maintain water balance organism.

Increased chewing muscles

Due to the "extra" movements of the jaw, hypertrophy may appear chewing muscles... the person is pressed to the top by the chewing muscles. They are in two parts and are located on either side of the jaw. The muscle begins at the lower edge of the zygomatic arch and ends at the outer surface of the lower branch.

Hypertrophy of the masticatory muscles causes a disturbance in the visual harmonious combination of the upper and lower parts of the face, and also causes pain in the masticatory muscles. The face becomes "square" or widened towards the bottom. Muscle hypertrophy occurs due to an increase in the load on them.

Hypertrophy of the masticatory muscles can be provoked by:

bruxism - teeth grinding;
constantly clenched jaws, up to the erasure of teeth;
pain in the chewing muscles.

Correction of the chewing muscles

With hypertrophy of the masticatory muscles in a person, a disproportion of facial features appears. In this case, constant pain in the jaw region may also be present. To correct this imbalance, a person needs to see a specialist for medical treatment. In order for muscle hypertrophy to pass, treatment must be started on time.

During treatment, a special drug is injected into the chewing muscle, in three to four places, which relaxes the muscle and causes local muscle relaxation. After a few days, the effect is visible, which will last for about six months.

Hypertrophy of the heart muscle

There are cases when there is a pathological enlargement of the heart, this is mainly due to an increase in the thickness of the heart muscle - the myocardium.

Hypertrophy of the left heart is more common than the right.

Hypertrophy of the heart can appear when:

congenital or acquired heart defects;
hypertension;
metabolic disorders, including obesity;
sharp loads when there is a sedentary lifestyle.

Symptoms of cardiac muscle hypertrophy

Slight hypertrophy of the heart muscle does not cause any changes in a person's well-being and may go unnoticed. The more the stage of the disease, the more pronounced the symptoms of the disease. One of the best options for diagnosing a disease is an ultrasound examination of the heart.

The presence of this disease can be assumed by the presence of the following symptoms:

breathing hard, breathing is difficult;
chest pain;
fast fatiguability;
unstable heart rate.

Increased pressure can provoke ventricular hypertrophy. The heart starts to work faster, the blood in the heart begins to press harder on the walls, thereby expanding and reducing the elasticity of the walls. This leads to the inability of the heart to work in the same mode.

Treatment of cardiac hypertrophy

At the initial stage, cardiac hypertrophy is amenable to drug treatment. Diagnostics is carried out in order to identify the cause that provoked the development of hypertrophy, and its elimination begins. If, for example, the disease has developed due to a sedentary lifestyle and excess weight, then the person is assigned small physical activity and his diet is adjusted. The products are introduced in accordance with the principles of a healthy diet.

If ventricular hypertrophy has reached large sizes, surgical intervention is performed and the hypertrophied site is removed.

Amyotrophy

Hypertrophy and muscle atrophy are the opposite concepts. If hypertrophy means an increase in muscle mass, then atrophy means a decrease in it. The fibers that make up the muscle, which do not receive a load for a long time, become thinner, their number decreases and in severe cases can disappear altogether.

Muscle atrophy can be caused by various negative processes in the human body, both hereditary and acquired. This could be, for example:

metabolic disease;
the consequence of endocrine diseases;
complication after an infectious disease;
intoxication of the body;
enzyme deficiency;
prolonged postoperative muscle rest.

Muscle Atrophy Treatment

The effectiveness of treatment depends on the stage at which the disease is. If the changes in the muscles are significant, they cannot be completely restored. The cause of the muscle atrophy is diagnosed and appropriate medication is prescribed. In addition to drug treatment, it is definitely recommended:

physiotherapy;
physiotherapy;
electrotherapy.

To keep the muscles in good shape, massage is prescribed, which should be done regularly.

Treatment is aimed at stopping destructive actions in the muscles, relieving symptoms and improving metabolic processes in the body.

The presence of a nutritious diet containing all the necessary vitamin elements is imperative.

Conclusion

Thus, we can conclude that significant physical effort is required to obtain skeletal muscle hypertrophy. If this is done to achieve beautiful body with a pronounced muscle mass, then the person will be required to perform regular strength exercises... Moreover, his diet should be based on the principles of proper nutrition.

However, there is a possibility of getting unwanted muscle hypertrophy, which poses a threat to human health, this: hypertrophy of the heart muscle and masticatory muscles. In most cases, the appearance of these diseases is associated with deviations and disturbances in the functioning of the human body. Therefore, timely diagnosis and control over your health is necessary to prevent the onset and development of the disease.

Healthy lifestyle and proper nutrition help a person stay in good sports uniform and avoid possible problems with health.