Isometriccontraction Isotonic contraction
It is useful for a person who is engaged in various physical exercises, and even more so, who trains on his own, to know how the contraction of the whole muscle occurs.
Muscles are able to develop maximum force when they are not contracted or contracted to a small extent. With isometric muscle contraction tightens, 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 the development of tension in the muscle without changing its length. An example of an isometric contraction would be a barbell hold.
During isometric contraction, almost all bridges between actin and myosin fibers form immediately, since there is no need to form new bonds in new places, since the muscle does not shorten. Therefore, the muscle can develop more force.
With isotonic muscle contraction shortens without losing tension.
occurs when one end of the muscle is free to move and the muscle shortens while developing a constant force. An example of an isotonic contraction would be a barbell lift. 
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 a separate sarcomere. With fast muscle contraction move very quickly. This suggests that a certain number of bridges between actin and myosin filaments must disintegrate at each moment of time so that they can arise in new places. As a result, a relatively weak force may be developed.
In fact, most abbreviations include both elements. 
So now we have an idea of what is isometric contraction muscles, isotonic contraction muscles, as well as the contraction of the whole muscle. With 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.
Getting an overview of skeletal muscles is very helpful. I recommend! Read.
Muscle physiology. Classification of muscles according to structural, biochemical and functional criteria
Part muscle tissue The human body includes striated (skeletal and cardiac) and smooth muscles. The first type of muscles ensures the maintenance of the posture, position in space and the movement of the body and its parts in it. The functions smooth muscles consist in maintaining blood pressure, moving food masses and removing end products of metabolism. The heart muscle consists of transversely striated mononuclear muscle cells, but has different properties compared to striated skeletal muscles. The regulation of 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).
Main 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 the nerve centers. In muscles, the chemical energy stored in the form of ATP is converted directly into mechanical and thermal energy.
The muscle consists of the abdomen (the contractile part, built from striated muscle tissue) and tendons, which 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 front abdominal wall) - tendons are wide and are called aponeurosis.
2. According to the location of the muscle bundles:
Cirrus - in them, muscle bundles are attached to the tendon on one or both sides, as in a bird's feather, and on the other hand they diverge. These muscles are able to contract strongly, but over short distances (strong muscles).
Muscles with a parallel arrangement of long muscle bundles. These muscles are not very strong, but can shorten up to 50% of their length (dexterity muscles).
3. According to the function performed and the effect on the joints: flexors and extensors, adductors and abductors, constrictors (sphincters) and dilators.
Exists two kinds muscle contractions - single and tetanic. single muscle contraction is the only type of contraction for the heart muscle, and in skeletal muscle 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 Fig.) and includes three phases: 1 - a latent period (from 2-3 to 10 ms), lasting from the moment of application of irritation to the start of contraction, 2 - a shortening phase or contraction (40-50 ms) and 3 - relaxation phase (about 50 ms). Under natural conditions, the impulses do not come singly, but in series of at least 15-50 impulses / s, to which the muscle responds with the appearance tetanic contraction(tetanus). It is based on the phenomenon of summation of several single contractions. Depending on the frequency of impulses, dentate and smooth tetanus are distinguished.
Figure 5 - Types of muscle contractions:
A - phases of a single contraction; B - solitary and tetanic contractions
jagged tetanus(incomplete) occurs when each subsequent impulse comes into the phase of muscle relaxation.
If the frequency of stimulation is higher, and each subsequent impulse enters the phase of muscle shortening, then full 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 (maximum) level occurs due to the involvement of new, previously unused fibers in the process of excitation. 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 contract tetanically in response. Skeletal muscles are in a state of constant tone due to constant background impulses from the motor zones of the CNS.
Muscle work(A) is the product of the load (F) and the distance (h). A \u003d F * h, or A \u003d F * dl, where dl is the amount of muscle shortening.
Relative muscle strength determines the maximum load that the muscle can lift. This value is much more dependent 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 process of contraction. Absolute Power is the ratio of relative strength 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, they talk about their tone and phasic contractions.
Tone- a state of continuous continuous tension.
phasic Muscle contractions are called short-term shortening of the muscle, followed by its relaxation.
The amount of contraction (degree of shortening) of the 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 the muscle increases its contractile effect, with strong stretching, muscle contraction weakens.
Average load rule : maximum muscle work occurs when medium , and not the maximum load values, since
at higher loads, fatigue quickly develops.
Modes of muscle contractions:
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, with pressure resistance);
3) auxotonic- a contraction in which both the tension and the 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 in time. Even at rest skeletal muscles are rarely completely relaxed. They usually hold some tension. tone. Muscle tone increases after heavy 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 supply of oxygen. This is achieved by activating the activity of the respiratory and cardiovascular systems. Strengthening metabolic processes during muscular work leads to the need for increased excretion of metabolic products, and, accordingly, increased activity of the kidneys and sweat glands. Hence, physical exercise increase the activity of physiological systems, have a stimulating effect on the motor system, lead to the improvement of motor skills, the development of mental functions. With hypodynamia in children, metabolic processes suffer, immunity, working capacity, including mental, decrease.
Muscle fatigue depends on the supply of oxygen and blood to it. The efficiency of using O 2 by the muscle is 20-25%, and with training it can reach 30%.
In each muscle, there are many motor, 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, there are: fast ones, which include an average of about 50, and slow ones - from several hundred to thousands of muscle cells.
Types of nerve fibers:
1) slow, restless(red, static, tonic) - these are thin, rich in blood vessels and myoglobin muscles, during work they show great strength, do not get tired for a long time, but the speed of their contractions is small. For example, they maintain vertical statics, hold certain parts of the body in a certain position, i.e. perform a supporting function. They 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 static and dynamic. Slow muscle cells make up the bulk of the motor units. They have a lot of myoglobin and myosin, where oxidation occurs. Such muscles are red in color and get tired a little.
2) fast, easily fatigued(white, dynamic, phasic): they have thick muscle bundles, fewer blood vessels and myoglobin, their rate of contraction is high as well as fatigue. Yielding in strength, they are able to produce a variety of small quick movements. Fast phasic aerobic muscles are slightly paler, since they contain less myoglobin, but a sufficiently large amount of myosin is still retained, and, consequently, oxidation processes proceed 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 take 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 underoxidized products (lactic acid), oxygen debt, and as a result, the fastest fatigue. An example 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 number is determined to a large extent by heredity. For example, in the human quadriceps femoris, the percentage of slow fibers can be 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 doing work that requires a lot of 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 in 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 the contraction of the heart) - peristalsis of the stomach and intestines, changes in the tone of blood vessels, maintaining the tone of the bladder - are caused by contraction of smooth muscles. The work of the heart is provided 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 the bones and are parallel to each other. Each muscle fiber (myocyte) includes many subunits - myofibrils, which are built from longitudinally repeating blocks (sarcomeres). The sarcomere is the functional unit of the contractile apparatus of the skeletal muscle. Myofibrils in the muscle fiber lie in such a way that the location of the sarcomeres in them coincides. This creates a pattern of transverse striation.
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. Between them are thicker myosin filaments.
The actin filament looks like two strands of beads twisted into a double helix, where each bead is a protein molecule. actin. In the recesses of actin helices, protein molecules lie at equal distances from each other. troponin attached to filamentous protein molecules tropomyosin.
Myosin filaments are made up of repeating protein molecules. myosin. Each myosin molecule has a head and tail. The myosin head can bind to the actin molecule, forming the 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) is an intracellular network of closed tubules and performs the function of depositing Ca ++ ions.
motor unit. The functional unit of skeletal muscle is motor unit(DE). DE - 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 MU occur simultaneously (when the corresponding motor neuron is excited). Individual MUs can fire and contract independently of each other.
Molecular mechanisms of contractionskeletal muscle
According to thread slip theory, muscle contraction occurs due to the sliding movement of actin and myosin filaments relative to each other. The thread sliding mechanism includes several successive events.
Myosin heads attach to actin filament binding sites (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, actin and myosin filaments move "one step" relative to each other (Fig. 2b).
The dissociation of actin and myosin and the restoration of the conformation of the head 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, C).
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, Z-discs of sarcomeres approach each other and the myofibril shortens (Fig. 2, D).
Conjugation of excitation and contractionin skeletal muscle
At rest, filament sliding does not occur in the myofibril, since the binding centers on the actin surface are closed by tropomyosin protein molecules (Fig. 3, A, B). Excitation (depolarization) of myofibrils and proper muscle contraction are associated with the process of electromechanical coupling, which includes a number of successive events.
As a result of neuromuscular synapse firing on the postsynaptic membrane, an EPSP occurs, which generates the development of an action potential in the area surrounding the postsynaptic membrane.
Excitation (action potential) spreads along the myofibril membrane and reaches the sarcoplasmic reticulum due to the system of transverse tubules. Depolarization of the sarcoplasmic reticulum membrane leads to the opening of Ca++ channels in it, through which Ca++ ions enter the sarcoplasm (Fig. 3, C).
Ca++ ions bind to the troponin protein. Troponin changes its conformation and displaces tropomyosin protein molecules that closed the actin binding centers (Fig. 3d).
Myosin heads join the opened binding centers, and the process of contraction begins (Fig. 3, E).
For the development of these processes, a certain period of time (10–20 ms) is required. The time from the moment of excitation of the muscle fiber (muscle) to the beginning of its contraction is called latent period of contraction.
Relaxation of the skeletal muscle
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 there is less and less binding, and eventually the actin and myosin filaments are completely disconnected; muscle relaxation occurs.
Contracture called persistent prolonged contraction of the muscle, which persists after the cessation of the stimulus. Short-term contracture may develop after tetanic contraction as a result of accumulation in the sarcoplasm a large number Ca++ ; long-term (sometimes irreversible) contracture can occur as a result of poisoning, metabolic disorders.
Phases and modes of skeletal muscle contraction
Phases of muscle contraction
When stimulating the skeletal muscle with a single impulse electric current above threshold 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 the processes of electromechanical coupling take place; muscle excitability during a single contraction changes in accordance with the phases of the action potential;
shortening phase (about 50 ms);
relaxation phase (about 50 ms).
 |
Rice. 4. Characteristics of a single muscle contraction. Origin of dentate and smooth tetanus. B- phases and periods of muscular contraction, Change in muscle length shown in blue action potential in muscle- 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 go along the motor nerves that innervate the muscle. Depending on the frequency of nerve impulses coming to the muscle, the muscle can contract in one of three modes (Fig. 4b).
Single muscle contractions occur at a low frequency electrical impulses. If the next impulse comes to the muscle after the completion of the relaxation phase, a series of successive single contractions occurs.
At a higher frequency of impulses, the next impulse may coincide with the relaxation phase of the previous contraction cycle. The amplitude of contractions will be summed up, there will be dentate tetanus- prolonged contraction, interrupted by periods of incomplete relaxation of the muscle.
With a further increase in the frequency of impulses, each subsequent impulse will act on the muscle during the shortening phase, resulting in smooth tetanus- prolonged contraction, not interrupted by periods of relaxation.
Frequency Optimum and Pessimum
The amplitude of tetanic contraction depends on the frequency of impulses irritating the muscle. Optimum frequency they call such a 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 enters the refractoriness phase (Fig. 4, A), as a result of which the tetanus amplitude decreases significantly.
Skeletal muscle work
The strength of skeletal muscle contraction is determined by 2 factors:
the number of MUs participating in the reduction;
the frequency of contraction of muscle fibers.
The work of the skeletal muscle is accomplished by a coordinated change in tone (tension) and length of the muscle during contraction.
Types of work of the skeletal muscle:
dynamic overcoming work occurs when the 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 inferior performance occurs when the muscle is functioning but is being stretched because the effort it makes is not enough to move or hold the body parts.
During the performance of work, the muscle can contract:
isotonic- the muscle shortens under constant tension (external load); isotonic contraction is reproduced only in the experiment;
isometric- muscle tension increases, but its length does not change; the muscle contracts isometrically when performing static work;
auxotonically- muscle tension changes as it shortens; auxotonic contraction is performed during dynamic overcoming work.
Average load rule- the muscle can perform maximum work with moderate loads.
Fatigue – physiological state muscle, which develops after a long work and is manifested by a decrease in the amplitude of contractions, lengthening of the latent period of contraction and relaxation phase. The causes of fatigue are: depletion of ATP, 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 CNS synapses and neuromuscular synapses.
Structural organization and reductionsmooth muscles
Structural organization. Smooth muscle is composed of single spindle-shaped cells ( myocytes), which are located in the muscle more or less randomly. The 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 in 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 conjugation of excitation and contraction. When a 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 an 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 the skeletal muscle, as a result of which relaxation occurs very slowly. Smooth muscles make 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 common 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 muscles are discussed in the section "Physiological mechanisms of homeostasis".
Table 7.1.Comparative characteristics of skeletal and smooth muscles
Property |
Skeletal muscles |
Smooth muscles |
Depolarization rate |
slow |
|
Refractory period |
short |
long |
The nature of the reduction |
fast phasic |
slow tonic |
Energy costs |
||
Plastic |
||
Automation |
||
Conductivity |
||
innervation |
motoneurons of the somatic NS |
postganglionic neurons of the autonomic NS |
Movements carried out |
arbitrary |
involuntary |
Sensitivity to chemicals |
||
Ability to divide and differentiate |
Plastic smooth muscles is manifested in the fact that they can maintain a constant tone both in a shortened and in a stretched 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 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 with you. Carry out the simplest experiment: expose your shoulder so that your biceps are visible, and put 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 is tensed more or less evenly during movement.
This muscle contraction is called isotonic(Greek isos - equal).
This mode of operation leads to movement - in fact, for which the muscle is intended. 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 in the body. There are no blood vessels in it, so the cartilage is fed very slowly due to diffusion - “soaking” 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. exorbitant work overloads the joints, and the cartilage layer becomes thinner, “erased”, causing the bones to literally creak. Osteoarthritis is the name of a joint disease associated with the aging of articular cartilage. Each movement in such a joint can cause pain, so the movement is limited, and you have to say goodbye to gymnastics.
Let's try to continue our simple physiological experiments. Try to tighten the biceps of the shoulder so that the 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 regimen that both saves your joints and trains muscle fibers, leaving the joy of movement for years to come!
Every movement, like a shadow, is followed by fatigue and fatigue, and the desire for relaxation and rest invariably leads to the cessation of classes. Here you are after our experiments, relax your shoulder and let your arm hang down freely 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 bicep tension you already know. Hold this position for twenty seconds. Now quickly come back to the wall, place the palm of your working hand on the wall with your fingers down and slowly squat, keeping your arm straight. Do you feel a stretch in your biceps? Yes, it is a strong and even a little painful, but a 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 the biceps much more than after normal bending. This condition has received a special name - post-isometric relaxation which you have 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 sipping.
So, isometric gymnastics is based on muscle tension WITHOUT MOVEMENT. It preserves the joints, prevents wear of the articular cartilage and the progression of arthrosis. In many exercises, the isometric contraction phase is followed by the stretch phase. This effective reception, relaxing the muscle, relieving muscle spasm and has a pronounced analgesic effect. Remember how nice it is to stretch after a long sitting - isometric gymnastics will 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.
Muscle stretching after isometric tension (post-isometric relaxation) is an effective method of muscle relaxation and pain relief.
Hello, my dear readers, admirers and other good and not so personalities!
Today we are waiting for archival and archival note of a scientific or so direction. We will talk in it 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 aware yet, then the ABC of Bodybuilding project is an educational resource, and therefore unusual in-depth articles periodically slip on it, revealing the essence of various pumping (and related) processes. In particular, the last such notes include: [why do people get fat?], [motivation in bodybuilding] and others like them. So, in terms of change own body it is important not just to mindlessly swing the pieces of iron and raise big 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 it can eventually result in. In general, today we will invest in our head in order to pump our body even better later. Actually, let's get to the point.
Note:
For better assimilation of the material, all further narration will be divided into subchapters.
Muscle contraction: how does it happen?
Each time you pick up a projectile (for example, a dumbbell) and begin to perform an exercise (for example, lifting a dumbbell for biceps), a process of contraction of skeletal muscles occurs. In previous notes (in particular, in this one [brain-muscle connection]) we have already considered how the process of muscle contraction itself occurs, therefore, in order not to repeat myself, I will give only a general scheme.
…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 types of graded muscle responses:
- wave summation - is formed by increasing the frequency of the stimulus;
- multiple motor unit summation - is formed by increasing the strength of the stimulus (increase in the number of motor neurons);
- stairs (treppe) - a reaction with a certain frequency / strength to a constant stimulus.
Speaking of muscles, it is impossible not to mention muscle tone- a phenomenon in which the muscles show a slight contraction even at rest, while maintaining their shape and ability to respond to the load at any time. You do not have to memorize all this, it will simply help you better understand the essence of the ongoing processes in the muscles with different types of muscle contractions.
What are the types of muscle contractions?
Do you know what to ensure better growth muscles, they need to be given different types of load, but not in the sense of weights or changing one exercise for another, but in different ways to influence the characteristics of the muscles. 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 in order and start with...
Dynamic contractions (DS)
Occur during movement or with the use of free weights - when the lifter lifts free weight and opposes the force of gravity. The most common type of DS is isotonic, in which the muscle changes its length as it contracts during movement. Isotonic contractions (IS) allow people (and animals) to carry out their usual activities, to move around. There are two types of IS:
- concentric - the most common and frequently encountered in everyday and sports activities. Imply shortening of the muscle due to its contraction (compression). Example - bending the arm in elbow joint, resulting in a concentric contraction of the muscle of the biceps of the shoulder, biceps. This contraction is often referred to as the positive phase of the projectile's rise;
- eccentric is the exact opposite of concentric. Occurs when a muscle lengthens during contraction. It occurs much less frequently in pumping practice and involves the control or slowing of movement on the initiative of an eccentric muscle agonist. Example - when hitting the ball with the foot, the quadriceps contracts concentrically, and the muscles rear surface hips contract eccentrically. The lower phase (extension/lowering) of dumbbell curls or pull-ups are also examples of ES. This type puts more strain on the muscle, increasing the chance of injury. This contraction is often referred to as the negative phase of projectile descent.
The features of eccentric contractions include a large generation of force - i.e. an athlete can reduce (in a controlled manner) a weight that is significantly greater in “tonnage” than his working lifting weight. Greater strength is provided by greater inclusion of fibers of the second type (fast muscle fibers). Thus, the exercise of concentrated lifting of the dumbbell to the biceps, 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 explosive strength, for example, in the bench press.
Note:
The muscles become 10% stronger during eccentric movements than during concentric contractions.
Most often in such cases, a dumbbell is taken that is far from the usual weight (for example 15 kg) per 3-7 kg. The positive phase is carried out by throwing the dumbbell up with the help of a partner or other hand, and the negative phase takes about 4 sec (against 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. Their minus is a high probability of injury (if you do everything without a head), so it’s better for beginners not to bother.
Static abbreviations (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 shopping bag) when the weight is pulling down but the muscles are contracting to keep the object level. Also great example isometric muscle contraction, is hanging at some point of the trajectory for an indefinite time. For example, when doing squats in the middle of the trajectory (half up), the quadriceps contract isometrically. The amount of force generated during an isometric contraction depends on the length of the muscle at the point of contraction. Each muscle has an optimal length at which there is a maximum 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 considered the main types of abbreviations that are most common in training practice, however, if you look at the initial classification, there are several more of them. Let's also analyze them so that you at least have an idea about them and can surprise your ignorant colleagues in the hall :).
Isokinetic contractions (Isokinetic)
In isokinetic contractions (Iso=constant, kinetic=movement) the neuromuscular systems can work at a constant speed in each step of the movement against a given resistance. This allows the working muscles and muscle groups to create a high degree of tension throughout the range of motion. This type of contraction is effective for the uniform development of muscle strength at any angle of movement. These are dynamic contractions, and during them the length of the muscle changes. The defining characteristic of muscle IS is that it results in movements at a constant speed.
IN gym a similar type of contraction is used on special isokinetic simulators-dynamometers Cybex, Nautilus and others. Swimming and rowing, constant speed activities, are also an isokinetic form of contraction.
The benefits of isokinetic contractions are as follows:
- lead to an improvement in 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;
- movement speed control can significantly reduce the likelihood of injury, which is especially important in postoperative and rehabilitation periods;
- lead to improved overall endurance and cardiac function.
Oxotonic contractions (Auxotonic)
This is a dynamic type of contractions of increased tension (increase in tension). When an athlete flexes their arms while holding the barbell, its mass apparently does not change throughout the entire range of motion. The force required to perform this movement is not constant, it depends on the physique, the leverage of the athlete, the angle of the limbs and the speed of movement.
Pliocentric contractions (Plyocentric)
It is a hybrid (combination), the muscle performs isotonic contraction from a stretched position. An activity that uses this type of muscle contraction to its fullest is called plyometric training or plyometrics. This type of activity combines well with the strength and power of the athlete, and is often recommended as the basis of 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 medical university) by types of abbreviations. Here, in fact, is she (clickable).
Influence of types of contractions on muscle length
The result of isotonic contractions is a change in the length of the muscle (at a constant force). Concentric IS shorten the muscle as the load is transferred, eccentric IS lengthen 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 a visual form, all this disgrace looks like this.
Type of muscle contractions while running
We figured out the activity by type of contractions, but the following question remained unconsidered: 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, lifting the hip and flexing the knee results in concentric isotonic contractions of the hip flexors and hamstrings (hamstring muscles). As you straighten your leg to push off the ground and make a propulsion motion, your hip extensors (hamstrings, gluteal muscle) and knees (quadriceps) perform concentric isotonic contractions.
Eccentric isotonic contractions are especially involved in downhill ( downhill). During normal running, the knee extensors and quadriceps contract to straighten the leg. When running downhill, the quads contract eccentrically. In addition, the tibialis anterior also contracts eccentrically, controlling the downward movement of your foot after the heel hits the ground. As for the involvement of different types of fibers during running, errands at a relatively calm pace (jogging) are used for their muscle activity predominantly slow twitch fibers. Increasing your speed allows you to recruit more fast-twitch muscle fibers.
What are basic exercises?
In fact, knowledge about the types of muscle contractions should even more sway athletes (especially beginners) towards doing the base, and here's why.
Many skeletal muscles contract isometrically to stabilize and protect active joints during movement. While barbell squats contract 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 during movement.
Thus, working with basic exercises, can be driven away at once muscle groups for several types of abbreviations. In fact, this will have a positive effect on their volumetric and power characteristics and will give a better incentive for growth.
Well, that's probably all for today, all the topics are covered, the questions are considered, the children are fed, so it's time to wrap up.
Afterword
The next one came to an end, who knows what, according to the score 🙂 note, in it we talked about the types of muscle contractions. Someone 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 we 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 not know anything about it until now?
P.P.S. Did the project help? Then leave a link to it in the status of your social network - plus 100 points to karma, guaranteed 🙂 .
