.J Muscle growth after birth. Even in the first half of the intrauterine period of development, muscles acquire the characteristic giving them shape and structure^ Subsequently, their length and thickness quickly increase. They grow in length according to the growth of 1 volume of skeletal bones by lengthening muscle fibers and especially tendons, with the help of which “muscles are attached to bones.” Growth in thickness to a small extent occurs due to the formation of suture fibers from existing in the muscles there are remnants of "primary muscle tissue. However, mainly (approximately 90%) growth in thickness occurs by increasing the diameter of the fibers." In newborns it does not exceed 10-15 thousandths of a millimeter, and by 3-4 years it increases by 2-2 ,5 times. In subsequent years, the diameter of muscle fibers largely depends on the individual characteristics of the body, and mainly on motor activity.
In a newborn, muscles account for 20-22% of the weight of the entire body, i.e., approximately half as much as in an adult, whose muscles most often make up 35-45% of body weight. Consequently, over the entire period from birth to adulthood, the increase in muscle weight should be twice as intense as the increase in total body weight. However, at first, until the child begins to walk, muscles grow even more slowly than
^^im^prgyanichm r. prdpm^ Thus, in the first 4 months of life, total body weight doubles, and muscle weight increases only by 60% and accounts for 16% of body weight. From the end of the first year of life, under the influence of training, muscle growth gradually becomes more intense^ and by 6 years to the share of muscles again accounting for about 22% of total body weight, and by 8 years - 27°/o. Muscles grow especially intensively in the period from 14-15 to 17-18 years. Thus, muscles account for an average of 30^_ body weight at 14 years old, and 40% at 18-20 years old.
"development of movements. By birth, the child’s motor system is sufficiently developed to perform a number of simple movements.
The ability of muscles to contract appears even earlier - already by the end of the second month of intrauterine life. Muscle tone gradually develops, and during prenatal development and infancy, the tone of the flexor muscles prevails over the tone of the extensor muscles, which is important for maintaining the natural position of the body in the uterus (Fig. 17).
By the end of the third month, the human fetus can clench its fingers into a fist in response to touching the hand. After another month, barely noticeable and very slow contractions of the muscles of the trunk and limbs, mainly extensors, begin to appear occasionally. These are the so-called movements. Gradually they become more frequent and so pronounced that the pregnant woman clearly feels them. Long before birth, respiratory movements appear, expressed in a slight alternating increase and decrease in the volume of the chest, as well as swallowing and sucking movements. The elementary coordination of movements necessary for flexion and extension of the limbs, for sucking, swallowing and breathing movements, for head movements, undoubtedly appears even before birth. However, the movements proceed extremely slowly.
Already in the first days of life, the child shows great motor activity. Basically, these are random movements of the limbs. When positioned on the stomach, the child turns his head to the side, then his torso and, as if rolling, lies on his back. If you hold it in a vertical position, the head tilts forward, since its center of gravity is in front of the fulcrum, i.e., the junction of the skull with the spine, and the tone of the posterior cervical muscles is insufficient to maintain the correct position of the head.
In the second month of life, the child turns his head towards the light and somewhat later towards the sound. When lying on his stomach, he raises his head, and by the end of the second month, leaning on his hands, he raises not only his head, but also his chest.
A three-month-old baby begins to roll over from his back to his stomach. The movements of his hands gradually become more varied
Rice. 19. The appearance of curves in the spine due to sitting and standing.
figurative. At the age of 4-5 months, they begin to be well controlled by vision: seeing a new object, the child reaches out to it, grabs it and, as a rule, drags it into his mouth.
By 7 months, the child maintains a sitting position well, and after another month he sits down independently and, holding on to various objects, rises to his feet. Gradually he begins to crawl on all fours, and by the end of the year or in the first months of the second of the year life, at first falling every now and then, and then more and more confidently walking around the room without outside help.
Mastering the vertical position of the torso or the whole body leads to a number of significant changes in the motor system: firstly, the tone and contractility of the extensor muscles sharply increases; Secondly, bends appear in the soil-_IPchnikP| i^vT-^r"t-"Q gn^gn^gt to maintain balance, have
springy ow and i nir pra_ hplbe, run.-jumping and facilitate muscle work while maintaining a vertical body position for a long time. the newborn's spine is weak along its entire length pronounced bulge facing posteriorly; in its lower part the convexity is more pronounced - this cross.pvp-k.opchikp.th bend. The cervical curve begins to form towards the end of the second month, when the tone of the posterior cervical muscles increases and the child begins to first raise his head while lying on his stomach, and then hold it with his body in an upright position. The forward-facing convexity of the cervical spine becomes well defined much later, when the child independently maintains a sitting position for a long time. At the same time, a backward-facing convexity of the middle part is clearly visible dialer - rough bend. Stagnant sitting position i~oSo"oen- But standing promotes education lumbar curve, addressed
convex forward. Usually this bend becomes noticeable only in the 2nd year of life (Fig. 19).
In preschool children, the curves are still just forming and are highly dependent on the position of the body. After lying for a long time, for example after a night's sleep, the cervical curve and especially the lumbar curve may completely disappear, reappearing and intensifying towards the end of the day under the influence of sitting and walking. Even at primary school age, the curves flatten significantly during the night. The variability of the bends gradually disappears.
Preschool children are characterized by extreme flexibility of the body, which is explained by the large thickness and pliability of intervertebral cartilage and late ossification of the vertebral epiphyses. The curves of the spine are formed and subsequently strengthened under the influence of pressure from the upper parts of the body. The direction of pressure depends on posture, i.e., sitting, standing and walking postures.
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Kabanov A. N. and Chabovskaya A. P.
K-12 Anatomy, physiology and hygiene of preschool children. Textbook for preschool teacher training colleges. M., “Enlightenment”, 1969. 288 with illus. The textbook is written according to the program
Structure, composition and properties of body cells. Also in
first half of the 19th century the cellular structure of organisms was established. The bulk of each cell is a viscous, mucus-like semi-liquid substance - the cytoplasm. It contains about
Growth and development
Patterns of growth and development. Body proportions change greatly with age (Fig. 2). In a newborn, the height of the head is approximately "L, and in an adult - "/8 of the total length
General overview of the human skeleton
The meaning of the musculoskeletal system. The musculoskeletal system, or musculoskeletal system, includes the skeleton and skeletal muscles. Skedet is a solid skeleton on which depends
L->
The corresponding parts are located in the lower limb (leg) thigh; two bones of the lower leg - tibia and fibula; foot, consisting of the bones of the tarsus, metatarsus and
Properties and development of bone tissue
Cartilage and bone tissue. During the development of vertebrates, the bony skeleton did not appear immediately. The ancestors of modern vertebrates had a cartilaginous skeleton. In a human embryo
Development of the human skeleton
Skeleton of a newborn. The first islands, or centers, of ossification appear already at the beginning of the second month of intrauterine development, and by the time of birth they are absent only in the bones.
Muscle work
The principle of leverage. By contracting, the muscles perform work, either fixing the position of the bones in the joint and making movement impossible, or, conversely, changing their relative position, i.e.
Development of basic properties of the motor system
Coordination of movements. Maintaining an upright body position requires the well-coordinated activity of nearly three hundred large and small muscles. Each muscle must contract
Developing correct posture
Normal posture. Posture, i.e. the usual posture when sitting, standing, walking, begins to form in early childhood. Normal, or correct, is considered such posture that
General overview of the structure and functions of the nervous system
Central and peripheral sections. The nervous system is divided into central and peripheral sections (color table V). The central section includes the spinal cord,
Conducting excitation in the nervous system
Excitement as a response to irritation. Phenomena associated with excitation have long been studied using isolated frog neuromuscular preparations, for which most often
Coordination of body functions
Reflex as a reaction of the whole organism. The flow of impulses generated by stimulation of visual, pain or other receptors enters the brain and becomes a source of coordinated,
Nervous system development
Newborn period. Another 3 months before the normal birth date, the fetal nervous system is sufficiently developed to ensure the functioning of the body in external conditions.
Conditioned reflexes and their formation
Pavlovian method of studying higher nervous activity. The idea has long arisen that feelings, thoughts and desires are associated with the existence of an unknowable stupidity. It was believed
Inhibition of conditioned reflexes
b^ Unconditional inhibition. In the cerebral cortex, as in other parts of the brain, excitation of any one area causes negative induction, i.e., a decrease in excitability in
Analytical and synthetic activity of the cerebral cortex
Analyze the synthesis of irritation. Countless, continuously occurring changes in the environment and in the body itself, acting as stimuli on the corresponding receptors. mills
Study of conditioned reflexes in humans
Conditioned reflex nature of human higher nervous activity. Beginning in 1906, N.I. Krasnogorsky, a student and follower of I.P. Pavlov, studied food conditioning in children
Features of higher nervous activity of children
Formation of the first conditioned reflexes. Higher nervous activity is manifested in the formation of conditioned reflexes. A premature baby can develop conditioned
Speech development
The meaning of speech components of complex stimuli. From the first months of life, a child is surrounded by people. He sees them, hears human speech, which very early becomes conventional
Isolation of individual signs of stimuli. At
In the formation of positive and negative conditioned reflexes to several similar complex stimuli, the process of isolating individual components or features occurs, allowing both
Types of higher nervous activity
Classification of types. Greek physician Hippocrates, who lived in the 4th century. BC, wrote that each person, based on the characteristics of his behavior, can be classified into one of four
Sleep and its physiological significance
p> Sleep and wakefulness. Regular alternation of sleep and wakefulness is a necessary condition for the normal functioning of the human body. During wakefulness, increased
Hygienic sleep organization
Children's sleep duration. Young infants sleep almost continuously, waking up only for feeding periods. A newborn baby sleeps 20-21 hours a day. Subsequently
Fatigue and the fight against it
Fatigue and tiredness. Any physical or mental work causes a number of changes in the state and reactions of the body. For example, attention, memory, vision and
Regime in preschool institutions
Main components of the mode. The correct regime is a rational and clear alternation of various types of activities and rest during the day, their occurrence in a certain, daily manner.
Hygienic requirements for conducting activities and games
Furniture. For preschool institutions, furniture (tables and chairs) of various sizes has been developed according to the height of the children. Furniture of the same size can be used by children
Childish nervousness
Disorders of higher nervous activity. In experiments on dogs, I.P. Pavlov discovered that serious disturbances in higher nervous activity can be caused if excessive force is used.
General patterns of analyzer functions
, . Analysis of irritation. Brain activity, aimed at organizing and coordinating the work of all organs, as well as orientation in the environment, requires precise and continuous
Skin analyzer
Skin analyzer meaning. Receptors located in the skin make it possible to touch, that is, to feel the impact of environmental irritants on the skin. Through human skin receptors
Internal analyzers
Information about your own body. In all organs there are various receptors that are sensitive to certain chemical changes, pressure, stretching, temperature changes
Olfactory and gustatory analyzers
The significance of the olfactory and gustatory analyzers. The receptors of the olfactory analyzer are located in the upper part of the right and left half of the nasal cavity, occupying a total area of approx.
C 36. Structure and development of the eye
The structure of the eye. The peripheral section of the visual analyzer, in other words, receptors sensitive to light, are located inside the organ of vision, or eye (color table XI), which
Farsightedness and myopia
v0 Natural children's farsightedness. In a newborn, the cornea and lens are more convex, and their size is almost the same as in adults. Under natural conditions, i.e. stretched
Perception of light and color
The light-sensitive apparatus of the eye. A ray of light, passing through the optical media of the eye, penetrates the retina and hits its outer layer (Fig. 51). This is where the viewer receptors are located.
Spatial vision
, ; Binocular Vision/In most animals, each eye has its own separate field of vision. A person sees a significant part of the visual fields of both eyes simultaneously in both the right and left
Organization of activities requiring visual strain
Excessive visual strain, if repeated frequently, contributes to the development of myopia, and often strabismus. Therefore, it is necessary to pay great attention to organizing such an environment,
The importance of the circulatory system
Circular movement of blood. The blood filling the cardiovascular system is in continuous circular motion - ^ color. table XII).. The role of the pump transferring
A. blood 43. blood composition
^ Blood plasma. “Blood is an opaque, red liquid, “in which there are many tiny blood cells, (color table X1U>_Zhig1kyad part of the blood is called plasma
Age characteristics of blood
Blood formation in children. In newborns, red bone marrow fills not only the spaces between the trabeculae of the spongy bones, but also the cavities inside the long diaphysis
Inflammation as a general defense reaction of the body
Penetration of foreign substances, especially microbes, into the skin or any organ of the body, as well as damage from a bruise, burn or wound almost always cause an inflammatory reaction: to
Immunity
“Natural immunity. Immunity is the body's immunity to infection. Susceptibility to a particular disease varies not only among different
The heart and its work
/) in The structure of the heart. The heart is located in the chest cavity almost along the midline of the body, behind the sternum and slightly to the left of it. The upper part of the heart from which it arises
Age-related features of the structure and functioning of the heart
Fetal circulation. The fetus, like an adult, has two circles of blood circulation - large and small. However, during intrauterine development, the body is supplied with oxygen
Movement of blood through vessels
Argeria, capillaries, veins. In their structure, arteries, capillaries and veins are very different from each other (Fig. 63). The thick wall of the arteries is mainly composed of smooth muscle and
Regulation of blood circulation
Meeting the body's need for oxygen. The body, in every organ of the body, has reserves of nutrients, but no reserves of oxygen. Therefore, oxygen delivery is carried out
Heart training
Reserve forces of the heart. The minute volume of blood ejected by the heart into the aorta changes dramatically depending on the body's need for oxygen. So, when running fast, when running hard
Structure of the respiratory organs
The meaning of breathing. Respiration is the exchange of gases between Mf^.ny " "p^chchyampm and the environment. ^ in humans, as in all mammals, this exchange is carried out specially
Breathing movements
Jl&C^OUJULfLmfi1&<£^ ^ G^^^Q Вдыхательные и выдыхательны? мышцы. Кровь, притекающая к легким, богата углекислотой, но бедна кис
Formation of pulmonary respiration in a newborn. Already
By the end of the 5th month of intrauterine development, weak respiratory movements of the chest become noticeable - at first rare, and later more frequent - up to 30-40 per minute. As you know, the fetus is surrounded
The importance of proper breathing
Breathing rhythm. In preschool children, breathing is usually uneven. The breathing rhythm changes, i.e. the alternation of inhalation and exhalation does not remain constant: then the inhalation is short
Air mode of preschool institutions
Microclimate. When building a home, a person creates a microclimate in it, that is, a local climate that is characterized by the physical properties of air (temperature, humidity, ionization
Entry of food into the digestive tract
The meaning of digestion. Food contains such substances. which without prrgtnyarntrgtt.ng^ nggeTTaDuikH nor mshut iitttntttShut from the digestive organs r krgya^ During processing occurs
Timing of eruption of primary and permanent teeth
Name of teeth Period of eruption of permanent milk teeth 6-8 months. 7-10 "14
Digestion of food
Pavlovian method of studying the functioning of the digestive glands. Digestion consists of breaking down complex particles of proteins, fats and carbohydrates into those that could, firstly, be digested
The functioning of the digestive organs in general
Work consistency. Throughout the long path of the digestive tract, the digestive organs work with amazing precision and consistency. The sight, smell or conversation is enough
Age-related features of the structure and functioning of the digestive organs
Digestive organs of a newborn. The digestive organs begin to function long before birth. However, until the end of the intrauterine period, the secretory function
Metabolism and energy in the body
Assimilation and dissimilation. Substances entering the baby undergo complex processes and turn into the substance of the cell itself. This is the assimilation of substances, their assimilation to substances class
The energy side of metabolism and nutritional standards
Daily energy expenditure. Energy expenditure by the human body largely depends on living conditions, the nature and amount of work performed, body weight, and state of health.
Physiological and hygienic principles of catering
Appetite. The functioning of the digestive organs largely depends on the desire to eat, in other words, on appetite. The sensation of appetite is associated with increased excitability of so-called foods
Infant feeding
Diet in infancy. The first months of life, the child’s nutrition is entirely provided by the mother’s body. The transition to regular food consumption occurs gradually over time.
Catering for children from 1 to 7 years old
Menu creation. By the end of the 1st year of life, the child gets used to a variety of foods and, as a rule, can be transferred to a common table. At first, they give pureed food in the form of porridges and
Gastrointestinal diseases in children
Dyspepsia. Dyspepsia (indigestion) manifests itself in infants as restlessness, frequent bowel movements, regurgitation or slight vomiting. Dyspepsia may be caused by disordered
Food hygiene
Requirements for food products. Food products supplied to children's institutions must be fresh and of good quality, without foreign impurities, and not contain pathogenic substances.
Urine formation
Ways of excretion of metabolic products. Each cell secretes breakdown products formed during the metabolic process. They enter the tissue fluid, and from there into the blood. Timely
Removing urine from the body
Urinary tract. From the renal pelvis, urine enters the ureter - a hollow tube about 30 cm long. The wall of the ureter contains smooth muscles. They contract peristaltically
Hormonal regulation of body functions
The significance of the endocrine glands. Zhede1ami__lu-trennoy secretion nyachyryatptgp ftprnniii) trp^i^t tissue which produces and secretes into the blood or.pimfl/ biologically atgtgv-nye
Internal secretion of a growing organism
The period of intrauterine development. Initially, intrauterine development is influenced by the hormones of the mother's body. Most endocrine glands are formed in the fetus
Male and female genital organs
The structure of the male genital organs. The function of the male reproductive organs is the formation and release of sperm. The organ in which they are formed is called the seminal organ.
Structure and functions of the skin
The meaning of skin. The outer covering of the body, or skin, protects the body from harmful environmental influences and prevents liquid or gaseous substances from entering it. To the core
Heat transfer from the skin under different meteorological conditions
As the air temperature rises, numerous blood vessels in the skin dilate and a large amount of blood flows through them. As a result, the skin heats up and heat is released into the surrounding air.
Skin lesions in various diseases
Causes of skin lesions in children. In children, skin lesions can occur due to various contagious and non-contagious diseases. The younger the child, the easier it occurs and the more severe it is.
Skin and clothing hygiene
Skin care. Skin hygiene is of great importance for the prevention of not only skin diseases, but also a number of other, especially gastrointestinal, diseases. For skin care you need to have
Hardening Basics
The meaning of hardening. Hardening the body is called increasing its resistance to sudden temperature fluctuations and other meteorological conditions. Hardening dos
Hardening agents
Indoor air. Air is the most accessible means of hardening throughout the year, even for those children for whom other types of hardening may be contraindicated for health reasons.
Acute infectious diseases
Measles. Measles is a highly contagious disease. Its causative agent is a filterable virus, very volatile and poorly viable outside the human body. A person with measles spreads it to
Chronic infectious diseases
Tuberculosis. Tuberculosis is a chronic infectious disease, the course and outcome of which largely depends on the body's resistance. The main source of infection is sick
Burns and frostbite
Thermal and chemical burns. Burns can be caused by flame, boiling water, steam, acids, alkalis, some medications (lapis, iodine, ammonia, etc.), electrical
Bites and foreign bodies entering the body
First aid for bites. In the summer, especially outside the city, children are often exposed to mosquito bites. Swelling, redness, and
Loss of consciousness
Fainting. Loss of consciousness caused by anemia of the brain is called fainting. The cause of fainting may be fatigue, severe excitement or nervous shock, hunger,
Hygienic education of children
Instilling hygiene skills in children. Hygienic education of children is aimed at instilling in them hygienic skills and imparting basic knowledge that substantiates these skills. One
Sanitary educational work with parents
Work with parents aimed at increasing hygienic knowledge in the care and upbringing of children should be carried out in preschool institutions according to a specially developed plan, if necessary
Anatomy, physiology and hygiene of preschool children
textbook for preschool teacher training colleges. Editor A. M. Pridantseva. Layout and design by artist V.I. Preobrazhenskaya. Cover by artist D.K. Ivanov. Color
3.3. Muscle growth and function
During intrauterine development, muscle fibers are formed heterochronically. Initially, the muscles of the tongue, lips, diaphragm, intercostal and dorsal muscles are differentiated, in the limbs - first the muscles of the arms, then the legs, in each limb first - the proximal sections, and then the distal ones. Embryonic muscles contain less protein and more (up to 80%) water. The development and growth of different muscles after birth also occurs unevenly. The muscles that provide motor functions, which are extremely important for life, begin to develop earlier and more. These are the muscles that are involved in breathing, sucking, grasping objects, i.e. the diaphragm, muscles of the tongue, lips, hands, intercostal muscles. In addition, the muscles involved in the process of learning and developing certain skills in children are trained and developed more.
A newborn has all the skeletal muscles, but they weigh 37 times less than an adult. Skeletal muscles grow and form until approximately 20-25 years of age, influencing the growth and formation of the skeleton. Muscle weight increases unevenly with age, and this process occurs especially quickly during puberty.
Body weight increases with age mainly due to an increase in the weight of skeletal muscles. The average weight of skeletal muscles as a percentage of body weight is distributed as follows: in newborns - 23.3; at 8 years old - 27.2; at 12 years old - 29.4; at 15 years old - 32.6; at 18 years old - 44.2.
Age-related features of growth and development of skeletal muscles. The following pattern of growth and development of skeletal muscles is observed at different age periods.
Period up to 1 year: more than the muscles of the pelvis, hips and legs, the muscles of the shoulder girdle and arms are developed.
Period from 2 to 4 years: in the arm and shoulder girdle, proximal muscles are much thicker than distal ones, superficial muscles are thicker than deep ones, functionally active ones are thicker than less active ones. Fibers grow especially quickly in the longissimus dorsi muscle and in the gluteus maximus muscle.
Period from 4 to 5 years: the muscles of the shoulder and forearm are developed, the muscles of the hands are underdeveloped. In early childhood, the muscles of the trunk develop much faster than the muscles of the arms and legs.
Period from 6 to 7 years: the development of hand muscles accelerates when the child begins to do light work and learn to write. The development of flexors is faster than the development of extensors.
In addition, flexors have greater weight and physiological diameter than extensors. The finger muscles, especially the flexors, which are involved in grasping objects, have the greatest weight and physiological diameter. Compared to them, the wrist flexors have relatively less weight and physiological diameter.
Period up to 9 years: the physiological diameter of the muscles causing finger movements increases, at the same time, the muscles of the wrist and elbow joints grow less intensively.
Period up to 10 years: the diameter of the flexor pollicis longus by 10 years reaches almost 65% of the length of the diameter of an adult.
Period from 12 to 16 years: the muscles that ensure the vertical position of the body grow, especially the iliopsoas, which plays an important role in walking. By the age of 15-16 years, the thickness of the fibers of the iliopsoas muscle becomes greatest.
The anatomical diameter of the shoulder in the period from 3 to 16 years increases in boys by 2.5-3 times, in girls - less.
The deep back muscles in the first years of life in children are still weak, and their tendon-ligamentous apparatus is also underdeveloped, but by the age of 12-14 these muscles are strengthened by the tendon-ligamentous apparatus, but less than in adults.
The abdominal muscles of newborns are not developed. From 1 year to 3 years, these muscles and their aponeuroses differ, and only by 14-16 years the anterior wall of the abdomen is strengthened almost in the same way as in an adult. Until the age of 9 years, the rectus abdominis muscle grows very intensively, its weight compared to the weight of a newborn increases almost 90 times, the internal oblique muscle - more than 70 times, the external oblique - 67 times, the transverse muscle - 60 times. These muscles resist the gradually increasing pressure of the internal organs.
In the biceps brachii and quadriceps femoris, muscle fibers thicken: by 1 year - twice; by 6 years - five times; by the age of 17 - eight times; by the age of 20 - 17 times.
Muscle growth in length occurs at the junction of muscle fibers and tendons. This process continues until the age of 23-25. From 13 to 15 years, the contractile part of the muscle grows especially quickly. By the age of 14-15, muscle differentiation reaches a high level. The growth of fibers in thickness continues up to 30-35 years. The diameter of the muscle fibers thickens: by 1 year - twice; by 5 years - five times; by the age of 17 - eight times; by the age of 20 - 17 times.
Muscle mass increases especially rapidly in girls at 11-12 years old, and in boys at 13-14 years old. In adolescents, skeletal muscle mass increases by 12% over two to three years, while in the previous 7 years it increased by only 5%. Skeletal muscle weight in adolescents is approximately 35% of body weight, and muscle strength increases significantly. The muscles of the back, shoulder girdle, arms and legs develop significantly, which causes increased growth of tubular bones. The harmonious development of skeletal muscles is facilitated by the correct selection of physical exercises.
Age-related features of the structure of skeletal muscles. The chemical composition and structure of skeletal muscles also change with age. The muscles of children contain more water and less dense substances than those of adults. The biochemical activity of red muscle fibers is greater than white ones. This is explained by differences in the number of mitochondria or in the activity of their enzymes. The amount of myoglobin (an indicator of the intensity of oxidative processes) increases with age. In a newborn, skeletal muscles contain 0.6% myoglobin, in adults - 2.7%. In addition, children contain relatively less contractile proteins - myosin and actin. With age, this difference decreases.
The muscle fibers of children contain relatively more nuclei, they are shorter and thinner, but with age both their length and thickness increase. The muscle fibers of newborns are thin, tender, their cross-striations are relatively weak and are surrounded by large layers of loose connective tissue. Tendons take up relatively more space. Many nuclei within muscle fibers do not lie near the cell membrane. Myofibrils are surrounded by distinct layers of sarcoplasm.
The following dynamics of changes in the structure of skeletal muscles depending on age is observed.
1. At 2-3 years, muscle fibers are twice as thick as in newborns, they are located more densely, the number of myofibrils increases, and sarcoplasm decreases, the nuclei are adjacent to the membrane.
2. At 7 years of age, the thickness of the muscle fibers is three times thicker than in newborns, and their transverse striations are clearly expressed.
3. By the age of 15-16, the structure of muscle tissue becomes the same as in adults. By this time, the formation of the sarcolemma is completed.
The maturation of muscle fibers can be traced by changes in the frequency and amplitude of biocurrents recorded from the biceps brachii muscle when holding a load:
in children 7-8 years old, as the time of holding the load increases, the frequency and amplitude of biocurrents decrease more and more. This proves the immaturity of some of their muscle fibers;
in children 12-14 years old, the frequency and amplitude of biocurrents do not change during 6-9 s of holding the load at maximum height or decrease at a later date. This indicates the maturity of the muscle fibers.
In children, unlike adults, muscles are attached to the bones further from the axes of rotation of the joints, therefore, their contraction is accompanied by less loss of strength than in adults. With age, the relationship between the muscle and its tendon changes significantly, growing more intensively. As a result, the nature of the attachment of the muscle to the bone changes, and therefore the efficiency increases. Around 12-14 years of age, the “muscle-tendon” relationship stabilizes, which is typical for an adult. In the upper extremity girdle, up to 15 years of age, the development of the muscle belly and tendons occurs equally intensively; after 15 and up to 23-25 years of age, the tendon grows more intensively.
The elasticity of children's muscles is approximately twice as large as that of adults. When contracting, they shorten more, and when stretching, they lengthen more.
Muscle spindles appear at 10-14 weeks of uterine life. An increase in their length and diameter occurs in the first years of a child’s life. In the period from 6 to 10 years, the transverse size of the spindles changes slightly. In the period of 12-15 years, muscle spindles complete their development and have the same structure as in adults at 20-30 years of age.
The formation of sensitive innervation begins at 3.5-4 months of uterine life, and by 7-8 months the nerve fibers reach significant development. By the time of birth, centripetal nerve fibers are actively myelinated.
The muscle spindles of a single muscle have the same structure, but their number and the level of development of individual structures in different muscles are not the same. The complexity of their structure depends on the amplitude of movement and the strength of muscle contraction. This is due to the coordination work of the muscle: the higher it is, the more muscle spindles it contains and the more complex they are. Some muscles do not have non-stretchable muscle spindles. Such muscles, for example, are the short muscles of the palm and foot.
Motor nerve endings (myoneural apparatus) appear in a child during the uterine period of life (at the age of 3.5-5 months). They develop in the same way in different muscles. By the time of birth, the number of nerve endings in the arm muscles is greater than in the intercostal muscles and lower leg muscles. In a newborn, motor nerve fibers are covered with a myelin sheath, which becomes very thick by the age of 7. By the age of 3-5 years, the nerve endings become significantly more complex, by the age of 7-14 they become even more differentiated, and by the age of 19-20 they reach full maturity.
Age-related changes in muscle excitability and lability. For the functioning of the muscular system, not only the properties of the muscles themselves are important, but also age-related changes in the physiological properties of the motor nerves that innervate them. To assess the excitability of nerve fibers, a relative indicator is used, expressed in units of time - chronaxia. In newborns, a more elongated chronaxia is observed. During the first year of life, the level of chronaxy decreases by approximately 3-4 times. In subsequent years, the value of chronaxy gradually shortens, but in school-age children it still exceeds the chronaxy of an adult. Thus, a decrease in chronaxy from birth to the school period indicates that the excitability of nerves and muscles increases with age.
For children aged 8-11 years, as for adults, flexor chronaxy is characteristically greater than extensor chronaxy. The difference in the chronaxy of antagonist muscles is most pronounced on the arms than on the legs. Chronaxy of distal muscles exceeds that of proximal muscles. For example, the chronaxy of the shoulder muscles is approximately two times shorter than the chronaxy of the forearm muscles. In less toned muscles, the chronaxia is longer than in more toned ones. For example, the biceps femoris and tibialis anterior muscles have a longer chronaxia than their antagonists, the quadriceps femoris and gastrocnemius. The transition from light to darkness lengthens chronaxy, and vice versa.
During the day, chronaxy changes in children of primary school age. After 1-2 general education lessons, a decrease in motor chronaxis is observed, and by the end of the school day it is often restored to its previous level or even increases. After easy general education lessons, motor chronaxia most often decreases, and after difficult lessons it increases.
As people grow older, fluctuations in motor chronaxy gradually decrease, while chronaxy in the vestibular apparatus increases.
Functional mobility, or lability, in contrast to chronaxy, determines not only the shortest time required for the occurrence of excitation, but also the time required to complete the excitation and restore the ability of the tissue to give new subsequent excitation impulses. The faster the skeletal muscle reacts, the more excitation impulses pass through it per unit time, the greater its lability. Consequently, muscle lability increases with increasing mobility of the nervous process in motor ones (accelerating the transition of excitation to inhibition), and vice versa - with increasing speed of muscle contraction. The slower the muscles react, the less lability they have. In children, lability increases with age; by the age of 14-15 it reaches the level of lability of adults.
Changes in muscle tone. In early childhood, there is significant tension in certain muscles, such as the hands and hip flexors, due to the involvement of skeletal muscles in generating heat at rest. This muscle tone is of reflex origin and decreases with age.
The tone of skeletal muscles is manifested in their resistance to active deformation during compression and stretching. At the age of 8-9 years, boys have greater muscle tone, such as the hamstrings, than girls. By the age of 10-11, muscle tone decreases, and then increases significantly again. The greatest increase in skeletal muscle tone is observed in adolescents aged 12-15 years, especially boys, in whom it reaches youthful values. During the transition from preschool to preschool age, there is a gradual cessation of participation of skeletal muscles in heat production at rest. At rest, the muscles become increasingly relaxed.
In contrast to voluntary tension of skeletal muscles, the process of voluntary relaxation is more difficult to achieve. This ability increases with age, so the stiffness of movements decreases in boys up to 12-13 years old, in girls - up to 14-15 years old. Then the reverse process occurs: stiffness of movement increases again from the age of 14-15, while in boys aged 16-18 it is significantly greater than in girls.
Sarcomere structure and mechanism of muscle fiber contraction. A sarcomere is a repeating segment of myofibril, consisting of two halves of a light (optically isotropic) disk (I-disc) and one dark (anisotropic) disk (A-disc). Electron microscopic and biochemical analysis revealed that the dark disk is formed by a parallel bundle of thick (diameter about 10 nm) myosin filaments, the length of which is about 1.6 μm. The molecular weight of the myosin protein is 500,000 D. The heads of myosin molecules (20 nm long) are located on the myosin filaments. The light discs contain thin filaments (5 nm in diameter and 1 µm in length), which are built from protein and actin (molecular weight - 42,000 D), as well as tropomyosin and troponin. In the region of the Z-line, delimiting adjacent sarcomeres, a bundle of thin filaments is held together by a Z-membrane.
The ratio of thin and thick filaments in the sarcomere is 2: 1. The myosin and actin filaments of the sarcomere are arranged so that the thin filaments can freely fit between the thick filaments, i.e., “move” into the A-disc, this is what happens during muscle contraction. Therefore, the length of the light part of the sarcomere (I-disc) can be different: with passive stretching of the muscle it increases to a maximum, and with contraction it can decrease to zero.
The contraction mechanism is the movement (pulling) of thin filaments along thick filaments to the center of the sarcomere due to the “rowing” movements of myosin heads, which periodically attach to thin filaments, forming transverse actomyosin bridges. By studying the movements of the bridges using the X-ray diffraction method, it was determined that the amplitude of these movements is 20 nm, and the frequency is 5-50 vibrations per second. In this case, each bridge is either attached and pulls the thread, or detached in anticipation of a new attachment. A huge number of bridges work at random, so their total thrust turns out to be uniform over time. Numerous studies have established the following mechanism of cyclic operation of the myosin bridge.
1. In the resting state, the bridge is charged with energy (myosin is phosphorylated), but it cannot connect with the actin filament, since a system of tropomyosin filament and troponin globule is wedged between them.
2. When the muscle fiber is activated and Ca+2 ions appear in the myoplasm (in the presence of ATP), troponin changes its conformation and moves the tropomyosin filament away, opening up the possibility of connection with actin for the myosin head.
3. The connection of the phosphorylated myosin head with actin sharply changes the conformation of the bridge (it “bends”) and moves the actin filaments one step (20 nm), and then the bridge breaks. The energy required for this results from the breakdown of the high-energy phosphate bond included in phosphorylactomyosin.
4. Then, due to a drop in the local concentration of Ca+2 and its disconnection from troponin, tropomyosin again blocks actin, and myosin is again phosphorylated due to ATP. ATP not only charges the systems for further work, but also promotes temporary uncoupling of the threads, i.e., it plasticizes the muscle, making it capable of stretching under the influence of external forces. It is believed that one ATP molecule is consumed per working movement of one bridge, and the role of ATPase is played by actomyosin (in the presence of Mg+2 and Ca+2). With a single contraction, a total of 0.3 µM ATP is consumed per 1 g of muscle.
Thus, ATP plays a dual role in muscle work: on the one hand, by phosphorylating myosin, it provides energy for contraction, on the other hand, being in a free state, it ensures muscle relaxation (its plasticization). If ATP disappears from the myoplasm, continuous contraction develops - contracture.
All these phenomena can be demonstrated on isolated actomyosin filament complexes: such filaments harden without ATP (rigor is observed), in the presence of ATP they relax, and when Ca+2 is added, they produce a reversible contraction similar to normal.
Muscles are penetrated by blood vessels, through which nutrients and oxygen are supplied to them with the blood, and metabolic products are carried out. In addition, muscles are rich in lymphatic vessels.
Muscles have nerve endings - receptors that sense the degree of contraction and stretching of the muscle.
The main muscle groups of the human body. The shape and size of muscles depend on the work they perform. The muscles are distinguished between long, broad, short and circular. Long muscles are located on the limbs, short ones - where the range of movement is small (for example, between the vertebrae). The broad muscles are located mainly on the torso, in the walls of the body cavities (for example, the abdominal muscles, back, chest). Circular muscles - sphincters - lie around the openings of the body, narrowing them when contracting.
Based on their function, muscles are divided into flexors, extensors, adductors, abductors, and internal and external rotators.
I. The muscles of the trunk include: 1) muscles of the chest; 2) abdominal muscles; 3) back muscles.
II. The muscles located between the ribs (intercostal muscles), as well as other muscles of the chest, are involved in the function of breathing. They are called respiratory muscles. These include the diaphragm, which separates the chest cavity from the abdominal cavity.
III. Well-developed chest muscles move and strengthen the upper limbs on the body. These include: 1) pectoralis major muscle; 2) pectoralis minor muscle; 3) serratus anterior muscle.
IV. The abdominal muscles perform various functions. They form the wall of the abdominal cavity and, thanks to their tone, keep the internal organs from moving, descending and falling out. By contracting, the abdominal muscles act on the internal organs like the abdominal press, facilitating the release of urine, feces and labor. Contraction of the abdominal muscles also helps the movement of blood in the venous system and the implementation of respiratory movements. The abdominal muscles are involved in bending the spinal column forward.
Due to possible weakness of the abdominal muscles, not only prolapse of the abdominal organs occurs, but also the formation of hernias. A hernia is the release of internal organs (intestines, stomach, greater omentum) from the abdominal cavity under the skin of the abdomen.
V. The muscles of the abdominal wall include: 1) rectus abdominis muscle; 2) pyramidalis muscle; 3) quadratus lumborum muscle; 4) broad abdominal muscles (external and internal, oblique and transverse).
VI. A dense tendon cord runs along the midline of the abdomen - the so-called linea alba. On the sides of it is the rectus abdominis muscle, which has a longitudinal fiber direction.
VII. The back contains numerous muscles along the spinal column. These are the deep muscles of the back. They are attached primarily to the processes of the vertebrae and participate in the movements of the spinal column backwards and to the side.
VIII. The superficial back muscles include: 1) trapezius back muscle; 2) latissimus dorsi muscle. They provide movement of the upper limbs and chest.
IX. Among the muscles of the head there are:
1) chewing muscles. These include: temporalis muscle; masticatory muscle; pterygoid muscles. Contractions of these muscles cause complex chewing movements of the lower jaw;
2) facial muscles. These muscles are attached to the skin of the face with one, and sometimes both, ends. When contracting, they shift the skin, creating a certain facial expression, i.e. one or another facial expression. Facial muscles also include the orbital muscles of the eye and mouth.
X. The neck muscles throw back the head, tilt and turn it.
XI. The scalene muscles raise the ribs, thus participating in inhalation.
XII. The muscles attached to the hyoid bone, when contracted, change the position of the tongue and larynx when swallowing and pronouncing various sounds.
XIII. The belt of the upper limbs is connected to the body only in the area of the sternoclavicular joint. It is strengthened by the muscles of the body: 1) trapezius muscle; 2) pectoralis minor muscle; 3) rhomboid muscle; 4) serratus anterior muscle; 5) the muscle that lifts the scapula.
XIV. The muscles of the limb girdle move the upper limb at the shoulder joint. The most important among them is the deltoid muscle. When contracted, this muscle flexes the arm at the shoulder joint and moves the arms to a horizontal position.
XV. In the shoulder area there is a group of flexor muscles in front, and extensor muscles in the back. Among the muscles of the anterior group are the biceps brachii, and the posterior group - the triceps brachii.
XVI. The muscles of the forearm are represented by flexors on the anterior surface, and extensors on the posterior surface.
XVII. Among the muscles of the hand there are: 1) palmaris longus; 2) flexors of the fingers.
XVIII. The muscles located in the lower extremity belt area move the leg at the hip joint, as well as the spinal column. The anterior muscle group is represented by one large muscle - the iliopsoas. The posteroexternal group of muscles of the pelvic girdle includes: 1) the large muscle; 2) gluteus medius muscle; 3) gluteus minimus muscle.
XIX. The legs have a more massive skeleton than the arms. Their muscles have greater strength, but less variety and a limited range of movements.
On the front of the thigh is the longest sartorius muscle in the human body (up to 50 cm). She bends her leg at the hip and knee joints.
The quadriceps femoris muscle lies deeper than the sartorius muscle, while it hugs the femur on almost all sides. The main function of this muscle is to extend the knee joint. When standing, the quadriceps muscle prevents the knee joint from bending.
On the back of the lower leg is the gastrocnemius muscle, which flexes the lower leg and flexes and slightly rotates the foot outward.
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3.2. Types and functional characteristics of muscle tissue in children and adolescents3.4. The role of muscle movements in the development of the body
The muscular system is an active part of the musculoskeletal system.
AFO of the musculoskeletal system
- Muscle mass in relation to body weight in children is significantly less than in adults. Thus, in newborns it is 23.3% of body weight, in an 8-year-old child – 27.7%, in a 15-year-old child – 32.6%, in an adult – 44.2%. Muscle mass in the postnatal period increases 37 times, while skeletal mass increases only 27 times.
The quantity and functionality of muscle tissue characterize the quality and degree of optimality of the entire process of somato-physical development.
Active processes of growth and differentiation of the muscular system play a coordinating and determining role in relation to the development of all life support systems - cardiovascular, respiratory, autonomic nervous systems, metabolic and energy supply systems. - The biochemical composition of muscles in children differs from adults. Thus, the content of myofibrillar proteins in the muscle tissue of newborns is 2 times less than in older children and adults. As the child grows, the content of tropomyosin and sarcoplasmic proteins in muscle tissue increases and the amount of glycogen, lactic acid and nucleic acids decreases. The water content in the muscles also decreases significantly.
- Muscle development in children is uneven. First of all, the large muscles of the shoulder and forearm develop, and later the muscles of the hand. Children under 6 years old cannot do fine work with their fingers. At the age of 6–7 years, a child can already engage in weaving and modeling. At this age, learning to write is possible. From 8 to 9 years old, children’s ligaments become stronger. Muscle development is enhanced and significant muscle growth is noted. At the end of puberty, muscle growth occurs not only in the arms, but also in the back, shoulder girdle and legs. At the age of 14-16 years, boys experience an almost twofold increase in both total muscle mass and muscle strength. After 15 years, small muscles also develop intensively, and the accuracy and coordination of small movements improves. Therefore, physical activity should be strictly dosed and not done at a fast pace. The development of motor skills in children does not occur evenly. By the age of 10–12 years, coordination of movements is quite perfect. However, young children are not yet capable of long-term productive work and prolonged muscle tension.
- During puberty, the harmony of movements is disrupted: awkwardness, angularity, and sharpness of movements appear as a result of disharmony between the rapidly increasing mass and the lag in their regulation.
- Physical exercise and sports are necessary for the normal development of children. Massage and gymnastics are widely used in children of all age groups. Children's excessive involvement in sports and attempts to achieve high results in a short time pose a threat to children's health. Hence the importance of observing age restrictions on one or another type of specialization in sports.
- During the period of growth processes, any weight loss is contraindicated. In adolescence, increased physical activity and dietary restrictions lead to a block in the development of organs and functions associated with reproduction, creating a risk for future motherhood or paternity, as well as for the consolidation of adequate sexual orientation.
- Bones form the basis of the human skeleton, being the frame and the place of attachment of muscles. Bone tissue develops in two alternative ways: directly from mesenchyme (membranous osteogenesis, characteristic of the integumentary bones of the skull) and through cartilaginous osteogenesis.
- The functions of bones are: protective - bones form a rigid frame for internal organs; fixing - for internal organs; support – for the whole body; motor - to move it in space; exchange
There are 3 stages in the process of bone formation and remodeling.
The first stage of osteogenesis is an intense anabolic process, during which the protein basis of bone tissue, the matrix, is created.
In the second stage, the formation of hydroxyapatite crystallization centers occurs, followed by osteoid mineralization.
The third stage of osteogenesis is the processes of remodeling and constant self-renewal of bone, regulated by the parathyroid glands and dependent on the provision of basic nutrients and vitamins with the leading value of vitamin D.
Osteogenesis processes are ensured by a normal level of calcium in the blood serum (2.44 ± 0.37 mmol/l). Normally, the regulation of calcium metabolism and maintaining its constancy in the blood is carried out through changes in the rate of intestinal absorption and renal excretion. If there is insufficient calcium in food or poor absorption from the intestines, the level of calcium in the blood begins to be maintained due to the resorption of calcium from the bones. - Features of the skeletal structure of a child. At the time of birth, the skull is represented by a large number of bones, the sutures (sagittal, coronoid, occipital) are open and begin to close only from 3 to 4 months of life. In full-term infants, the lateral fontanelles are closed; the small fontanel is open in 25% of newborns, mainly in premature infants, and closes no later than 4–8 weeks after birth. The large fontanel, located at the intersection of the coronal and longitudinal sutures, is open in all newborns, its dimensions range from 3 × 3 to 1.5 × 2 cm. The time of closure of the large fontanel is individual, normally this occurs by 1 year, but possibly earlier ( 9 – 10 months), and later (1.5 years).
- The spine of a newborn is devoid of physiological curves. Cervical lordosis forms after the child begins to lift and hold his head (between 2 and 4 months). At 6–7 months, thoracic kyphosis forms when the child sits up independently. After the start of standing and walking (9 - 12 months), an anterior curve forms in the lumbar spine. The final formation of physiological curves ends at early school age. Due to the incomplete formation of the spine, imperfect muscle fixation, uneven traction of muscle groups under the influence of incorrect posture and uncomfortable furniture, sideways curvature of the spine (scoliosis) easily occurs and pathological posture develops.
- The newborn's chest is wide and short with horizontal ribs. The transverse diameter is 25% larger than the average longitudinal diameter. Subsequently, the chest grows in length, and the anterior ends of the ribs descend. From the age of 3, costal breathing becomes effective. By the age of 12, the chest seems to move in shape to the position of maximum exhalation. A sharp increase in the transverse diameter of the chest occurs by the age of 15.
- The pelvic bones are relatively small in young children, their growth is most intense in the first 6 years, and in girls these bones further grow during puberty.
- Cartilaginous tissue is part of the skeleton in the form of cartilaginous coverings of the articular surfaces of bones, cartilage of intervertebral discs, costal cartilages, and also forms extraskeletal supporting structures (cartilage of the trachea, bronchi, etc.). In the early stages of intrauterine development, cartilage tissue forms the skeleton and accounts for 45% of body weight. During development, cartilage tissue is replaced by bone tissue. As a result, in an adult, the mass of all cartilage does not exceed 2% of body weight. Cartilage tissue consists of chondrocytes and a matrix, in which fibers and ground substance are distinguished. There are hyaline, fibrous, and elastic cartilages.
- Ligaments are connective tissue formations in the form of cords and plates, which represent one of the types of continuous connection of bones (syndesmosis) and are part of the strengthening apparatus of the joints, with which their development is closely related. In newborns, the connections are anatomically formed, but less strong and more extensible than in adults. Ligaments are characterized by high elasticity, high tensile strength and relatively low extensibility. Together with the articular capsule and muscles, the ligaments provide strengthening of the joints and contact of the articular surfaces of the bones.
- Joints begin to form in the early embryonic period from mesenchyme. Joint gaps appear in the shoulder and hip joints at the 6th week of intrauterine development, in the elbow and knee joints - at the 8th week, and in the wrist joints - at the 8th - 9th week.
- By the time of birth, the articular-ligamentous apparatus is anatomically formed. Subsequently, mineralization of the cartilage occurs (by 14–16 years), the relief of the synovial membrane becomes more complex, and the innervation of the joint improves.
- Milk teeth erupt after birth in a certain sequence. Teeth of the same name on each half of the jaw erupt simultaneously. The lower teeth usually erupt earlier than the upper teeth. The exception is the lateral incisors - the upper teeth appear before the lower ones. Formula for determining the number of primary teeth: n – 4, where n is the child’s age in months. By the age of 2, the child has all 20 baby teeth. In the first period (from eruption to 3 - 3.5 years), the teeth are closely spaced, the bite is orthognathic (the upper teeth cover the lower ones by one third) due to insufficient development of the lower jaw. The second period (from 2 to 6 years) is characterized by the transition of the bite to a straight line, the appearance of physiological gaps between the teeth, and tooth wear. The replacement of baby teeth with permanent teeth begins at age 5. At the age of about 11 years, the second painters appear. The third teeth (wisdom teeth) erupt between the ages of 17 and 25, and sometimes later. To roughly estimate the number of permanent teeth up to 12 years of age, regardless of gender, use the formula: X (number of permanent teeth) = 4 n – 20, where n is the number of years the child has turned.
FEATURES OF DEVELOPMENT OF THE CHILD'S MUSCULAR SYSTEM
In the embryo, muscles begin to develop at the 6-7th week of pregnancy. Until the age of 5, the child’s muscles are not sufficiently developed, the muscle fibers are short, thin, tender and can hardly be felt in the subcutaneous fat layer.
Children's muscles grow during puberty. In the first year of life they make up 20–25% of body weight, by 8 years – 27%, by 15 years – 15–44%. An increase in muscle mass occurs due to a change in the size of each myofibril. In muscle development, an age-appropriate motor regimen plays an important role; at older ages, playing sports.
Training, repetition, and improving quick skills play a big role in the development of children's muscle activity. As the child grows and muscle fiber develops, the intensity of muscle strength increases. Indicators of muscle strength determined using dynamometry. The greatest increase in muscle strength occurs at the age of 17–18 years.
Different muscles develop unevenly. In the first years of life, large muscles of the shoulders and forearms are formed. Up to 5–6 years of age, motor skills develop; after 6–7 years of age, the ability to write, sculpt, and draw develops. From the age of 8–9 years, the volume of the muscles of the arms, legs, neck, and shoulder girdle increases. During puberty, there is an increase in the volume of the muscles of the arms, back, and legs. At 10–12 years of age, coordination of movements improves.
During puberty, due to an increase in muscle mass, angularity, awkwardness, and abruptness of movements appear. Physical exercises during this period must be of a strictly defined volume.
In the absence of motor load on the muscles (hypokinesia), a delay in muscle development occurs, obesity, vegetative-vascular dystonia, and impaired bone growth may develop.
For various sports, there is an acceptable age for participating in competitions at a children's sports school.
At 7–8 years old, sports, rhythmic gymnastics, mountain skiing, and figure skating are allowed.
From the age of 9, trampoline classes, biathlon, Nordic combined, ski jumping, and chess are allowed.
At the age of 10 you are allowed to start playing volleyball, basketball, wrestling, rowing, handball, fencing, football, and hockey.
At the age of 12 – boxing, cycling.
At the age of 13 – weightlifting.
At the age of 14 - clay pigeon shooting.
STUDY OF THE MUSCULAR SYSTEM
The muscular system is examined visually and instrumentally.
The degree and uniformity of development of muscle groups, their tone, strength, and motor activity are assessed visually and palpation.
Muscle strength in young children is determined by an attempt to take away a toy. In older children, manual dynamometry is performed.
During an instrumental examination of the muscular system, mechanical and electrical excitability is measured using electromyographs and chronaximometers.
source: Directory of Children's Diseases.
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The muscular system is organically connected with the skeletal system, since they jointly provide human movement.
The muscular system in children is poorly developed. The weight of muscles in relation to the weight of the whole body in children is less than in adults, as can be seen from the following data:
- in a newborn - 23.3%;
- for a child 8 years old - 27.2%;
- for a 15-year-old teenager - 32.6%;
- for young men 17-18 years old - 44.2%.
Children's muscles differ in their structure, composition and functions from the muscles of an adult. The muscles in children are paler and more tender in appearance, richer in water, but poorer in protein and fat, as well as extractive and inorganic substances. Only by the age of 15-18 does the amount of water in the muscles decrease, they become denser, and the content of protein, fat and inorganic substances in them increases. At this age, the mass of tendons also increases compared to muscles, and therefore their elasticity and elasticity increase.
Children's muscle development is uneven. They develop larger muscles, such as those in the shoulder and forearm, first, with smaller muscles developing later. Thus, a 4-5 year old child has relatively developed muscles of the shoulder and forearm, but the muscles of the hand are still far from developed, and therefore fine finger work at this age is not yet available to children. The qualitative function of the muscles of the hand develops sufficiently in a child at the age of 6-7 years, when children can already engage in work such as weaving, modeling and other exercises with low-resistance material. The development of the muscles of the hand at this age makes it possible to gradually teach the child to write. But writing exercises at this age should be short-term, so as not to tire the still far from strong muscles of the hand.
An increase in the rate of development of all muscles and an increase in muscle strength in children is observed after 8-9 years, when ligaments are also strengthened and a significant increase in muscle volume is noted. In subsequent years, muscle strength increases steadily. Muscle strength increases especially rapidly in adolescents at the end of puberty. During these same years, an intensive increase in muscle mass occurs.
At the end of puberty, not only does the strength of the arm muscles increase, but the muscles of the back, shoulder girdle and legs also develop powerfully. According to Dementyev's research, the greatest increase in dead strength occurs between the ages of 15 and 18 years. After 15 years, small muscles also develop intensively, due to which the accuracy and coordination of small movements are improved and economy of movements is achieved, which makes it possible to achieve the greatest results with the least expenditure of effort during physical (manual) labor. At the same time, movement technique is also improved.
In children and adolescents, fatigue of working muscles occurs more quickly than in adults. But at the same time, muscle fatigue in children goes away faster, since this is favored by faster metabolism and a more abundant supply of oxygen to them, which restores the excitability of the tired muscle and increases its temporarily weakened elasticity. All this suggests that when organizing and conducting physical exercises, sports activities and physical labor for children and adolescents, it is necessary not to overly burden their muscles, dose the load and conduct these activities at a slow pace with appropriate pauses for rest.
The development of motor skills in children and adolescents does not occur evenly, but spasmodically. By the age of 6-7, the child already has fluent control of his muscles, but precise movements are still difficult for him and are accompanied by great effort. When a child is forced to make precise movements, he quickly gets tired. Imperfect movements in children at this age depend on the insufficient development of coordination mechanisms in the central nervous system.
Coordination of movements, expressed in their accuracy and dexterity, becomes more perfect in children aged 8-12 years. At the same time, children’s mobility increases and their movements become more varied. However, children of primary and partly middle school age are still not capable of long-term productive physical work and prolonged muscle tension. This circumstance must be taken into account when organizing physical education classes and work activities for children.
By the age of 10-13, the child already has some harmony of movements. But during puberty, this harmony is disrupted, since at this time the teenager’s motor apparatus is rebuilt. In this regard, primitive mechanisms (movements) are released from regulation by the higher parts of the central nervous system. Outwardly, in adolescents this manifests itself in an abundance of movements, awkwardness, some angularity, lack of coordination and impaired inhibition. By the end of puberty, these deficiencies in the adolescent’s motor skills are leveled out, and the development of the motor system is basically completed.
The above-mentioned features of the development of muscles and motor skills of children and adolescents put forward a number of hygienic requirements aimed, on the one hand, at protecting their muscular system, and on the other, at its development and strengthening. Considering the relatively rapid fatigue of muscles in children and adolescents and their lack of training, it is necessary to avoid prolonged and especially excessive physical stress, keeping in mind the possible dire consequences that can lead to crippling of a growing organism and a delay in its development. This applies not only to children of preschool and primary school age, but also to adolescents studying in high school and vocational schools.
To ensure normal muscle development in children and adolescents, moderate physical exercise is necessary, be it sports, agricultural or other physical labor. When working, muscles receive a more abundant flow of blood containing nutrients and oxygen. The blood that flows into a muscle while working nourishes not only it, but also the bones to which it is attached, as well as ligaments. Muscle work also has a positive effect on the formation of red blood cells in the bone marrow, thereby improving the composition of the blood. Muscular work has a beneficial effect on the entire body, in particular on organs such as the heart and lungs, and activates metabolic processes.
The activity of muscles is organically connected with the work of the brain and nerves, which mutually influence each other. As noted above, muscle exercise promotes the development of the cerebral cortex. The education of mental qualities, such as perception, memory, will, is associated with rational physical education. The work of the brain is more productive when its nutrition with blood delivered to it is enhanced. Thus, moderate physical exercise activates mental activity. However, with excessive muscle contractions, fatigue occurs not only in the muscles, but also in the nervous system.
Excessive muscle tension, especially when it occurs for a long time, has a harmful effect on the functioning of the entire body and can lead to serious diseases of the heart, lungs and other organs. With such excessive prolonged muscle tension, the heart works much more intensely, the heart muscle gets tired, as a result of which its contractions become slower. With prolonged tension in the muscles of the hands when playing the piano, sewing and writing, a disease known as writer's cramp sometimes occurs, which is expressed by severe pain in the muscles of the hand and the inability to continue working. All this must be kept in mind when conducting educational work with children and adolescents.
However, not only excessive prolonged muscle tension has an adverse effect on the body, but also insufficient work of individual muscle groups. The consequence of this is disorders in individual parts of the body, affecting the entire body. Thus, with a prolonged stationary sitting position without breaks for active rest in the form of movements of the whole body, the blood circulation of the abdominal organs (stomach, intestines and liver) is disrupted, which can result in constipation. Therefore, it is so important during sedentary work to arrange breaks for rest, which should be accompanied by free movements of all the muscles of the body as much as possible. Such rest after prolonged stationary sedentary work will be much more effective if it is carried out in the fresh air.
The most important thing in the hygiene of the muscular system of children and adolescents is its exercise, training, which gradually involves individual muscle groups (in their mutual connection) in movements and thereby ensures the development of muscles and improves motor skills. Learning new movements, for example, during the initial training in writing, gymnastics, playing musical instruments, and certain types of physical labor, requires children not only to spend significant amounts of muscle, but also to experience considerable neuropsychic stress, which entails physical and mental fatigue. Systematic, gradually increasing, but at the same time strictly dosed training of individual muscle movements in the process of learning the above activities makes these movements familiar, easy and enjoyable. If these activities are not excessive in time and load, then they usually do not cause fatigue in a trained child and teenager. In connection with the above, the enormous hygienic and pedagogical importance of training the muscular system becomes obvious.
From a hygienic point of view, it is extremely important to ensure the comprehensive development of the muscles of children and adolescents and to avoid unilateral stress on one or another muscle group. With a unilateral load on any one muscle group, its excessive development occurs due to some underdevelopment of the remaining muscle groups, and this circumstance negatively affects the activity of the entire organism. Only comprehensive muscle exercise ensures the normal physical development of the growing organism as a whole and contributes to the improvement of the morphological and functional properties of individual organs and systems.
At primary school age, the main type of physical exercise is outdoor games. At this age, some strength exercises are already available, but only those that do not require strong tension. Gymnastic exercises at primary school age become more important compared to preschool age, but they are not yet the main type of physical education for children in this period. Only in middle and high school age do gymnastics and sports become the main types of physical education among adolescents, since at this age the muscular system has developed sufficiently for this kind of exercise.
When addressing issues of physical education among children and adolescents, it is not enough to take into account only the characteristics of the skeletal and muscular systems. In this regard, the characteristics of the cardiovascular system of children and adolescents are of great importance. Only taking into account all factors of the development of the body can ensure the correct organization of educational work among children and adolescents and the implementation of activities among them in the field of individual hygiene.
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