What kind of muscle work is called dynamic. Muscles and their work

Goals: based on self-observation, form the concept of muscle work, the role of load and rhythm of work on the development of fatigue, and consolidate knowledge of physics.

b) educational: identifying human working conditions that increase
muscle performance.

c) developing - to continue developing students’ skills
compare, contrast, summarize facts from different fields of science and
transfer knowledge from one area of ​​activity to another.

Equipment: video fragment “Muscle work”, flashcards, dumbbells, dynamometer, stopwatch. Presentation (application)

Before the lesson, the class is divided into 5 groups of 5-6 people in each. Tasks on flashcards are completed in a group.

At the beginning of the lesson, a problematic question is posed to which students must answer:

“How do muscles do work?” “What determines muscle work and fatigue?

During the classes

a) the mechanism of muscle action.

In order to answer the first question, you need to remember from your physics course, what is work? What mechanisms are used to do work? Job- this is a contraction of a muscle during which it can lift or move any load. (A=mhn)

Now you remember what mechanical work is and you know that simple mechanisms called levers are used to perform it. Let's think about it, do we encounter levers in living nature? Give examples.

These figures show examples of the action of levers in the human body.

In the figure (Lever of the second kind, shows how we can hold a load in our hand. The weight of the load is balanced by the force of the muscle).

By contracting, the muscles move the bones, acting on them like 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 and extensor muscles. For example, when you flex your arm, the biceps brachii muscle contracts and the triceps brachii muscle relaxes. This occurs because stimulation of the biceps muscle through the central nervous system causes the triceps muscle to relax.

Skeletal muscles are attached to both sides of the joint and, when contracted, produce movement in it. Typically, the muscles that perform flexion - flexors - are located in front, and the muscles that perform extension - extensors - are located behind the joint. Only in the knee and ankle joints, the anterior muscles, on the contrary, produce extension, and the posterior muscles - flexion.

So, when muscles tense and contract, they do work. But does any mechanism require control? and any work requires a certain amount of energy.

To answer the first part of the question, let’s watch a fragment of the video.

So, what system regulates muscle function? (spinal cord and brain);

Where are the centers of muscle movement? (cerebral cortex; anterior central sulcus)

We found out which system controls muscle function. But you also know from your physics course that any work requires a certain amount of energy.

What energy does the muscles use? Striated muscles are “engines” in which chemical energy is converted into mechanical energy.

Where does the chemical energy in the muscles come from? Let's watch the video clip.

– in muscle fibers the breakdown of organic substances occurs with the participation of oxygen, as a result of which energy is released

It is known that muscles use 33% of chemical energy for movement, and 67% of energy is consumed in the form of heat. That is why in the cold a person tries to move more, warming himself up using the energy generated by the muscles.

b) Fatigue

Can a muscle work indefinitely? Why?

A temporary decrease in performance that occurs as a result of work is called fatigue. It has been established, however, that fatigue occurs primarily not in the muscle itself, but in the central nervous system. Metabolism in the nervous system and muscles changes temporarily. During prolonged work, substances accumulate that interfere with the conduction of excitation and muscle contraction. Rest is necessary to restore the functionality of parts of the nervous system and muscles. Muscle performance is directly proportional to the rate of fatigue. What factors influence the rate of muscle fatigue? - load size, type of work (staticor dynamic) and rhythm. To find out exactly how these factors affect muscle performance, you are encouraged to study this problem experimentally.

But first, let's find out what kind of experiences you would offer yourself.

In front of you are cards with an algorithm for working on the task, you are given 10 minutes.

(work in groups)

Practical work No. 1

"The influence of the magnitude of the load on the development of fatigue."

Exercise: Consistently bend your arm with dumbbells of different weights (1, 3, 6 kg) at the same speed. In each case, count the number of movements, note the time of onset of fatigue (per second) and calculate the work done (A = F S n, F = 1 kg = 10 N, 1 kg = 1 9.8 H = 10 N

where S is the distance; n is the number of movements.) Enter the data obtained into the table.

Conclusion: Maximum muscle performance is observed at medium load

Practical work No. 2

“The influence of work rhythm on the development of fatigue”

Exercise: Bend your arm with dumbbells of the same mass at different tempos: slow, medium and fast. Record the number of movements, the time of onset of fatigue and the work performed in the table.

Conclusion.The greatest performance and its

duration is traceable

at an average work pace.

Practical work No. 3

"The influence of the type of muscle contraction on the development of fatigue."

Exercise:

A) Take a load weighing 3-5 kg ​​and hold it with an outstretched arm at shoulder level. Notice the time when the hand begins to fall.

b) Take the same weight in your hand and raise it to the same level and lower it. note the time of fatigue in this case.

V) Compare dynamic and static work.

Conclusion: Muscles get tired faster when static, because when the muscle is in a monotonous position, decay products accumulate in it and the nervous system gets tired, resulting in pain.

For the body, static work is tiring because with prolonged static tension of the muscles, the blood vessels that feed them are compressed. Through compressed arteries, the supply of oxygen and nutrients to the muscles worsens, and through compressed veins, the outflow of blood containing decay products is disrupted.

During dynamic work, different muscle groups contract alternately. The nervous system, controlling the work of muscles, adapts their work to the current needs of the body. This allows them to work economically.

Practical work No. 4

“The influence of muscle training on the development of fatigue”

The ability of muscles to perform work depends on their training, which increases muscle strength and has a beneficial effect on the muscles and on the condition of the skeleton.
In this group, the work is carried out by two students: one is engaged in the sports section, the other - only in physical education lessons.

Conclusion. The better developed the muscles, the longer their work, despite the increase in load, and the slower the onset of fatigue.

Two people argued about how best to carry a load: alternately with the right and left hands without resting, or to carry it in the right hand, then rest and carry it again in the same hand?

Answer, when was the working condition of the right hand restored most quickly, during rest or when working with the left hand? What is the importance of active rest for the muscular system?

And now we will conduct another experiment - demonstrating experiments with a dynamometer.

On the desk:

I Right hand rest 30 sec Right hand
II Right hand left Right hand

What's the conclusion? - The right hand rests better when the left hand works, because the excitement that occurs when the left hand works causes an inhibition process in the centers of the right hand of the brain, and the rest of the right hand becomes more complete. The Russian scientist physiologist, creator of the well-known work “Reflexes of the Brain,” worked on studying the influence of various factors on human performance. is the creator of “Physiology of Labor”.

The functionality of the right is restored faster
hands when working with the left hand. Active leisure faster
relieves fatigue of the muscles that were taken
participation in work

(For muscle function, nerve impulses and energy are required, which is generated as a result of the oxidation of organic substances in the presence of oxygen.)

Testing the assimilation of new material

Why does your back get more tired than your arms when washing clothes by hand?

The back muscles function in a static mode, that is, they help maintain the same posture for a long time. With static force, the muscles are in a state of tension. With the simultaneous contraction of many muscle fibers, the work cannot be very long - the muscles get tired. Hands do dynamic work. The muscles contract alternately.

1. What does muscle work depend on?

2. What is fatigue?

3. What conditions influence the development of fatigue?

4. What is used to restore muscle performance? What does a sedentary lifestyle lead to?

Muscle work is a necessary condition for their life. Prolonged inactivity of muscles leads to their atrophy and loss of performance. Training muscles helps increase their volume, strength and performance, which affects the development of the entire body. Think about whether there is enough physical activity in your daily routine.

Grades are given for independent answers and the work of each group.

Homework.

Think about and create physical exercises that would develop different muscle groups to maintain proper posture and muscle performance.

1.Structure and functions of striated muscle cells.

Cardiac striated muscle tissue found in the muscular lining of the heart (myocardium) and the mouths of the large vessels associated with it. The main functional property of cardiac muscle tissue is the ability for spontaneous rhythmic contractions, the activity of which is influenced by hormones and the nervous system. This tissue enables the heart to contract, which keeps blood circulating throughout the body. The source of development of cardiac muscle tissue is myoepicardial plate of the visceral layer of the splanchnotome (coelomic lining in the cervical part of the embryo). The cells of this plate (myoblasts) actively multiply and gradually turn into cardiac muscle cells - cardiomyocytes (cardiac myocytes). Arranging in chains, cardiomyocytes form complex intercellular connections - insert discs, connecting them in cardiac muscle fibers. Mature cardiac muscle tissue is formed by cells - cardiomyocytes, connected to each other in the area of ​​​​the intercalary discs and forming a three-dimensional network of branching and anastomosing cardiac muscle fibers.

Structure.

The structural element of striated muscle tissue is no longer a cell, but a fiber, which can easily be isolated during maceration. The fiber has the shape of a cylinder with a flat, smooth surface and rounded ends. In the muscle, the fibers are arranged longitudinally, and their length varies and in some cases reaches 12.5 cm. In short muscles it coincides with their length, but in long muscles the fibers usually end before reaching their end. The thickness of the fibers ranges from 10 to 100 microns. The outside of the muscle is covered with sarcolemma (sarcos - meat, lemma - shell). The plasma membrane of the sarcolemma protrudes into the cytoplasm (sarcoplasm) of the fiber at certain intervals, crossing it. The system of transverse tubes thus formed is called the T-system. This structure contributes to the rapid propagation of the impulse in the muscle fiber. The bulk of the muscle fiber consists of myofibrils located in the cytoplasm, which in the muscle fiber has received the special name sarcoplasm. There are many nuclei in the fiber, the number of which, depending on the length of the fiber, reaches several tens and even hundreds. But, despite this, the total mass of the nuclei is small compared to the mass of the fiber.

The mechanism of muscle fiber contraction.

In resting muscle fibers in the absence of motor neuron impulses, myosin cross bridges are not attached to actin myofilaments. Tropomyosin is positioned in such a way that it blocks areas of actin that can interact with myosin cross bridges. Troponin inhibits myosin-ATPase activity and therefore ATP is not broken down. The muscle fibers are in a relaxed state.

When a muscle contracts, the length of the A-discs does not change, the J-discs shorten, and the H-zone of the A-discs may disappear (Fig. 4.3.).

Fig.4.3. Muscle contraction. A - Cross bridges between actin and myosin are open. The muscle is in a relaxed state. B - Closure of cross bridges between actin and myosin. The heads of the bridges perform rowing movements towards the center of the sarcomere. Sliding of actin filaments along myosin filaments, shortening of the sarcomere, development of traction.

These data formed the basis for the creation of a theory explaining muscle contraction by the sliding mechanism (sliding theory) thin actin myofilaments along thick myosin ones. As a result, myosin myofilaments are retracted between the surrounding actin ones. This leads to shortening of each sarcomere, and therefore the entire muscle fiber.

Distinctive features of white and red muscle fibers.

White muscle fibers are fast.

Red muscle fibers are slow.

2. Muscle work.

When muscles contract or tense, they produce work. It can be expressed in the movement of the body or its parts. This kind of work is done when lifting weights, walking, running. This is a dynamic job. When holding parts of the body in a certain position, holding a load, standing, maintaining a pose, static work is performed. The same muscles can perform both dynamic and static work.

By contracting, the muscles move the bones, acting on them like 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 and extensor muscles. For example, when you flex your arm, the biceps brachii muscle contracts and the triceps brachii muscle relaxes. This occurs because stimulation of the biceps muscle through the central nervous system simultaneously causes relaxation of the triceps muscle.

The work of muscles is controlled by the nervous system, it ensures the consistency of their actions, adapts their work to the real situation, and makes it economical. Scientists have found that the activity of human skeletal muscles is of a reflex nature. Involuntary withdrawal of the hand from a hot object, breathing 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, they become fatigued. This is a normal physiological phenomenon. After rest, muscle performance is restored.

The rate at which fatigue develops depends on the state of the nervous system, the rhythm of work, the magnitude of the load, and muscle fitness.

Constant exercise and physical labor help to increase muscle volume, increase their strength and performance.

Dependence of muscle work and power on load.

Since the main task of skeletal muscles is to perform muscle work, in experimental and clinical physiology they evaluate the amount of work that a muscle does and the power it develops during work.

According to the laws of physics, work is the energy expended to move a body with a certain force over a certain distance: A = FS. If a muscle contraction occurs without load (in isotonic mode), then the mechanical work is zero. If at maximum load the muscle does not shorten (isometric mode), then the work is also zero. In this case, chemical energy is completely converted into thermal energy.

According to the law of average loads, a muscle can perform maximum work under average loads.

When contracting skeletal muscles in natural conditions, mainly in the mode of isometric contraction, for example, with a fixed position, they speak of static work; when performing movements, they speak of dynamic work.

The force of contraction and the work done by the muscle per unit time (power) do not remain constant during static and dynamic work. As a result of prolonged activity, the performance of skeletal muscles decreases. This phenomenon is called fatigue. At the same time, the force of contraction decreases, the latent period of contraction and the period of relaxation increase.

The static mode of operation is more tiring than the dynamic one. Fatigue of an isolated skeletal muscle is primarily due to the fact that in the process of performing work, products of oxidation processes accumulate in the muscle fibers - lactic and pyruvic acids, which reduce the possibility of generating PD. In addition, the processes of resynthesis of ATP and creatine phosphate, necessary for the energy supply of muscle contraction, are disrupted. Under natural conditions, muscle fatigue during static work is mainly determined by inadequate regional blood flow. If the contraction force in isometric mode is more than 15% of the maximum possible, then oxygen “starvation” occurs and muscle fatigue progressively increases.

In real conditions, it is necessary to take into account the state of the central nervous system - a decrease in the force of contractions is accompanied by a decrease in the frequency of neuronal impulses, due to both their direct inhibition and the mechanisms of central inhibition. Back in 1903, I.M. Sechenov showed that the restoration of the performance of tired muscles of one hand is significantly accelerated when performing work with the other hand during the rest period of the first. Unlike simple rest, such rest is called active.

The performance of skeletal muscles and the rate of development of fatigue depend on the level of mental activity: a high level of mental stress reduces muscle endurance.

Static and dynamic work.

During static work, muscle contraction is not associated with the movement of body parts. For example, the muscles that provide the posture of a sitting or standing person perform static work. Dynamic work is when individual parts of the human body move. Human physical activity consists of static and dynamic work. It should be noted that during static work, load tolerance depends on the functional state of certain muscle groups, and during dynamic work, it also depends on the efficiency of the systems that supply energy (cardiovascular, respiratory), as well as on their interaction with other organs and systems. The maximum tension, as well as the maximum time of tension that a certain muscle group is capable of developing and maintaining, depend on its local functional power. Under dynamic work conditions, endurance and maximum power are determined by the efficiency of energy production mechanisms and their consistency with other functional systems of the body. The work can be local, regional and general. If up to a third of the total muscle mass of the body is involved in the work, then it is designated as local. Regional work involves one-third to two-thirds of the entire body's muscles. When activating even more muscle mass, the work is defined as general. Of practical importance is the classification of the intensity of muscle work depending on energy consumption, based on the maximum aerobic capabilities of the subject. The maximum of aerobic capacity is most fully characterized by the maximum of oxygen consumption - (aerobic power).

Question 1. How do muscles do work?

When muscles contract or tense, they produce work. It can be dynamic or static.

Question 2. What kind of work is called dynamic? static?

Muscle work can be expressed in the movement of the body or its parts. The kind of work that is done when lifting weights, walking, running is dynamic work. When holding parts of the body in a certain position, holding a load, standing, maintaining a pose, static work is performed. The same muscles can perform both dynamic and static work.

Question 3. What work is done when holding the load?

When holding a load, static work is performed.

Question 4. How do flexor and extensor muscles work?

For example, when you flex your arm, the biceps brachii (flexor muscle) contracts and the triceps brachii (extensor muscle) relaxes. At the same time, the arm bends. This occurs because stimulation of the biceps muscle through the central nervous system simultaneously causes relaxation of the triceps muscle. Conversely, when the arm is extended, the biceps brachii muscle (flexor muscle) relaxes, and the triceps muscle (extensor muscle) contracts. At the same time, the arm extends.

Question 5. Is it true that all muscle activity is reflexive in nature? Justify your answer.

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

Question 6. Why do muscles get tired?

If muscles work without rest, they become fatigued. This is a normal physiological phenomenon. After rest, muscle performance is restored.

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

Question 7. What determines the rate of development of muscle fatigue?

The rate at which fatigue develops depends on the state of the nervous system, the rhythm of work, the magnitude of the load, and muscle fitness.

THINK

1. What is the difference between static and dynamic muscle work?

In either case, the muscles still do the work. But during dynamic work, muscles move the human body (in motion, walking, swimming, lifting weights, etc.), they contract and produce energy. And during static work, the muscles “froze” (maintaining a stable body position in a motionless state) in one position. During static work, muscles get tired faster.

2. Why is standing for a long time more tiring than walking?

When standing, the same muscle groups are under tension and waste energy (static load is more energy-intensive than motor), and for example, when walking, the flexor and extensor muscles work alternately and have time to rest.

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Muscle work and strength

Body movement occurs due to muscle contraction. When muscles contract, they do work. When muscles contract, the bones move closer or further away, moving the body or its parts, lifting or holding a load. The muscles that provide movement are divided into flexors And extensors , adductors and abductors, rotating the bone clockwise and counterclockwise.

The same muscle cannot bend and straighten bones in a joint, and the movement of the bones and with them parts of the body is produced by at least two muscles (in fact, there are much more of them). The muscles are not always located where their force is applied.

Amplitude- the range of movements depends on the length of the muscle fibers, and the strength depends on the cross-sectional area of ​​the muscle bundle. To bend the hand into a fist, the muscles must be of sufficient length. That is why the muscles that flex and extend the fingers are located on the forearm, the muscles that lower and raise the shoulder are on the torso, etc. The muscles of the opposite action are called antagonists , and muscles acting in one direction synergists . They work in harmony.

When the flexor muscles contract, the extensor muscles relax. When the extensors contract, the flexors relax. The somatic part of the nervous system regulates the work of skeletal muscles.

Both muscle groups can be simultaneously in a relaxed state (arms hang freely along the body). When holding weights with outstretched arms, the flexor and extensor muscles work together to press the bones together. Here they act as synergists.

Any work involves energy consumption. The source of energy in the body is biological oxidation and breakdown of organic substances. When muscles contract, energy consumption and waste of organic substances, most often glucose, increase.

Muscle fatigue

During work, harmful substances accumulate in the muscles. Long, continuous, monotonous work causes muscle fatigue. After rest, fatigue goes away, the muscles are again able to contract and produce work. Why is this happening?

When the muscles rest, the blood removes harmful substances from the cells. Rest is necessary to restore muscle strength.

A person’s performance and productivity depend on his ability to organize his working time. A large load on the muscles, frequent, fussy movements quickly lead to fatigue. When performing physical work, it is necessary to observe the averages, i.e. optimal rhythm and load. The optimal work rhythm and load are determined by a person’s age, physical and professional preparedness. Each person, by improving their professional skills, can increase their productivity. Physical education and sports have a beneficial effect on improving a person’s performance.

Dynamic and static muscle work

Work associated with moving a body or load in space is called dynamic , and work related to holding a certain position or load - static . To determine which of them causes muscle fatigue faster, we will conduct an experiment.

Take a briefcase with books, time it with a stopwatch and hold the briefcase in your outstretched hand for as long as you can.

At first the hand is motionless. Then she imperceptibly begins to descend and rises with a jerk. This is the first sign of fatigue. The face turns red. The hand begins to tremble. At the end of the experience, noticeable trembling may begin. Coordination of movements decreases. The body may sway and the briefcase may fall out of your hand. Finally, the hand with the briefcase lowers. The experiment is over.

As a rule, it is not possible to hold the load for long, and fatigue sets in quickly. If you relax and do dynamic work: raising and lowering the briefcase to the level of the mark, it turns out that this work can be done for much longer without noticeable signs of fatigue.

With static work, all muscles that usually work as antagonists are involved in action, but with dynamic work, they work in turn: first some, then others. In addition, during static work, the blood supply to the muscles is often difficult, because some vessels are compressed. This does not happen during dynamic operation. Moreover, the movement of muscles accelerates the outflow of blood from them, saturated with carbon dioxide and other decay products.

During dynamic work, fatigue occurs later if the load is average and the work proceeds at an average rhythm, that is, not too fast and not too slow. For each person, the required rhythm of work and optimal load are selected individually, depending on their physical condition and health.

You need to be able to work and rest correctly: take short breaks, switching from one type of activity to another. Alternating physical and mental stress relieves fatigue and increases performance.

When contracting, the muscles do work: they bend or straighten the bones in the joint, abduct or bring them towards each other, and rotate. Muscles acting in one direction are called synergists, and those in opposite directions are called antagonists. The somatic part of the nervous system regulates muscle function. The energy due to which contraction occurs is released as a result of biological oxidation of the organic substances of the muscle itself. There are static and dynamic work. The greatest effect of dynamic work is achieved with average (optimal) loads and an average rhythm. Static work is more tiring than dynamic work. Strength, endurance and speed of muscle work increase with training.