Think or super training without delusion. Vadim Protasov - Think! Or super training without delusions

Reflecting on the title of the future article, it was not by chance that I chose the option that was written just above - the reader will easily recognize in it a collage composed of the titles of two, perhaps, the most popular among amateur athletes, books about bodybuilding. “Think! Steroid-Free Bodybuilding "by Stuart McRobert and" Super Training "by Mike Mentzer rocked the amateur sports world and revolutionized what seemed like conventional training theory. It would be more accurate to say that Mentzer was the first to try to create at least some kind of theory, before him most of the popular books and articles on bodybuilding were just collections of various and often conflicting training principles, and catalogs of famous exercises with weights. Mentzer urged to consider bodybuilding as a science, but, for some reason, chose philosophy and logic as the basis, not physiology. Just as Euclid once created his geometry, relying on a number of axioms about the properties of space, so Mentzer created his "Supertraining" relying on the axiom about the role of the last "failure" repetition in the mechanism of triggering muscle growth, without bothering to give any physiological explanation for his hypothesis. But, as we know, in addition to the geometry of Euclid, there are the geometries of Lobachevsky and Minkowski, based on other axioms, but also internally completely not contradictory and logical. Inspired by the excellent style and unshakable confidence of the author of "Supertraining" in his rightness, having built up, following his advice, 10 kilograms of "natural" muscles in six months, I became an ardent supporter of Mentzer's ideas. Having decided to find a physiological confirmation of the "teacher" axiom, I plunged headlong into a new field of knowledge for myself - human physiology and biochemistry. The result was unexpected for me, but more on that later.

Let me draw the readers' attention to the monstrous situation in which the theory of modern "iron" sports finds itself. All sports magazines are full of articles with new super-trendy training systems. “The movement must be powerful and explosive,” some argue. “Only a slow, controlled movement” - others contradict them. "If you want to build mass - work with large weights." "The weight of the projectile does not matter - the main thing is the technique and the feeling of muscle work." Arnold Schwarzenegger advises to train six times a week in the morning and in the evening. Mike Mentzer forbids his students to appear in the hall more than twice a week. The pros paint a set of six biceps exercises. MacRobert urges not to train your arms with isolated exercises at all. Powerlifters almost never run to failure during their cycles. Mentzer assures that the work is not to failure - it's wasted time. Pros from Joe Weider's team advise going much further than failure with forced reps and striptease. This listing can be continued indefinitely, but it is not the abundance of mutually exclusive principles of training that amazes, but the fact that each of them has its own supporters who have managed to get results from their use. This fact made it possible in wide circles to spread the opinion that there is no system. I claim that there is a system! And the patient reader will soon be able to see for himself.

And so, I managed to create a more or less complete theory of training, explaining at the physiological level (of course in general terms) the effect of training on the human muscular apparatus and allowing to find answers to most of the questions of interest to the reader.

Books (1)

Think! Or "Super training" without delusions

“Think! Steroid-Free Bodybuilding "by Stuart McRobert and" Super Training "by Mike Mentzer rocked the amateur sports world and revolutionized what seemed like conventional training theory.

It would be more accurate to say that Mentzer was the first to try to create at least some kind of theory, before him most of the popular books and articles on bodybuilding were just collections of various and often conflicting training principles, and catalogs of famous exercises with weights.

Mentzer urged to consider bodybuilding as a science, but, for some reason, chose philosophy and logic as the basis, not physiology. Just as Euclid once created his geometry, relying on a number of axioms about the properties of space, so Mentzer created his "Supertraining" relying on the axiom about the role of the last "failure" repetition in the mechanism of triggering muscle growth, without bothering to give any physiological explanation for his hypothesis.

But, as we know, in addition to the geometry of Euclid, there are geometries of Lobachevsky and Minkowski, based on other axioms, but also internally completely not contradictory and logical. Inspired by the excellent style and unshakable confidence of the author of "Supertraining" in his rightness, having built up, following his advice, 10 kilograms of "natural" muscles in six months, I became an ardent supporter of Mentzer's ideas.

Having decided to find a physiological confirmation of the "teacher" axiom, I plunged headlong into a new field of knowledge for myself - human physiology and biochemistry. The result was unexpected for me ...

Reader Comments

Kyzmadrom/ 11/18/2015 This is the best work in the world today on sports topics! I graduated from the Sports University but began to understand only after reading Vadim's Work!

Seryoga/ 08.16.2015 Super! Got to the point. Collected so many articles in one!

novel/ 19.02.2015 The theory of training and the structure of muscles are excellently stated.
You will not find ready-made training programs here, but reading this book will give you an understanding of all the mechanisms. You can make programs for yourself, depending on your individual characteristics.

grishustrik/ 03/27/2014 This work does not pretend to be a title - a book because it is only a large summary.

Vladimir/ 01/17/2014 This is the best book from everything that is on the topic.

Andrey/ 08.08.2012 Ilya, there are a bunch of complexes in the internet, only the sense from them is 0. If you want to feed a person, don't give him a fish, but a fishing rod.

Paul/ 15.10.2011 Well done! The only one who got to the point, now everything fell into place ... Great job!)

Seva/ 06/26/2011 He is the only one who brought together different research and methods, processed and gave in an accessible form ... but at the expense of the complexes of classes, it’s not for lamers that there’s a book that doesn’t need to be written ...

Ilya/ 5.06.2011 Book - for reading in the toilet, so that after reading it could be used for its intended purpose. The author collected a bunch of theory and dumped it in his book. He did not even bother to write a set of classes, citing the fact that he is an amateur, and the complexes should be written by professionals. If the author himself cannot compose a complex, then what can he teach at all ?! How does he train himself ?! Anyone can write a similar book by copying and pasting various techniques and dumping them in a heap. The book can be read for general development, nothing more. You will not find a set of training in it.

Current page: 1 (the book has a total of 9 pages)

Vadim Protasenko

Think! Or "Super training" without delusions

Introduction

Reflecting on the title of the future article, it was not by chance that I chose the option that was written just above - the reader will easily recognize in it a collage composed of the titles of two, perhaps, the most popular among amateur athletes, books about bodybuilding. “Think! Steroid-Free Bodybuilding "by Stuart McRobert and" Super Training "by Mike Mentzer rocked the amateur sports world and revolutionized what seemed like conventional training theory. It would be more accurate to say that Mentzer was the first to try to create at least some kind of theory, before him most of the popular books and articles on bodybuilding were just collections of various and often conflicting training principles, and catalogs of famous exercises with weights. Mentzer urged to consider bodybuilding as a science, but, for some reason, chose philosophy and logic as the basis, not physiology. Just as Euclid once created his geometry, relying on a number of axioms about the properties of space, so Mentzer created his "Supertraining" relying on the axiom about the role of the last "failure" repetition in the mechanism of triggering muscle growth, without bothering to give any physiological explanation for his hypothesis. But, as we know, in addition to the geometry of Euclid, there are the geometries of Lobachevsky and Minkowski, based on other axioms, but also internally completely not contradictory and logical. Inspired by the excellent style and unshakable confidence of the author of "Supertraining" in his rightness, having built up, following his advice, 10 kilograms of "natural" muscles in six months, I became an ardent supporter of Mentzer's ideas. Having decided to find a physiological confirmation of the "teacher" axiom, I plunged headlong into a new field of knowledge for myself - human physiology and biochemistry. The result was unexpected for me, but more on that later.

Let me draw the readers' attention to the monstrous situation in which the theory of modern "iron" sports finds itself. All sports magazines are full of articles with new super-trendy training systems. “The movement must be powerful and explosive,” some argue. “Only a slow, controlled movement” - others contradict them. "If you want to build mass - work with large weights." "The weight of the projectile does not matter - the main thing is the technique and the feeling of muscle work." Arnold Schwarzenegger advises to train six times a week in the morning and in the evening. Mike Mentzer forbids his students to appear in the hall more than twice a week. The pros paint a set of six biceps exercises. MacRobert urges not to train your arms with isolated exercises at all. Powerlifters almost never run to failure during their cycles. Mentzer assures that the work is not to failure - it's wasted time. Pros from Joe Weider's team advise going much further than failure with forced reps and striptease. This listing can be continued indefinitely, but it is not the abundance of mutually exclusive principles of training that amazes, but the fact that each of them has its own supporters who have managed to get results from their use. This fact made it possible in wide circles to spread the opinion that there is no system. I claim that there is a system! And the patient reader will soon be able to see for himself.

And so, I managed to create a more or less complete theory of training, explaining at the physiological level (of course in general terms) the effect of training on the human muscular apparatus and allowing to find answers to most of the questions of interest to the reader.

I foresee doubts of skeptics - a person without a special education climbs into the jungle of a science that is new to himself, and even gains the audacity to present his own theories to the public. Well, if scientists do not care about the problems of bodybuilding, then they have to rely on their own strength, in the end, "the rescue of drowning people is the work of the drowning people themselves." And so, if you are ready, then go ahead!

What You Should Know About Muscle Structure and How Muscles Work

There are three types of muscle tissue: skeletal, smooth and heart... The function of the heart tissue is clear from the name, and I think there is no need to explain its role. We often do not even know about the existence of smooth muscles, since these are muscles of internal organs, and we are deprived of the opportunity to directly control them, however, as well as the heart muscle. Meanwhile, it is smooth muscles that contract the walls of blood vessels, produce intestinal contraction, facilitating the movement of food, and perform many other vital functions. The task of skeletal muscles is to move parts of the skeleton relative to each other (hence the name). It is these muscles that we are trying with such persistence to build on our body, and it is their structure and properties that we will consider in the future.

Let's look into the cage.

As you know, all body tissues have a cellular structure, and muscles are no exception. Therefore, I will have to give a short excursion into cytology - the science of the cell, and remind readers of the role and properties of the basic structures of the cell.

In a rough approximation, a cell consists of two most important, interconnected parts - cytoplasm and kernels.

Core- contains molecules DNA, which contain all hereditary information. DNA is a polymer twisted in a double helix, each helix of which is composed of a huge number of four types of monomers called nucleotides. The sequence of nucleotides in the chain encodes all proteins in the body.

The nucleus is responsible for cell multiplication - division... Cell division begins with the division of a DNA molecule into two helices, each of which is capable of completing a pair from a set of free nucleotides and again turns into a DNA molecule. Thus, the amount of DNA in the nucleus doubles, then the nucleus is divided into two parts, and then the whole cell.

Cytoplasm Is everything that surrounds the nucleus in the cell. It consists of the cytosol (cell fluid), which includes various organelles, such as mitochondria, lysosomes, ribosomes, and others.

Mitochondria- these are the energy stations of the cell, in them, with the help of various enzymes, the oxidation of carbohydrates and fatty acids occurs. The energy released during the oxidation of substances goes to the addition of a third phosphate group to the molecule Adenesine diphosphate(ADP) with formation Adenesine triphosphate(ATP) - a universal source of energy for all processes in the cell. By detaching the third phosphate group and again turning into ADP, ATP releases the previously stored energy.

Enzymes or Enzymes- substances of a protein nature, which increase the rate of chemical reactions by hundreds and thousands of times. Almost all vital chemical processes in the body occur only in the presence of specific enzymes.

Lysosomes- rounded vesicles containing about 50 enzymes. Lysosomal enzymes break down the material absorbed by the cell and the cell's own internal structures (autolysis). Lysosomes, merging into phagosomes, are able to digest whole organelles to be disintegrated.

Ribosomes- organelles on which the assembly of the protein molecule takes place.

Cell membrane- the cell membrane, it has selective permeability, that is, the ability to pass some substances and retain others. The task of the membrane is to maintain the constancy of the internal environment of the cell.

Muscle structure.

The structural and functional unit of skeletal muscle is symplast or muscle fiber- a huge cell in the form of an extended cylinder with pointed edges (hereinafter referred to as symplast, muscle fiber, muscle cell, one and the same object should be understood). The length of a muscle cell most often corresponds to the length of a whole muscle and reaches 14 cm, and its diameter is equal to several hundredths of a millimeter. Muscle fiber, like any cell, is surrounded by a membrane - sarcolema... Outside, individual muscle fibers are surrounded by loose connective tissue, which contains blood and lymph vessels, as well as nerve fibers. Groups of muscle fibers form bundles, which, in turn, are combined into a whole muscle, placed in a dense cover of connective tissue, which passes at the ends of the muscle into tendons that are attached to the bone.

Fig. 1

The force caused by the contraction of the length of the muscle fiber is transmitted through the tendons to the bones of the skeleton and sets them in motion.

The control of the contractile activity of the muscle is carried out using a large number motoneurons(Fig. 2) - nerve cells, whose bodies lie in the spinal cord, and long branches - axons as part of the motor nerve, they approach the muscle. Entering the muscle, the axon branches into many branches, each of which is connected to a separate fiber. Thus, one motor neuron innervates a whole group of fibers (the so-called neuromotor unit) that works as a whole.

Fig. 2

The muscle consists of many nerve-motor units and is able to work not with all its mass, but in parts, which allows you to regulate the strength and speed of contraction.

To understand the mechanism of muscle contraction, it is necessary to consider the internal structure of the muscle fiber, which, as you already understood, is very different from a normal cell. To begin with, muscle fiber is multinucleated. This is due to the peculiarities of fiber formation during fetal development. Symplasts (muscle fibers) are formed at the stage of embryonic development of the body from precursor cells - myoblasts... Myoblasts (unformed muscle cells) divide intensively, merge and form muscle tubules with a central arrangement of nuclei. Then synthesis begins in the muscle tubes myofibrils(see below for the contractile structures of the cell), and the formation of the fiber is completed by the migration of nuclei to the periphery. By this time, the nuclei of the muscle fiber have already lost their ability to divide, and only the function of generating information for protein synthesis remains behind them.

But not all myoblasts follow the path of fusion, some of them separate in the form of satellite cells located on the surface of the muscle fiber, namely in the sarcolem, between the plasma membrane and the basement membrane - the constituent parts of the sarcolem. Satellite cells, unlike muscle fibers, do not lose their ability to divide throughout life, which ensures an increase in muscle fiber mass and their renewal. The restoration of muscle fibers in the event of muscle damage is possible thanks to satellite cells. With the death of the fibers hidden in its membrane, satellite cells are activated, divide and transform into myoblasts. Myoblasts merge with each other and form new muscle fibers, in which the assembly of myofibrils then begins. That is, during regeneration, the events of embryonic (intrauterine) muscle development are completely repeated.

In addition to multinucleation, a distinctive feature of the muscle fiber is the presence in the cytoplasm (in the muscle fiber it is commonly called sarcoplasm) of thin filaments - myofibrils (Fig. 1), located along the cell and stacked parallel to each other. The number of myofibrils in the fiber reaches two thousand. Myofibrils are contractile elements of the cell and have the ability to decrease their length when a nerve impulse arrives, thereby tightening the muscle fiber. Under the microscope, it can be seen that the myofibril has a transverse striation - alternating dark and light stripes. With the contraction of the myofibril, the light areas decrease their length and, with full contraction, disappear altogether. To explain the mechanism of myofibril contraction, about fifty years ago, Hugh Huxley developed a sliding filament model, then it was confirmed in experiments and is now generally accepted.

Fiber contraction mechanism.

The alternation of light and dark stripes in the myofibril filament is determined by the ordered arrangement of thick filaments of myosin protein and thin filaments of actin protein along the length of the myofibril; thick filaments are contained only in dark areas (A-disk) (Fig. 3), light areas (I-disk) do not contain thick filaments, in the middle of the I-disk there is a Z-line - thin actin filaments are attached to it. The area of ​​the myofibril, consisting of an A-disk (dark stripe) and two halves of I-disks (light stripes), is called a sarcomere. The reduction in the length of the sarcomere occurs by drawing in thin filaments of actin between thick filaments of myosin. The sliding of the actin filaments along the myosin filaments occurs due to the presence of lateral branches of the myosin filaments, called bridges. The head of the myosin bridge interlocks with actin and changes the angle of inclination to the axis of the filament, thereby, as it were, advancing the filament of myosin and actin relative to each other, then unhooking, interlocking again and again makes a movement. The movement of myosin bridges can be compared to the strokes of oars on galleys. As the movement of the galley in the water occurs due to the movement of the oars, so the sliding of the threads occurs due to the rowing movements of the bridges, the essential difference is only that the movement of the bridges is asynchronous.


Fig. 3

A thin filament consists of two spirally twisted filaments of actin protein. The grooves of the spiral chain contain a double chain of another protein, tropomyosin. In a relaxed state, myosin bridges are unable to bind to actin, since the adhesion sites are blocked by tropomyosin. When a nerve impulse enters the motor motoneuron axon, the cell membrane changes the polarity of the charge, and from special terminal cisterns located around each myofibril along its entire length, calcium ions (Ca ++) are released into the sarcoplasm (Fig. 4).


Fig. 4

Under the influence of Ca ++, the tropomyosin thread enters deeper into the groove and frees up space for myosin to adhere to actin, the bridges begin the stroke cycle. Immediately after the release of Ca ++ from the terminal tanks, it begins to be pumped back, the concentration of Ca ++ in the sarcoplasm decreases, tropomyosin moves out of the groove and blocks the adhesion points of the bridges - the fiber relaxes. A new impulse again releases Ca ++ into the sarcoplasm, and everything is repeated. With a sufficient pulse frequency (at least 20 Hz), individual contractions almost completely merge, that is, a state of stable contraction is achieved, called tetanic contraction or smooth tetanus.

Muscle energy.

Naturally, energy is required to move the bridge. As I mentioned earlier, the ATP molecule is the universal source of energy in a living organism. Under the action of the enzyme ATPase, ATP is hydrolyzed, detaching the phosphate group in the form of orthophosphoric acid (H3PO4), and is converted into ADP, while energy is released.

ATP + H2O = ADP + H3PO4 + energy.

The head of the myosin bridge, in contact with actin, has ATPase activity and, accordingly, the ability to break down ATP and obtain the energy necessary for movement.

The stock of ATP molecules in the muscle is limited, therefore, energy expenditure during muscle work requires constant replenishment. The muscle has three sources of energy reproduction: the breakdown of creatine phosphate; glycolysis; oxidation of organic matter in mitochondria.

Creatine phosphate has the ability to detach a phosphate group and convert to creatine, attaching a phosphate group to ADP, which is converted to ATP.

ADP + creatine phosphate = ATP + creatine.

This reaction is called the Loman reaction. The reserves of creatine phosphate in the fiber are not large, so it is used as an energy source only at the initial stage of muscle work, until the activation of other more powerful sources - glycolysis and oxygen oxidation. At the end of the muscle work, the Loman reaction goes in the opposite direction, and the reserves of creatine phosphate are restored within a few minutes.

Glycolysis - the process of the breakdown of one glucose molecule (C6H12O6) into two molecules of lactic acid (C3H6O3) with the release of energy sufficient to "charge" two ATP molecules, takes place in the sarcoplasm under the influence of 10 special enzymes.

C6H12O6 + 2H3PO4 + 2ADP = 2C3H6O3 + 2ATP + 2H2O.

Glycolysis proceeds without oxygen consumption (such processes are called anaerobic) and is able to quickly restore ATP stores in the muscle.

Oxidation takes place in mitochondria under the influence of special enzymes and requires oxygen consumption, and, accordingly, time for its delivery. Such processes are called aerobic. Oxidation occurs in several stages, first there is glycolysis (see above), but the two pyruvate molecules formed during the intermediate stage of this reaction are not converted into lactic acid molecules, but penetrate into mitochondria, where they are oxidized in the Krebs cycle to carbon dioxide CO2 and water H2O and provide energy for the production of 36 more ATP molecules. The overall equation for the glucose oxidation reaction looks like this:

C6H12O6 + 6O2 + 38ADP + 38H3PO4 = 6CO2 + 44H (2) O + 38ATP.

In total, the breakdown of glucose through the aerobic pathway provides energy for the restoration of 38 ATP molecules. That is, oxidation is 19 times more efficient than glycolysis.

Types of muscle fibers.

Skeletal muscles and the muscle fibers that form them differ in many parameters: speed of contraction, fatigue, diameter, color, etc. Traditionally, red and white, slow and fast, glycolytic and oxidative fibers are distinguished.

The rate of contraction of muscle fibers is determined by the type of myosin. The isoform of myosin, which provides a high rate of contraction, - fast myosin is characterized by a high activity of ATPase, and, accordingly, the rate of ATP consumption. The isoform of myosin with a slower rate of contraction - slow myosin, is characterized by a lower ATPase activity. Fibers with a high ATPase activity and a rate of ATP consumption are usually called fast fibers, fibers characterized by a low ATPase activity and a lower rate of ATP consumption are called slow fibers.

To replenish energy costs, muscle fibers use the oxidative or glycolytic pathway of ATP formation.

Oxidizing, or red, muscle fibers of small diameter are surrounded by a mass of capillaries and contain a lot of the protein myoglobin (it is the presence of this protein that gives the fibers a red color). Numerous mitochondria of red fibers have high levels of oxidative enzyme activity. A powerful network of capillaries is required to deliver large amounts of oxygen with the blood, and myoglobin is used to transport oxygen inside the fiber from the surface to the mitochondria. The energy of red fibers is obtained by oxidation of carbohydrates and fatty acids in the mitochondria.

Glycolytic, or white, muscle fibers have a larger diameter, their sarcoplasm contains a significant amount of glycogen granules, mitochondria are not numerous, the activity of oxidative enzymes is significantly inferior to the activity of glycolytic ones. Glycogen, also called "animal starch", is a complex polysaccharide with a high molecular weight serving as a reserve nutrient for white fiber. Glycogen breaks down to glucose, which is used as fuel for glycolysis.

Fast fibers with high ATPase activity and, accordingly, the rate of energy expenditure require a high rate of ATP reproduction, which can only be provided by glycolysis, since, unlike oxidation, it proceeds directly in the sarcoplasm and does not require time to deliver oxygen to mitochondria and deliver energy from them to myofibrils. Therefore, fast fibers prefer the glycolytic pathway of ATP reproduction and, accordingly, belong to white fibers. For the high rate of energy production, white fibers pay with quick fatigue, since glycolysis, as can be seen from the reaction equation, leads to the formation of lactic acid, the accumulation of which increases the acidity of the medium and causes muscle fatigue and ultimately stops its work.

Slow fibers, characterized by low ATPase activity, do not require such a rapid replenishment of ATP reserves and use the oxidation pathway to meet energy requirements, that is, they are referred to as red fibers. Due to this, slow fibers are low fatigue and are able to maintain relatively low but long-term stress.

There is also an intermediate type of fiber with high ATPase activity, and an oxidative-glycolytic way of ATP reproduction.

The type of muscle fiber depends on the motor neuron that innervates it. All fibers of one motor neuron belong to the same type. An interesting fact is that when a slow motor neuron is connected to a fast fiber of the axon and vice versa, the fiber is reborn, changing its type. Until recently, there were two points of view on the dependence of the type of fiber on the type of motor neuron, some researchers believed that the properties of the fiber are determined by the frequency of impulses of the motor neuron, others that the effect of the influence on the type of fiber is determined by hormone-like substances coming from the nerve (these substances have not yet been isolated) ... Recent studies show that both points of view have a right to exist, the effect of a motor neuron on a fiber is carried out in both ways.

Regulation of the strength and speed of muscle contraction.

As you know from your own experience, a person has the ability to arbitrarily regulate the strength and speed of muscle contraction. This feature is implemented in several ways. You are already familiar with one of them - this is the control of the frequency of nerve impulses. By giving the fiber single commands to cut, it is possible to achieve slight tension in it. For example, the muscles supporting the posture are slightly tense, even when the person is resting. By increasing the frequency of the pulses, it is possible to increase the contraction force to the maximum possible for a given fiber under the given operating conditions, which is achieved when the individual pulses merge into tetanus.

The force developed by the fiber in the tetanus state is not always the same and depends on the nature and speed of movement. Under static stress (when the length of the fiber remains constant), the force developed by the fiber is greater than when the fiber contracts, and the faster the fiber contracts, the less force it can develop. The fiber develops the maximum force under conditions of negative movement, that is, when the fiber is lengthened.

In the absence of external load, the fiber contracts at its maximum speed. With an increase in the load, the rate of contraction of the fiber decreases and upon reaching a certain level of the load, it drops to zero; with a further increase in the load, the fiber lengthens.

The reason for the difference in fiber strength for different directions of movement is easy to understand by considering the example already given with rowers and oars. The fact is that after the completion of the "stroke" the myosin bridge is for some time in a state of adhesion to the actin filament, imagine that the paddle after the stroke is also not immediately removed from the water, but is submerged for some time. In the case when the rowers swim forward (positive movement), the oars, which remain submerged after the completion of the stroke, slow down the movement and interfere with the swim, at the same time, if the boat is towed backwards, and the rowers resist this movement, then the submerged oars also interfere movement, and the tug has to make great efforts. That is, during the contraction of the fiber, the linked bridges interfere with the movement and weaken the strength of the fiber, with negative movement - lengthening of the muscle - the uncoupled bridges also interfere with the movement, but in this case they seem to support the descending weight, which allows the fiber to develop greater strength. The difference between static tension and positive and negative movement is easiest to understand by looking at Figure 5.

So, we have considered the main factors affecting the strength and speed of contraction of an individual fiber. The force of contraction of an entire muscle depends on the number of fibers involved in the work at a given time.


Fig. 5
Involvement of fibers in the work.

When an excitatory signal (triggering impulse) arrives from the CNS (central nervous system) to motor neurons (located in the spinal cord), the motor neuron membrane is polarized, and it generates a series of impulses directed along the axon to the fibers. The stronger the effect on the motor neuron (membrane polarization), the higher the frequency of the impulse generated by it - from a small starting frequency (4–5 Hz) to the maximum possible frequency for a given motor neuron (50 Hz or more). Fast motoneurons are able to generate a much higher frequency impulse than slow ones, so the force of contraction of fast fibers is much more subject to frequency regulation than the force of slow ones.

At the same time, there is also a feedback with the muscle, from which inhibitory signals are received, which reduce the polarization of the motor neuron membrane and reduce its response.

Each motor neuron has its own threshold of excitability. If the sum of the excitatory and inhibitory signals exceeds this threshold and the required level of polarization is reached on the membrane, then the motoneuron is involved in work. Slow motor neurons, as a rule, have a low threshold of excitability, while fast ones have a high threshold. The motor neurons of the whole muscle have a wide range of values ​​for this parameter. Thus, with an increase in the CNS signal strength, an increasing number of motor neurons are activated, and motor neurons with a low threshold of excitability increase the frequency of the generated impulse.

When a light effort is required, for example, when walking or jogging, a small number of slow motor neurons and a corresponding number of slow fibers are activated; due to the high endurance of these fibers, this work can be maintained for a very long time. As the load of the central nervous system increases, it is necessary to send an ever stronger signal, and a larger number of motor neurons (and, consequently, fibers) are involved in the work, and those that have already worked increase the force of contraction, due to an increase in the frequency of impulses coming from the motor neurons. As the load increases, fast oxidative fibers are included in the work, and upon reaching a certain level of load (20% -25% of the maximum), for example, during an uphill or final spurt, the strength of oxidative fibers becomes insufficient, and the signal sent by the central nervous system turns on work fast - glycolytic fibers. Fast fibers significantly increase the strength of muscle contraction, but, in turn, quickly get tired, and more and more of them are involved in the work. If the level of external load does not decrease, work will soon have to be stopped due to fatigue, as a result of the accumulation of lactic acid.

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