Muscle work fatigue. Muscle fatigue, the theory of fatigue of an isolated muscle and the whole organism

Physical fatigue is a temporary decrease or cessation of muscle performance caused by their work. Fatigue is recorded on the ergogram; it manifests itself in the fact that the height of muscle contraction decreases or there is a complete cessation of its contractions. When tired, the muscle often cannot fully relax and remains in a state of prolonged shortening (contracture). Fatigue is first the result of changes in function nervous system, and above all the brain, impaired transmission of nerve impulses between neurons and between the motor nerve and muscle, and then as a result of changes in the functions of the muscle itself.

Since the functions of the nervous system and receptors of muscles, joints and tendons decrease with fatigue, there are violations of coordination of movements.

muscle fatigue is the result of not only changes in the functions of the nervous and muscular systems, but also changes in the regulation of the nervous system of all autonomic functions.

Fatigue during dynamic work occurs as a result of changes in metabolism, the activity of the endocrine glands and other organs, and especially the cardiovascular and respiratory systems. A decrease in the efficiency of the cardiovascular and respiratory systems disrupts the blood supply to working muscles, and, consequently, the delivery of oxygen and nutrients and the removal of residual metabolic products.

The rate of onset of fatigue depends on the state of the nervous system, the frequency of the rhythm in which the work is performed, and on the magnitude of the load (load). Increasing the load and increasing the rhythm accelerates the onset of fatigue.

With fatigue, fatigue often appears - a feeling of fatigue that is absent if the work is interesting. Conversely, when work is done without interest, fatigue sets in earlier and is greater, although there are no signs of fatigue. The ability to come into a state of fatigue is called fatigue. Fatigue is also caused by the environment in which it previously occurred. If the work was interesting and did not cause fatigue and exhaustion, then the environment in which it was carried out does not cause fatigue and exhaustion. A change in the environment in which fatigue occurred repeatedly, or a long, many-day rest, leads to the disappearance of the conditioned reflex to fatigue.

Muscle fatigue is a normal physiological process. Recovery of muscle performance occurs already during the performance of work. After the end of work, the working capacity is not only restored, but also exceeds its initial level before work.

Rice. 32. Change in working capacity on days of rest after limiting work

Fatigue must be distinguished from overwork.

Overfatigue is a violation of the functions of the body, a pathological process caused by chronic fatigue, the summation of fatigue, since there are no conditions for restoring the body's working capacity.

It is important to prevent the occurrence of overwork. The onset of overwork is facilitated by unhygienic working conditions, exercise, environment, malnutrition.

With overwork, chronic headaches, great irritability, apathy, lethargy, daytime drowsiness, sleep disturbance at night and insomnia, loss of appetite, muscle weakness appear. The coordination of muscular work and vegetative functions is disturbed, there is a decrease in metabolism and a drop in body weight, an increase, and sometimes a significant slowdown in heart rate, a decrease in blood pressure, a decrease in respiratory volume, etc. There is no desire to work, physical education and sports, especially the kind that caused overwork.

Creation of normal hygienic conditions for physical labor and exercise, switching to a new interesting view physical labor and sports, transfer to another environment, long rest, increased time spent in the fresh air and sleep, improved nutrition, intake of carbohydrates and vitamins eliminate overwork.

How does the load affect the development of muscle fatigue and how to quickly restore strength?

After exercise, in principle, muscle pain is a completely normal state of the body that does not require special treatment and does not cause anxiety.

If pain occurs, without a specific clear cause, then you should consult a specialist to determine the exact diagnosis. Muscle weakness can be caused by a number of different circumstances, described below.

Injuries and fractures- the main factors of muscle pain.
With injuries of soft or bone-cartilaginous tissues, pain is a response. As a rule, with such factors, the doctor prescribes a remedy that will relieve muscle tension and soothe pain.

After the muscle structures begin to relax, the acid irritates the nerve endings and an uncomfortable sensation occurs. In this case, a glass of water with a pinch of baking soda will help reduce the pain that comes from tension.

Stress. With a moral disorder and stress loads, a feeling of discomfort in the muscles appears.
Most often, pain in the ligaments occurs at night and in the morning. In science, this phenomenon is called fibromyalgia - a form of myalgia. Most often binds cervical region spine, knees and lower back.
Bad posture.
As a result bad posture there is a deformation of the bone and cartilage tissues, which automatically “pull” the muscles behind them. As a result, there is a burning sensation along the muscle fibers.
Chronic diseases of bone and cartilage tissues and blood vessels:

arthritis, arthrosis, osteochondrosis are the first causes of muscle pain and a constant feeling of fatigue. The destruction of bone tissue entails deformation in muscle and soft tissues;
flat feet is a problem in which the feet become flat and this makes walking much more difficult.
This may cause muscle pain in the legs from the foot to the knee;
thrombophlebitis and varicose veins veins - vascular diseases, in which venous elasticity is disturbed and blood blockages occur. Inflamed veins tend to bulge out and cause severe pain. There may be a burning sensation and severe muscle discomfort along the entire length of the affected vein;
neuralgia also often causes muscle fatigue.
Seizures resulting from disruption of the peripheral nervous system cause severe weakness. At rest, the muscles do not hurt. In this case, you should not take painkillers, as you need to overcome neuralgic symptoms and muscle fatigue will go away on its own;
obesity is a common cause of muscle fatigue.
The fact is that a fat figure and big mass body, is a constant load on physical state organism. When walking, legs, back, neck often hurt, aching pains in the muscles in these areas occur. With such a disease, myalgia does not go away on its own, since the muscles have a constant load.

There are two ways out here - either lose weight or take pharmaceutical drugs that can relieve pain in the muscles.

Pain during pregnancy. Pregnancy is a strong physical and moral stress on the body, and the occurrence of muscle discomfort in this position is normal for all women who are expecting a baby.

The feeling of muscle fatigue can be an independent phenomenon or a symptom of a serious illness.

After exertion and excessive stress, the so-called “strength” or muscle pain syndrome occurs. Under normal conditions, it passes in a few days without outside intervention. If a person feels muscle pain and weakness for no particular reason, this is a cause for concern and contact a specialist.

Important! Muscle fatigue cannot be ignored, as it can be a signal of a serious illness.

Medicines for muscle pain

Medicines for muscle fatigue (www.ustalosty.net)

Before you begin to deal with muscle pain, it is important to understand the cause of its occurrence.

If the feeling of muscle fatigue has arisen as a result of muscle strain due to physical activity, external pharmaceutical preparations can be used:

anesthetics such as Menovazin or Novocain;
warming or cooling ointments based on medicinal plants and products of animal origin - bee venom, snake venom, chondroitin, mink fat;
cooling medicines based on mint, camphor or lemon balm.

If muscle fatigue is the result of an injury or fracture, then it is better to use oral pain relievers.

Before taking such funds, it is better to consult a doctor.

Traditional medicine against myalgia

Folk recipes against muscle fatigue (okeydoc.ru)

In addition to medicines, there are a number of folk recipes that can relax muscles, eliminate heaviness in various parts of the body and tone muscle mass.

Examples of the most effective recipes that help with pain in different parts of the body, even in the heart muscle, are described below.

With frequent muscle fatigue associated with overweight or constant physical exertion, you can use this home remedy: for 3 teaspoons of dry chopped bay leaves, you need 1 tablespoon of dried juniper. 6 teaspoons of vegetable or animal fat are added to the resulting herbal mixture. The slurry must be stirred until a homogeneous mass is obtained and the affected areas are treated overnight.
Plants have a relaxing and soothing property that will relieve pain and fatigue in the muscles for several hours.
Natural honey, mixed in equal proportions with chopped black radish, will perfectly relieve muscle fatigue if a compress is applied to a sore limb, neck or lower back.
Perfectly helps with fatigue during pregnancy, after training or hard physical labor.
With chronic muscle weakness, the following remedy will perfectly help: 25 grams of dried barberry bark must be poured with a glass of alcohol and insisted for a week in a dark, cool place.
Use ready-made infusion inside before meals 3 times a day, 30 drops of the product.

Important! Before using any traditional medicine, it is important to make sure that there are no contraindications and an allergic reaction.

Prevention of muscle fatigue

Prevention of muscle fatigue (klinikanikonova.ru)

In order not to feel fatigue and weakness in the muscles after small physical exertion, it is necessary to gradually strengthen them.

To do this, you need to perform a small set of exercises daily. Also, do not forget about healthy eating. In order for the muscles to be strong and healthy, it is necessary to include vitamins, minerals, protein, and iron in the diet. Be sure to include dairy products rich in calcium, meat and fish containing phosphorus and protein in the daily menu. Fresh vegetables, berries and fruits are a 100% source of nutrients not only for muscle mass but for the whole organism as a whole.

Chronic diseases of the heart and blood vessels are one of the most popular causes of fatigue.

In conclusion, I would like to note that there are many reasons for muscle fatigue.

Fatigue and weakness can appear after physical exertion, as a result of illness or stress. With chronic muscle weakness, it is necessary to visit a doctor to identify the true cause of muscle pain.

It is worth noting separately bad habits and their effect on the muscles of the body. Drinking alcohol or smoking constricts blood vessels, which significantly weakens the muscles.

When using tranquilizers or narcotic substances, a person may feel tired all the time.

Causes of muscle fatigue

Fatigue is a temporary decrease or loss of efficiency of the body, organ or tissue that occurs after exercise. Fatigue is a normal physiological process that causes the muscle to stop working.
With prolonged rhythmic stimulation, fatigue develops in the muscle, manifested by a gradual decrease in the amplitude of contractions of this muscle, up to the complete cessation of its contraction, despite continued irritation.

With fatigue, the latent period of contractions increases, the phase of muscle relaxation lengthens, and excitability decreases. The greater the frequency of stimulation, the faster fatigue sets in. The cause of fatigue is the accumulation of metabolic products in the muscle.

In an isolated muscle, a decrease in efficiency during prolonged irritation is really due to the fact that during its contraction metabolic products accumulate - phosphoric acid, which binds Ca2 + ions, lactic acid, etc. They greatly contribute to muscle fatigue.

The main causes of fatigue during long-term exercises of high and moderate power are factors associated with a decrease in the level of energy supply to working muscles (depletion of intramuscular glycogen reserves, accumulation of products of incomplete oxidation of fats, excessive accumulation of NH3 and IMF, development of a hypoglycemic state), as well as a violation of electrochemical conjugation in working muscles and deterioration of the central nervous system in conditions of severe hyperthermia, dehydration and a shift in the electrolyte balance of the body.

Thus, when performing long-term exercises of high and moderate power, the causes leading to fatigue are complex. In the body, the muscle is constantly supplied with blood, and therefore it constantly receives a certain amount of nutrients, and is also freed from decay products that could disrupt its function.

In most cases, the primary link in the development of fatigue during long-term exercises of high and moderate power is changes in the volume and nature of intramuscular energy substrates.

In a wide range of efforts during long-term work (starting from 25% VO2 max and above), a significant proportion of ATP resynthesis falls on the oxidation of carbohydrates. Fat oxidation is only characteristic of exercise, the relative power of which does not exceed 50% of the VO2 max level.

Causes of muscle fatigue

Changes in the concentration of glucose, fatty acids and lactate in the blood during prolonged exercise

Anaerobic energy sources (CrF and glycogen) have a noticeable effect on the energy of work only in those types of long-term exercises, the relative power of which exceeds the values of lactate and creatine phosphate thresholds, localized at the level of 60-75% VO2 max.

Due to the changing nature of the energy supply during long-term work, the dynamics of the main biochemical parameters of the blood also changes (Fig. 1). The content of glucose in the blood during the execution long work decreases markedly when the duration of the exercise exceeds 90 minutes.

Specific causes of fatigue during prolonged work may be due to the inability of the working muscles to maintain set speed resynthesis of ATP due to a decrease in carbohydrate reserves, as well as disturbances in the activity of the central nervous system due to the accumulation of ammonia and ketone bodies in the body.

Thus, when performing any exercise, it is possible to single out the leading, most loaded links of metabolism and the functions of body systems, the capabilities of which determine the ability of an athlete to perform exercises at the required level of intensity and duration.

These can be regulatory systems (CNS, autonomic nervous, neurohumoral), autonomic support systems (respiration, blood circulation, blood) and executive (motor) system.

Comprehensive analysis of the problem of fatigue in sports, carried out by physiologists, biochemists, as well as specialists in the field of theory and methodology sports training(Y.M.

Kots, N.N. Yakovlev, V.N. Volkov, N.I. Volkov, V.D. Monogarov, V.N. Platonov and others), convincingly showed that fatigue should be considered as a consequence of the failure of any component in a complex system of organs and functions, or as a violation of the relationship between them. Any organ and its function can become the leading link in the development of fatigue if there is a discrepancy between the level of physical activity and the available functional reserves.

Therefore, the root cause of a decrease in efficiency can be the depletion of energy reserves, tissue hypoxia, a decrease in enzymatic activity under the influence of the "working" metabolism of tissues, a violation of the integrity of functional structures due to the insufficiency of their plastic support, a change in homeostasis, a violation of nervous and hormonal regulation, etc.

Elucidation of the mechanisms of fatigue plays an important role in the practice of sports to substantiate the key provisions of sports training.

In particular, fatigue is regarded as a factor that stimulates the mobilization of functional resources, determines the boundaries of the optimal volume of training effects and ensures the effectiveness of adaptation, the success competitive activity and prevention of readjustment.

Scientific advances in the fight against muscle fatigue

Researchers from Columbia University (New York) found that muscle fatigue after prolonged exercise is caused by excess calcium penetration into muscle cells.

What's more, they've found a leak-resolving agent that markedly increased endurance in lab mice, according to the journal Proceedings of the National Academy of Sciences.

For a long time, muscle fatigue and soreness after exercise was thought to be caused by the accumulation of lactic acid. However, in last years physiologists questioned this theory. To shed light on this issue, scientists led by Andrew Marks (Andrew Marks) studied the condition of the muscles in mice after three weeks of physical activity (swimming for several hours daily) and in athletes after three days of intense cycling.

It turned out that muscle fatigue after exercise was accompanied by a change in the chemical structure of the so-called ryanodine receptor, which plays an important role in muscle contraction. This process caused the appearance of a small "leak" in the cell membrane (membrane), due to which calcium began to continuously flow into the muscle cell. As a result, there was a noticeable decrease in muscle strength and, at the same time, an enzyme that damaged muscle fibers was activated.

Marx and his colleagues also managed to find a remedy that could eliminate the "leak" by stopping the flow of calcium - a drug called S107.

Mice treated with this drug remained energetic for longer and were able to withstand physical exercise, the researchers said. It is assumed that S107 will be able to block the feeling of muscle fatigue in humans.

According to scientists, this drug may be especially relevant for combating chronic fatigue in heart failure.

Earlier studies have shown that severe weakness in patients with this disease - sometimes they are unable to get out of bed or brush their teeth - is also accompanied by a "leak" of calcium. However, unlike athletes, in people with heart failure, this process is irreversible.

In the near future, scientists plan to test the drug S107 in patients with heart failure. If the experiments are successful, the drug may go on sale in a few years, experts say.

Muscle fatigue is manifested in the fact that it stops contracting despite stimulation.

As a result, there is a feeling of muscle fatigue

There are two mechanisms for fatigue:

1) Peripheral- inside the muscles:

lactic acid accumulates, the medium becomes acidic, protein denaturation occurs;
glycogen stores are running out, and the supply of glucose with the blood is limited.

2) Central fatigue (nervous-psychic, plays a leading role in muscle fatigue) develops in the cerebral cortex, while the flow of impulses to the motor neurons of the spinal cord stops.

To restore the working capacity of any muscle group after central fatigue, not complete rest is more favorable, but intensive work of another muscle group - “active rest”.

Physiologist Ivan Mikhailovich Sechenov proved that the right hand rests faster if the left hand works during its rest.

During dynamic work (when movements occur), fatigue occurs more slowly than during static work (when the muscle is constantly contracted and does not move), due to better blood flow and active rest.

Biology and medicine

FATIGUE FEATURES DURING VARIOUS TYPES OF PHYSICAL LOADS

One of the main signs of fatigue is a decrease in performance, which in the process of performing various physical exercises changes according to different reasons; therefore, the physiological mechanisms of the development of fatigue are not the same.

They are determined by the power of the work, its duration, the nature of the exercises, the complexity of their implementation, etc.

By doing cyclic work maximum power, the main reason for the decrease in working capacity and the development of fatigue is a decrease in the mobility of the main nervous processes in the central nervous system with a predominance of inhibition due to a large flow of efferent impulses from the nerve centers to the muscles and afferent impulses from the working muscles to the centers.

It destroys the working system of interconnected activity of cortical neurons. In addition, the level of ATP and creatine phosphate in neurons decreases, and the content of the inhibitory mediator, gamma-aminobutyric acid, increases in brain structures. In this case, a change in the functional state of the muscles themselves, a decrease in their excitability, lability and relaxation rate, is of essential importance in the development of fatigue.

With cyclic />a#0/rae submaximal power, the leading causes of fatigue are the inhibition of the activity of the nerve centers and changes in the internal environment of the body.

The reason for this is a large lack of oxygen, due to which hypoxemia develops, the pH of the blood decreases, and the content of lactic acid in the blood increases by 20-25 times.

Oxygen debt reaches maximum values - 20-22 liters. Under-oxidized metabolic products, being absorbed into the blood, impair the activity of nerve cells. The intense activity of the nerve centers is carried out against the background of oxygen deficiency, which leads to the rapid development of fatigue.

Cyclic work of high power leads to the development of fatigue due to discoordination of motor and vegetative functions. For several tens of minutes, a very intense work of the cardiovascular and respiratory systems must be maintained to provide the intensively working organism with the necessary amount of oxygen.

During this work, the oxygen demand slightly exceeds the oxygen consumption and the oxygen debt reaches 12-15 liters. The total energy consumption during such work is very high, while up to 200 g of glucose is consumed, which leads to some decrease in it in the blood. There is also a decrease in the blood hormones of some endocrine glands (pituitary gland, adrenal glands).

The duration of performing cyclic work of moderate power leads to the development of protective inhibition in the central nervous system, depletion of energy resources, stress on the functions of the oxygen transport system, glands of the internal system, and changes in metabolism.

Glycogen stores in the body decrease, which leads to a decrease in blood glucose. A significant loss of water and salts by the body, a change in their quantitative ratio, a violation of thermoregulation also lead to a decrease in performance and fatigue in athletes. In the mechanism of the development of fatigue during prolonged physical work, changes in protein metabolism and a decrease in the functions of the endocrine glands can play a certain role.

At the same time, the concentration of gluco- and mineralcorticoids, catecholamines and thyroid hormones decreases in the blood. As a result of these changes, as well as as a result of the long-term influence of monotonous afferent stimuli, inhibition occurs in the nerve centers.

The inhibition of the activity of these centers leads to a decrease in the efficiency of the regulation of movements and a violation of their coordination. With prolonged performance of work in different climatic conditions, the development of fatigue, in addition, can be accelerated by a violation of thermoregulation.

At various types acyclic movements, the mechanisms for the development of fatigue are also not the same. In particular, when performing situational exercises, with various forms of variable power work, higher parts of the brain and sensory systems experience greater loads, since athletes need to constantly analyze the changing situation, program their actions and switch the pace and structure movement, leading to fatigue.

In some sports (for example, football), an essential role belongs to the lack of oxygen supply and the development of oxygen debt.

When performing gymnastic exercises and in martial arts, fatigue develops due to a deterioration in brain throughput and a decrease in the functional state of the muscles (their strength and excitability decrease, the speed of contraction and relaxation decreases). In static / w&mie, the main causes of fatigue are the continuous tension of the nerve centers and muscles, the shutdown of the activity of less stable muscle fibers and the large flow of afferent and efferent impulses between the muscles and motor centers.

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Fatigue is a temporary decrease or loss of efficiency, i.e. the result of previous work. Muscle fatigue in the body under conditions of blood circulation depends not only on the amount of long-term work done by it, but on the number of excitation waves that come to it, causing its contraction.

With the same frequency of stimulation and other equal conditions, fatigue appears earlier with a greater load on the muscle. With the same load and other conditions being equal, fatigue sets in earlier with more frequent stimuli. At the beginning of work, the height of contractions increases, and then the signs of developing fatigue are a gradual decrease in the height of contractions, an increase in their duration, and an increase in contracture.

The development of fatigue depends on changes in metabolism, blood circulation, temperature and other conditions. The higher the metabolism and better blood circulation, the later fatigue occurs. It occurs much earlier when the muscle is contracting, being stretched by a load during isometric contraction, and later when it is contracting without a load, and therefore without tension.

If the muscle is brought to complete fatigue by irritation with an electric current, then after a change in the direction of the current, its performance is immediately restored.

This recovery is explained by a change in the state of muscle proteins and shifts of ions at the current poles. An isolated muscle reduces its work or even stops contracting when the glycogen store is half the original amount. These facts do not support the exhaustion theory (Schiff, 1868), which explains muscle fatigue by the use of substances that release energy for its work. However, glycogen reserves in the human body are limited and amount to 300-400 g. With very intensive work, they are consumed in 1.5-2 hours, which leads to such a decrease in blood sugar, in which work becomes impossible.

The introduction of sugar into the body restores its performance.

The theory of muscle poisoning during fatigue with a special poison accumulating in it - kenotoxin (Weihardt, 1904) turned out to be unfounded. But there is evidence that fatigue is sometimes associated with poisoning of excitatory structures by metabolic products, mainly phosphoric and lactic acids at the time of their formation.

Residual products of metabolism, as it were, clog the body and cause fatigue - the theory of clogging (Pfluger, 1872).

The accumulation of phosphoric and lactic acids reduces muscle performance.

An isolated muscle fiber, unlike a whole muscle, gets tired much later with the same number of irritating impulses. This is due to the fact that the end products of metabolism are removed from it faster. In a trained muscle, due to the large acceleration of the analysis and synthesis of substances that ensure its work, fatigue occurs later. After flushing blood vessels isolated muscle, brought to complete fatigue, therefore, after the removal of part of the residual metabolic products from it, it again begins to decline despite the fact that the supply of carbohydrates and oxygen has not been restored.

These facts prove that the residual decay products of substances formed in the working muscle are one of the causes of its fatigue.

There is also a theory of strangulation (M. Verworn, 1903), attributing leading role exhausted by lack of oxygen.

It is known that work can continue for tens of minutes and even hours without fatigue, when the level of oxygen consumption is below the limit of its intake, possible for the worker (true steady state). When oxygen consumption reaches a maximum, it can be at a constant level, but does not provide the body's need for oxygen (apparent, or southern, stable state) and work in this case can last no more than 10-40 minutes.

Fatigue is a normal physiological process that leads to the cessation of work.

During breaks in work, the working capacity of the muscles is restored. Therefore, the validity of the participation of petty and phosphoric acids in the onset of fatigue does not allow us to draw an absurd conclusion that labor is harmful, since it allegedly leads to poisoning.

It is impossible to put an equal sign between the fatigue of an isolated muscle and the fatigue of the whole organism, in which the onset of fatigue depends on a change in the functions of the nervous system and endocrine glands and on a change in the regulation of the central nervous system of metabolism, blood circulation and respiration.

The development of fatigue depends on a decrease in the efficiency of the circulatory system, especially the heart, and the respiratory system.

Muscle performance after fatigue is restored as a result of the oxidation of these products. Therefore, oxygen consumption during muscular work increases significantly. If there is not enough oxygen, then with intensive muscular work there is a lack of oxygen - oxygen debt.

In conditions of oxygen deficiency during work, the functions of the nervous system decrease, which is the main cause of fatigue. Oxygen debt is repaid due to increased blood circulation and breathing, not only during work, but also after its completion.

MUSCLE FATIGUE

This repayment of the oxygen debt ends only after the complete oxidation of the residual metabolic products formed during work, and the complete completion of the recovery processes.

In the neuromuscular preparation, fatigue develops in the region of the myoneural junction.

The basic theory of fatigue, attributing the main role to its development in the central nervous system of the whole organism, was formulated by I, M, Sechenov (1902).

Essential for the onset of fatigue is the functional state of the brain, which changes: with hypoxemia, hypoglycemia, hyperthermia, accumulation of metabolites in the blood, shifts in functions internal organs especially the cardiovascular and respiratory systems.

Foreign scientists, seeing that humoral theories alone cannot explain fatigue, began to study the fatigue of nerve conductors. They argued that under the influence of a long passage of excitation impulses (for example, during stimulation with an electric current), the nerve conductors get tired.

The Russian physiologist N. E. Vvedensky, having criticized a number of errors in the experiments of Western scientists, proved on the facts that the nerve conductors are practically inexhaustible and that in the nerves the physiological conduction of excitation occurs with a minimum expenditure of energy. Consequently, the cause of fatigue lay not in the muscle and not in the nerve conductor. Naturally, the thought of scientists turned to the study of the performance of nerve cells.

I.M. Sechenov was one of the first who managed to show where the threads of fatigue stretched through a vivid and interesting experience. The intensified study of questions of the physiology of labor in our country began precisely with his brilliant works. Excellent research I. M. Sechenov "Participation of the nervous system in the working movements of a person" and "Essay on the working movements of a person" and to this day serve as desktop guides for researchers studying the physiology of labor. Dealing with the issues of fatigue, I. M. Sechenov sought not only the causes of fatigue, but also sought to find rational measures to combat this condition.

Imagine Ivan Mikhailovich Sechenov sitting at a simple device somewhat reminiscent of the ergograph described above. Only on Sechenov's ergograph was no longer one finger working, but the whole hand, the movements of which were similar to those that are made when sawing firewood. The load rises and falls in a certain rhythm with each wave of the hand. 4 hours pass, the hand has already made 4800 movements, the height of lifting the load decreases more and more, fatigue is approaching. With this inevitable phenomenon, the inquisitive mind of the scientist decides to fight, he is looking for that “healing medicine” that could eliminate fatigue.

The scientist finds that short-term work of the left hand relieves fatigue right hand much faster than a long rest.

I. M. Sechenov explained this as follows: short-term work of the left (non-working) hand gives rise to impulses of excitation in the sensory nerves of the muscles, rushing to the central nervous system, where they, as it were, rearrange the work of the nervous system, exciting and refreshing it, tuning it to a new fruitful work rhythm. If this is so, I. M. Sechenov argued, then a slight electrical stimulation of the left hand should also relieve fatigue. In fact, it turned out that way: just as external beneficial stimuli that give us a good and pleasant mood (song and music, competition and interest in work), causing excitation of analyzers, * increase the efficiency of the nervous system and our brain, so does the insignificant work of the unemployed left hand or weak electrical stimulation of it reduce fatigue. Thus, I. M. Sechenov showed that the essence of fatigue is rooted in the processes occurring in the central nervous system.

Many Soviet physiologists (N. K. Vereshchagin, S. I. Krapiventseva, M. E. Marshak, G. V. Popov, A. D. Slonim and others) have been and are studying the phenomenon discovered by I. M. Sechenov. . Recently, for example, the Soviet scientist Sh. A. Chakhnashvili showed that the restoration of the working capacity of a tired hand occurs not only during active rest associated with the activity of the other hand, but also during short-term work performed during rest. lower limbs, muscles of the trunk and neck, chewing muscles. It turned out that the contraction of the neck muscles (when moving the head) during a 10-second rest increases the recovery of a tired arm by 61-75% compared with a "passive" rest of the same duration.

* The analyzer is a complex formation that includes a receptor, a sensory nerve and a nerve center in the cerebral cortex. Receptors (from the Latin word recipio - I perceive) are sensitive nerve endings in a muscle or other organ (eye, ear). The perception of external and internal stimuli is carried out not by receptors, as such, but by the entire system of the analyzer as a whole. The doctrine of analyzers was first introduced into physiological science.

Strength and muscle work

The strength of a muscle is determined by the maximum load it can lift. This power can be very great. The strength of a muscle, ceteris paribus, does not depend on its length, but on its cross section: the larger the physiological cross section of the muscle, i.e. the sum of the cross sections of all its fibers, the greater the load that it is able to lift. To be able to compare the strength of different muscles, the maximum load that a muscle is able to lift is divided by the number of square centimeters of its physiological cross section.

The work of the muscle is measured by the product of the lifted load by the amount of shortening of the muscle, i.e. expressed in kilogram meters or gram centimeters.

Muscle power, measured by the amount of work per unit time, also reaches maximum value at medium loads. Therefore, the dependence of work and power on the load is called the rule of average loads.

Muscle fatigue, the theory of fatigue of an isolated muscle and the whole organism

Fatigue is a temporary decrease in the efficiency of a cell, organ or the whole organism, which occurs as a result of work and disappears after rest. The decrease in the efficiency of a muscle isolated from the body during its prolonged irritation is due to two main reasons. The first of these is that during contractions, metabolic products accumulate in the muscle (in particular, lactic acid, which is formed during the breakdown of glycogen), 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. 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 ATP and creatine phosphate resynthesis, which are necessary for contraction, are disrupted. To study muscle fatigue in humans in the laboratory, ergographs are used - devices for recording the amplitude of movement rhythmically performed by a group of muscles.

Fatigue is a temporary decrease or loss of performance, that is, the result of the previous one. Muscle fatigue in the body under conditions of blood circulation depends not only on the amount of long-term work done by it, but on the number of excitation waves that come to it, causing its contraction. With the same frequency of stimulation and other equal conditions, fatigue appears earlier with a greater load on the muscle. With the same load and other conditions being equal, fatigue sets in earlier with more frequent stimuli. At the beginning of work, the height of contractions increases, and then the signs of developing fatigue are a gradual decrease in the height of contractions, an increase in their duration, and an increase in contracture. The development of fatigue depends on changes in blood circulation, and other conditions. The higher the metabolism and better blood circulation, the later fatigue occurs. It occurs much earlier when the muscle is contracting, being stretched by a load during isometric contraction, and later when it is contracting without a load, and therefore without tension.

If you bring the muscle to complete fatigue with irritation, then after changing the direction of the current, its performance is immediately restored. This recovery is explained by a change in the state of the muscle and shifts of ions at the current poles. An isolated muscle reduces its work or even stops contracting when the glycogen store is half the original amount. These facts do not support the theory of exhaustion (Schiff, 1868), which explains muscle fatigue by the use of substances that release it for its work. However, glycogen reserves in the human body are limited and amount to 300-400 g. With very intensive work, they are consumed in 1.5-2 hours, which leads to such a decrease in sugar content in which work becomes impossible. The introduction of sugar into the body restores its performance.

The accumulation of phosphoric and lactic acids reduces muscle performance. An isolated muscle fiber, unlike a whole muscle, gets tired much later with the same number of irritating impulses. This is due to the fact that the end products of metabolism are removed from it faster. In a trained muscle, due to the large acceleration of the analysis and synthesis of substances that ensure its work, fatigue occurs later. After washing the blood vessels of an isolated muscle, brought to complete fatigue, therefore, after removing some of the residual metabolic products from it, it again begins to contract despite the fact that the supply of carbohydrates and oxygen has not been restored. These facts prove that the residual decay products of substances formed in the working muscle are one of the causes of its fatigue.

There is also a theory of suffocation (M. Vervorn, 1903), which attributes the main role in fatigue to a lack of oxygen. It is known that work can continue for tens of minutes and even hours without fatigue, when the level of oxygen consumption is below the limit of its intake, possible for the worker (true steady state). When oxygen consumption reaches a maximum, it can be at a constant level, but does not provide the body's need for oxygen (apparent, or southern, stable state) and work in this case can last no more than 10-40 minutes.

Fatigue is a normal physiological process that leads to the cessation of work. During breaks in work, the working capacity of the muscles is restored. Therefore, the validity of the participation of petty and phosphoric acids in the onset of fatigue does not allow us to draw an absurd conclusion that labor is harmful, since it allegedly leads to poisoning. It is impossible to put an equal sign between the fatigue of an isolated muscle and the fatigue of the whole organism, in which the onset of fatigue depends on a change in the functions of the nervous system and endocrine glands and on a change in the regulation of the central nervous system of metabolism, blood circulation and respiration. The development of fatigue depends on a decrease in the efficiency of the circulatory system, especially the heart, and the respiratory system.

Under normal conditions, during prolonged physical work, muscle excitation and contraction are two interrelated processes that occur when oxygen is consumed, since they are carried out due to very complex chemical processes, culminating in the oxidation of residual metabolic products. Muscle performance after fatigue is restored as a result of the oxidation of these products. Therefore, oxygen consumption during muscular work increases significantly. If there is not enough oxygen, then with intensive muscular work there is a lack of oxygen - oxygen debt. In conditions of oxygen deficiency during work, the functions of the nervous system decrease, which is the main cause of fatigue. Oxygen debt is repaid due to increased blood circulation and breathing, not only during work, but also after its completion. This repayment of the oxygen debt ends only after the complete oxidation of the residual metabolic products formed during work, and the complete completion of the recovery processes.

In the neuromuscular preparation, fatigue develops in the region of the myoneural junction. The basic theory of fatigue, attributing the main role to its development in the central nervous system of the whole organism, was formulated by I, M, Sechenov (1902).

There is numerous evidence of the leading role of the central nervous system in the development of fatigue. Tired occurs under the action of conditioned stimuli. With fatigue, the inhibition of conditioned and unconditioned reflexes increases. The development of fatigue is affected by the influx of afferent impulses; in the brain, emotions. Conscious, voluntary muscle activity is more tiring than involuntary, automatic. Essential for the onset of fatigue is the functional state of the brain, which changes: with hypoxemia, hypoglycemia, hyperthermia, accumulation of metabolites in the blood, shifts in the functions of internal organs, especially the cardiovascular and respiratory systems.

The main indicators characterizing the activity of muscles are their strength and performance.

Muscle strength. Force is a measure of the mechanical impact on a muscle from other bodies, which is expressed in newtons or kg-forces. At isotonic contraction in the experiment, the force is determined by the mass of the maximum load that the muscle can lift (dynamic force), in the isometric - by the maximum tension that it can develop (static force).

A single muscle fiber develops a tension of 100-200 kgf during contraction.

The degree of muscle shortening during contraction depends on the strength of the stimulus, morphological properties and physiological state. long muscles are reduced by a greater amount than short ones.

A slight stretching of the muscle, when the elastic components are tensed, is an additional irritant, increases muscle contraction, and with a strong stretch, the force of muscle contraction decreases.

The tension that myofibrils can develop is determined by the number of transverse bridges of myosin filaments interacting with actin filaments, since the bridges serve as a site for interaction and development of effort between two types of filaments. At rest, a fairly significant part of the transverse bridges interacts with actin filaments. With a strong muscle stretch, the actin and myosin filaments almost cease to overlap and slight cross-links form between them.

The amount of contraction also decreases with muscle fatigue.

An isometrically contracting muscle develops the maximum possible tension for it as a result of the activation of all muscle fibers. This muscle tension is called maximum strength. The maximum strength of a muscle depends on the number of muscle fibers that make up the muscle and their thickness. They form the anatomical diameter of the muscle, which is defined as the area of the transverse section of the muscle, drawn perpendicular to its length. The ratio of the maximum strength of a muscle to its anatomical diameter is called relative muscle strength measured in kg/cm2.

Physiological diameter of the muscle- the length of the transverse section of the muscle, perpendicular to the course of its fibers.

In muscles with a parallel course of fibers, the physiological diameter coincides with the anatomical one. In muscles with oblique fibers, it will be more anatomical. Therefore, the strength of muscles with oblique fibers is always greater than that of muscles of the same thickness, but with longitudinal fibers. Most muscles of domestic animals and especially birds with oblique fibers are feathery. Such muscles have a larger physiological diameter and have greater strength (Fig. 83).

Rice. 83. Anatomical (a-a) and physiological (b-b) diameters of muscles with different arrangement of fibers:

A - parallel fiber type; B - one-pinnate; B - bipinnate; G - multi-pinnate.

The strongest are the multi-pinnate muscles, followed by the single-pinnate, double-pinnate, semi-pinnate, fusiform and longitudinally fibrous muscles.

Many, one, and bipernate muscles have great strength and endurance (they get tired a little), but a limited ability to shorten, and other types of muscles shorten well, but quickly get tired.

A comparative indicator of the strength of different muscles is absolute muscle strength- the ratio of the maximum strength of the muscle to its physiological diameter, i.e. the maximum load that a muscle lifts divided by the total area of all muscle fibers. It is determined with tetanic stimulation and with optimal initial muscle stretch. In farm animals, the absolute strength of skeletal muscles ranges from 5 to 15 kg-force, on average 6-8 kg-force per 1 cm2 of physiological diameter. In the process of muscular work, the diameter of the muscle increases and, consequently, the strength of this muscle increases.

Muscle work. With isometric and isotonic contraction, the muscle does work.

When evaluating the activity of muscles, usually only the external work they do is taken into account.

The work of the muscle in which the movement of the load and bones in the joints occurs is called dynamic.

Work (W) can be defined as the product of the mass of the load (P) by the height of the lift (h)

W= P h J (kg/m, g/cm)

It is established that the amount of work depends on the magnitude of the load. The dependence of work on the magnitude of the load is expressed by the law of average loads: the greatest work is done by the muscle at moderate (average) loads.

Maximum muscle work is also performed with an average contraction rhythm. (law of average speeds).

muscle power defined as the amount of work per unit of time. It reaches a maximum in all types of muscles, also with medium loads and with an average rhythm of contraction. Fast muscles have the most power.

Muscle fatigue . Fatigue- temporary decrease or loss of efficiency of an individual cell, tissue, organ or organism as a whole, occurring after loads (activity). Muscle fatigue occurs during their prolonged contraction (work) and has a certain biological significance, signaling the depletion (partial) of energy resources.

Decrease when tired functional properties muscles: excitability, lability and contractility. The height of muscle contraction with the development of fatigue gradually decreases. This decrease can reach the complete disappearance of contractions. Lowering, the contractions become more and more stretched, especially due to the lengthening of the relaxation period: at the end of the contraction, the muscle does not return to its original length for a long time, being in a state of contractures(extremely slow muscle relaxation). Skeletal muscles tire before smooth muscles. In skeletal muscles, first the white fibers get tired, and then the red ones.

Of the various ideas about the mechanism of fatigue, one of the earliest theories to explain fatigue was exhaustion theory, proposed by K. Schiff. According to this theory, the cause of fatigue is the disappearance of energy substances in the muscle, in particular glycogen. However, a detailed study showed that in muscles that are tired to the limit, the glycogen content is still significant. Later, E. Pfluger put forward theory of organ clogging by products of working decay (theory poisoning). According to this theory, fatigue is explained by the accumulation of a large amount of lactic, phosphoric acids and a lack of oxygen, as well as other metabolic products that disrupt the metabolism in a working organ and its activity stops.

Both of these theories are formulated on the basis of data obtained in experiments on an isolated skeletal muscle and explain fatigue in a one-sided and simplified way.

A further study of fatigue in the conditions of the whole organism found that metabolic products appear in a tired muscle, the content of glycogen, ATP, and creatine phosphate decreases. Changes occur in the contractile proteins of the muscle. There is a binding or reduction of the sulfhydryl groups of actomyosin, as a result of which the process of ATP synthesis and decomposition is disrupted. Violations in the chemical composition of the muscle, located in the whole body, are less pronounced than in the isolated one due to the transport function of the blood.

Research N.E. Vvedensky found that fatigue primarily develops in the neuromuscular synapse due to its low lability.

Synapse fatigue is due to several factors.

Firstly, with prolonged stimulation in the nerve endings, the supply of the mediator decreases, and its synthesis does not keep pace with consumption.

Secondly, the accumulated metabolic products in the muscle reduce the sensitivity of the postsynaptic membrane to acetylcholine, resulting in a decrease in the magnitude of the postsynaptic potential. When it drops to a critical level, no excitation occurs in the muscle fiber.

I.M. Sechenov (1903) - investigating the performance of muscles when lifting a load on the ergograph designed by him for two hands, found that the performance of a tired right hand is restored more fully and faster after active rest, i.e. rest followed by the work of the left hand. A similar kind of influence on the performance of a tired hand is exerted, combined with rest, by stimulation by an induction current of sensitive (afferent) nerve fibers hands of the other hand, as well as footwork associated with lifting weights, and general motor activity.

Thus, active rest, accompanied by moderate work of others muscle groups, turns out to be more effective tool fight fatigue locomotive system than simple peace.

The reason for the most effective restoration of the working capacity of the locomotor apparatus in conditions of active rest, Sechenov with good reason, associated with the effect on the central nervous system of afferent impulses from muscle, tendon receptors of working muscles.

In the body, in various parts of the reflex arc, fatigue primarily occurs in the nerve centers, especially in the cells of the cerebral cortex.

It has now been established that the functional state of the muscles is under the influence of the central nervous system and, above all, the cerebral cortex. This influence is carried out through the somatic nerves, the autonomic nervous system and the endocrine glands.

Impulses from the spinal cord and brain come to the muscle along the motor nerves, causing its excitation and contraction, accompanied by a change in the physicochemical properties and functional state of the muscle.

The impulses coming through the sympathetic fibers to the muscle enhance the processes of metabolism, blood supply and muscle performance. The mediators of the sympathetic system - adrenaline and noradrenaline - have the same effect.

However, there is still no unified theory explaining the causes of fatigue, the essence of fatigue, because under natural conditions, fatigue of the body's motor apparatus is a multifactorial process.

The onset of muscle fatigue can be delayed through exercise. It develops and improves the functionality of all body systems: nervous, respiratory, circulatory, excretory, etc.

When training, muscle volume increases as a result of the growth and thickening of muscle fibers, muscle endurance increases. The content of glycogen, ATP and creatine phosphate increases in the muscle, the processes of decay and restoration of substances involved in metabolism are accelerated. As a result of training, the coefficient of oxygen utilization during muscle work increases, recovery processes increase due to the activation of all enzymatic systems, and energy consumption decreases. During training, the regulatory function of the central nervous system is improved, and first of all, the cerebral cortex.