How is human muscle strength measured? How and what does a dynamometer measure? Let's find out together. Absolute and relative strength

Muscle strength. Units. In the SI system, force is expressed in newtons(N). In physiological practice, muscle strength is usually determined by maximum weight load that can be lifted when it contracts. Under the conditions of a whole organism, it is determined “become”, “carpal” strength, flexor strength, etc.

Factors that determine muscle strength. Anatomical structure: pennate muscles (the fibers are located obliquely, at an angle to the longitudinal axis) are capable of developing much greater tension than muscles with parallel fibers. In this regard, it is customary to determine the so-called physiological cross-section of the muscle, i.e. the sum of the cross sections of all the fibers that make up the muscle. In pennate muscles, the physiological cross-section significantly exceeds the anatomical (geometric) one. The muscles of mastication are among the strongest.

The concept of “specific muscle strength” is distinguished - the ratio of the total muscle force in Newtons to the physiological cross-section of the muscle (N/cm 2). The specific force is in the range of 50-150N/cm2. Specific muscle strength is also expressed in kilograms per square centimeter (kg/cm2). So, for the triceps muscle it is 17 kg/cm2, for the shoulder flexor - 8kg/cm2, for calf muscle- 1kg/cm 2, for smooth muscle- 1kg/cm2. IN different muscles body ratio between the number of slow and fast muscle fibers not the same and very different different people, as well as at different periods of life. A single muscle fiber is capable of developing tension up to 0.2 N.

Initial muscle length also affects the strength of its contraction. With moderate preliminary stretching of the muscle, the force of its contraction increases, and with strong stretching, it decreases, until there is no contraction due to the absence of engagement zones between the actin and myosin filaments. At the optimal length (at rest), at which all the heads of the myosin filaments are able to contact the actin filaments, the force of muscle contraction increases to the maximum. Preliminary stretching of a muscle increases its elastic traction, which also leads to an increase in its subsequent contraction. This is accomplished by the protein titin, the filaments of which are attached to the Z-plate at one end and to myosin at the other and stretch like a spring.

With strong shortening of the muscle, the affinity of troponin for Ca 2+ decreases (for unknown reasons), which limits the maximum force of contraction.

Number of excited fibers also affects the force of a single muscle contraction. It is determined by the strength of stimulation in an experiment or the number of excited motor neurons under natural conditions.

Force of tetanic contraction muscles depends on the severity of the summation of contractions in each muscle fiber, which is determined by the frequency of impulses - it increases to the optimum.

Muscle work (A). In mechanics, work is defined as the product of the force (F) applied to a body by the distance (L) of its movement under the influence of this force:

A = F×L (J).

Muscle fatigue. During muscular work, a person develops fatigue over time - strength muscle contractions gradually decreases, and eventually a moment comes when the person is no longer able to continue working. The rate at which fatigue develops depends on the rhythm of work and the size of the load. A large load or too frequent rhythm of work leads to the rapid development of fatigue, as a result of which the work performed is insignificant. The greatest work happens with a certain average, optimal for a given person, rhythm of work and an average, optimal load (the rule of average loads). At any strength isometric contraction muscle work is zero, despite energy consumption and developing fatigue. The cause of fatigue is the accumulation of K + in T-tubules (with frequent contractions), the accumulation of lactic acid, and the consumption of energy material.

Muscle power(work done per unit time) in the SI system is expressed in watts (J/s 2). Maximum power corresponds to performing the greatest amount of work in the minimum amount of time. However, in this case, fatigue quickly develops.

1.3.5. Structural and functional features of smooth muscles

Location of actin and myosin in smooth muscles it is not so ordered, Z-membranes and sarcomeres are absent in them, therefore, microscopic examination does not reveal the transverse striations characteristic of skeletal muscle, which determines the name of these muscles - smooth. The shape of smooth muscle cells is spindle-shaped, the fiber diameter in the thickened part is 2-10 µm, length 50-400 µm. The cell has one nucleus and relatively few mitochondria. The SPR is represented by flat vesicles located in close proximity to the inner surface of the cell membrane. It contains few Ca 2+ ions.

Neuromuscular junctions differ from those of striated muscles, and the difference is most pronounced in the sympathetic nervous system. Postganglionic fibers (axons of ganglionic sympathetic neurons) along their course among the myocytes form numerous thickenings (extensions), from which the mediator is released. The latter diffuses in the intercellular space and interacts with postsynaptic receptors, which are located evenly throughout the membrane of smooth muscle cells, which leads to stimulation or inhibition of organ functions (for example, inhibition of intestinal motility, increased heart function, narrowing of a blood vessel). In the smooth muscles of the bronchi and large arteries, the nervous influence is transmitted without generating AP; the contraction of these muscles provides EPSP.

Features of the properties of smooth muscles. Excitability b. Resting potential most smooth muscle cells is -60-70 mV, in myocytes with spontaneous activity, - -30-60 mV. Action potential longer (10-50 ms) than in skeletal muscles - up to 10 ms. In some myocytes, after the initial rapid repolarization, a plateau is formed, which lengthens the AP to 500 ms; it is associated with the entry of Na + and Ca 2+ into the cell. Membrane depolarization is caused mainly by the diffusion of Ca 2+ into the cell.

Conductivity. The structural and functional unit of smooth muscles is a bundle of muscle fibers. The interaction between individual myocytes is carried out thanks to gap junctions, which have low electrical resistance, and closely located contacting elements of neighboring muscle fibers. Thanks to this, the electric field of one cell in the beam provides excitation of another. Therefore, individual smooth muscle cells of the bundle are not excited in isolation. The speed of propagation of the PD within the beam is 5-10 cm/s. Moreover, to excite all the myocytes of the bundle, excitation of one myocyte is not enough (initial excitation of several cells is necessary).

Contractility. Contractions of smooth muscle are determined by the nature of the propagation of excitation described above - a bundle of smooth muscle fibers contracts as a single whole (a bundle is a functional unit of smooth muscle). The activity of smooth muscle myosin ATPase is 40-80 times lower than the activity of myosin ATPase of striated muscle. The greater the ATPase activity of myosin, the faster the muscle fiber contracts. Therefore, smooth muscle contracts much more slowly than skeletal muscle. For the same reason, less ATP is spent on smooth muscle contraction (economical). In addition, smooth muscle does not tire during prolonged activity - it is adapted to long-term maintenance of tone.

Main feature electromechanical coupling in smooth muscle is that that the main role in pairing plays the role of Ca 2+ entering the cell (when it is excited), since its reserves in the SPR of smooth muscle cells are insignificant. Other important feature is that that the smooth muscle regulatory protein is calmodulin(the presence of troponin has not been established), which binds to Ca 2+. The Ca 2+ - calmodulin complex activates a special enzyme (myosin light chain kinase), which transfers the phosphate group from ATP to the head of the myosin cross bridge. The phosphorylated myosin head interacts with actin. This leads to conformational changes in myosin bridges, which ensures the sliding of actin filaments relative to myosin filaments.

Smooth muscle contraction may be the result and chemomechanical coupling(without the formation of AP), due to the interaction of the mediator with membrane receptors and the activation of various enzyme systems that cause the interaction of actin and myosin, which ensures muscle contraction.

Relaxation of smooth muscle cells caused by inactivation of calcium channels due to restoration of the original MP values. Activation of the calcium pump in the myocyte membrane and the SPR ensures the removal of Ca 2+ into the SPR and from the cell hyaloplasm and a decrease in its concentration, as a result of which myosin light chain kinase is inactivated, which leads to the cessation of phosphorylation of myosin heads, and therefore they lose the ability to interact with actin .

Automatic inherent in cells - pacemakers (pacemakers). It is based on a spontaneously occurring slow depolarization (prepotential) - when the CP is reached, an AP occurs. Spontaneous depolarization is primarily due to the diffusion of Ca 2+ into the cell. The frequency of generated APs depends on the rate of slow depolarization and the ratio of MF and CP: the smaller the MF, the closer it is to the CP, and the easier it is for APs to arise. Automaticity is practically not expressed in the smooth muscles of arteries, seminal ducts, iris, and ciliary muscles. Their functions are completely determined by the ANS.

Plastic is expressed in the fact that when smooth muscles are stretched, their tension initially increases and then decreases to the initial level. Thus, the property of plasticity is manifested in the fact that smooth muscle may not change tension both in a shortened and in an extended state. This feature of smooth muscle prevents excessive pressure build-up in the hollow muscles. internal organs when they are full (bladder, stomach, etc.).

However smooth muscle strain may cause activation reduction processes. This phenomenon, in particular, is characteristic of arterioles, which is one of the important mechanisms for regulating their tone and regional blood flow in some organs (brain, kidneys, heart). Stimulation of contraction in this case occurs as a result of the fact that when pacemaker cells are stretched, mechanically controlled channels are activated, resulting in the emergence of an action potential, which, through its electric field and gap junctions, ensures the occurrence of action potential in neighboring cells. Excessive distension of the bladder also causes it to contract and evacuate urine. A similar reaction is observed with organ denervation and pharmacological blockade of the intraorgan system.

Energy supply for smooth muscle contraction is also carried out due to ATP molecules, the resynthesis of which occurs mainly through anaerobic glycolysis.

Questions for self-control

1. Name the main structural elements of muscle fiber that ensure its excitation and contraction.

2. What is the functional significance of the muscle fiber membrane in performing its contractile function?

3. What is myofibril, what is its significance in the mechanism of muscle contraction?

4. List the properties of muscle tissue.

5. List the main functions of skeletal muscles.

6. What is called muscle contractility?

7. Why is the action potential considered the initiator of muscle contraction? Give appropriate explanations.

7. Draw the skeletal muscle action potential obtained from intracellular abduction. Specify its amplitude in mV.

8. Draw, comparing in time, the action potential and the cycle of a single contraction of a skeletal muscle. Name the phases of muscle contraction.

9. Briefly describe the role of calcium ions in the mechanism of muscle contraction.

10. What processes that ensure muscle contraction consume ATP energy?

11. What is the direct cause of the sliding of actin and myosin filaments, providing muscle contraction? Why?

12. Is the process of muscle relaxation active (with the expenditure of ATP energy) or passive (without the expenditure of ATP energy)?

13. Name the energy sources that provide ATP resynthesis.

14. Name the types of contraction of skeletal muscles depending on the conditions of contraction and the nature of irritation.

15. Name the three phases of a single muscle contraction. What is the main process that occurs in the first phase?

16. What factors influence the strength of a single muscle contraction?

17. Why does increasing the force of muscle irritation increase the force of its contraction?

18. Why does preliminary moderate stretching of an isolated muscle increase the force of its contraction during a single stimulation?

19. What is called tetanic muscle contraction? What phenomenon underlies the tetanus mechanism?

20. What is called the summation of muscle contractions?

21. Under what conditions of skeletal muscle irritation does tetanus occur instead of single contractions? What types of tetanus do you know?

22. Which phase of a single contraction must each subsequent stimulation occur in order for serrated or smooth tetanus to occur? What factors influence the height of the smooth tetanus of an isolated muscle?

23. What is the dependence of the height of the smooth tetanus on the frequency of muscle stimulation (in dynamics)?

24. What frequency of muscle irritation is called optimal, and what is called pessimal?

25. Does a motor unit obey the “all or nothing” law? Why?

26. In what parts of the central nervous system are motor neurons located, the axons of which innervate skeletal muscles?

27. What is called the tone of skeletal muscles, does their fatigue develop, and is energy consumption high?

28. What is the dependence of the work of an isolated skeletal muscle on the magnitude of the load?

29. List structural features smooth muscle.

30. List the features of the resting potential and action potential of smooth muscle compared to those of striated muscle.

31. Name the functional features of smooth muscle compared to skeletal muscle.

32. What is the plasticity of smooth muscles, what is its significance for the functioning of internal hollow organs?

34. What is the functional unit of smooth muscle? Why?

35. List the main properties of the heart muscle.

36. What are the features of pacemaker cells of cardiac pacemakers?

IN Under conditions of isometric contraction, muscles exhibit maximum static force.

Maximum static force and maximum voluntary static muscle force

AND An zometrically contracting muscle develops the maximum possible tension for it when the following three conditions are simultaneously met:

activation of all motor units (muscle fibers) of a given muscle;

mode of complete tetanus in all its motor units;

muscle contraction during resting length.

IN in this case isometric tension muscle corresponds to its maximum static force.

M The maximum force (MS) developed by a muscle depends on the number of muscle fibers that make up a given muscle and on their thickness. The number and thickness of fibers determine the thickness of the muscle as a whole, or, in other words, the cross-sectional area of ​​the muscle (anatomical diameter). The ratio of the MC of a muscle to its anatomical diameter is called the relative strength of the muscle. It is measured in newtons or kilograms of force per 1 cm2 (N/cm2 or kg/cm2).

A the anatomical diameter is defined as the area of ​​the cross-section of the muscle drawn perpendicular to its length. A transverse section of the muscle, drawn perpendicular to the course of its fibers, allows us to obtain the physiological diameter of the muscle. For muscles with parallel fibers, the physiological diameter coincides with the anatomical one. The ratio of the MC of a muscle to its physiological diameter is called the absolute strength of the muscle. It ranges from 0.5-1 N/cm2.

AND Measuring muscle strength in a person is carried out with his. voluntary effort, the desire to contract the necessary muscles as much as possible. Therefore, when they talk about muscle strength in a person, we are talking about maximum voluntary strength (MVS; in sports pedagogy, this concept is equivalent to the concept of “absolute muscle strength”). It depends on two groups of factors: muscular (peripheral) and coordination (central nervous).

TO muscle (peripheral) factors that determine MPS include:

mechanical conditions for the action of muscle traction - the lever arm of the muscle force and the angle of application of this force to the bone levers;

muscle length, since muscle tension depends on its length;

diameter (thickness) of the activated muscles, since, other things being equal, it is manifested muscle strength the greater, the larger the total diameter of voluntarily contracting muscles;

muscle composition, i.e. the ratio of fast and slow muscle fibers c. contracting muscles.

TO Coordination (central nervous) factors include a set of central nervous coordination mechanisms for controlling the muscular apparatus - mechanisms of intramuscular coordination and mechanisms of intermuscular coordination.

M intramuscular coordination mechanisms determine the number and frequency of impulses of motor neurons of a given muscle and the relationship of their impulses in time. Through these mechanisms, the central nervous system regulates the MVC of a given muscle, i.e., determines how close the force of voluntary contraction of a given muscle is to its MS. The MPS indicator of any muscle group, even one joint, depends on the strength of contraction of many muscles. The perfection of intermuscular coordination is manifested in the adequate selection of the “necessary” synergistic muscles, in limiting the “unnecessary” activity of the antagonist muscles of this and other joints and in increasing the activity of the antagonist muscles that provide fixation of adjacent joints, etc.

T Thus, controlling muscles to express their MVC is a challenging task for the central nervous system. This makes it clear why, under normal conditions, the MVC of muscles is less than their MC. The difference between the MS of muscles and their MPS is called strength deficit.

WITH sludge deficiency in humans is determined as follows. Using a special dynamometer, the MVC of the selected muscle group is measured, then its MS. To measure MS, the nerve innervating a given muscle group is stimulated with electrical impulses. The strength of electrical stimulation is selected so as to excite all motor nerve fibers (motoneuron axons). In this case, a frequency of stimulation is used that is sufficient to cause complete tetanus of muscle fibers (usually 50-100 impulses/s). Thus, all muscle fibers of a given muscle group contract, developing the maximum possible tension (MS) for them.

WITH The more perfect the central control of the muscular apparatus, the smaller the silt deficiency of a given muscle group. The magnitude of the strength deficit depends on three factors:

psychological, emotional, state (attitude) of the subject;

the required number of simultaneously activated muscle groups

the degree of perfection of their voluntary control.

P first factor. It is known that in certain emotional states a person can exhibit such strength that far exceeds his maximum capabilities under normal conditions. Such emotional (stressful) states include, in particular, the state of an athlete during a competition. Under experimental conditions, a significant increase in MPS indicators (i.e., a decrease in strength deficit) is detected when the subject is strongly motivated (interested), in situations that cause his strong emotional reaction, for example, after an unexpected sharp sound (gunshot). The same is observed with hypnosis and taking certain medications. At the same time, the positive effect (increase in MVC, decrease in strength deficit) is more pronounced in untrained subjects and weaker (or completely absent) in well-trained athletes. This indicates a high degree of perfection of the central control of the muscular system in athletes.

IN second factor. Under the same measurement conditions, the greater the number of simultaneously contracting muscle groups, the greater the magnitude of the strength deficit. For example, when the MVC of the muscles that only adduct the pollicis is measured, the strength deficit in different subjects is 5-15% of the MS of these muscles. When determining the MPS of the muscles that adduct the pollicis and flex its terminal phalanx, the strength deficit increases to 20%. With maximum voluntary contraction of large muscle groups of the lower leg, the strength deficit is 30% (Ya.M. Kots).

T third factor. Its role is proven by various experiments. It has been shown, for example, that isometric training performed at a specific limb position leads to a significant increase in MVC measured in the same position. If measurements are taken in other positions of the limb, then the increase in MPS turns out to be insignificant or absent altogether. If the increase in MPS depended only on an increase in the diameter of the trained muscles (peripheral factor), then it would be detected at. measurements in any position of the limb. Consequently, in this case, the increase in MVC depends on more advanced central control of the muscular system in the trained position than before training.

R The role of the coordination factor is also revealed when studying the indicator of relative voluntary strength, which is determined by dividing the MVC indicator by the value of the muscle diameter (Since in humans only the anatomical diameter of the muscle can be measured, for most muscles it is not the absolute voluntary force that is determined (the ratio of the MVC to the physiological diameter), but relative (the ratio of the MPS to the anatomical diameter). In sports pedagogy, the concept of “relative strength” denotes the ratio of the MPS to the weight of the athlete.). Thus, after a 100-day training using isometric exercises, the MVC of the muscles of the trained arm increased by 92%, and their cross-sectional area by 23% (Fig. 28). Accordingly, the relative voluntary force increased on average from 6.3 to 10 kg/cm2. Therefore, systematic training can help improve voluntary muscle control. The MVC of the muscles of the untrained arm also increased slightly due to last factor, since the cross-sectional area of ​​the muscles of this arm has not changed. This shows that improved central muscle control can occur across symmetrical muscle groups (training effect "carry-over" phenomenon).

How It is known that the fast motor units of the muscle are the most high-threshold (“less excitable”). Their contribution to the total muscle tension is especially large, since each of them contains many muscle fibers. Fast muscle fibers are thicker, have more myofibrils, and therefore their force of contraction is higher than that of slow motor units. This makes it clear why MPS depends on muscle composition: the more fast muscle fibers they contain, the higher their MPS.

TO When an athlete is faced with the task of developing significant muscle strength during a competitive exercise, he must systematically use exercises in training that require the manifestation of great muscle strength (at least 70% of his MVC). In this case, voluntary muscle control is improved, and in particular the mechanisms of intramuscular coordination, ensuring the inclusion of as many motor units of the main muscles as possible, including the highest threshold, fast motor units.

“Zozhnik” translated, revised and edited Greg Nukols’s great basic article on how muscle volume and strength are interconnected. The article explains in detail, for example, why the average powerlifter is 61% stronger than the average bodybuilder for the same muscle size.

You've probably seen this picture in the gym: a huge muscular guy doing squats with a 200-pound barbell, puffing and doing a small number of repetitions. Then a guy with much less massive legs but can easily do more reps lifts the same barbell.

A similar picture can be repeated in the bench press or deadlift. Yes, and from the school biology course we were taught: muscle strength depends on cross-sectional area(roughly speaking, it depends on the thickness), but science shows that this is a strong simplification and the situation is not entirely true.

Cross-sectional area of ​​the muscle.

As an example, watch an 85 kg guy bench press 205 kg:

However, much more massive guys cannot come close to such figures in the bench press.

The answer is simple: strength is influenced by many other factors besides muscle size.

The average man weighs about 80 kg. If a person is not trained, then about 40% of his body weight is skeletal muscle or about 32 kg. Despite the fact that the growth of muscle mass very much depends on genetics, on average, a man is able to increase his muscle mass by 50% over 10 years of training, that is, add another 16 kg of muscle to his 32 kg of muscle.

Most likely, 7-8 kg of muscle from this increase will be added in the first year of hard training, another 2-3 kg over the next couple of years, and the remaining 5-6 kg over 7-8 years of hard training. This is a typical picture of muscle growth. With an increase in muscle mass of approximately 50%, muscle strength will increase by 2-4 times.

Roughly speaking, if on the first day of training a person can lift a weight of 10-15 kg on his biceps, then subsequently this result can increase to 20-30 kg.

With the squat: if in your first training you squat with a 50 kg barbell, this weight can increase to 200 kg. This is not scientific data, just as an example - how strength indicators can increase. When doing biceps curls, the strength can increase by about 2 times, and the weight in squats can increase by 4 times. But at the same time, muscle volume increased by only 50%. That is it turns out that in comparison with the increase in mass, the strength grows 4-8 times more.

Of course, muscle mass is important for strength, but perhaps not decisive. Let's go over the main factors that influence strength and mass.

Muscle fibers

Research shows that the larger the muscle fiber, the greater its strength.

This graph shows a clear relationship between the size of muscle fibers and their strength:

How does strength (vertical scale) depend on the size of muscle fibers (horizontal scale). Research: From Gilliver, 2009.

However, if absolute strength tends to increase with a larger volume of muscle fibers, relative strength (strength in relation to size), on the contrary, decreases.

Let's figure out why this happens.

There is an indicator for determining the strength of muscle fibers relative to their volume - “specific tension” (let’s translate it as “specific force”). To do this, you need to divide the maximum force by the cross-sectional area:

Muscle Fibers: Bodybuilders have 62% lower fiber strength than lifters

So the point is that specific force depends very much on the type of muscle fiber.

In this study, scientists found that the muscle fiber density of professional bodybuilders was as much as 62% lower than that of professional lifters.

That is, relatively speaking, the muscles of the average powerlifter are 62% stronger than the muscles of the average bodybuilder with the same volume.

Moreover, bodybuilders' muscle fibers are also 41% weaker than those of untrained individuals based on their cross-sectional area. That is, per square centimeter of thickness, the muscles of bodybuilders are weaker than those of those who have not trained at all (but in general, bodybuilders, of course, are stronger due to the total volume of their muscles).

This study compared different muscle fibers and found that The strongest muscle fibers are 3 times stronger than the weakest ones of the same thickness - this is a very big difference.

Muscle fibers grow faster in cross-sectional area than in strength

So both of these studies showed that As the size of muscle fibers increases, their strength decreases relative to their thickness.. That is they grow in size more than in strength.

The dependency is: when the cross-sectional area of ​​a muscle doubles, its strength increases by only 41%, and not 2 times.

In this plan correlates better with muscle fiber strength diameter fibers, not cross-sectional area (please add this correction to your school biology textbooks!)

Ultimately, scientists reduced all the indicators to this graph:

Horizontal: increase in cross-sectional area of ​​the muscle. The blue line is the increase in diameter, the red line is the overall increase in force, the yellow line is the increase in specific force (how much the force increases with increasing cross-sectional area).

The conclusion that can be drawn is that as muscle volume increases, so does strength, but the increase in muscle size (i.e., cross-sectional area) outpaces the increase in strength. These are averages collected from a number of studies and some studies have different data.

For example, in this study, over 12 weeks of training in experimental subjects, the cross-sectional area of ​​the muscles increased by an average of 30%, but at the same time specific force has not changed (that is, we read between the lines, the strength also increased by about 30%).

The results of this study are similar: cross-sectional area of ​​the muscle increased by 28-45% in participants after 12 weeks of training, but specific force did not change.

On the other hand, these 2 studies (one and two) showed an increase in specific muscle strength in the absence of growth in the muscles themselves in volume. That is, the strength has increased, but the volume has not, and thanks to this combination, it turns out that the specific force has increased.

In all 4 of these studies, strength increased over diameter muscles, but in comparison with cross-sectional area strength increased only if the muscle fibers did not grow.

So let's recap the important topic with muscle fibers:

• People vary greatly in the number of muscle fibers of one type or another.. Remember: specific force On average, lifters (training strength) have 61% more muscle fibers than bodybuilders (training volume). Roughly speaking, with muscles of the same volume, lifters are stronger by an average of 61%.
• The weakest muscle fibers are 3 times weaker than the strongest. Their number in each person is determined genetically. This means that the hypothetically maximum possible difference in muscle strength of the same volume varies up to 3 times.
• Specific strength (force per square centimeter of cross-section) does not always increase with training. The fact is that muscle cross-sectional area grows, on average, faster than strength.

Muscle attachment site

An important factor in strength is how the muscles attach to the bones and the length of the limbs. As you remember from your school physics course, the larger the lever, the easier it is to lift the weight.

If you apply force at point A, it will take much more force to lift the same weight compared to point B.

Accordingly, the further the muscle is attached (and the shorter the limb), the greater the leverage and the more weight can be lifted. This partly explains why some fairly thin guys are able to lift much more than some particularly bulky guys.

For example, this study suggests that differences in strength based on muscle insertion site in knee joint for different people it is 16-25%. I'm so lucky with genetics.

Moreover, with muscle growth in volume moment of power increases: this happens because as the muscle grows in volume, the “angle of attack” changes slightly and this partly explains the fact that strength grows faster than volume.

Andrew Vigotsky's research has excellent pictures that clearly demonstrate how this happens:

The most important thing is the conclusion: the last picture demonstrates how, as muscle thickness (cross-sectional area) increases, the angle of application of force changes, which means it becomes easier for larger muscles to move the lever.

The ability of the nervous system to activate more fibers

Another factor in muscle strength, regardless of volume, is the ability of the central nervous system (CNS) to activate as many muscle fibers as possible to contract (and relax antagonistic fibers).

Roughly speaking, the ability to most effectively transmit the correct signal to muscle fibers - to tense some fibers and relax other fibers. You've probably heard that in ordinary life we ​​are able to transfer only a certain normal force to our muscles, but at a critical moment the force can increase many times over. In this place, examples are usually given of how a person lifts a car to save the life of a loved one (and there are indeed quite a few such examples).

However, scientific research has not yet been able to fully prove this.

Scientists compared the strength of “voluntary” muscle contraction, and then, using electrical stimulation, achieved even more - 100% tension in all muscle fibers.

As a result, it turned out that "voluntary" contractions are about 90-95% of the maximum possible contractile force, which was achieved using electrical stimulation ( it is not clear what error and influence such “stimulating” conditions had on the antagonist muscles, which need to be relaxed to obtain greater strength - approx. Zozhnik).

Scientists and the author of the text draw conclusions: it is quite possible that some people can significantly increase strength by training brain-to-muscle signaling, but majority people are not able to significantly increase strength simply by improving the ability to activate more fibers.

Normalized muscle strength (NSM)

The maximum contractile force of a muscle depends on the volume of the muscle, the strength of the muscle fibers of which it consists, on the “architecture” of the muscle, roughly speaking, on all the factors that we indicated above.

According to research, muscle volume is responsible for approximately 50% of the difference in strength indicators from different people.

Another 10-20% of the difference in strength is explained by “architectural” factors such as insertion site and fascial length.

The remaining factors responsible for the remaining 30-40% of the difference in strength do not depend on muscle size at all.

In order to consider these factors, it is important to introduce the concept of normalized muscle strength (NSM) - this is the strength of the muscle in comparison with its cross-sectional area. Roughly speaking, how strong a muscle is compared to its size.

Most studies (but not all) show that NMR increases with training. But at the same time, as we discussed above (in the section on specific strength), an increase in volume in itself does not provide such an opportunity, this means that an increase in strength is ensured not only by an increase in volume, an improvement in the passage of muscle signals, but by other factors (the same which are responsible for the remaining 30-40% of the difference in strength).

What are these factors?

Improving the quality of connective tissues

One of these factors is With increased training, the quality of connective tissue that transmits forces from muscles to bones improves.. As the quality of connective tissue increases, the greater part of the forces is transferred to the skeleton, which means the strength increases with the same volume (that is, the normalized strength increases).

According to research, up to 80% of the strength of a muscle fiber is transferred to the surrounding tissues, which attach the muscle fibers to the fascia using a number of important proteins (endomysium, perimysium, epimysium and others). This force is transferred to the tendons, increasing the total force transmitted from the muscles to the skeleton.

This study, for example, shows that BEFORE NSM training(force of the entire muscle per cross-sectional area) was 23% higher than the specific strength of muscle fibers(strength of muscle fibers per cross-sectional area of ​​those fibers).

AND AFTER NSM training(specific force of the entire muscle) was 36% higher(specific strength of muscle fibers). It means that The strength of the entire muscle during training grows better than the strength of the sum of all muscle fibers.

Scientists attribute this to the growth of connective tissue, which allows for more efficient transfer of force from fibers to bones.

Tendons are shown schematically above and below, with muscle fiber between them. With increasing training (right picture), the connective tissue around the muscle fibers, the quantity and quality of the connections, also grows, allowing the force of the muscle fiber to be more efficiently transmitted to the tendons.

The idea that the quality of force transmitting fibers improves with training (and the figure above) comes from a 1989 study and is still mostly theory.

However, there is a 2010 study that supports this position. In this study, while muscle fiber measurements (specific force, peak strength) remained unchanged, total strength for the entire muscle increased by an average of 17% (but with wide variation between individuals: from 6% to 28%).

Anthropometry as a factor of strength

In addition to all of these muscle strength factors, overall body anthropometry also influences the amount of force produced and how effectively that force can be transmitted through joint flexion (and regardless of the moment force of individual joints).

Let's take the barbell squat as an example. Hypothetical situation: 2 equally trained people with muscles of the same size and fiber composition, identically attached to the bones. If person A has a thigh that is 20% longer than person B, then person B should hypothetically squat with 20% more weight.

However, in reality, everything does not happen quite like that, due to the fact that when the length of the bones changes, the place of muscle attachment also changes proportionally.

Thus, if person A’s thigh is 20% longer, then the place where the muscles attach to the thigh bone (the amount of leverage) is also proportional - 20% further - which means that the length of the thigh is offset by the gain in muscle attachment further from the joint. But this average. In reality, anthropometric data, of course, varies from person to person.

For example, it has been observed that powerlifters with a longer shin and short femur tend to squat heavier than those with a longer femur relative to the shin. A similar observation applies to shoulder length and the barbell chest press.

Regardless of all other factors, the anthropometry of the body makes a difference in strength, but measuring this factor is difficult because it is difficult to separate it from others.

Specificity of training

You are well aware of the specificity of training: what you train is what improves. Science says specificity works across a variety of aspects of training. Much of this effect works because the nervous system learns to make certain movements more efficiently.

Here's a simple example. This study is often used as an example to illustrate the principle of specificity:

• Group 1 trained with a weight of 30% of 1RM - 3 repetitions until muscle failure.
• Group 2 trained with a weight of 80% of 1RM - and did only 1 repetition until muscle failure.
• Group 3 trained with a weight of 80% of 1RM - 3 repetitions until muscle failure.

As expected, the greatest improvement in strength was achieved by group 3 - training with heavy weights and 3 sets per exercise.

However, when at the end of the study, the maximum number of repetitions with a weight of 30% of 1RM was tested among all groups, then best result showed the group that trained with 30% of 1RM. Accordingly, when checking maximum weight At 1RM, results improved better among those who trained at 80% of 1RM.

Another interesting detail in this study: when they began to check how the results in static strength changed (it was not trained in any of the 3 groups), the results in the growth of this indicator were the same, since all 3 groups did not specifically train this strength indicator.

As experience and technique improves, strength increases. Moreover, in complex multi-joint exercises where large muscle groups the effect of training is greater than in small muscles.

This graph shows how, as the number of repetitions increases (horizontal scale), the proportion of errors in the exercise decreases.

Dynamometers measure the hand muscle tone in children and adults in order to determine the overall performance and strength of a person, as well as to monitor the dynamics of the recovery process after injuries, in the process of training athletes, for carrying out dynamometry during clinical examination of the population. Modern instruments display force in decanewtons (daN). This unit is analogous to the kilogram-force (kgf).

Working principle of a dynamometer

Dynamometer operation is based on the law of physics, according to which the deformation occurring in a spring or other elastic body, is directly proportional to the force (tension) applied to the body. This law is named after Hooke, an English scientist who lived in the 17th century.

Hooke's law says that in response to the deformation of a body, a force appears that tends to return the initial shape and original size of this body. It is called elastic force.

The simplest dynamometer is a combination of two devices - power and reference!

The force applied to the device is the deformation of its power link. By means of an electrical signal (or mechanical), the deformation is transmitted to the reference link, which can be digital or analog.

The unit of measurement of the device is newton (N), an international unit of force.

If the scale shows the weight of a person’s body, then the readings of the dynamometer can be used to judge the force that a person applies to deform the instrument spring.

Modern device for dynamometry is a control and measuring device that is widely used in medicine to measure the tensile or compressive force in people, measured in newtons, as well as the moment of force in kilogram-force.

The design of the device allows a person to completely independently measure their muscle strength!

Main types of dynamometers in medicine

The first dynamometer devices, which were spring mechanisms, were created in the mid-18th century. The spring in them, under the influence of the load, stretched to a certain length. The divisions on the scale indicating the elongation of the spring corresponded to the mass of the load. Some time later, a dial device with a round spring of a closed circuit was invented. After devices with stretching mechanisms, structures that operate under pressure were invented.

Today there are the following types of dynamometers:

• Mechanical.
• Hydraulic.
• Electronic.

Devices with a mechanical operating principle are:

• Lever.
• Spring.

There are models of dynamometer devices that use two types of power devices at once!

The following types of devices are most often used in medical practice::

Electronic designs use types of inductive, piezoelectric and other sensors. As the sensor deforms, the resistance increases and, as a result, the currents change. As a result, the force of pressure on the sensor is directly proportional to the strength of the electrical signal transmitted by the device.

An electric dynamometer is a high-precision, small-sized and light-weight device!

What is the difference between a wrist or hand dynamometer and a deadlift dynamometer?

In medicine, dynamometer devices are used to determine strength, assess the performance and endurance of the human body. With the help of these simple devices, you can make a fairly accurate conclusion about the condition of a person’s muscles.

For medical purposes, mainly hand-held dynamometers and machine models are used!

Option hand dynamometer determines the muscle strength of the fingers of a person squeezing it with his hand. Hence the second name – carpal. This device is widely used by physiotherapists to evaluate the dynamics of the recovery of a patient’s muscle strength after an injury. Wrist dynamometers widely used in forwarding and transport companies when testing newly hired employees. They are also used in law enforcement agencies, the Ministry of Emergency Situations and the armed forces, in organizations professional sports and fitness clubs.

Today, hand-held devices of mechanical and electronic modifications are produced. The accuracy of measurements with their help depends on the person’s compliance with certain rules when taking measurements.

These rules are very simple and are as follows:

• The second, free hand must be relaxed and lowered down.
• Then it needs to be moved to the side and positioned perpendicular to the body.
• The arm with the device should be extended forward.
• On command, you should squeeze the dynamometer with your hand as hard as possible.

According to this algorithm, the strength of each hand is measured one by one, several times in a row.

From the results obtained for each hand, the one that is better is selected!

As muscle mass increases during training, the indicators obtained using a dynamometer improve.

Accurate absolute indicators It is quite difficult to obtain, since they are influenced by many subjective factors. Therefore, as a rule, the value of the relative strength of the hands is taken into account. To calculate it, the force measured by a dynamometer in kilograms is multiplied by one hundred and then divided by the person’s body weight. For people who are not involved in professional sports, the relative indicator is 45-50 units for women and 60-70 units for men.

With the help of backbone dynamometers, you can test all the muscles that flex and extend the human body for static strength and endurance!

The machine is similar in appearance to foot expander. Its components are a handle, a footrest, a cable, a measuring device equipped with a sensor, and a counting device.

To measure muscle strength, a person needs:

• Stand with both feet on the footrest of the device.
• Tilt your body forward, bending at the waist.
• Grasp the handle of the dynamometer with both hands.
• Do not bend your knees.
• Then the handle of the device must be pulled upward with all your might.

Calculation principle relative indicators for machine tools is the same as for manual ones. But the index values ​​are much higher. With an index of up to 170 units, deadlift strength is assessed as low. Indicators from 170 to 200 units indicate strength below average. The strength of the body straightening muscles is considered average when the index value is from two hundred to two hundred and thirty. An index from 230 to 260 units indicates above-average values. And more than two hundred and sixty are indicators of high trunk extension strength.

Why do you need to know strength indicators?

A person's muscle strength is influenced by his gender and age, body weight and level of fatigue. The strength indicator largely depends on the time of day and the type of muscle training.

It has been noted that in the middle of the day, as a rule, the maximum value of this indicator is recorded. And in the morning and evening - minimal.

At the same time, the normal muscle strength of a particular person may be weakened due to the fact that:

• He suffers from some disease or experiences temporary discomfort.
• The person is in a state of depression or stress.
• For a number of reasons, his body’s usual diet and daily routine were disrupted.

Often these indicators are lower in older people and in people who do not maintain proper physical shape.

Doctors prescribe to patients the measurement of muscle strength on a dynamometer to monitor the physical development of both children and adolescents, and adults.

When taking measurements, it is necessary to ensure that in the initial position the arrow of the device is at the zero mark!

After measurement, the readings must be recorded. This will help doctors further assess changes in a person’s health status over a certain period of time.

For those who have low levels of muscle strength, doctors recommend engaging in an acceptable sport. After all physical exercise are made not only to build biceps. First of all, they strengthen the body’s immunity and increase its performance.

Review of popular models and prices for medical dynamometers

Several types of medical dynamometer devices are produced in Russia. Among them there are mechanical and electronic models. For adults and children, backbone and wrist devices are available in different price categories.

Hand dynamometer DK-25, DK-50, DK-100, DK-140

The listed models belong to the category of spring mechanical devices. They are intended to measure muscle strength in humans of different ages and health status. Devices for dynamometry are needed in clinics and dispensaries, in health resorts and clinical institutions, in sections various types sports

The principle of operation, shape and size of these models differ little from each other. The main difference is in the measurement range.

The numbers included in the name of the device indicate the upper limit of the range!

In particular, DK-25 is a hand dynamometer that allows you to measure force up to a maximum of 25 decanewtons. The DK-140 device has an upper measurement limit of 140 decanewtons.

The cost of manual spring models ranges from 3100 to 3900 rubles.

These models are hand-held electronic devices manufactured to measure hand muscle strength in patients. They are used in clinics, hospitals, rehabilitation centers, and school medical offices. They are also used in professional and amateur sports and in physiological practice.

Device DMER-120 produced for adults. When you compress the dynamometer body with your hand, the applied muscle force is converted into an electrical signal of a certain frequency. The obtained readings are processed in a digital microprocessor. The device is equipped with a liquid crystal display with an indicator on which the final result is displayed. It can be used to measure in the range from 2 to 120 daN.

There is a version of this model with an indicator located outside the device!

The price of the model is about four thousand rubles. The version with a remote indicator costs 500 rubles more. The design has an autonomous power supply system from battery cells.

DMER-30- This is a children's dynamometer. It measures the strength of arm muscles in older and middle-aged children.

It is convenient for a child to hold this device in his hand, as it has a small body!

In addition, the device is very light - it weighs only 90 grams. The device can operate in two modes. Normal mode must be turned off manually after measurements. In economical

This mode provides automatic self-shutdown of the device one minute after taking the measurement. The maximum measurement limit in this device is 30 daN. The cost of this model is 3400-3600 rubles.

This dynamometer has a measuring range from 20 to 200 daN. The body of the stand force meter is made of silumin material and coated with varnish. The spring part is made of nickel-plated steel.

The device determines the static endurance and strength of the flexor and extension muscles of the human body!

The device is equipped with a special mirror, thanks to which you can see the scale readings during the application of muscle effort.

A deadlift dynamometer is used in offices physical therapy, in orthopedic and neurological clinics, in research laboratories and in sports.

The price of a dynamometer is in the range of 9950-12250 rubles.