Isometriccontraction Isotonic contraction
It is useful for a person engaged in various physical exercises, and even more so for those who train on their own, to know how the contraction of an entire muscle occurs.
Muscles are able to develop maximum force when they are not contracted or contracted to a small extent. With isometric muscle contraction tenses, but does not shorten. That is, isometric contraction
occurs when the two ends of a muscle are held apart at a fixed distance and stimulation causes tension to develop in the muscle without changing its length. An example of an isometric contraction would be holding a barbell.
During isometric contraction, almost all bridges between actin and myosin fibers are formed immediately, since there is no need to form new connections in new places, since the muscle does not shorten. Therefore, the muscle can develop greater force.
With isotonic muscle contraction shortens without losing tension.
is carried out when one end of the muscle is free for movement, and the muscle shortens, at this time developing a constant force. An example of an isotonic contraction would be lifting a barbell. 
Only with very fast movements can the force be relatively small.
The dependence of muscle effort on the speed of muscle contraction is explained by the functioning of an individual sarcomere. With fast muscle contraction move very quickly. This suggests that at each moment of time a certain number of bridges between actin and myosin filaments must disintegrate so that they can arise in new places. As a result, a relatively weak force may develop.
In fact, most acronyms involve both elements. 
So now we have an idea of what it is isometric contraction muscles, isotonic contraction muscles, as well as about the contraction of a whole muscle. During an isometric contraction, the muscle tenses but does not shorten. With isometric muscle contraction can develop more force. With isotonic muscle contraction shortens without losing tension. Most abbreviations include both elements.
Taking an overview of skeletal muscles is very helpful. I recommend! Read.
Physiology of muscles. Classification of muscles according to structural, biochemical and functional criteria
Included muscle tissue The human body includes striated (skeletal and cardiac) and smooth muscles. The first type of muscles ensures the maintenance of posture, position in space and movement of the body and its parts in it. Functions smooth muscles consist of maintaining blood pressure, moving food masses and removing end products of metabolism. The heart muscle consists of cross-striated mononuclear muscle cells, but has different properties compared to striated skeletal muscle. Regulation of the tone and contractile activity of smooth muscles is carried out by the sympathetic and parasympathetic nervous systems. Skeletal muscle contractions occur in response to nerve impulses coming from the spinal cord.
There are more than 600 muscles in the human body, their share of the human body weight is approximately 30% (35–45% in men and 28–32% in women).
Basic functional properties of muscles:
1) excitability;
2) conductivity;
3) contractility.
Excitation and contraction of muscles is carried out under the influence of nerve impulses coming from nerve centers. In muscles, chemical energy stored in the form of ATP is converted directly into mechanical and thermal energy.
The muscle consists of a belly (the contractile part, built from striated muscle tissue) and tendons that attach the muscle to the skeleton.
Skeletal muscle groups:
1. By shape– narrow and wide. In narrow (fusiform) muscles (for example, on the limbs) the tendons are narrow and long, in wide (ribbon-shaped, for example, on the anterior abdominal wall) – the tendons are wide and are called aponeurosis.
2. According to the location of muscle bundles:
Cirrus - in them, muscle bundles are attached to the tendon on one or both sides, as in a bird’s feather, and diverge on the other side. These muscles are capable of contracting strongly, but over short distances (strong muscles).
Muscles with parallel arrangement of long muscle bundles. These muscles are not very strong, but can shorten up to 50% of their length (dexterous muscles).
3. According to the function performed and the effect on the joints: flexors and extensors, adductors and abductors, compressors (sphincters) and dilators.
Exists two types muscle contractions - single and tetanic. Single muscle contraction is the only type of contraction for the heart muscle, and in skeletal muscles it has an artificial etiology and occurs in response to a single electrical signal and the occurrence of an action potential (AP). Such a contraction, lasting » 100 ms, has a waveform (see figure) and includes three phases: 1 – latent period (from 2-3 to 10 ms), lasting from the moment of application of stimulation to the start of contraction, 2 – shortening phase or contraction (40-50 ms) and 3 – relaxation phase (about 50 ms). Under natural conditions, impulses do not arrive singly, but in series of at least 15-50 impulses/s, to which the muscle responds by producing tetanic contraction(tetanus). It is based on the phenomenon of summation of several single contractions. Depending on the frequency of the impulses, serrated and smooth tetanus are distinguished.
Figure 5 – Types of muscle contractions:
A – single contraction phases; B – single and tetanic contractions
Serrated tetanus(incomplete) occurs when each subsequent impulse comes into the muscle relaxation phase.
If the frequency of stimulation is higher, and each subsequent impulse comes in the phase of muscle shortening, then complete summation occurs, and the tetanic contraction is of a continuous nature - smooth tetanus(full).
An increase in the response under the action of submaximal stimuli to a certain (maximal) level occurs due to the involvement of new, previously uninvolved fibers in the excitation process. In the case of a further increase in irritation (supermaximal level), the response no longer increases, and vice versa, with very strong stimuli (5-10 or more thresholds), a pessimal response can be achieved.
In the whole organism, motor neurons send bursts of action potentials to motor units, which respond tetanically. Skeletal muscles are in a state of constant tone due to constant background impulses from the motor areas of the central nervous system.
Muscle work(A) is the product of the load (F) and the distance (h). A = F*h, or A = F*dl, where dl is the amount of muscle shortening.
Relative muscle strength determines the maximum load that a muscle can lift. This value depends much more on the thickness of the muscle than on its length.
The strength of muscle contraction is determined by the number of motor units involved in the contraction process. Absolute Power is the ratio of relative force to area cross section muscle expressed in cm 2. For example, the absolute strength of the biceps is 11.9 kg∕cm 2, calf muscle– 5.9 kg∕cm 2.
To assess the functional activity of muscles, we talk about their tone and phasic contractions.
Tone– a state of prolonged continuous tension.
Phasic Muscle contractions are short-term shortening of a muscle followed by its relaxation.
The magnitude of contraction (degree of shortening) of a muscle depends on its morphological properties and physiological state. The greater the thickness of the muscle, the greater the load it can lift during its contraction. Long muscles are reduced by a greater amount than short ones. Moderate stretching of a muscle increases its contractile effect; with strong stretching, muscle contraction weakens.
Rule of average loads : maximum muscle work occurs when average , and not the maximum load values, since
with more high loads Fatigue develops quickly.
Muscle contraction modes:
1) isotonic- a contraction in which shortening occurs muscle fibers, but the same tension will remain (for example, when lifting a load);
2) isometric– a contraction in which the length of the muscle fibers does not change, but the tension in it increases (for example, when resisting pressure);
3) auxotonic- a contraction in which both the tension and length of the muscle change.
The strength of muscle contraction is determined by the number of active muscle fibers involved in the contraction, the frequency of nerve impulses and the presence of synchronization of the activity of individual muscle fibers over time. Even at rest skeletal muscles They are rarely completely relaxed. Usually some tension remains in them - tone. Muscle tone increases after heavy physical exercise and during psycho-emotional stress.
With regular physical training the number of muscle fibers does not change, but their diameter increases due to an increase in the number of myofibrils in the fibers.
Muscular work is associated with significant energy costs and, therefore, requires an increased flow of oxygen. This is achieved by activating the activity of the respiratory and cardiovascular systems. Increased metabolic processes during muscle work leads to the need for increased release of metabolic products, and, accordingly, increased activity of the kidneys and sweat glands. Hence, physical activity increase activity physiological systems, have a stimulating effect on the motor system, leading to the improvement of motor skills and the development of mental functions. When children are physically inactive, metabolic processes suffer, immunity and performance, including mental performance, decrease.
Muscle fatigue depends on its supply of oxygen and blood. The efficiency of using O2 by the muscle is 20-25%, and with training it can reach 30%.
In each muscle there are many motor units, or motor units - a certain number of muscle cells innervated by one nerve cell, and each myocyte has its own nerve ending.
Among the motor units, they are distinguished: fast, which includes on average about 50, and slow - from several hundred to thousands of muscle cells.
Types of nerve fibers:
1) slow, tireless(red, static, tonic) - these are thin muscles, rich in blood vessels and myoglobin, during work they show great strength, do not get tired for a long time, but the speed of their contractions is low. For example, they maintain vertical statics, hold individual parts of the body in a certain position, i.e. perform a supporting function. These also include the external muscles of the eyeball. Slow phasic contractions provide muscle tone, and therefore such contractions are called tonic. They are necessary to maintain balance in statics and dynamics. Slow muscle cells make up the bulk of motor units. They contain a lot of myoglobin and myosin, where oxidation occurs. Such muscles are red in color and are less fatigued.
2) fast, easily tired(white, dynamic, phasic): they have thick muscle bundles, fewer blood vessels and myoglobin, their contraction speed is high as well as fatigue. While inferior in strength, they are capable of making a variety of small, quick movements. Fast phasic aerobic muscles are slightly paler because they contain less myoglobin, but a fairly large amount of myosin is still retained, and therefore oxidation processes occur intensively. In such muscles, fatigue develops faster than in those described above. In terms of the number of muscle cells in a motor unit, fast phasic muscles occupy second place after slow ones. Anaerobic muscles provide the fastest contractions. They are low in myoglobin and myosin. The cells that make up fast anaerobic muscles are white. Anaerobic glycolysis occurs in such muscles, therefore, as a result of the accumulation of under-oxidized products (lactic acid), oxygen debt, and as a result, the fastest fatigue. Examples of such muscles are the muscles of the fingers and eyes.
3) fast, fatigue resistant(intermediate).
All three types of fibers can be contained in the same muscle, and the ratio of their numbers is determined to a large extent by heredity. For example, in the human quadriceps muscle, the percentage of slow fibers can range from 40 to 98%. The more slow fibers, the more muscle adapted for endurance work. Conversely, people with a high percentage of fast, strong fibers are more capable of work that requires greater strength and speed of muscle contraction.
The strength of muscle contraction is determined by the number of active muscle fibers involved in the contraction, the frequency of nerve impulses and the presence of synchronization of the activity of individual muscle fibers over time. Even at rest, skeletal muscles are rarely completely relaxed. Usually they retain some tension - tone. Muscle tone increases after heavy physical exercise and during psycho-emotional stress.
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 of 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) period of contraction (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).
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Rice. 4. Characteristics of a single muscle contraction. Origin of serrated and smooth tetanus. B– phases and periods of muscle contraction, 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
Property |
Skeletal muscles |
Smooth muscle |
Depolarization rate |
slow |
|
Refractory period |
short |
long |
Nature of contraction |
fast phasic |
slow tonic |
Energy costs |
||
Plastic |
||
Automatic |
||
Conductivity |
||
Innervation |
motor neurons of the somatic NS |
postganglionic neurons of the autonomic nervous system |
Performed movements |
arbitrary |
involuntary |
Chemical sensitivity |
||
Ability to divide and differentiate |
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 the participation of the nervous system, due to the fact that some myocytes are able to spontaneously generate rhythmically repeating action potentials.
To understand the essence of the isometric gymnastics method, I suggest you plunge into the interesting world of the physiology of muscle contraction, that is, find out how the muscles of our body work. Carry out a simple experiment: expose your shoulder so that your biceps is visible, and place your other hand on it. Begin to slowly bend your bare arm at the elbow - you will feel a contraction of the biceps. The weight of the arm remains the same, so the muscle tenses more or less evenly during movement.
This muscle contraction is called isotonic(Greek isos – equal).
This mode of operation leads to movement - in fact, what the muscle is intended for. But note that not only the muscle moves, but also the bones and joints. They are the weak link that wears out the fastest. Joint cartilage is one of the most vulnerable tissues of the body. There are no blood vessels in it, so the cartilage is nourished very slowly due to diffusion - “impregnation” of nutrients from neighboring bones, and, unfortunately, for this reason it is practically not restored.
Active movements, and even with a load, seriously load the articular cartilage. excessive work overloads the joints, and the cartilage layer becomes thinner, “erased,” causing the bones to literally creak. Arthrosis is the name of a joint disease associated with the aging of articular cartilage. Every movement in such a joint can cause pain, so movement is limited, and you have to say goodbye to gymnastics.
Let's try to continue our simple physiological experiments. Try to tighten your biceps brachii so that your forearm and shoulder remain motionless. Do you feel muscle tension? Of course, but at the same time the hand is motionless, there is no movement in the joint. This mode of operation is called isometric. A regime that protects your joints and trains muscle fibers, leaving you with the joy of movement for many years!
Every movement, like a shadow, is followed by exhaustion and fatigue, and the desire for relaxation and rest invariably leads to the cessation of exercise. So after our experiments, relax your shoulder and let your arm hang freely down like a tree branch - feel the degree of muscle relaxation and remember this feeling. Let's move on to the last experiment.
Start bending the elbow joint of one arm, and try to keep it from moving with the other - this is the isometric biceps tension you already know. Hold this position for twenty seconds. Now quickly walk with your back to the wall, place the palm of your working hand on the wall, fingers down, and slowly squat down, keeping your arm straight. Do you feel a stretch in your biceps? Yes, this is a strong and even slightly painful, but pleasant feeling.
Stretch your arm for no more than 10 seconds. Now relax and lower your hand down. I am sure that now you feel the relaxation of your biceps much more than after regular curls. This condition received a special name - post-isometric relaxation, which you just learned how to do on your own. I think it becomes clear to you that stretching and relaxing muscles after isometric tension is much more effective than regular stretching.
So, isometric gymnastics is based on muscle tension WITHOUT MOVEMENT. It preserves joints, prevents wear and tear of articular cartilage and the progression of arthrosis. In many exercises, the isometric contraction phase is followed by a stretch phase. This effective technique, muscle relaxant, relieving muscle spasm and has a pronounced analgesic effect. Remember how nice it is to stretch after a long sitting - isometric gymnastics will both train and relax target muscle– the one that needs to be loaded specifically for your pathology or problem.
Conclusions:
Isometric contraction of a muscle is its tension without movement in the joint.
Isometric gymnastics, strengthening muscles, spares joints and cartilage.
Stretching the muscle after isometric tension (post-isometric relaxation) is an effective technique for muscle relaxation and pain relief.
Hello, my dear readers, admirers and other good and not so good personalities!
Today we are waiting for an archivally important and archival note of a scientific or similar nature. In it we will talk about the types of muscle contractions, what they are, what they are and how to use them in your daily training activities.
So, make yourself comfortable, let's start gesturing.
Types of muscle contractions. What, why and why?
If you are not yet aware, the ABC of Bodybuilding project is an educational resource, and therefore unusual in-depth articles periodically appear on it, revealing the essence of various pumping (and related) processes. In particular, the latest such notes include: [why do people get fat?], [motivation in bodybuilding] and others like them. So, in matters of change own body it’s important not to just mindlessly pump hardware and lift heavy weights, it is important to understand what is happening in the muscles at this particular moment, what type of load is applied to them and what this can ultimately lead to. In general, today we will invest in our heads, so that later we can pump up our body even better. Actually, let's get closer to the point.
Note:
For better assimilation of the material, all further narration will be divided into subchapters.
Muscle contraction: how does it happen?
Every time you pick up an apparatus (for example, a dumbbell) and begin to perform an exercise (for example, a dumbbell curl), a process of contraction of skeletal muscles occurs. In previous notes (in particular in this one [brain-muscle connection]) we have already looked at how the process of muscle contraction itself occurs, therefore, in order not to repeat myself, I will give only a general diagram.
...and visual animation (click and launch the application by pressing “play”).
The motor center (motor unit) consists of a motor neuron and a certain number of innervated fibers. Muscle contraction is the response of a muscle unit to the action potential of its motor neuron.
Total exists 3 type of graduated muscle responses:
- wave summation – formed by increasing the frequency of the stimulus;
- multiple motor unit summation – formed by increasing the strength of the stimulus (increasing the number of motor neurons);
- staircase (treppe) - a reaction with a certain frequency/strength to a constant stimulus.
Speaking of muscles, one cannot fail to mention muscle tone- a phenomenon in which muscles exhibit slight contraction even at rest, maintaining their shape and ability to respond to the load at any time. You don’t have to remember all this, it will just help you better understand the essence of the ongoing processes in the muscles during different types of muscle contractions.
What types of muscle contractions are there?
Did you know that to ensure better growth muscles, they need to be given different types of load, but not in the sense of weight or changing one exercise to another, but to influence the characteristics of the muscles differently. This is what we are talking about - static and dynamic contraction of skeletal muscles. Static and dynamic work combine five types of muscle contractions, each of which is divided into two forms of movement: concentric and eccentric.
Let's go through each one in order and start with...
Dynamic contractions (DC)
Occurs during movement or with the use of free weights - when the athlete lifts free weight and resists gravity. The most common type of DS are isotonic - those in which the muscle changes its length when it contracts during movement. Isotonic contractions (IS) allow people (and animals) to carry out their usual activities and move around. There are two types of IS:
- concentric – the most common and frequently encountered in everyday and sports activities. They imply shortening of a muscle due to its contraction (compression). Example - bending the arm in elbow joint, resulting in a concentric contraction of the biceps brachii and biceps muscles. This contraction is often called the positive lifting phase of the projectile;
- eccentric is the exact opposite of concentric. Occurs when a muscle lengthens during contraction. It occurs much less frequently in pumping practice and involves control or slowing down of movement at the initiative of an eccentric muscle agonist. Example - when kicking a ball, the quadriceps contracts concentrically, and the muscles back surface the hips contract eccentrically. The lower phase (extension/lowering) of a dumbbell curl or a pull-up are also examples of ES. This type puts more stress on the muscle, increasing the likelihood of injury. This contraction is often called the negative phase of the projectile's descent.
The features of eccentric contractions include greater force production - i.e. an athlete can reduce (in a controlled manner) weight that is significantly greater in “tonnage” than his working lifting weight. Greater strength comes from greater inclusion of type 2 fibers (fast twitch muscle fibers). Thus, the concentrated dumbbell biceps lift exercise, or rather its negative phase, allows you to more actively include white fibers in the work. This feature is often used by advanced athletes to improve explosiveness, such as in the bench press.
Note:
The muscles become rigid 10% stronger during eccentric movements than during concentric contractions.
Most often, in such cases, a dumbbell is taken that is distant from the usual weight (for example, 15 kg) per 3-7 kg. The positive phase is carried out by throwing the dumbbell upward with the help of a partner or another hand, and the negative phase takes about 4 sec (vs. 2 sec rise). Such eccentric training is sometimes very useful because... create extensive damage to muscle fibers, which leads to an increase in protein synthesis, subsequently the phenomenon of supercompensation and better muscle hypertrophy. The downside is the high probability of injury (if you do everything without a head), so it’s better for beginners not to bother.
Static contractions (SS)
The name itself speaks for itself, static, i.e. no movement, no change in lengthening/shortening. Such contractions are called isometric. An example is holding an object in front of you (a bag in a store), when the weight is pulling down, but the muscles are contracting to keep the object at the desired level. Also excellent example isometric muscle contraction is hovering at some point in the trajectory for an indefinite time. For example, when performing squats in the middle of the trajectory (halfway up), the quadriceps contract isometrically. The amount of force produced during an isometric contraction depends on the length of the muscle at the point of contraction. Each muscle has an optimal length at which maximum strength is observed. isometric strength. Resultant force isometric contractions exceeds the force produced by dynamic contractions.
For clarity, I will give examples demonstrating different types of muscle contractions (clickable).
We have looked at the main types of contractions that are most common in training practice, however, if you look at the initial classification, there are several more of them. Let's also look at them so that you at least have an idea about them and can surprise your ignorant colleagues in the hall :).
Isokinetic contractions
In isokinetic contractions (Iso=constant, kinetic=movement), the neuromuscular systems can operate at a constant speed at each stage of movement against a given resistance. This allows the working muscles and muscle groups to create a high degree of tension throughout the entire range of motion. This type of contraction is effective for uniform development of muscle strength at any angle of movement. These are dynamic contractions, and they change the length of the muscle. The defining characteristic of IS muscles is that they result in movements at a constant speed.
IN gym a similar type of contraction is used on special isokenetic dynamometer simulators Cybex, Nautilus and others. Swimming and rowing, constant speed activities, are also isokinetic forms of contractions.
The benefits of isokinetic contractions include:
- lead to improved neuromuscular coordination, increasing the number of fibers involved in the work;
- lead to an increase muscle strength the entire muscle throughout the entire range of motion;
- controlling the speed of movement can significantly reduce the likelihood of injury, which is especially important in the postoperative periods and periods of rehabilitation;
- lead to improved overall endurance and cardiac function.
Oxotonic contractions
This is a dynamic type of contraction of increased tension (increasing tension). When an athlete flexes his arms while holding a barbell, its mass obviously does not change throughout the entire range of motion. The force required to perform this movement is not constant, but depends on the athlete's body type, leverage, limb angle, and speed of movement.
Plyocentric contractions
It is a hybrid (combination), the muscle performs isotonic compression from an extended position. Activities that utilize this type of muscle contraction to its fullest extent are called plyometric training or plyometrics. This type of activity is good for cumulatively developing the strength and power of the athlete, and is often recommended as a basis for women's training.
So, in order to finally settle all of the above, I will give a combined picture-presentation (which I found in the archives of a foreign sports and medical university) on the types of abbreviations. Here, in fact, she is (clickable).
Effect of contraction types on muscle length
The result of isotonic contractions is a change in muscle length (at constant force). Concentric IS - shortens the muscle as the load moves, eccentric - lengthens the muscle as it resists the load. The result of isometric contractions is an increase muscle tension, however, neither lengthening nor shortening of the muscle occurs.
In visual form, all this disgrace looks like this.
Type of muscle contractions during running
We have dealt with activity based on the type of contractions, but the following question remains unexamined: what type of contractions takes place in running. In general, errands are a universal tool that covers several types of contractions at once, in particular: isotonic, concentric and eccentric. Contractions occur within slow and fast twitch muscle fibers.
During running, hip elevation and knee flexion produce concentric isotonic contractions of the hip flexors and hamstrings (hamstring muscles). As you straighten your leg to push off the ground and make a forward movement, your hip extensors (hamstrings, gluteal muscle) and knees (quadriceps) perform concentric isotonic contractions.
Eccentric isotonic contractions are especially included during downhill ( downhill). During normal running, the knee extensors and quadriceps contract to straighten the leg. When running downhill, the quadriceps contract eccentrically. In addition, the tibialis anterior muscle also contracts eccentrically, controlling the downward movement of your leg after your heel strikes the ground. As for the involvement of different types of fibers during running, running errands at a relatively calm pace (jogging) is used for its muscle activity, predominantly slow-twitch fibers. Increasing speed allows for greater recruitment of fast-twitch muscle fibers.
What do basic exercises give?
In fact, knowledge about the types of muscle contractions should sway athletes (especially beginners) even more towards performing the base, and here's why.
Many skeletal muscles contract isometrically to stabilize and protect active joints during movement. While the barbell squat contracts the quadriceps femoris concentrically (during the ascending phase) and eccentrically (during the descending phase), many of the more deep muscles hips contract isometrically for stabilization hip joint while driving.
Thus, working with basic exercises, you can drive away at once muscle groups for several types of abbreviations. In fact, this will have a positive effect on their volume-strength characteristics and provide a better incentive for growth.
Well, that’s probably all for today, all the topics have been covered, questions have been addressed, the children have been fed, so it’s time to wrap things up.
Afterword
The next, who knows what, note has come to an end 🙂, in it we talked about the types of muscle contractions. Some may say that it is not practical - perhaps, but the theory and understanding of all pumping processes are also very important in building a shaped body, so let's absorb it!
That’s all for now, let me take my leave, until we meet again!
PS. Friends, do you use this information in your training, or did you know nothing about it until now?
P.P.S. Did the project help? Then leave a link to it in your social network status - plus 100 points for karma, guaranteed :)
