Types of rations Below are brief description nutrients included in ready-made diets that go on sale (Table.

Chapter 6. Types of digestion While writing this chapter, I repeatedly turned to reference literature, but, frankly, the deeper I delved into the essence of the problem, the more contradictions I found in the descriptions of digestive processes. I believe that this state of affairs is due

Strengthening exercises muscle corset spine in the early stages of spondylosis. When spondylosis is localized in the cervical region, it should be used as widely as possible. isometric exercises, described in the treatment section cervical osteochondrosis. Not recommended

There are three modes of muscle contraction:

Isotonic;

Isometric;

Mixed (auxometric).

The isotonic mode of muscle contraction is characterized by a predominant change in length muscle fiber, without a significant change in voltage. This mode of muscle contraction is observed, for example, when lifting light and medium weight loads.

The isometric mode of muscle contraction is characterized by a predominant change in muscle tension, without a significant change in length. An example would be changes in the state of the muscles when a person tries to move a large object (for example, when trying to move a wall in a room).

Mixed (auxometric) type of muscle contraction, the most realistic, most common option. Contains components of the first and second options in different proportions depending on actual environmental conditions.

Types of muscle contraction

There are three types of muscle contraction:

Single muscle contraction;

Tetanic muscle contraction (tetanus);

Tonic muscle contraction.

In addition, tetanic muscle contraction is divided into serrated and smooth tetanus.

A single muscle contraction occurs under conditions of action on the muscle of threshold or suprathreshold electrical stimuli, the interpulse interval of which is equal to or greater than the duration of a single muscle contraction. In a single muscle contraction, three time periods are distinguished: latent period, shortening phase and relaxation phase (see Fig. 3).

Rice. 3 Single muscle contraction and its characteristics.

LP – latent period, FU – shortening phase, FR – relaxation phase

Tetanic muscle contraction (tetanus) occurs when the skeletal muscle is exposed to a threshold or suprathreshold electrical stimulus, the interpulse interval of which is less than the duration of a single muscle contraction. Depending on the duration of the interstimulus intervals of the electrical stimulus, either jagged or smooth tetanus may occur when exposed to it. If the interpulse interval of the electrical stimulus is less than the duration of a single muscle contraction, but greater than or equal to the sum of the latent period and the shortening phase, serrated tetanus occurs. This condition is met when the frequency of the pulsed electrical stimulus increases in a certain range.

If the duration of the interpulse interval of the electrical stimulus is less than the sum of the latent period and the shortening phase, smooth tetanus occurs. In this case, the amplitude of smooth tetanus is greater than the amplitude of both single muscle contraction and serrated tetanic contraction. With a further decrease in the interpulse interval of the electrical stimulus, and therefore with an increase in frequency, the amplitude of tetanic contractions increases (see Fig. 4).

Rice. 4 Dependence of the shape and amplitude of tetanic contractions on the frequency of the stimulus. – the beginning of the action of the stimulus, - the end of the action of the stimulus.

However, this pattern is not absolute: at a certain frequency value, instead of the expected increase in the amplitude of smooth thetatnus, the phenomenon of its decrease is observed (see Fig. 5). This phenomenon was first discovered by the Russian scientist N.E. Vvedensky and was called pessimum. According to N.E. Vvedensky, the basis of pessimal phenomena is the mechanism of inhibition.

Rice. 5. Dependence of the amplitude of smooth tetanus on the frequency of the stimulus. The designations are the same as in Figure 5.

The contraction is isometric, in which the length of the muscle fibers remains unchanged, but their tension increases.

Large medical dictionary. 2000 .

See what “isometric contraction” is in other dictionaries:

Contraction of a muscle, expressed in increasing its tension while maintaining a constant length (for example, contraction of a muscle of a limb, both ends of which are fixed motionless). In the body to I. m.s. the tension developed by the muscle when attempting... is approaching.

ISOMETRIC CONTRACTION (or CRAMP)- A contraction of a muscle that causes tension but no movement, as when pushing against a wall - there is no actual contraction of the muscle, and its length does not change... Explanatory dictionary of psychology

isometric muscle contraction- izometrinis raumens susitraukimas statusas T sritis Kūno kultūra ir sportas apibrėžtis Raumens susitraukimas, kurio metu raumens ilgis beveik nekinta, tik patrumpėja sutraukiančios raumenį skaidulėlės – miofibrilės, tiek pat ištempdamos… …Sporto terminų žodynas

Isometric contraction- (Greek isos - equal, identical, similar; metron - measure) contraction of a muscle with its tension, which, however, did not entail movement and shortening of the muscle. See: Cramps... Encyclopedic Dictionary of Psychology and Pedagogy

Isometric contraction- muscles (isometricus, from the Greek isos equal + metron, meron size, measure) - muscle contraction, when its length remains constant, does not change ...

Isometric contraction m.- (isos equal + metron measure, size) – muscle contraction, in which the length of the muscle fibers remains unchanged, but tension and tone increase... Glossary of terms on the physiology of farm animals

Contraction of a muscle under constant tension, expressed in a decrease in its length and an increase cross section. In the body I. m.s. is not observed in its pure form. To purely I. m.s. movement of the unloaded limb is approaching; at… … Great Soviet Encyclopedia

Shortening or tension of muscles in response to irritation caused by motor discharge. neurons. The M. s model has been adopted, according to which, when the surface of the muscle fiber membrane is excited, the action potential first spreads through the system... ... Biological encyclopedic dictionary

MUSCLE CONTRACTION- main function muscle tissue shortening or tightening of muscles in response to irritation caused by the shock motor neurons. M. s. is the basis of all movements human body. There are M. s. isometric, when the muscle develops force... ... Psychomotorics: dictionary-reference book

MUSCLES- MUSCLES. I. Histology. Generally morphologically, the tissue of the contractile substance is characterized by the presence of differentiation of its specific elements in the protoplasm. fibrillar structure; the latter are spatially oriented in the direction of their reduction and... ... Great Medical Encyclopedia

When executing strength exercises in various operating modes.

Definition

Isometric muscle work mode

Overcoming mode of muscle work (concentric mode of muscle work)

The muscle works in overcoming mode, if her length decreases. As an example - bending the arm in elbow joint holding a dumbbell in his hand. Overcoming mode is muscle work. When working in this mode, the force developed by the muscles is greater than the external force (it would be more correct, of course, to say that the moment of force developed by the muscles is greater than the moment of the external force). The muscle seems to “overcome” the external load. In English literature this mode of muscle contraction is called concentric.

Inferior mode of muscle work (eccentric mode of muscle work)

The muscle works in inferior mode, If its length increases. As an example, extend the arm at the elbow joint while holding a dumbbell in your hand. Yielding mode is a type of dynamic mode. When working in this mode, the force developed by the muscle is less than the moment of external force (it would be more correct to say the moment of muscle force is less than the external moment of force). The muscle seems to “give way” to the external force. In English-language literature this mode is called eccentric mode muscle work.

Various modes of muscle work are illustrated in Fig. 1 and Fig. 2.

Attention should be paid to the fact that antagonist muscles work in different modes when performing movements. For example, when bending an arm, the flexor muscles shorten (overcoming mode), and the extensor muscles (their antagonists) lengthen (yielding mode).

Changes that occur in muscles directly or immediately after a training session (acute training effect)

Numerous studies have proven that the implementation physical exercise in eccentric (yielding mode, when the muscle lengthens) mode causes b O greater structural damage to muscle fibers than other modes of muscle contraction. These damages primarily affect the Z-disks of sarcomeres, as well as cytoskeletal proteins.

From a biochemical point of view, eccentric exercises (exercises performed in an eccentric mode) pose a significant impact on the body. O greater stress than exercise performed in other modes: the level of creatine kinase in the blood (an enzyme contained in muscle fibers and released into the blood when they are destroyed) when working in the eccentric mode is significantly higher than the corresponding indicator when working in the concentric (overcoming) and isometric modes.

If you measure muscle strength after performing exercises in the eccentric mode, it turns out that it decreases significantly more than when performing exercises in the concentric mode. What does this mean? This suggests that more muscle fibers are damaged in the eccentric mode.

Changes that occur in muscles after long-term exercise (cumulative training effect)

It has been shown that long-term adaptation of skeletal muscles to exercises performed in an eccentric mode manifests itself in several O greater hypertrophy of skeletal muscles compared to other modes. Eccentric strength training results in increased skeletal muscle strength and stiffness.

When performing strength exercises in isometric mode the degree of overlap of muscle and tendon fibers increases, the tendon thickens somewhat and the area of ​​attachment of the tendon to the bone increases. That is why it is recommended to perform isometric exercises at the end of the workout (about 15 minutes). It is believed that this can reduce the number of injuries to the human musculoskeletal system.

If a muscle contracts in a dynamic mode (concentric or eccentric mode), after some time the length of the muscle fibers increases and the length of the tendon decreases. Computer modeling (U. Proske, D.L. Morgan, 2001) confirmed the feasibility of lengthening the muscle part and shortening the tendon part. The authors showed that long-term adaptation to performing eccentric exercises is manifested in an increase in the number of sarcomeres in the myofibrils of muscle fibers and a decrease in the tendon part. This leads to a change in the optimal length of the muscle when active tension develops.

When performing strength exercises in a dynamic mode (concentric or eccentric), the number of nerve fibers innervating the skeletal muscle increases (4-5 times more than in the isometric mode).

Literature

1. Samsonova A.V., Barnikova I.E., Azanchevsky V.V. The influence of strength training performed in various contraction modes on the hypertrophy of human skeletal muscles // Proceedings of the department. biomechanics. Sat. articles /Ed. A.V. Samsonova. V.N. Tomilova. - St. Petersburg, 2010. - P. 115-131.

Muscle contraction is a vital function of the body associated with defensive, respiratory, nutritional, sexual, excretory and other physiological processes. All types of voluntary movements - walking, facial expressions, movements eyeballs, swallowing, breathing, etc. are carried out by skeletal muscles. Involuntary movements (except for heart contraction) - peristalsis of the stomach and intestines, changes in the tone of blood vessels, maintenance of bladder tone - are caused by contraction smooth muscles. The work of the heart is ensured by the contraction of the cardiac muscles.

Structural organization of skeletal muscle

Muscle fiber and myofibril (Fig. 1). Skeletal muscle consists of many muscle fibers that have points of attachment to bones and are located parallel to each other. Each muscle fiber (myocyte) includes many subunits - myofibrils, which are built from blocks (sarcomeres) repeating in the longitudinal direction. The sarcomere is the functional unit of the contractile apparatus of skeletal muscle. The myofibrils in the muscle fiber lie in such a way that the location of the sarcomeres in them coincides. This creates a pattern of cross striations.

Sarcomere and filaments. Sarcomeres in the myofibril are separated from each other by Z-plates, which contain the protein beta-actinin. In both directions, thin actin filaments. In the spaces between them there are thicker myosin filaments.

Actin filament externally resembles two strings of beads twisted into a double helix, where each bead is a protein molecule actin. Protein molecules lie in the recesses of actin helices at equal distances from each other. troponin, connected to thread-like protein molecules tropomyosin.

Myosin filaments are formed by repeating protein molecules myosin. Each myosin molecule has a head and tail. The myosin head can bind to an actin molecule, forming a so-called cross bridge.

The cell membrane of the muscle fiber forms invaginations ( transverse tubules), which perform the function of conducting excitation to the membrane of the sarcoplasmic reticulum. Sarcoplasmic reticulum (longitudinal tubules) It is an intracellular network of closed tubes and performs the function of depositing Ca++ ions.

Motor unit. The functional unit of skeletal muscle is motor unit(DE). MU is a set of muscle fibers that are innervated by the processes of one motor neuron. Excitation and contraction of the fibers that make up one motor unit occur simultaneously (when the corresponding motor neuron is excited). Individual motor units can be excited and contracted independently of each other.

Molecular mechanisms of contractionskeletal muscle

According to thread sliding theory, muscle contraction occurs due to the sliding movement of actin and myosin filaments relative to each other. The thread sliding mechanism involves several sequential events.

Myosin heads attach to actin filament binding centers (Fig. 2, A).

The interaction of myosin with actin leads to conformational rearrangements of the myosin molecule. The heads acquire ATPase activity and rotate 120°. Due to the rotation of the heads, the actin and myosin filaments move “one step” relative to each other (Fig. 2, B).

Disconnection of actin and myosin and restoration of the head conformation occurs as a result of the attachment of an ATP molecule to the myosin head and its hydrolysis in the presence of Ca++ (Fig. 2, B).

The cycle “binding – change in conformation – disconnection – restoration of conformation” occurs many times, as a result of which actin and myosin filaments are displaced relative to each other, the Z-disks of sarcomeres come closer and the myofibril is shortened (Fig. 2, D).

Pairing of excitation and contractionin skeletal muscle

In the resting state, thread sliding in the myofibril does not occur, since the binding centers on the actin surface are closed by tropomyosin protein molecules (Fig. 3, A, B). Excitation (depolarization) of the myofibril and muscle contraction itself are associated with the process of electromechanical coupling, which includes a series of sequential events.

As a result of the activation of a neuromuscular synapse on the postsynaptic membrane, an EPSP arises, which generates the development of an action potential in the area surrounding the postsynaptic membrane.

Excitation (action potential) spreads along the myofibril membrane and, through a system of transverse tubules, reaches the sarcoplasmic reticulum. Depolarization of the sarcoplasmic reticulum membrane leads to the opening of Ca++ channels in it, through which Ca++ ions enter the sarcoplasm (Fig. 3, B).

Ca++ ions bind to the protein troponin. Troponin changes its conformation and displaces the tropomyosin protein molecules that covered the actin binding centers (Fig. 3, D).

Myosin heads attach to the opened binding centers, and the contraction process begins (Fig. 3, E).

The development of these processes requires a certain period of time (10–20 ms). The time from the moment of excitation of a muscle fiber (muscle) to the beginning of its contraction is called latent period of contraction.

Skeletal muscle relaxation

Muscle relaxation is caused by the reverse transfer of Ca++ ions through the calcium pump into the channels of the sarcoplasmic reticulum. As Ca++ is removed from the cytoplasm open centers binding becomes less and less and eventually the actin and myosin filaments are completely disconnected; muscle relaxation occurs.

Contracture called a persistent, long-term contraction of a muscle that persists after the cessation of the stimulus. Short-term contracture may develop after tetanic contraction as a result of accumulation in the sarcoplasm large quantity Ca++ ; long-term (sometimes irreversible) contracture can occur as a result of poisoning and metabolic disorders.

Phases and modes of skeletal muscle contraction

Phases of muscle contraction

When irritating a skeletal muscle with a single impulse electric current superthreshold force, a single muscle contraction occurs, in which 3 phases are distinguished (Fig. 4, A):

latent (hidden) contraction period (about 10 ms), during which the action potential develops and electromechanical coupling processes occur; muscle excitability during a single contraction changes in accordance with the phases of the action potential;

shortening phase (about 50 ms);

relaxation phase (about 50 ms).

Rice. 4. Characteristics of a single muscle contraction. Origin of serrated and smooth tetanus. B– phases and periods of muscle contraction, B– modes of muscle contraction that occur at different frequencies of muscle stimulation. Change in muscle length shown in blue, muscle action potential- red, muscle excitability- purple.

Modes of muscle contraction

Under natural conditions, a single muscle contraction is not observed in the body, since a series of action potentials occur along the motor nerves innervating the muscle. Depending on the frequency of nerve impulses coming to the muscle, the muscle can contract in one of three modes (Fig. 4, B).

Single muscle contractions occur at low frequency electrical impulses. If the next impulse enters the muscle after the completion of the relaxation phase, a series of successive single contractions occurs.

At a higher impulse frequency, the next impulse may coincide with the relaxation phase of the previous contraction cycle. The amplitude of contractions will be summed up, and there will be serrated tetanus- prolonged contraction, interrupted by periods of incomplete muscle relaxation.

With a further increase in the pulse frequency, each subsequent pulse will act on the muscle during the shortening phase, resulting in smooth tetanus- prolonged contraction, not interrupted by periods of relaxation.

Optimum and pessimum frequency

The amplitude of tetanic contraction depends on the frequency of impulses irritating the muscle. Optimum frequency they call the frequency of irritating impulses at which each subsequent impulse coincides with the phase of increased excitability (Fig. 4, A) and, accordingly, causes tetanus of the greatest amplitude. Pessimum frequency called a higher frequency of stimulation, at which each subsequent current pulse falls into the refractory phase (Fig. 4, A), as a result of which the amplitude of the tetanus decreases significantly.

Skeletal muscle work

The strength of skeletal muscle contraction is determined by 2 factors:

- the number of units involved in the reduction;

frequency of contraction of muscle fibers.

The work of skeletal muscle is accomplished through a coordinated change in tone (tension) and length of the muscle during contraction.

Types of skeletal muscle work:

• dynamic overcoming work occurs when a muscle, contracting, moves the body or its parts in space;

• static (holding) work performed if, due to muscle contraction, parts of the body are maintained in a certain position;

• dynamic yielding operation occurs when a muscle functions but is stretched because the force it makes is not enough to move or hold parts of the body.

During work, the muscle can contract:

• isotonic– the muscle shortens under constant tension (external load); isotonic contraction is reproduced only in experiment;

• isometrics– muscle tension increases, but its length does not change; the muscle contracts isometrically when performing static work;

• auxotonic– muscle tension changes as it shortens; auxotonic contraction is performed during dynamic overcoming work.

Rule of average loads– the muscle can perform maximum work under moderate loads.

Fatigue – physiological state muscle, which develops after prolonged work and is manifested by a decrease in the amplitude of contractions, an extension of the latent period of contraction and the relaxation phase. The causes of fatigue are: depletion of ATP reserves, accumulation of metabolic products in the muscle. Muscle fatigue during rhythmic work is less than synapse fatigue. Therefore, when the body performs muscular work, fatigue initially develops at the level of the synapses of the central nervous system and neuromuscular synapses.

Structural organization and reductionsmooth muscles

Structural organization. Smooth muscle consists of single spindle-shaped cells ( myocytes), which are located in the muscle more or less chaotically. Contractile filaments are arranged irregularly, as a result of which there is no transverse striation of the muscle.

The mechanism of contraction is similar to that of skeletal muscle, but the rate of filament sliding and the rate of ATP hydrolysis are 100–1000 times lower than in skeletal muscle.

The mechanism of coupling of excitation and contraction. When the cell is excited, Ca++ enters the cytoplasm of the myocyte not only from the sarcoplasmic reticulum, but also from the intercellular space. Ca++ ions, with the participation of the calmodulin protein, activate the enzyme (myosin kinase), which transfers the phosphate group from ATP to myosin. Phosphorylated myosin heads acquire the ability to attach to actin filaments.

Contraction and relaxation of smooth muscles. The rate of removal of Ca++ ions from the sarcoplasm is much less than in skeletal muscle, as a result of which relaxation occurs very slowly. Smooth muscles perform long tonic contractions and slow rhythmic movements. Due to the low intensity of ATP hydrolysis, smooth muscles are optimally adapted for long-term contraction, which does not lead to fatigue and high energy consumption.

Physiological properties of muscles

The general physiological properties of skeletal and smooth muscles are excitability And contractility. Comparative characteristics of skeletal and smooth muscles are given in table. 6.1. Physiological properties and features of the cardiac muscle are discussed in the section “Physiological mechanisms of homeostasis”.

Table 7.1.Comparative characteristics of skeletal and smooth muscles

Plastic smooth muscles is manifested in the fact that they can maintain constant tone both in a shortened and in an extended state.

Conductivity smooth muscle tissue is manifested in the fact that excitation spreads from one myocyte to another through specialized electrically conductive contacts (nexuses).

Property automation smooth muscle is manifested in the fact that it can contract without participation nervous system, due to the fact that some myocytes are capable of spontaneously generating rhythmically repeating action potentials.