Efficiency is the ability of a person to perform the maximum amount of physical or mental work for a long time and with a certain efficiency. During a work shift, performance varies widely. This is due to the fact that it is influenced both by factors external to the person (nature of work, environmental conditions, work and rest regimes, working posture, organization of the work process from the point of view of ergonomics), and internal (motivation, degree of perfection labor skills, human functional reserves).
In a production environment, performance changes throughout the work shift and is conventionally divided into four phases. The first phase is the run-in phase , during which the activity of the central nervous system increases, the level of metabolic processes in the worker’s body increases, and the activity of the cardiovascular and respiratory systems increases. The duration of this phase depends on the type of activity. It is always shorter during physical labor than during mental labor. Moreover, the more physically difficult the work, the faster the development occurs.
The second phase is the phase of relatively stable performance , characterized by an optimal, from the point of view of achieving a useful result, level of functioning of the body systems that ensure the functioning of the body’s systems, maximum labor efficiency. The duration of the period of stable performance depends on the physical severity and nervous tension of the work (the harder the work, the shorter the period of stable performance), on the psychophysiological state of the person, and on hygienic working conditions.
The third phase is the phase of decreased performance , associated with the development of fatigue. The fourth phase is the phase of secondary increase in performance at the end of the working day. It is based on a conditioned reflex mechanism associated with the upcoming end of work and subsequent rest. A person’s professional performance changes similarly throughout the working week.
The reason for decreased performance throughout the working day, week or year is fatigue. During work, fatigue manifests itself in a decrease in muscle strength and endurance, deterioration in coordination of movements, an increase in energy expenditure when performing the same work, a slowdown in the speed of information processing, memory deterioration, difficulty concentrating and switching attention from one type of activity to another. Subjectively, fatigue manifests itself in a feeling of tiredness, causing a desire to stop working or reduce the load.
During dynamic work with an intensity below the fatigue limit, the restoration of high-energy phosphates used during muscle contraction occurs throughout the work itself, during muscle relaxation (micropauses). ). If the duration of muscle relaxation corresponds to the time required for the synthesis of ATP and the removal of metabolic products from them, then such work is low-tiring . During dynamic work of high intensity, there is no possibility of continuous restoration of ATP during the work itself. This is explained by the fact that the duration of periods of muscle relaxation is less than the time required for the ongoing restoration of its energy potential. Restoration of energy reserves and removal of lactic acid from muscles does not occur completely.
The physiological mechanisms of neuropsychic fatigue are not precisely known. Typical symptoms of such fatigue are a slowdown in the transmission and comprehension of information, a decrease in the efficiency of mental activity in general, and a weakening of sensory and sensorimotor functions. Such fatigue not only reduces performance, but sometimes leads to a decrease in a person’s social activity, irritability, emotional instability, causeless anxiety and even depression.
Neuropsychic fatigue occurs in the following situations:
1) during long and intense mental work, requiring increased concentration of attention, solving complex production problems under time pressure;
2) during heavy physical labor;
3) with monotonous monotonous work;
4) when working in conditions of low light, high temperature, noise and vibration;
5) in case of frequent conflict situations in the team, lack of interest in work, discrepancy between a person’s psychophysiological capabilities and the nature of his work activity.
Unlike muscle fatigue, fatigue of central origin (neuropsychic) can disappear quickly. This happens, for example, in situations where one type of activity is replaced by another; a person finds himself in stressful situations that threaten his life; if new information appears that increases interest in the work. Since fatigue in the neuropsychic sphere can pass so quickly, this indicates that its root cause is neither a decrease in energy substrates in the nervous structures, nor the accumulation of metabolic products in them, nor insufficient blood supply to the brain.
Any type of work will not lead to the development of overwork and overstrain and, on the contrary, will have a positive impact on a person’s performance and health if one adheres to the physiological principles of its rational organization.
End of work -
This topic belongs to the section:
Physiology of excitable tissues
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General physiology of excitable tissues
Irritability is the ability of living matter to actively change the nature of its life activity under the influence of a stimulus. Reactions of individual cells and tissues to the action of an irritant
Structural and functional organization of the cell membrane
According to Robertson's definition, a cell can be considered as a triphasic system, which consists of a nucleocytoplasmic matrix, a membrane phase and an external phase. Membranes account for about 2/3
Ion channels
Ion channels are formed by proteins; they are very diverse in their structure and mechanism of action. More than 50 types of channels are known, each nerve cell has more than 5 types of channels. State asset
Electrical phenomena in tissues
1.2.1. Discovery of “animal electricity” At the end of the 18th century. (1786), professor of anatomy at the University of Bologna Luigi Galvani conducted a series of experiments that laid the foundation for
Local potential (local response)
When excitable tissue is irritated, PD does not always occur. In particular, if the strength of the stimulus is small, depolarization will not reach a critical level, and naturally, impulse propagation will not occur.
Laws of irritation of excitable tissues
The response of excitable tissue to the action of a stimulus depends on two groups of factors: the excitability of the excitable tissue and the characteristics of the stimulus. Cell excitability changes
1. Will the value of the resting potential change if the concentration of K+ ions inside the nerve cell is artificially increased by 30%? A. the resting potential will decrease to 0
Physiology of nerve fibers and nerves
2.1.1. Structure of a nerve fiber Nerve fibers are processes of neurons through which communication between neurons is carried out, as well as
High lability
2.1.7. Axon transport The presence of processes in a neuron, the length of which can reach 1 m (for example, axons innervating the muscles of the limbs), creating
Functional role of axon transport
− Antegrade and retrograde transport of proteins and other substances are necessary to maintain the structure and function of the axon and its presynaptic terminals, as well as for processes such as axo
Synaptic transmission of excitation
A synapse (Greek synapsis - connection) is a specialized structure that ensures the transmission of excitatory or inhibitory influences between two excitable cells. Through synapse nar
Level 1-2 tests for self-testing of knowledge
Goals: based on self-observation, form the concept of muscle work, the role of load and rhythm of work on the development of fatigue, and consolidate knowledge of physics.B) educational: identifying human working conditions that increase
muscle performance.
c) developing - to continue developing students’ skills
compare, contrast, summarize facts from different fields of science and
transfer knowledge from one area of activity to another.
Equipment: video fragment “Muscle work”, flashcards, dumbbells, dynamometer, stopwatch. Presentation (application)
Before the lesson, the class is divided into 5 groups of 5-6 people in each. Tasks on flashcards are completed in a group.
At the beginning of the lesson, a problematic question is posed to which students must answer:
“How do muscles do work?” “What determines muscle work and fatigue?
During the classes
A) the mechanism of muscle action.
In order to answer the first question, you need to remember from the physics course, what is work? What mechanisms are used to do work? Job - this is a contraction of a muscle during which it can lift or move any load. (A=mhn)
Now you remember what mechanical work is and you know that simple mechanisms called levers are used to perform it. Let's think about it, do we encounter levers in living nature? Give examples.
These figures show examples of the action of levers in the human body.
In the figure (Lever of the second kind, shows how we can hold a load in our hand. The weight of the load is balanced by the force of the muscle).
By contracting, the muscles move the bones, acting on them like levers. The bones begin to move around the fulcrum under the influence of the force applied to them.
Movement in any joint is provided by at least two muscles acting in opposite directions. They are called flexor and extensor muscles. For example, when you flex your arm, the biceps brachii muscle contracts and the triceps brachii muscle relaxes. This occurs because stimulation of the biceps muscle through the central nervous system causes the triceps muscle to relax.
Skeletal muscles are attached to both sides of the joint and, when contracted, produce movement in it. Typically, the muscles that perform flexion - flexors - are located in front, and the muscles that perform extension - extensors - are located behind the joint. Only in the knee and ankle joints, the anterior muscles, on the contrary, produce extension, and the posterior muscles - flexion.
So, when muscles tense and contract, they do work. But does any mechanism require control? and any work requires a certain amount of energy.
To answer the first part of the question, let’s watch a fragment of the video.
So, what system regulates muscle function? (spinal cord and brain);
Where are the centers of muscle movement? (cerebral cortex; anterior central sulcus)
We found out which system controls muscle function. But you also know from your physics course that any work requires a certain amount of energy.
What energy does the muscles use? Striated muscles are “engines” in which chemical energy is converted into mechanical energy.
Where does the chemical energy in the muscles come from? Let's watch the video clip.
– in muscle fibers the breakdown of organic substances occurs with the participation of oxygen, as a result of which energy is released
It is known that muscles use 33% of chemical energy for movement, and 67% of energy is consumed in the form of heat. That is why in the cold a person tries to move more, warming himself up using the energy generated by the muscles.
B) Fatigue
Can a muscle work indefinitely? Why?
A temporary decrease in performance that occurs as a result of work is called fatigue. It has been established, however, that fatigue occurs primarily not in the muscle itself, but in the central nervous system. Metabolism in the nervous system and muscles changes temporarily. During prolonged work, substances accumulate that interfere with the conduction of excitation and muscle contraction. Rest is necessary to restore the functionality of parts of the nervous system and muscles. Muscle performance is directly proportional to the rate of fatigue. What factors influence the rate of muscle fatigue? - load size, type of work (staticor dynamic) and rhythm. To find out exactly how these factors affect muscle performance, you are encouraged to study this problem experimentally.
But first, let's find out what kind of experiences you would offer yourself.
In front of you are cards with an algorithm for working on the task, you are given 10 minutes.
(work in groups)
Practical work No. 1
"The influence of the magnitude of the load on the development of fatigue."
Exercise: Consistently bend your arm with dumbbells of different weights (1, 3, 6 kg) at the same speed. In each case, count the number of movements, note the time of onset of fatigue (per second) and calculate the work done (A = F S n, F = 1 kg = 10 N, 1 kg = 1 9.8 H = 10 N
Where S is the distance; n is the number of movements.) Enter the data obtained into the table.
| Hand path (m) | Number of movements | Work (J) | Beginning of fatigue | Signs of fatigue |
|
| 1 | 0.5 n1 = | n1 = | A1 = | t1 = | 䦋㌌㏒㧀좈琰茞ᓀ㵂Ü |
| 3 | 0.5 n2 = | n2 = | A2 = | t2 = | 䦋㌌㏒㧀좈琰茞ᓀ㵂Ü |
| 6 | 0.5 n3 = | n3 = | A3 = | t3 = | 䦋㌌㏒㧀좈琰茞ᓀ㵂Ü |
Conclusion: Maximum muscle performance is observed at medium load
Practical work No. 2
“The influence of work rhythm on the development of fatigue”
Exercise: Bend your arm with dumbbells of the same mass at different tempos: slow, medium and fast. Record the number of movements, the time of onset of fatigue and the work performed in the table.
| Rhythm | Hand path (m) | Number of movements | Work (J) | Beginning of fatigue | Signs of fatigue |
| Rare | 0.5 n1 = | n1 = | A1 = | t1 = | 䦋㌌㏒㧀좈琰茞ᓀ㵂Ü |
| Average | 0.5 n2 = | n2 = | A2 = | t2 = | 䦋㌌㏒㧀좈琰茞ᓀ㵂Ü |
| Clean | 0.5 n3 = | n3 = | A3 = | t3 = | 䦋㌌㏒㧀좈琰茞ᓀ㵂Ü |
Conclusion. The greatest performance and its
duration is traceable
at an average work pace.
Practical work No. 3
"The influence of the type of muscle contraction on the development of fatigue."
Exercise:
A) Take a load weighing 3-5 kg and hold it with an outstretched arm at shoulder level. Notice the time when the hand begins to fall.
b) Take the same weight in your hand and raise it to the same level and lower it. note the time of fatigue in this case.
V) Compare dynamic and static work.
Conclusion: Muscles get tired faster when static because When the muscle is in a monotonous position, decay products accumulate in it and the nervous system gets tired, resulting in pain.
For the body, static work is tiring because with prolonged static tension of the muscles, the blood vessels that feed them are compressed. Through compressed arteries, the supply of oxygen and nutrients to the muscles worsens, and through compressed veins, the outflow of blood containing decay products is disrupted.
During dynamic work, different muscle groups contract alternately. The nervous system, controlling the work of muscles, adapts their work to the current needs of the body. This allows them to work economically.
Practical work No. 4
“The influence of muscle training on the development of fatigue”
The ability of muscles to perform work depends on their training, which increases muscle strength and has a beneficial effect on the muscles and on the condition of the skeleton.
In this group, the work is carried out by two students: one is engaged in the sports section, the other - only in physical education lessons.
Conclusion. The better developed the muscles, the longer their work, despite the increase in load, and the slower the onset of fatigue.
Two people argued about how best to carry a load: alternately with the right and left hands without resting, or to carry it in the right hand, then rest and carry it again in the same hand?
Answer, when was the working condition of the right hand restored most quickly, during rest or when working with the left hand? What is the importance of active rest for the muscular system?
And now we will conduct another experiment - demonstrating experiments with a dynamometer.
On the desk:
I Right hand rest 30 sec Right hand
II Right hand left Right hand
What's the conclusion? - The right hand rests better when the left hand works, because the excitation that occurs when the left hand works causes an inhibition process in the centers of the right hand of the brain, and the rest of the right hand becomes more complete. The Russian scientist physiologist I.M. worked on studying the influence of various factors on human performance. Sechenov, creator of the well-known work “Reflexes of the Brain”. THEM. Sechenov is the creator of “Physiology of Labor”.
The functionality of the right is restored faster
hands when working with the left hand. Active leisure faster
relieves fatigue of the muscles that were taken
participation in work
(For muscle function, nerve impulses and energy are required, which is generated as a result of the oxidation of organic substances in the presence of oxygen.)
Testing the assimilation of new material
Why does your back get more tired than your arms when washing clothes by hand?
The back muscles function in a static mode, that is, they help maintain the same posture for a long time. With static force, the muscles are in a state of tension. With the simultaneous contraction of many muscle fibers, the work cannot be very long - the muscles get tired. Hands do dynamic work. The muscles contract alternately.
1. What does muscle work depend on?
2. What is fatigue?
3. What conditions influence the development of fatigue?
4. What is used to restore muscle performance? What does a sedentary lifestyle lead to?
Muscle work is a necessary condition for their life. Prolonged inactivity of muscles leads to their atrophy and loss of performance. Training muscles helps increase their volume, strength and performance, which affects the development of the whole organism. Think about whether there is enough physical activity in your daily routine.
Grades are given for independent answers and the work of each group.
Homework.
Think about and create physical exercises that would develop different muscle groups to maintain proper posture and muscle performance.
Foreign scientists, seeing that fatigue cannot be explained by humoral theories alone, began to study the fatigue of nerve conductors. They argued that under the influence of prolonged passage of excitation impulses (for example, when irritated by electric current), the nerve conductors become tired.
The Russian physiologist N. E. Vvedensky, having criticized a number of errors in the experiments of Western scientists, proved with facts that nerve conductors are practically tireless and that in the nerves the physiological conduction of excitation occurs with minimal waste of energy. Consequently, the cause of fatigue lay not in the muscle or in the nerve conductor. Naturally, the scientists’ thoughts turned to studying the performance of nerve cells.
One of the first who, through a vivid and interesting experiment, was able to show where the threads of fatigue stretch was I.M. Sechenov. Intensified study of issues of labor physiology in our country began precisely with his brilliant works. The excellent studies of I.M. Sechenov “Participation of the nervous system in human working movements” and “Essay on human working movements” to this day serve as desktop guides for researchers studying the physiology of labor. While dealing with issues of fatigue, I.M. Sechenov looked not only for the causes of fatigue, but also sought to find rational measures to combat this condition.
Let us imagine Ivan Mikhailovich Sechenov sitting at a simple device somewhat reminiscent of the ergograph described above. Only on the Sechenov ergograph it was no longer just one finger, but the whole hand, the movements of which were similar to those made when sawing wood. The weight rises and falls in a certain rhythm with each swing of the arm. 4 hours pass, the hand has already made 4800 movements, the height of lifting the load is decreasing more and more, fatigue is approaching. The inquisitive mind of the scientist decides to fight this inevitable phenomenon; he is looking for that “healing medicine” that could eliminate fatigue.
The scientist finds that short-term use of the left hand relieves fatigue of the right hand much faster than long rest.
I.M. Sechenov explained this as follows: short-term work with the left (non-working) hand gives rise to excitation impulses in the sensory nerves of the muscles, rushing to the central nervous system, where they seem to rebuild the work of the nervous system, exciting and refreshing it, setting it up for a new fruitful working rhythm. If this is so, I.M. Sechenov reasoned, then light electrical stimulation of the left hand should also relieve fatigue. In fact, this turned out to be the case: just as external beneficial stimuli that give us a good and pleasant mood (song and music, competition and interest in work), causing excitement of the analyzers, * increase the performance of the nervous system and our brain, so does minor work of the unoccupied left hand or weak electrical stimulation reduces fatigue. Thus, I.M. Sechenov showed that the essence of fatigue is rooted in the processes occurring in the central nervous system.
Many Soviet physiologists have been and are studying the phenomenon discovered by I.M. Sechenov (N.K. Vereshchagin, S.I. Krapiventseva, M.E. Marshak, G.V. Popov, A.D. Slonim, etc.) . Recently, for example, the Soviet scientist Sh. A. Chakhnashvili showed that restoration of the working capacity of a tired arm occurs not only with active rest associated with the activity of the other arm, but also with short-term work performed during rest by the lower extremities, muscles of the trunk and neck , chewing muscles. It turned out that contraction of the neck muscles (while moving the head) during a 10-second rest increases the recovery of the tired arm by 61-75% compared to “passive” rest of the same duration.
* The analyzer is a complex formation that includes a receptor, a sensory nerve and a nerve center in the cerebral cortex. Receptors (from the Latin word recipio - I perceive) are sensitive nerve endings in a muscle or other organ (eye, ear). The perception of external and internal stimuli is carried out not by receptors as such, but by the entire analyzer system as a whole. The doctrine of analyzers was first introduced into physiological science.
A person’s ability to perform physical (muscular) work for a long time is called physical performance. The amount of physical performance of a person depends on age, gender, fitness, environmental factors (temperature, time of day, oxygen content in the air, etc.) and the functional state of the body. To compare the physical performance of different people, calculate the total amount of work performed in 1 minute, divide it by body weight (kg) and obtain relative physical performance (kg * m / min per 1 kg of body weight). On average, the level of physical performance of a 20-year-old boy is 15.5 kg*m/min per 1 kg of body weight, and for a young athlete of the same age it reaches 25. In recent years, determining the level of physical performance is widely used to assess general physical development and condition health of children and adolescents.
Prolonged and intense physical activity leads to a temporary decrease in the physical performance of the body. It's physiological the condition is called fatigue. It is currently shown that the process of fatigue primarily affects the central nervous system, then the neuromuscular junction and, in last but not least, the muscle. For the first time, the importance of the nervous system in the development of fatigue processes in the body was noted by I.M. Sechenov. Proof of the validity of this conclusion can be considered the fact that interesting work does not cause fatigue for a long time, and uninteresting work very quickly, although muscle loads in the first case may even exceed the work performed by the same person in the second case.
Fatigue is a normal physiological process developed evolutionarily to protect the body's systems from systematic overwork, which is a pathological process and is characterized by a disorder of the nervous system and other physiological systems of the body.
7.2.5. Age-related characteristics of muscle systems
The muscular system undergoes significant structural and functional changes during ontogenesis. Formation of muscle cells and muscle development as structural units of the muscular system occurs heterochronically, i.e. are first formed those skeletal ones muscles that are necessary for the normal functioning of the child’s body at this age stage. The process of “rough” muscle formation ends by 7-8 weeks of prenatal development. After birth, the process of formation of the muscular system continues. In particular, intensive growth of muscle fibers is observed up to 7 years and during puberty. By the age of 14-16 years, the microstructure of skeletal muscle tissue is almost completely mature, but the thickening of the muscle fibers (improvement of their contractile apparatus) can last up to 30-35 years.
The development of the muscles of the upper extremities is ahead of the development of the muscles of the lower extremities. In a one-year-old child, the muscles of the shoulder girdle and arms are much better developed than the muscles of the pelvis and legs. Larger muscles are always formed before smaller ones. For example, the muscles of the forearm are formed before the small muscles of the hand. The muscles of the arms develop especially intensively at 6-7 years of age. The total muscle mass increases very quickly during puberty: for boys - at 13-14 years old, and for girls - at 11-12 years old. Below are data characterizing the mass of skeletal muscles in the process of postnatal ontogenesis.
Much The functional properties of muscles also change during ontogenesis. Increases excitability and lability muscle tissue. Changes muscle tone. The newborn has increased muscle tone, and the flexor muscles of the limbs predominate over the extensor muscles. As a result, the arms and legs of infants are often in a bent state. They have a poorly expressed ability of muscles to relax (some stiffness in the movements of children is associated with this), which improves with age. Only after 13 - 15 years of age do movements become more flexible. It was at this age The formation of all sections of the motor analyzer ends.
In the process of development of the musculoskeletal system, the motor qualities of muscles change: speed, strength, agility and endurance. Their development occurs unevenly. First of all, speed and agility are developed.
Speed (speed) of movements characterized by the number of movements that a child is able to produce per unit of time. It is determined by three indicators:
1) the speed of a single movement,
2) time of motor reaction and
3) frequency of movements.
Single movement speed increases significantly in children from 4-5 years of age and reaches adult levels by 13-15 years. By the same age, the adult level also reaches simple motor reaction time, which is determined by the speed of physiological processes in the neuromuscular system. Maximum voluntary frequency of movements increases from 7 to 13 years, and in boys at 7-10 years it is higher than in girls, and from 13-14 years the frequency of movements in girls exceeds this figure in boys. Finally, the maximum frequency of movements in a given rhythm also increases sharply at 7–9 years. In general, the speed of movement develops to its maximum by the age of 16-17 years.
Until the age of 13-14 years, most development is completed dexterity, which is associated with the ability of children and adolescents to carry out precise, coordinated movements. Therefore, dexterity is related to:
1) with spatial accuracy of movements,
2) with temporal accuracy of movements,
3) with the speed of solving complex motor problems.
The preschool and primary school periods are the most important for the development of dexterity. The greatest increase in movement accuracy observed from 4 - 5 to 7 - 8 years. Interestingly, sports training has a beneficial effect on the development of dexterity and in 15-16 year old athletes the accuracy of movements is two times higher than in untrained adolescents of the same age. Thus, until the age of 6 - 7 years, children are not able to make subtle, precise movements in an extremely short time. Then spatial precision of movements gradually develops, A behind it is a temporary one. Finally, Lastly, the ability to quickly solve motor problems improves in various situations. Agility continues to improve until age 17-18.
Largest strength gain observed in middle and high school age, strength increases especially intensively from 10 - 12 years to 16 -17 years. In girls, the increase in strength is activated somewhat earlier, from 10 to 12 years, and in boys, from 13 to 14 years. However, boys are superior to girls in this indicator in all age groups.
Endurance develops later than other motor qualities. characterized by the time during which a sufficient level of performance of the body is maintained. There are age, gender And individual differences in endurance. The endurance of preschool children is low, especially for static work. An intensive increase in endurance for dynamic work is observed from 11 to 12 years old. So, if we take the volume of dynamic work of 7-year-old children as 100%, then for 10-year-olds it will be 150%, and for 14-15-year-olds it will be more than 400%. From the age of 11-12, children also rapidly increase their endurance to static loads. In general, by the age of 17-19, endurance is about 85% of the adult level. It reaches its maximum level by 25 - 30 years.
Development of movements and mechanisms of their coordination It is most intense in the first years of life and adolescence. In a newborn, the coordination of movements is very imperfect, and the movements themselves have only a conditional-reflex basis. Of particular interest is the swimming reflex, the maximum manifestation of which is observed approximately 40 days after birth. At this age, the child is able to make swimming movements in the water and stay on it until 1 5 minutes. Naturally, the child's head must be supported, since his own neck muscles are still very weak. Subsequently, the swimming reflex and other unconditioned reflexes gradually fade away, and motor skills are formed to replace them. All basic natural movements characteristic of a person (walking, climbing, running, jumping, etc.) and their coordination are formed in a child mainly before 3 - 5 years. Moreover, the first weeks of life are of great importance for the normal development of movements. Naturally, even in preschool age, coordination mechanisms are still very imperfect. Despite this, children are able to master relatively complex movements. In particular, it is V At this age they learn tool movements, i.e. motor skills and skills to use tools (hammer, wrench, scissors). From 6 to 7 years old, children master writing and other movements that require fine coordination. By the beginning of adolescence, the formation of coordination mechanisms is generally completed, and all types of movements become available to adolescents. Of course, improving movements and their coordination with systematic exercises is also possible in adulthood (for example, athletes, musicians, etc.).
Improving movements is always closely related to the development of the child’s nervous system. In adolescence, coordination of movements is very often somewhat disrupted due to hormonal changes. Usually by 15 - ] 6 years this temporary deterioration disappears without a trace. The general formation of coordination mechanisms ends at the end of adolescence, and by the age of 18–25 they fully reach the level of an adult. The age of 18-30 is considered “golden” in the development of human motor skills. This is the age at which his motor abilities flourish.
Fatigue means temporary decrease in performance cell, organ or organism, which arises as a result of work and disappears after rest.
Muscle fatigue. If single rhythmic stimulation is applied to an isolated muscle with an inductive current at a frequency of 1-2 times per second and its contractions are recorded on the kymograph drum ( myogram), then the following phenomena can be noted. During the first period of the experiment, an increase in the magnitude of muscle contractions is observed. Increased muscle performance is the result of an increase in metabolic processes, excitability and lability. Then, over a long period of time, a constant amplitude of muscle contractions is observed. Subsequently, there is a gradual decrease in the contractile effect of the muscle until the absence of its response, which indicates the development of fatigue (Fig. 68).
Analysis of myograms shows that as fatigue develops, the duration of a single muscle contraction increases, mainly due to delayed muscle relaxation. Subsequently, the latent period of contraction and the threshold of irritation increase. With the development of fatigue, muscle chronaxy increases significantly. The causes of muscle fatigue are the accumulation of metabolic products (lactic, phosphoric acid, etc.), a decrease in oxygen supply and depletion of energy resources.
Neuromuscular fatigue. Sufficiently strong (or frequent) stimulation is applied to the nerve and a curve of muscle contractions is recorded on the kymograph drum. With prolonged irritation of the nerve, a gradual decrease in the amplitude of contractions and even the absence of a muscle response is observed (see Fig. 68). A weakening of the strength of the applied irritation or a decrease in its frequency is also not accompanied by a response from the muscle, which indicates the development of fatigue in the neuromuscular preparation (see Fig. 68, B).
In order to answer the question in which structure of the neuromuscular preparation fatigue first develops, let us move on to direct stimulation of the muscle with stimuli of initial strength or frequency. In this case, restoration of the mechanical reaction of the muscle is observed. It is logical to assume that fatigue developed either in the nerve or in the myoneural synapse. The works of N. E. Vvedensky have established that the nerve is practically indefatigable. Consequently, fatigue primarily develops in the region of the myoneural synapse of the neuromuscular preparation of the frog, which is associated with depletion of transmitter reserves in the nerve fiber terminals. In addition, if we compare the lability of various formations of the neuromuscular preparation, it turns out that the functional mobility of the myoneural synapse is the lowest (Fig. 69). In this regard, fatigue occurs faster in the synapse, as in a structure with lower lability.
Domestic physiologists I.M. Sechenov, I.P. Pavlov, A.A. Ukhtomsky, L.A. Orbeli approached the problem of fatigue of the entire organism from the position of the leading role of the central nervous system in it. In an organism whose unity is ensured by the joint activity of central and peripheral nervous mechanisms, fatigue develops first of all in the nerve centers.
The speed of onset of fatigue during prolonged physical or mental work is influenced by a person’s lifestyle, the conditions of his diet, sleep, the state of the central nervous system, the degree of fitness, etc.
At the end of the last century, physiologists began to study individual manifestations of fatigue. The Italian scientist Mosso proposed ergographic method research in humans about the process of fatigue that occurs during muscular work. Using the device ergograph The influence of the rhythm of the work performed and the size of the load lifted on the rate of fatigue occurrence was studied. The essence of the ergographic method is that the subject is asked, by straightening and bending the finger of the upper limb fixed in the device, to raise and lower a certain weight in rhythm with the beats of a metronome. Finger movements are recorded on the kymograph drum. The curve of muscle contractions recorded using an ergograph is called an ergogram (Fig. 70). It was found that the development of fatigue is primarily influenced by the rhythm of the work performed.
I.M. Sechenov studied fatigue by recording muscle contractions when lifting a load on an ergograph designed by him. I.M. Sechenov discovered that the performance of a tired hand during its rest is restored more fully and better if the other hand does the work during this period. The same effect on the performance of a tired hand is exerted by irritation by the induction current of the afferent nerves of the hand of the other hand, as well as footwork associated with lifting weights, and motor activity in general.
An analysis of established facts allowed I.M. Sechenov to come to the conclusion that rest, accompanied by moderate work of muscle groups, is a more effective means of combating fatigue of the musculoskeletal system than rest - passive rest. The concept appeared in physiology leisure.
The increase in performance after active rest is due to an increase in the excitability of neurons in the central nervous system under the influence of nerve impulses coming from proprioceptors, as well as the adaptive-trophic effect of the sympathetic nervous system on tired muscle groups (I. M. Sechenov, L. A. Orbeli).
Thus, the best way to combat fatigue is to change the form of work, replacing one type of activity with another.