The following modes of muscle contraction are distinguished:

1. Isotonic contractions. The length of the muscle decreases, but the tone does not change. They do not participate in the motor functions of the body.

2. Isometric contraction. The length of the muscle does not change, but the tone increases. They form the basis of static work, for example when maintaining body posture.

3. Auxotonic contractions. Both the length and tone of the muscle change. With their help, body movement and other motor acts occur.

Maximum muscle strength- this is the maximum tension that a muscle can develop. It depends on the structure of the muscle, its functional state, initial length, as well as gender, age, and level of training of the person.

Depending on the structure, muscles with parallel fibers (for example, sartorius), fusiform (biceps brachii), and feathery (gastrocnemius) are distinguished. These types of muscles have different physiological cross-sectional area is the sum of the cross-sectional areas of all the muscle fibers that form the muscle. The largest physiological cross-sectional area, and, consequently, strength, is found in the pennate muscles. The smallest in muscles with parallel fibers.

With moderate stretching of the muscle, the force of its contraction increases, but with overstretching it decreases. With moderate heating, the strength also increases, and with cooling it decreases. Muscle strength decreases due to fatigue, metabolic disorders, etc. The maximum strength of various muscle groups is determined by dynamometers (wrist, deadlift, etc.).

To compare the strength of different muscles, determine them specific or absolute strength. It is equal to the maximum force divided by square meters. see muscle cross-sectional area. The specific strength of the human gastrocnemius muscle is 62 kg/cm2, the triceps muscle is 16.8 kg/cm2, and the masseter muscle is 10 kg/cm2.

Muscle work is divided into dynamic and static Dynamic performed when moving cargo. During dynamic work, the length of the muscle and its tension change. Therefore, the muscle works in an auxotonic mode. At static during work there is no movement of the load, i.e. the muscle works in isometric mode.

Dynamic work is equal to the product of the weight of the load and the height of its lifting or the amount of muscle shortening (A = M h). Work is measured in kg m, joules. The dependence of the amount of work on the load obeys the law of average loads. As the load increases, muscle work initially increases. At medium loads it becomes maximum. If the increase in load continues, the work decreases. The size of the work is also influenced by its rhythm. Maximum muscle work is carried out at an average rhythm. Of particular importance in calculating the amount of workload is the definition of muscle power - this is the work performed per unit of time (P=A·T). The unit of measurement is watt (W).

Muscle fatigue

Fatigue- This is a temporary decrease in muscle performance as a result of work. Fatigue of an isolated muscle can be caused by its rhythmic stimulation. As a result, the strength of contractions progressively decreases. The higher the frequency, strength of irritation and magnitude of the load, the faster fatigue develops. With fatigue, the single contraction curve changes significantly. The duration of the latent period, the shortening period and especially the relaxation period increases, but the amplitude decreases. The stronger the muscle fatigue, the longer the duration of these periods. In some cases, complete relaxation does not occur. Developing contracture is a state of prolonged, involuntary muscle contraction.

Muscle work and fatigue are studied using ergography. In the last century, based on experiments with isolated muscles, 3 theories of muscle fatigue were proposed.

1. Schiff's theory: Fatigue is a consequence of depletion of energy reserves in the muscle.

2. Pfluger's theory: fatigue is caused by the accumulation of metabolic products in the muscle.

3. Verworn theory: Fatigue is due to a lack of oxygen in the muscle.

Indeed, these factors contribute to fatigue in experiments on isolated muscles. ATP resynthesis is disrupted in them, lactic and pyruvic acids accumulate, and the oxygen content is insufficient. However, in the body, intensively working muscles receive the necessary oxygen and nutrients, and are freed from metabolites due to increased general and regional blood circulation. Therefore, other theories of fatigue have been proposed. In particular, a certain role in fatigue belongs to neuromuscular synapses. Fatigue at the synapse develops due to depletion of neurotransmitter stores. However, the main role in fatigue of the musculoskeletal system belongs to the motor centers of the central nervous system. In the last century I.M. Sechenov found that if the muscles of one arm become fatigued, their performance is restored faster when working with the other arm or legs. He believed that this was due to the switching of excitation processes from one motor center to another. He called rest with the inclusion of other muscle groups active.

It has now been established that motor fatigue is associated with inhibition of the corresponding nerve centers, as a result of metabolic processes in neurons, deterioration in the synthesis of neurotransmitters, and inhibition of synaptic transmission.

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 a complete cessation of its contractions occurs. When fatigued, the muscle often cannot relax completely and remains in a state of prolonged shortening (contracture). Fatigue is first the result of changes in the functions of the nervous system, and primarily the brain, disruption of the transmission of nerve impulses between neurons and between the motor nerve and the muscle, and then a consequence of changes in the functions of the muscle itself.

Since fatigue decreases the functions of the nervous system and receptors of muscles, joints and tendons, disturbances in coordination of movements occur.

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 all autonomic functions by the nervous system.

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 performance of the cardiovascular and respiratory systems disrupts the blood supply to working muscles, and therefore 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 the size of the load (load). Increasing the load and increasing the rhythm accelerates the onset of fatigue.

When you are tired, tiredness often appears - a feeling of fatigue that is absent if the work is of interest. On the contrary, when work is done without interest, fatigue sets in earlier and is greater, although there are no signs of fatigue. The ability to become tired 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 fatigue, then the environment in which it was carried out does not cause fatigue and fatigue. A change in the environment in which fatigue has repeatedly occurred, or many days of long rest lead to the disappearance of the conditioned reflex to fatigue.

Muscle fatigue is a normal physiological process. Restoration of muscle performance occurs already during work execution. After finishing work, performance is not only restored, but also exceeds its original level before work.

Rice. 32. Change in performance on rest days after extreme work

Fatigue must be distinguished from overwork.

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

It is important to prevent the occurrence of overwork. The onset of overwork is facilitated by unhygienic working conditions, physical exercise, the external environment, and poor nutrition.

When overwork occurs, chronic headaches, great irritability, apathy, lethargy, daytime drowsiness, sleep disturbance at night and insomnia, loss of appetite, and muscle weakness appear. The coordination of muscular work and vegetative functions is disrupted, there is a decrease in metabolism and a drop in body weight, an increase in heart rate and sometimes a significant slowdown in heart rate, a decrease in blood pressure, a decrease in tidal volume, etc. There is no desire to engage in work, physical education and sports, especially those types of sports. which caused fatigue.

Creating normal hygienic conditions for physical labor and physical exercise, switching to a new interesting type of physical labor and sports, transferring to another environment, long rest, increasing time spent in the fresh air and sleep, improving nutrition, taking carbohydrates and vitamins eliminates overwork.

When playing sports, your body experiences a lot of physical stress - all this changes the condition of your muscles. After intense work they become tired and change. In this article I will tell you how load affects the development of muscle fatigue, what processes occur in muscle tissue and how this affects training. This knowledge should be in the treasury of everyone who is involved in bodybuilding, whether amateur or professional, girl or man.

This is a physiological process that causes a decrease in the performance of muscle fibers due to intense or prolonged work, while their length, strength and speed of contraction decrease.

After removal of the load, they remain partially reduced and can restore their performance after rest.

Mechanism of muscle fatigue

To obtain energy, muscles break down the adenosine triphosphate (ATP) molecule into adenosine phosphate (ADP). This reaction releases energy, which is used for contraction. Muscle tissue constantly reproduces ATP molecules, which allows it to work without stopping.

If oxygen is supplied to the muscles in a timely manner, they synthesize ATP from glucose, releasing carbon dioxide and water during the reaction. If there is not enough oxygen, the reaction does not proceed completely. As a result of synthesis, a by-product is formed - lactic acid (lactate), which accumulates and causes a rapid increase in fatigue.

What causes muscle fatigue

Scientists have identified several causes of muscle fatigue:

1. Depletion of energy resources - carbohydrate reserves contained in muscles in the form of glycogen.
2. Accumulation of metabolic products in tissues.
3. Impaired transmission of nerve impulses in the central nervous system and decreased neuromuscular communication.

What load affects the development of muscle fatigue?

The more intensely a muscle works, the faster it gets tired.

Intensity can be of two types:

• High speed of movement (for example, in sprinting).
• The great effort required to lift a weight (in weightlifting or powerlifting).

On the contrary, a light, not intense load can be maintained by the body for many hours. An example of such work is walking. In this case, energy is supplied to the muscles by the aerobic system through the oxidation of fats with oxygen.

Types of muscle fatigue

• Energy fatigue.

Our body has several mechanisms for energy synthesis:

• The phosphate mechanism of ATP synthesis uses the available phosphate reserves in the muscles. It quickly re-synthesizes ATP from ADP using the high-energy substance creatine phosphate (CrP). But the KrF reserves are only enough for 8-10 seconds of work at maximum intensity.
• Once creatine phosphate is depleted, muscles begin to burn carbohydrates to synthesize phosphates. Glucose is stored in muscle tissue and liver in the form of glycogen. The amount of glycogen varies among people with different levels of training, but on average it is enough for 60-90 minutes of intense exercise. Energy from carbohydrates can be synthesized both with the participation of oxygen - aerobically, and without it - anaerobically.

After depleting carbohydrate reserves, the athlete switches to energy supply only through the breakdown of fats, while he loses the ability to perform exercises with high intensity. At this point, a decrease in muscle speed and strength occurs.

• Fats can only be broken down in the presence of oxygen. When muscle fibers are fed only by fat, they can no longer perform maximum power movements. But they can do long-term light work for a very long time, because the reserves of fat in the body are practically inexhaustible.

Energy fatigue occurs after 60-90 minutes of high-intensity training, it is associated with the depletion of glycogen reserves, weakness appears in the legs and arms, and under such conditions it is very difficult to continue exercising. When energy fatigue sets in, you can quickly restore the functionality of the muscular system - just saturate the body with fast carbohydrates (sugar or glucose).

• Fatigue due to accumulation of metabolic products.

If during light physical activity, for example walking, muscle nutrition can be carried out entirely by burning fat. Then, with an increase in the intensity of movements, the mechanism of carbohydrate breakdown is included in energy exchange.

With a further increase in intensity, the rate of carbohydrate oxidation increases, but due to a lack of oxygen, some of the glucose is broken down anaerobically. This produces lactic acid (lactate), which accumulates in muscle tissue. Such processes often occur when an athlete, in a long-distance race, sharply increases the pace at the finish line.

The accumulation of lactate quickly leads to fatigue. Painful sensations occur. Due to the high concentration of lactic acid, cell walls are damaged, and their contents enter the blood. High lactate content in muscle tissue impairs coordination abilities, leads to microtrauma and reduces metabolic rate.

• Nervous-impulse fatigue.

This type of muscle fatigue involves a change in the process of impulse transmission in the neuromuscular junction. This is due to the inability to maintain high performance of the nerve cell for a long time; it decreases under the influence of load. If the intensity level remains high for a long time, the nerve cell becomes blocked and stops transmitting nerve impulses to the muscle.

Symptoms of muscle fatigue

As fatigue increases, the height and speed of muscle contraction decreases. The athlete begins to perform explosive work more slowly. The running speed and jumping height decrease, the frequency and amplitude of movement decreases. There is a decrease in coordination, the technique of performing the exercise is disrupted.

This is due to the fact that the white muscle fibers that use carbohydrate energy have stopped receiving nutrition or have become acidic due to the accumulation of lactic acid.

Possible consequences and complications

A high concentration of lactate causes micro-tears in the fibers, which can cause injury. High lactic acid content reduces the recovery of creatine phosphate and reduces the rate of fat breakdown.

Muscles must be given enough time to develop, otherwise overtraining may occur.

Signs of overtraining:

• Long-term restoration of heart rate to normal values ​​after exercise and rapid heart rate at rest.
• Rapid onset of fatigue, decreased athletic performance.
• Lack of appetite.
• Pain in muscles, ligaments and joints.
• Increased nervousness and anxiety.
• Insomnia.
• Increased sweating.

As a result, interest in activities decreases, the risk of injury increases, and immunity decreases. To restore the body, you need to sharply reduce the intensity of training for 1-2 weeks.

How to eliminate muscle fatigue

To fully restore muscle tone after an intense workout, the body requires 24 to 96 hours of rest.

To remove 95% of lactic acid from a muscle, the body may require more than 1 hour and 20 minutes of passive rest. To speed up this process you need to do light work. For example, continuous jogging will allow you to get rid of lactate twice as quickly as with passive rest.

This will return the muscle fiber to its original length and relax it.

If you notice signs of overtraining, you should take the following steps:

• Eliminate mental stress.
• Do pleasant things, have fun, take a walk in the fresh air.
• Take a bath, go to the sauna, get a massage.
• Reduce training intensity by at least 50% over the next week.

You cannot continue exercising with the same intensity as before. Passive rest is not recommended; in this case, recovery will take twice as long.

Sports nutrition and anti-fatigue products

1. Amino acids quickly restore muscles damaged during training; these compounds are involved in all physiological processes. , will increase the production of necessary hormones and improve the general condition of the body.
2. Creatine is a substance that is directly involved in the energy metabolism of ATP and ADP. Creatine neutralizes acids that cause fatigue, including lactic acid. According to scientific research and reviews.
3. For quick recovery, athletes need to eat a sufficient amount of foods rich in vitamins and minerals, including: raw vegetables, fruits and herbs.
4. Fish oil contains omega-3 polyunsaturated fatty acids, which are involved in the functioning of all body systems, from the brain to the restoration of joints.

The effect of fatigue on the immune system

Physical activity, infections and immunity are closely related. Moderate aerobic exercise stimulates the immune system, while long-term grueling exercise, on the contrary, suppresses it. Physical overload can lead to tissue damage and create pockets of inflammation.

When the training intensity exceeds 70% of the maximum capabilities, their positive effect on the immune system disappears.

Conclusion

Muscle fatigue is a natural process that protects the muscles and nervous system from destruction. We experience fatigue due to nutrient depletion, lactic acid buildup, and decreased neuromuscular connections. During bodybuilding, it is very important to listen to your muscles, not to overtrain, and to follow a sleep and nutrition regimen. Only in this case can you get maximum results from your training.

If you are interested in this article, share it on social networks. Subscribe to my group on Vkontakte and Facebook, where you will find training complexes, tips on sports nutrition and recommendations for creating a beautiful and attractive body.

In contact with

The muscle cannot produce work continuously. With prolonged continuous work, a gradual decrease in muscle performance occurs. This condition is called muscle fatigue. With muscle fatigue, the force of muscle contraction decreases, and the contractions themselves become slower. In this case, there is an extension of the latent period of muscle excitation and a decrease in its excitability. The onset of muscle fatigue depends on the frequency of their contractions. Contracting too frequently causes fatigue. The duration of muscle performance also depends on the amount of load falling on it. For each muscle, a certain optimal contraction frequency and load magnitude can be found at which the muscle’s performance is maintained for the longest time. This leads to a practical conclusion that the magnitude of the load and the rhythm of movement affect the performance of a person engaged in physical labor, and, consequently, the amount of work he performs.

A decrease in muscle performance is caused by nervous and chemical factors. Initially, fatigue occurs in the nerve centers that affect muscle function, and then in the endings of the motor nerves on the muscle fibers (in synapses). As a result, the nature of impulses coming from the nervous system to the muscles changes, which leads to a decrease in the strength and speed of muscle contractions. The dependence of the speed of onset of muscle fatigue on the state of the nervous system has been proven by special experiments and observations. It is known, in particular, the influence of mental and emotional influences (for example, music, singing) on ​​human performance. It has also been proven in special experiments on animals that irritation of the sympathetic nerves reduces muscle fatigue. It is believed that this increases metabolic processes in a tired muscle.

The influence of chemical factors is that in the working muscle the metabolic products (lactic acid, etc.) are not completely oxidized due to insufficient oxygen supply. The accumulation of these metabolic products contributes to muscle fatigue.

In the whole body, muscle performance depends on the functional state of many organ systems: cardiovascular, respiratory, endocrine glands, etc.

Systematic training (exercises) plays a major role in improving performance. During physical training, changes occur not only in the muscles (muscle development and the associated increase in their strength), but also in all other organ systems, in particular the cardiovascular and respiratory systems are strengthened. Thus, in trained people, the heart muscle is better developed and contracts with greater force, so the volume of blood ejected by the heart per contraction and per minute is greater (although the heart rate is slower). Breathing in trained people is deeper, which contributes to better oxygen saturation of the blood (although the breathing rate is reduced). Training leads to improved health and increased endurance of a person.

Physical exercise is one of the methods used in medical practice (physical therapy) to quickly restore the health of patients.

In our country, much attention is paid to physical education and sports as one of the conditions for the comprehensive harmonious development of the human personality. A person in a communist society will be characterized by a harmonious combination of spiritual wealth and moral purity with physical perfection.

Fatigue is a temporary decrease or loss of performance, i.e. the result of a previous one. Fatigue of a muscle in the body under blood circulation conditions depends not only on the amount of long-term work performed by it, but on the number of excitation waves arriving at it, causing its contraction. With the same frequency of irritation and other equal conditions, fatigue appears earlier with greater muscle load. Under the same load and other equal conditions, fatigue occurs earlier with more frequent irritations. At the beginning of work, the height of contractions increases, and then 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 sets in. It occurs much earlier when the muscle contracts, being stretched by a load during isometric contraction, and later when it contracts without a load, and therefore without tension.

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

The theory of muscle poisoning during fatigue by a special poison accumulating in it - kenotoxin (Weichardt, 1904) turned out to be unfounded. But there is evidence that fatigue is sometimes associated with poisoning of excited structures by metabolic products, mainly phosphoric and lactic acids at the time of their formation. Residual metabolic products seem to 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 explained by the fact that the end products of metabolism are removed from it faster. In a trained muscle, due to the great acceleration of analysis and synthesis of substances that ensure its functioning, fatigue occurs later. After washing the blood vessels of the isolated muscle, which has been brought to the point of complete fatigue, therefore, after removing part of the residual metabolic products from it, it begins to contract again despite the fact that the supply of carbohydrates and oxygen has not been restored. These facts prove that residual decay products of substances formed in the working muscle are one of the reasons for its fatigue.

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

Fatigue is a normal physiological process that leads to cessation of work. During breaks from work, muscle performance is restored. Therefore, the validity of the participation of fine and phosphoric acids in the onset of fatigue does not allow us to draw the absurd conclusion that work is harmful, since it supposedly leads to poisoning. It is impossible to equate the fatigue of an isolated muscle with the fatigue of the whole organism, in which the onset of fatigue depends on changes in the functions of the nervous system and endocrine glands and on changes in the regulation of metabolism, blood circulation and respiration by the central nervous system. The development of fatigue depends on a decrease in the performance 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 through very complex chemical processes that culminate 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 muscle work increases significantly. If there is not enough oxygen supplied, then during intense muscular work a lack of oxygen occurs - an oxygen debt. In conditions of insufficient oxygen during work, the functions of the nervous system decrease, which is the main cause of fatigue. The oxygen debt is repaid thanks to increased blood circulation and breathing, not only during work, but also after it ends. This repayment of the oxygen debt ends only after the complete oxidation of residual metabolic products formed during work and the complete completion of reduction processes.

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

There is ample evidence of the leading role of the central nervous system in the development of fatigue. Tiredness occurs when exposed to conditioned stimuli. When tired, the inhibition of conditioned and unconditioned reflexes increases. The development of fatigue is influenced by the influx of afferent impulses; into the brain, emotions. Conscious, voluntary muscle activity is more tiring than involuntary, automatic activity. 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, changes in the functions of internal organs, especially the cardiovascular and respiratory systems.