How are muscles worked? Static and dynamic work. Muscle work Muscle work briefly

By contracting, the muscles bring the bones closer or further away, move the body or its parts, hold them in a certain position, lift or hold the load, i.e. are doing the work. It can be dynamic or static. Dynamic work is performed by the muscles during any movement. Static work is performed while maintaining the posture of the body, holding its parts in a certain position, holding the load. Static work tires the skeletal muscles more than dynamic work.

muscle strength

When doing work, the muscles tense up. The amount of muscle tension is called its strength. The strength of different muscles is not the same. It depends on the number of muscle fibers, the degree of excitation of the muscle and the angle of its attachment. Different muscles have different numbers of fibers. Most of them are in the feathery and bipennate muscles. The more fibers a muscle contains, the more tension it can develop, the stronger it is. The strength of a muscle depends on its physiological diameter. This is a mental cut drawn through all its fibers. The more fibers in the muscle, the greater the physiological diameter.

Strong excitation causes a contraction of more muscle fibers. The muscle shows great strength. The angle at which the muscle attaches to the bone can be acute or obtuse. The muscle develops the greater the tension, the farther from the joint it is attached and the greater the angle of its attachment. The work performed by the muscles depends on the strength of the muscles (a stronger muscle can do more work), the rate of muscle contractions and the amount of load.

The higher the rate of contraction of the muscle and the greater the load or resistance, the greater the work done by the muscle. But the performance of the muscles lasts longer with an average value of the rate of contractions and load. With rhythmic work, muscle fatigue develops more slowly. Working muscles consume energy. It is formed in the muscles themselves as a result of the breakdown of carbohydrates and the oxidation of other organic substances. Part of this energy is spent on the work produced by the muscles, part is released in the form of heat.

For the formation of energy, it is necessary for organic substances and oxygen to enter the muscles, and carbon dioxide and other substances to be removed from the muscles. Muscle activity causes or stops nerve impulses. Hence, muscles are connected to many organ systems of the body: the nervous, respiratory, digestive, excretory, and circulatory systems.

In children and adolescents, there is an increase in the mass of skeletal muscles, their strength increases. But the muscles of adolescents differ from the muscles of adults in some features of the structure and functioning. So, the muscles of children are almost twice as elastic as the muscles of adults. Therefore, when contracting, they shorten, and when stretched, they lengthen by a large amount. In children, the muscles are attached to the bones further from the axes of rotation of the joints, as a result of which they contract with less loss of strength than the muscles of an adult.

Physical training affects the work done by the muscles. It increases the volume and size of the muscles. Therefore, their strength increases, the contractile properties of the muscles and their ability to relax improve. Well-developed, trained muscles produce work with less tension than weak, poorly trained ones. This explains the fact that an experienced dancer “rests” during the performance of tours or fouettes, while an inexperienced one gets very tired.

"Human Anatomy and Physiology", M.S. Milovzorova

The pelvic muscles begin on the bones of the pelvic girdle and attach to the femur. They surround the hip joint from all sides and provide all possible movements in it. The external muscles of the pelvis The external muscles of the pelvis are strongly developed only in humans due to upright posture, they hold the body in an upright position. The gluteus maximus muscle (B, 16) is located under the skin, closes ...

The femur is covered with muscles on all sides. Leg extensor - quadriceps femoris (18) - has 4 heads. One of the heads (19) - the rectus femoris - flexes the thigh at the hip joint and straightens the lower leg. All 4 heads with a common tendon, in the thickness of which the patella lies, are attached to the tibia. This is the strongest muscle...

Muscles on the leg are unevenly distributed. Part of the tibia is not covered by them. There are 11 muscles in the lower leg. Part of the muscle attaches to the bones of the tarsus and metatarsal bones, exerting an effect on the entire foot, and the other part attaches to the phalanges of the fingers, setting the toes in motion. There are only three extensor muscles on the lower leg, and eight flexors. A large number of flexors of the foot and fingers ...

The muscles of the head are divided into chewing and facial muscles according to their functions. The former set the lower jaw in motion, the latter are involved in facial expressions. The muscles of the neck keep the head in balance, participate in the movements of the head and neck. With their help, neck-tonic reflexes are carried out. Part of the muscles of the neck is involved in swallowing and pronouncing sounds and words. The sternocleidomastoid muscle (1) begins on the sternum ...

The muscles of the foot are located on the sole and back side. They produce the movements of the fingers and hold the arches of the foot. Muscles are antagonists and synergists. Depending on the conditions of action, the muscles perform different movements. So, the iliopsoas muscle is a hip flexor of the free leg, and when supported by two nopis, it flexes the torso. The brachialis muscle under normal conditions flexes the forearm, but if it is fixed - ...

Main article: Muscles

muscle contraction

The movements of the human body are carried out due to the work of certain muscle groups. Muscles are associated with special nerve cells and their fibers.

Static muscle work is

Each of the motor nerve cells, that is, each motor neuron, through its fibers, enters into communication with tens and hundreds of muscle fibers.

When a motor neuron is excited, chemicals are released from the terminal part of its fiber, which, acting on the muscle fiber, excite it and, as a result, the muscle contracts, performing a certain job.

Types of muscle work

There are two types of skeletal muscle work: static and dynamic.

Static muscle work

As a result of the static work of the muscles, the human body and its individual parts are held for a certain time in the required position.

This includes, for example, a straight stance, the position of arms laid aside or up, pre-launch position, etc. Static work does not set the body in motion, but only ensures that it is held in the desired position for a certain time (Fig.

Dynamic muscle work

As a result of the dynamic work of the muscles, the human body and its individual parts produce a variety of movements - for example, walking, running, jumping, pronunciation of words, etc.

(Fig. 21, 22).

Muscle fatigue

When the muscles perform work after a certain time, their fatigue occurs. The reason for this is as follows:

First, fatigue occurs in the nerve cells of the brain that regulate the work of muscles, as a result of their prolonged excitation, the processes of excitation in them decrease, the cells go into a state of inhibition.

Secondly, as a result of prolonged physical labor, the supply of food in the muscle fibers is depleted, and therefore the energy necessary to perform muscle work is also depleted.

Thirdly, when doing work for a short time, but at a high speed, oxygen starvation occurs in the body.

Material from the site http://wiki-med.com

With the onset of fatigue, the force of contraction of muscle fibers begins to gradually decrease and the muscle fibers, more and more relaxing, stop contracting.

As a result, the movement gradually slows down and then stops completely. Fatigued muscle fibers sometimes cannot relax after contraction, a condition called muscle contracture (or cramps). Sometimes when running fast, it is observed in the calf muscles.

The body of people who systematically engage in physical labor, physical culture and sports is well trained. Therefore, the processes of fatigue in their muscles do not come soon.

With a good development of the muscles, with the strengthening of their fibers and tendons, conditions are created, in turn, for better development and greater strengthening of the bones.

On this page, material on the topics:

• what happens to muscles during static work

• showing the work of naked muscles

• muscle work in daily life

• improper muscle function

• what are the types of muscle work

Questions for this article:

• Explain the static work of muscles.

• What is dynamic muscle work?

• How does muscle fatigue occur?

• What changes occur in well-developed muscles?

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Aerobic muscle performance

Maximum aerobic power depends mainly on the density of mitochondria in muscle fibers, the concentration and activity of oxidative enzymes, and the rate of oxygen supply deep into the fiber.

The amount of oxygen available for oxidative reactions is limited both by the factors of the overall performance of the body, which I have already considered, and by a number of local intramuscular factors, among which one can single out muscle capillarity, myoglobin concentration, muscle fiber diameter (the smaller the fiber diameter, the better it is supplied oxygen and the higher its relative aerobic capacity).

The rate of ATP production due to oxidation reaches its maximum values ​​at the 2-3rd minute of work, which is associated with the need to deploy many processes that ensure the delivery of oxygen to mitochondria. The retention time of maximum aerobic power is approximately 6 minutes, then aerobic power decreases due to fatigue of all actively working body systems.

Accordingly, to increase the aerobic power of the muscles, the training load should last at least 2 minutes (to reach the maximum energy production rate). It makes no sense to tighten the load for longer than 6 minutes, when training exactly the power, since then it (power) decreases.

Repeated repetition of such loads is effective.

In conclusion, I want to give a summary table of the training effect on the performance of muscles in various modes of operation, which I gleaned from M. Hosni's dissertation, devoted to the study of the biochemical foundations of interval training. To develop the appropriate qualities, Hosni recommends the following methodological techniques:

This concludes my presentation of the basics of muscle performance training and proceeds to the analysis of the main factors that determine the muscle volume of an athlete.

Well, we have already considered the main methods of training that contribute to the development of strength and strength endurance of muscles.

It is time to start considering training methods that fully contribute to muscle hypertrophy, for which it is necessary to determine the tissue and intracellular structures, the development of which determines the athlete's muscle volumes. I already touched on this issue a little in the second part, now let's dwell on it in a little more detail. As you remember, muscle volume is primarily determined by the number of muscle fibers (cells) in the muscle body, the size of these fibers themselves, as well as the volume of intercellular substance, represented mainly by blood vessels and connective tissue that separates individual fibers from each other. and their bundles.

Of no small importance for the visual volumes of an athlete are fat reserves in the body, however, the contribution of fats can hardly be called a contribution to "muscle" volumes, and the standards of competitive bodybuilding require minimization of such a contribution, so training methods that lead to an increase in the fat component of an athlete's volumes, I consider I will not, they are already well known to everyone.

An increase in the number of muscle fibers in humans has never been reliably recorded in experiments, although, as I said earlier, hyperplasia does not seem to me such an incredible phenomenon, after it has been recorded in animals, but in order not to be considered an empty dreamer, I I will include hyperplasia as a cause of muscle hypertrophy, until there are reliable experiments that have recorded an increase in the number of muscle fibers in humans.

And so, we can only rely on muscle capillarization, an increase in the volume of muscle fibers and the growth of connective tissue. The volume of muscle fibers is controlled primarily by the number of muscle nuclei in the fiber. It is on the number of nuclei, ceteris paribus, that the total amount of protein synthesized by the muscle fiber per unit time depends. And this factor is undeservedly ignored by many experts when considering the causes of muscle hypertrophy under the influence of training.

As you remember, satellite cell division, initiated by factors that appear in the muscle fiber when it is damaged, leads to an increase in the number of muscle nuclei. But the nuclei serve as the root cause, and other cellular structures increase the volume of the fiber, such as myofibrils, sarcoplasm, mitochondria, etc. Here are the data on the potential for muscle growth due to various cellular and intercellular structures in F.

Factors. Approximate contribution to the increase in muscle size,%:

• Capillarization 3-5
• Mitochondria 15-25
• Sarcoplasm (cellular fluid) 20-30
• Connective tissues 2-3
• Muscle fibrils 20-30
• Glycogen 2-5

As you can see, a significant contribution to muscle volume is made by the number and cross section of myofibrils in the muscle fiber. A comparable effect on muscle size is exerted by the volume of the sarcoplasm and the mitochondria located in it.

Thus, one should distinguish between myofibrillar and sarcoplasmic hypertrophy. At first glance, the potential for sarcoplasmic hypertrophy (cellular fluid + mitochondria + glycogen) even exceeds the growth potential due to contractile structures, but upon closer examination it becomes clear that sarcoplasmic hypertrophy is in a subordinate relationship to myofibrillar hypertrophy.

Each myofibril requires the presence in the cell of a certain amount of sarcoplasm and mitochondria, designed to ensure their (myofibrils) functioning. The growth of myofibrillar structures will automatically lead to a corresponding increase in sarcoplasmic structures. Moreover, the percentages given by Hatfield raise some doubts, especially since the author does not indicate the source of his information. So, for example, in the textbook of biological chemistry, authored by T.T.

Berezov and B.F. Korovkin provides somewhat different information. Chemical analysis of muscle tissue shows that 70-80% of muscle mass is water and 20-30% is a dry residue consisting of proteins, lipids and carbohydrates. The percentage of proteins found in the dry residue is as follows: contractile proteins - 35%, sarcoplasmic proteins - 45% and stromal proteins (connective tissue) - 20%.

That is, the percentages of proteins are close to those given by Hatfield, but we should not forget that these are mass ratios, not volume ratios.

According to the same source, myofibrils occupy about 80% of the volume of the muscle fiber, that is, all other structures in addition to the myofibrils themselves, in total, account for no more than 20% of the cell volume. Accordingly, the ratio between myofibrillar and sarcoplasmic hypertrophy turns out to be somewhat different than follows from the data given by Hatfield: myofibrillar hypertrophy can give up to 80% increase in fiber volumes, and sarcoplasmic hypertrophy only 20%.

But for a person striving for maximum muscle development, these 20 percent should not be neglected.

It is clear that the relative volume of the sarcoplasm of the muscle cell also depends on the activity of using myofibrils, that is, on the volume of work regularly performed by the muscles.

The relationship between the concentration of mitochondria in a cell and its energy needs, I think, does not raise questions, but why an increase in energy consumption increases the volume of the sarcoplasm of a muscle cell is worth explaining.

Sarcoplasm is not only cellular fluid (water), it is also millions of molecules of various substances suspended and dissolved in it. These are, first of all, large molecules of protein-enzymes, designed to ensure the flow of many vital chemical reactions, including energy-providing ones.

These are reserves of organic fuel - ATP, creatine phosphate, glycogen, fatty acids and amino acids. These are myoglobin molecules. These are, after all, all kinds of ions (K+, Ca++, Na+, Mg++, etc.).

But the bulk of the sarcoplasm is created not even by the listed substances themselves, but by the water surrounding them. Substances dissolved and suspended in the sarcoplasm, by their very presence, bind and retain a certain number of water molecules in the cell.

The accumulation in the cell of the substances listed above proportionally increases the volume of the sarcoplasm. You are well acquainted with the effect of a sharp increase in the volume of the sarcoplasm of muscle fibers during training, due to the fluid that has flooded into the cells from the intercellular space and blood plasma.

With glycolysis, which is activated during muscle activity, glucose breaks down into lactic acid in a ratio of 1: 2 (one glucose molecule - two molecules of lactic acid). Since two acid molecules bind more water molecules than one glucose molecule, the activation of glycolysis increases the cell's need for fluid, and water rushes into the muscle fibers, which leads to their swelling and a noticeable increase in muscle volume. However, this temporary increase in volume should not be confused with muscle growth, as soon as lactic acid is removed from the muscles, the volume of cellular fluid will return to normal.

It is interesting that an increase in the volume of the sarcoplasm can occur not only due to the simple accumulation of the substances listed above in it. The sarcoplasm of muscle fibers is somewhat different from the sarcoplasm of other cells, this is due to the presence of structures such as myofibrils in muscle fibers. Each myofibril is surrounded by a dense network of the sarcoplasmic reticulum, consisting of terminal cisterns with Ca ++ ions (ions are released into the sarcoplasm during contraction), and an interweaving of the so-called T-tubules that connect the terminal cisterns with the sarcolemma (fiber sheath) and provide a signal to contract.

Muscles and their work. Muscle work

That is, each myofibril is rigidly surrounded by a certain volume of sarcoplasmic structures. The volume of these structures is proportional to the surface area of ​​the myofibrils in the fiber. Accordingly, the larger the diameter of individual myofibrils, the smaller the volume of the sarcoplasm surrounding the myofibril in relation to the volume of contractile proteins inside this myofibril (the higher the proportion of contractile proteins in the fiber).

But, the larger the volume of each myofibril, the more difficult it is to provide its energy needs, since the path of energy transfer from the surface of the myofibril (where the main energy sources are located - mitochondria) is longer. Accordingly, with the activation of muscle activity, the adaptation of fibers to changes in living conditions can be aimed at splitting large myofibrils into several small ones.

In the case of splitting of myofibrils, their mass remains unchanged, however, their number increases and, accordingly, the surface area of ​​myofibrils increases, which must inevitably be accompanied by an increase in the volume of the sarcoplasmic reticulum. That is, muscle cell hypertrophy occurs without an increase in the volume of contractile proteins - sarcoplasmic hypertrophy is observed. Bearing in mind that the volume of the muscle fiber sarcoplasm can be increased both due to the accumulation of various substances responsible for the energy production of the cell, and due to the splitting of myofibrils in the process of ergonomic adaptation to an increasing amount of work, we can say that sarcoplasmic hypertrophy is an adaptive response of muscles to an increase in the amount of work performed regularly by the muscles.

From the above brief analysis, it becomes clear that there are no special specific training methods aimed solely at increasing muscle volume.

Muscle hypertrophy, to one degree or another, is promoted by the previously considered training methods aimed at developing strength (due to the development of contractile structures) and muscle strength endurance (sarcoplasmic hypertrophy). More precisely, the development of a number of cellular structures can contribute to the development of such muscle qualities as strength, strength endurance and volume (see Fig. 1)

Rice.

As you understand, to maximize the development of strength, endurance, muscle volume, you should use training that affects all the main factors that contribute to the development of relevant qualities.

Muscles, contracting or tensing, produce work. It can be expressed in the movement of the body or its parts. Such work is done by lifting weights, walking, running. This is dynamic work. When holding parts of the body in a certain position, holding a load, standing, maintaining a posture, static work is performed. The same muscles can perform both dynamic and static work.

By contracting, the muscles move the bones, acting on them as levers. The bones begin to move around the fulcrum under the influence of the force applied to them.

Movement in any joint is provided by at least two muscles acting in opposite directions. They are called flexor muscles and extensor muscles. For example, when the arm is flexed, the biceps brachii contracts and the triceps relaxes. This is because excitation of the biceps through the central nervous system simultaneously causes relaxation of the triceps.

The work of the muscles is controlled by the nervous system, it ensures the consistency of their actions, adapts their work to the real situation, makes it economical. Scientists have found that the activity of human skeletal muscles has a reflex character. Involuntary withdrawal of a hand from a hot object, respiratory movements, walking, various labor movements - all these are motor reflexes of varying complexity.

Without work, muscles atrophy over time. However, if the muscles work without rest, their fatigue occurs. This is a normal physiological phenomenon. After rest, muscle performance is restored.

The development of muscle fatigue is primarily associated with the processes occurring in the central nervous system. Fatigue also contributes to the accumulation in the muscle during the work of metabolic products. During rest, the blood carries away these substances, and the performance of muscle fibers is restored.

The rate of development of fatigue depends on the state of the nervous system, the rhythm of work, the magnitude of the load, and the fitness of the muscles.

Regular sports, physical labor contribute to an increase in muscle volume, an increase in their strength and performance.

Smooth muscles: structure and work. Smooth muscles are part of the walls of internal organs: the stomach, intestines, uterus, bladder and others, as well as most blood vessels. Smooth muscles contract slowly and involuntarily. They are composed of small uninuclear spindle-shaped cells.

The basis of smooth muscle contractility, as well as striated muscle, is the interaction of actin and myosin proteins. However, the actin and myosin filaments are not arranged in smooth muscle cells in the same order as in striated ones. The sliding speed of actin relative to myosin is small: 100 times less than in striated muscles. Therefore, smooth muscles contract so slowly - within tens of seconds. But thanks to this, they can remain in a reduced state for a very long time.

With a short cessation of work, i.e., during rest, the performance of the muscles is quickly restored, since the blood removes harmful metabolic products from them. In trained people, this happens very quickly. In people who do not strain their body with physical exercises, the blood flow in the muscles is weaker, so the metabolic products are taken out slowly, and after physical exertion, people feel pain in the muscles for a long time.

• The muscles of trained people are capable of developing fantastic efforts. For example, a heavyweight athlete was able to squeeze a barbell weighing 2844 kg on his back. That's almost three tons! If a person is in a state of strong excitement, then his physical abilities sometimes reach an incredible level. During the earthquake in Japan, the mother pulled the child out of the rubble, lifting a concrete slab with her bare hands, which then could only be moved by a crane. How to strengthen your muscles? First, under the influence of constant training, muscle cells gradually increase in size. This occurs due to the active synthesis of new molecules of contractile proteins - actin and myosin. The larger the muscle cell, the more effort it is able to develop, which means that the muscles become stronger. Secondly, it is necessary to train the nerve centers that control the muscles so that these centers can simultaneously involve a larger number of muscle cells in the work. This process is called synchronous muscle activation.
• Even the simplest movements require the participation of a large number of muscles. For example, in order to take one step, a person needs to contract and relax about 300 muscles.

• The efficiency of the muscles is not very high, and a significant part of the energy expended by them goes to heat production. And it's not bad at all. After all, we need to maintain a constant body temperature.

  Where can you get heat? Here the muscles provide us with warmth. Remember, when we are cold, we start jumping up and down, clapping our hands, etc. In this way, we force the muscles to contract more intensively, which means they produce more heat.

Test your knowledge

1. 1. How do muscles do work?
2. What is dynamic work? static?
3. What is the work done while holding the load?
4. How do flexor and extensor muscles work?
5. Is it true that all muscular activity is reflex in nature? Justify your answer.
6. Why do muscles get tired?
7. What determines the rate of development of muscle fatigue?

Think

1. What is the difference between static and dynamic muscle work
2. Why is standing for a long time more tiring than walking?

By contracting or tensing, muscles do work. Distinguish between dynamic and static work. Movement in the joints is provided by at least two muscles that act opposite to each other. The work of the muscles is controlled by the nervous system, this work is reflex in nature.

1. How is the work of skeletal muscles?

In the implementation of the movement, usually several muscle groups are involved. Muscles that simultaneously produce movement in one direction in a given joint are called synergists (shoulder, biceps of the shoulder). Muscles that perform the opposite function (two-headed, triceps muscles of the shoulder) are antagonists. The work of different muscle groups occurs in concert: if the flexor muscles contract, then the extensor muscles relax during this time. In the coordination of movements, the main role belongs to the nervous system.

Muscles contract reflexively, i.e. under the action of nerve impulses from the central nervous system. Impulses coming along the nerve fiber cause excitation in the muscle fibers, which is manifested by their contraction. When performing voluntary movements, only those fibers that are directly excited by a nerve impulse are reduced. In human skeletal muscles, the muscle fibers are isolated from each other, and the excitation that occurs in one of them does not spread to the neighboring ones. Skeletal muscles are capable of very fast movements. In order for the muscle to be in a contracted state for a long time, the impulses come to it in whole series and follow with great frequency. Each next nerve impulse comes to the muscle before it has time to relax after the previous one.

Muscle work has an important feature. If the nerve impulse came to the muscle fiber and turned out to be able to cause its excitation, then the muscle fiber contracts with the maximum possible force for it. It cannot be reduced to half strength. Thus, the contraction force of the entire muscle does not depend on whether its individual fibers have contracted badly or well, but only on the total number of muscle fibers that have contracted at the moment.

2. How does muscle contraction occur?

Muscle contraction is based on the sliding of actin filaments between myosin filaments, which leads to shortening of the sarcomere, and hence the fiber. This process requires Ca 2+ ions and ATP energy. The striated muscle tissue contracts arbitrarily, under the influence of impulses coming along the nerve fiber.

3. What is the essence of muscle fatigue?

Fatigue is a temporary decrease in the working capacity of a cell, organ (including muscles), the body as a whole, which occurs as a result of work and disappears after rest. material from the site

Fatigue is associated, firstly, with the processes that develop in the nervous system, in the nerve centers (their fatigue) involved in the control of movement. Secondly, fatigue develops in connection with the processes that occur in the muscle itself (accumulation of metabolic products in it - lactic acid, etc.). Physical fatigue is a normal physiological phenomenon. After rest, working capacity is not only restored, but may also exceed the initial level. THEM. Sechenov showed that working capacity is restored faster with active rest than with complete rest. At the same time, temporary restoration of the working capacity of the muscle of the tired arm can be achieved by including the muscles of the other arm or the muscles of the lower extremities in the work. This once again proves that fatigue develops primarily in the nerve centers.

The rate of development of fatigue depends on the load and rhythm (heart rate). With an increase in load or with an increase in the rhythm, the load comes faster. Muscular work reaches its maximum level at medium loads and medium contraction speeds.

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On this page, material on the topics:

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Describe how muscles work. and got the best answer

Answer from Elena Novichenko[guru]
The main properties of muscle tissue are excitability, conductivity and contractility. Muscle work is based on these properties. Due to the contraction of the abdomen of the muscle, it shortens and the two points of attachment of the muscle converge (the movable point approaches the fixed one). As a result, movement occurs in this part of the body. The fixed point of muscle attachment is the beginning of the muscle, and the movable point is its end. The beginning of the muscles is close to the body or to its midline, and the end, on the contrary, is removed.
As a rule, several muscles are simultaneously involved in the execution of a movement. Muscles that simultaneously move in the same direction are called synergists (for example, the shoulder flexors). Muscles that perform movement in opposite directions are called antagonists (for example, flexor muscles - extensors of the shoulder).
Muscles work reflexively, that is, they contract under the influence of nerve impulses coming from the central nervous system along the axons of motor neurons to each muscle cell. Under the influence of a nerve impulse received by a muscle cell, an action potential arises in its membrane and calcium ions are released. Calcium ions trigger the entire mechanism of muscle cell contraction. Thus, a sufficient amount of calcium ions is an important condition for normal muscle function. For each individual nerve impulse, the muscle responds with a contraction. The nature of muscle contraction depends on the frequency of incoming nerve impulses and the duration of their arrival. Under natural conditions, the contracted muscle is in a state of tetanus (long-term strong contraction) at a frequency of 40-50 nerve impulses per second. Tetanus results from the summation of individual muscle contractions. At a frequency of 10 - 20 pulses / sec, the muscle is in a state of tone, i.e., some contraction, which is necessary to maintain the posture, the implementation of movements

Answer from Alisa Guziy[active]
Muscle work
Coordinated work of the flexor and extensor muscles. In the performance of any movement by a person, two groups of oppositely acting muscles take part: the flexors and extensors of the joints.
Flexion in the joint is carried out with the contraction of the flexor muscles and the simultaneous relaxation of the extensor muscles.
The coordinated activity of the flexor and extensor muscles is possible due to the alternation of the processes of excitation and inhibition in the spinal cord. For example, the contraction of the flexor muscles of the arm is caused by the excitation of the motor neurons of the spinal cord. Simultaneously, the extensor muscles relax. This is due to the inhibition of motor neurons.
The flexor and extensor muscles of the joint can simultaneously be in a relaxed state. So, the muscles of the hand hanging freely along the body are in a state of relaxation.
Muscle work. When contracting, the muscle acts on the bone as a lever and performs mechanical work. Any muscle contraction is associated with energy expenditure. The sources of this energy are the decay and oxidation of organic substances (carbohydrates, fats, nucleic acids). Organic substances in muscle fibers undergo chemical transformations in which oxygen is involved. As a result, cleavage products are formed, mainly carbon dioxide and water, and energy is released.
The blood flowing through the muscles constantly supplies them with nutrients and oxygen and carries away carbon dioxide and other decay products from them.

Answer from 3 answers[guru]

Hey! Here is a selection of topics with answers to your question: Describe how muscles work.

The movements of the human body are carried out due to the work of certain muscle groups. Muscles are associated with special nerve cells and their fibers. Each of the motor nerve cells, that is, each motor neuron, through its fibers, enters into communication with tens and hundreds of muscle fibers. When a motor neuron is excited, chemicals are released from the terminal part of its fiber, which, acting on the muscle fiber, excite it and, as a result, the muscle contracts, performing a certain job.

There are two types of skeletal muscle work: static and dynamic.

Static muscle work

As a result of the static work of the muscles, the human body and its individual parts are held for a certain time in the required position. This includes, for example, a straight stance, the position of arms laid aside or up, pre-launch position, etc. Static work does not set the body in motion, but only ensures that it is held in the desired position for a certain time (Fig. 20) .

Dynamic muscle work

As a result of the dynamic work of the muscles, the human body and its individual parts produce a variety of movements. For example, walking, running, jumping, pronunciation of words, etc. (Fig. 21, 22).

When the muscles perform work after a certain time, their fatigue occurs. The reason for this is as follows:

Firstly, fatigue of the nerve cells of the brain that regulate the work of muscles occurs as a result of their prolonged excitation, the processes of excitation in them decrease, the cells go into a state of inhibition.

Secondly, as a result of prolonged physical labor, the supply of food in the muscle fibers is depleted, and therefore the energy necessary to perform muscle work is also depleted.

Thirdly, when doing work for a short time, but at a high speed, oxygen starvation occurs in the body. material from the site

With the onset of fatigue, the force of contraction of muscle fibers begins to gradually decrease and the muscle fibers, more and more relaxing, stop contracting. As a result, the movement gradually slows down and then stops completely. Fatigued muscle fibers sometimes cannot relax after contraction, a condition called muscle contracture (or cramps). Sometimes when running fast, it is observed in the calf muscles.