Live long and train - aging, training, muscles. How to build muscle in older men Why muscles disappear in old age
Anatomically, newborns have all skeletal muscles, but relative to body weight they make up only 23% (in an adult 44%). The number of muscle fibers in the muscles is the same as in an adult. However, the microstructure muscle fibers is different. The fibers are smaller in diameter and have more nuclei. As it grows, the fibers thicken and elongate. This occurs due to the thickening of myofibrils, pushing the nuclei to the periphery. The size of muscle fibers stabilizes by age 20.
The muscles of children are more elastic than those of adults, i.e. shorten more quickly during contraction and lengthen during relaxation. The excitability and lability of newborns is lower than that of adults, but increases with age.
In newborns, even during sleep, the muscles are in a state of tone. The development of different muscle groups occurs unevenly. At 4-5 years of age, the muscles of the forearm are more developed, while the muscles of the hand lag behind in development. Accelerated maturation of hand muscles occurs at 5-6 years. Moreover, extensors develop more slowly than flexors. With age, the ratio of muscle tone changes. In early childhood, the tone of the muscles of the hand, hip extensors, etc. is increased. Gradually the distribution of tone is normalized.
Indicators of strength and muscle work during growth.
With age, the strength of muscle contractions increases. This is explained not only by a decrease muscle mass, but also by improving motor reflexes. For example, hand strength increases by 5-6 times from age 5 to 16, and leg muscle strength increases by 2-2.5 times. Strength indicators up to 10 years of age are greater in boys. From 10-12 years old - for girls. The ability for fast and precise movements is achieved by the age of 14, endurance by 17. At 10-11 years old, a child is able to perform work with a power of 100 W, 18-19 years old - 250-300 W.
Physiology of processes of intercellular transmission of excitation. Conducting excitation along the nerves.
The function of rapid transmission of excitation to and from a nerve cell is performed by its processes - dendrites and axons, i.e. nerve fibers. Depending on their structure they are divided into pulpy having a myelin sheath, and pulpless. This shell is formed Schwann cells, which are modified glial cells. They contain myelin, which is mainly composed of lipids. It performs isolating and trophic functions. One Schwann cell forms the sheath per 1 mm of nerve fiber. Areas where the shell is discontinuous, i.e. not covered with myelin, called Ranvier interceptions . Interception width 1 µm.
Functionally, all nerve fibers are divided into 3 groups:
Type A fibers- These are thick fibers with a myelin sheath. This group includes 4 subtypes:
And alpha- motor fibers of skeletal muscles and afferent nerves coming from muscle spindles - stretch receptors. Conduction speed 70-120 m/s.
And beta– afferent fibers coming from pressure and touch receptors of the skin. Speed 30-70 m/s.
And gamma– efferent fibers going to muscle spindles (15-30 m/s).
And delta– afferent fibers from temperature and pain receptors of the skin (12-30 m/s).
Group B fibers– thin myelin fibers, which are preganglionic fibers of the autonomic efferent pathways. Conduction speed 3-18 m/s.
Group C fibers– unmyelinated postganglionic fibers of the autonomic nervous system. Speed 0.5-3 m/s.
The conduction of excitation along the nerves is subject to the following laws:
Law of anatomical and physiological integrity of nerves, i.e. the nerve is able to perform its function only under both of these conditions. The first violations occur during cutting, the second - due to the action of substances that block conduction, for example, novocaine.
The law of two-way conduction of excitation. It spreads in both directions from the site of irritation. In the body, excitation most often goes through afferent pathways to the neuron, and through efferent pathways from the neuron. This distribution is called orthodromic . Very rarely does the opposite or antidromic
spread of excitement. Law of isolated conduction.
Excitation is not transmitted from one non-nerve fiber to another fiber that is part of the same nerve trunk. Law without decremental implementation.
Excitation is carried out along the nerves without decrement, i.e. without attenuation.
Nerve fibers have the properties of an electrical cable, which is not very well insulated. The mechanism of excitation is based on the occurrence of local current. As a result of the generation of an action potential in the axon hillock and the reversal of the membrane potential, the axon membrane acquires a positive charge. On the outside it becomes negative, on the inside it becomes positive. The membrane of the underlying unexcited axon is charged in the opposite way. Therefore, between these areas along the outer and internal surfaces membranes begin to pass local currents. These currents depolarize the membrane of the underlying unexcited portion of the nerve to a critical level, and an action potential is also generated in it. Then the process is repeated and a more distant part of the nerve is excited, etc.
Since local currents flow uninterrupted along the membrane of the pulpless fiber, this conduction is called continuous . With continuous conduction, local currents cover a large surface area of the fiber, so they require a long time to pass through a section of the fiber. As a result, the range and speed of transmission along the non-pulp fiber is small.
In the pulp fibers, areas covered with myelin have high electrical resistance. Therefore, continuous conduction of the action potential is impossible. When an action potential is generated, local currents flow only between adjacent nodes. According to the “all or nothing” law, the node of Ranvier closest to the axon hillock is excited, then the adjacent underlying node, etc. This is called saltatory (jump). With this mechanism, local currents do not weaken, and nerve impulses travel over a greater distance and at high speed.
You can gain muscle mass even if you have reached middle age (from 40 to 60 years old) or beyond it.
Our laboratory and others have repeatedly shown that older people's muscles also grow and become stronger.
Marcas Bamman, director of the Center for Exercise Medicine at the University of Alabama at Birmingham
As part of the study Exercise dosing to retain resistance training adaptations in young and older adults., which was conducted by Bamman, men and women aged 60–70 did strength training. Their muscle development occurred at the same rate as that of 40-year-olds.
But the process of muscle growth differs between young and old people.
Skeletal muscles are made up of different types of fibers. When we reach middle age, two types of changes occur.
Marcas Bamman
Some fibers die, especially if the muscles are not exercised. Sedentary adults lose 30 to 40% of their total muscle fibers by age 80. The remaining fibers shrink and atrophy with age. If we exercise, the size of atrophied muscle fibers increases, but not their number.
It turns out that despite training, your number of muscle fibers will not increase. However, the atrophied fibers will start working and increase in size, so the muscles will still become bigger and stronger.
How to Train for Muscle Growth in Middle and Old Age
The point is to exercise regularly. Start going to the gym and create a workout plan.
To trigger the biochemical processes necessary to increase the strength of muscle fibers, it is worth exercising until the muscles fail.
In Bamman's study, participants trained with specially selected weights so that subjects could perform 8 to 12 repetitions until exhaustion. After this it was time to rest. Participants repeated each set two or three times and went to the gym three times a week.
If you have never done strength training, consult a fitness trainer or specialist.
A clear example of the fact that you can build muscle even in old age is 73-year-old CrossFitter Jacinto Bonilla, who does more than many young people could ever dream of.
Changes in posture and gait are universal, associated with aging, as are changes in skin and hair.
The skeleton supports the structure of the body. Joints are the areas where bones come together. They allow the skeleton to be flexible for movement. Thus, the bones do not directly contact each other. Movable joints of bones are provided by the joints, the soft cartilage in the joint, the synovium around the joint, and the periarticular (synovial) fluid.
Muscles provide strength and power to move the body. Coordination is controlled by the brain, but depends on changes in the muscles and joints. Changes in muscles, joints, and bones affect posture and gait, and lead to weakness and slower movement.
Bone mass and bone density are lost with age, especially in women after menopause. Bones lose calcium and other minerals.
The spine is made up of bones called vertebrae. Between each bone is an intervertebral disc, which is a gel-like cushion (hyaline cartilage). Over time, the spinal trunk becomes shorter as the intervertebral discs gradually lose fluid and become thinner.
In addition, the vertebrae lose some of their minerals, making each one thinner. The spine bends and contracts. The joints between the upper and lower articular processes also undergo changes, since irregularly shaped new growths of bone substance, caused by aging, form at their edges.
The long bones of the arms and legs, although they become more fragile due to the loss of minerals, do not change in length. This makes the arms and legs longer compared to a shortened spine.
With age, joints become stiff and less flexible. The fluid in the joints may decrease and the cartilage may begin to rub against each other and break down. There is also deposition of salts in the joints, their calcification - calcification.
Hip and knee joints most often subject to degenerative changes in articular cartilage. The finger joints lose cartilage and the bones become slightly thicker. Changes in the bones of the fingers - osteoarthritis, is more common in women and can be hereditary.
Some joints, such as the ankle, tend to change very little with aging.
Body mass index decreases, partly due to loss muscle tissue(atrophy). The speed and extent of muscle changes depends on genetic predisposition. Muscle changes often begin in the 20s for men and 40s for women.
Lipofuscin (age pigment) and fat are deposited in muscle tissue. Muscle fibers contract. Muscle tissue is replaced more slowly, and lost muscle tissue may be replaced by tough fibrous tissue. This is especially noticeable in the hands, which become thin and bony.
Changes in muscle tissue, combined with normal age-related changes in nervous system, can tone muscles, reducing the ability to contract. Muscles can become stiff and lose tone with age, even with regular exercise.
Bones become more fragile and may break more easily. Overall height decreases, mainly due to shortening of the spinal trunk.
Inflammation, pain, stiffness and deformity can result from the breakdown of joint structures. Almost all older people suffer from joint changes ranging from minor to severe arthritis.
The posture may become more inclined (curved) and the knees and hips more bent. The neck may become slanted, the shoulders narrow, and the pelvis, on the contrary, becomes wider.
Movement slows down and may become restricted. The gait becomes slower, the steps are shorter and smaller. Walking may become unsteady, and hand tremors may appear. Older people get tired much easier and spend less energy.
Strength and endurance also undergo changes. Losing muscle mass reduces strength. However, endurance may be slightly increased due to changes in muscle fibers. Aging athletes with healthy hearts and lungs may find that their performance increases in endurance events and decreases in events requiring short bursts. high speed work.
Common problems
Osteoporosis is a common problem, especially for older women. Bones become brittle, and vertebral compression fractures can cause pain and decreased mobility. Osteoporosis is a condition that is characterized by progressive loss of bone density, thinning of bone tissue and increased vulnerability to fractures. Osteoporosis can be the result of disease, nutritional or hormonal deficiency, or old age. Regular physical exercise and vitamin and mineral supplements can reduce and even reverse bone density loss.
Muscle weakness contributes to fatigue, weakness, and decreased tolerance for activity. The risk of injury increases as changes in gait, unsteadiness and loss of balance can lead to falls.
Some older people report decreased reflexes. It is most often caused by changes in the muscles and tendons rather than changes in the nerves. Decreased knee reflex or ankle jerk may occur. Some changes, such as the positive Babinski reflex, are not a normal part of aging.
Involuntary movements (muscle tremors and small movements called fasciculations) are more common in older people. Older adults who are inactive or immobile may experience weakness or unusual sensations (paresthesias).
Muscle contractures can occur in people who are unable to move independently or who stretch their muscles through exercise.
Osteoarthritis is a chronic disease of joint cartilage and bone, often thought to result from "wear and tear", although there are other causes such as birth defects, trauma and metabolic disorders. The joints appear larger, are stiff and painful, and usually cause discomfort during prolonged, or even normal, activity throughout the day. Osteoarthritis is associated with the aging process and can affect any joint. The cartilage in the affected joint gradually wears away, eventually causing bone friction. Bone spurs develop on exposed bone surfaces, causing pain and inflammation.
Prevention of age-related changes in the spine, bones, muscles and joints
Physical exercise is one of the the best ways slow down or prevent problems with muscles, joints and bones. A moderate exercise program will help you maintain strength and flexibility. Exercise helps bones stay strong. Check with your healthcare provider before starting a new exercise program.
A well-balanced diet with sufficient calcium is very important. Women should be especially careful to get enough calcium and vitamin D as they age. Postmenopausal women and men over 65 years of age need 1,200 to 1,500 mg of calcium and 400 to 800 international units of vitamin D per day.
Flexibility exercises, in their simplest form, stretch and lengthen muscles. Disciplines that include breath-controlled stretching and meditation include yoga and tai chi. The benefits of flexibility can go beyond physical improvements and stress reduction, but also promote a sense of well-being.
Sarcopenia- gradual loss of muscle mass is a common consequence of aging, and is one of the main risk factors for disability in old age. State skeletal muscles plays important role in maintaining health, and sarcopenia leads to an increased risk of fractures and other injuries, mainly in older people.
International Association for the Prevention of Osteoporosis, conducted research in this area and identified nutritional factors that contribute to the loss of muscle mass, and foods useful for maintaining muscle mass. A group of scientists analyzed data from international studies on nutrition to prevent sarcopenia, in particular the consumption of protein, vitamin D/Ca and other nutrients, maintaining acid-base balance.
“The most effective way to combat sarcopenia is exercise,” says Professor Jean Phillipe Bonjour, co-author and professor of medicine in bone diseases at the University of Geneva. “However, proper nutrient intake and maintaining acid-base balance are also important elements in maintaining muscle mass and fighting aging.”
In the study, scientists identified the following important dietary factors for the prevention of sarcopenia:
Proteins play an important role in maintaining muscle mass. Scientists suggest consuming 1–1.2 g/kg body weight per day to maintain skeletal muscle and optimal bone health in older adults (contraindications: renal impairment).
Vitamin D is a very important element in the preservation of bone and muscle tissue. The sun's rays provide us with the necessary vitamin D, but sometimes it is necessary to take vitamins. Especially additional dose Vitamin D is recommended for older adults for optimal musculoskeletal health.
Acid-base balance. Excess intake of acids (meats and whole grains), combined with low intake of alkaline foods (vegetables and fruits), has a negative impact on the musculoskeletal system. In this case, it is necessary to adjust the diet, include as many vegetables as possible in the daily diet.
New research has shown that vitamin B12 and folic acid also play an important role in improving muscle function and strength.
Research is also needed on non-nutritional interventions, such as hormones, to determine the effect of antioxidants and anti-inflammatory compounds in preventing sarcopenia, Sciencedaily reports.
Dr Ambrish Mital, Head, Center for Endocrinology and Diabetes, New Delhi, emphasized the need for further research in this area. “Preventing sarcopenia will reduce the number of fractures in the elderly population. Currently, available evidence suggests that power training And proper nutrition have a synergistic effect in the prevention and treatment of sarcopenia,” reports Mital.
“We really hope that further research will shed light on other more effective ways prevention and treatment of diseases such as sarcopenia.”
Anna Baralovskaya
Muscle fibers develop from mononuclear, poorly differentiated spindle-shaped cells - myoblasts, which, merging, turn into multinucleated myosymplasts. At the 5-6th week of embryogenesis, myofibrils appear in the latter. Subsequently, in the prenatal period, the number of myofibrils in myosymplasts increases, the diameter of muscle fibers increases, and synaptic contacts with nerve fibers. Some of the myoblasts that are part of the sarcolemma of the muscle fiber turn into satellite cells, which are activated whenever muscle fibers are damaged in postnatal ontogenesis.
By the time of birth, the formation of all muscles is basically completed, however, development associated with their internal structure still continues, ending at approximately 25 years.
In the first years of a child’s life, the structure of skeletal muscle tissue retains features characteristic of the prenatal period: poor development of the myofibrillar apparatus - a small number of myofibrils, their loose arrangement in the fiber, a wealth of sarcoplasm in the fiber, an abundance of connective tissue cells between the fibers of skeletal muscles, underdevelopment of collagen and elastic fibrils their frame, the primitiveness of neuromuscular contacts (synapses), their location throughout the muscle. At birth, the thickest muscle fibers are the diaphragm, and the thinnest are in the lower leg muscles.
As the child grows and develops motor skills, the internal structure of the muscles changes. The contractile apparatus of muscle fibers becomes more developed, as a result of which the transverse striations become clearer. In the first 3 years, the number of myofibrils in the fibers increases by 4-5 times, and the diameter of the muscle fiber increases by 1.5 times. In this case, the muscle fibers change from round to multifaceted. Blood vessels develop, blood supply to muscle fibers improves, and the innervation apparatus actively develops. The growth of muscle fibers in length occurs at the ends of the fiber in response to traction created by the growing bones to which the muscle is attached.
In the period from 3 to 7 years, the number of myofibrils in the fiber increases 15-20 times compared to newborns, and accordingly, the diameter of the muscle fibers also increases.
As the muscular system develops, only the microstructure of the muscle fibers changes. Muscle composition, i.e. ratio in the muscle of slow and fast fibers, is determined genetically and remains unchanged throughout life. The total number of muscle fibers in the muscle also remains almost unchanged. The increase in muscle mass occurs due to an increase in the size of each muscle fiber. The increase in the diameter of the muscle fiber is based on the intensive synthesis of muscle contractile proteins - actin and myosin, leading to an increase in the number of myofibrils.
In preschool and junior school age(5-8 years) a restructuring of the innervation apparatus of the muscles occurs: the size and differentiation of the elements of muscle, tendon and joint receptors increase. During this period, a redistribution of the position of sensitive muscle spindles in the skeletal muscles occurs - located in the newborn’s muscle evenly along the length, they are then concentrated in the end sections of the muscles that are subject to the greatest stretching. The structure of motor myoneural synapses - motor plaques - is improved.
NEURO-TENDON SPINDLES - sensitive spindle-shaped encapsulated formations, the excitation of the receptors of which occurs when the tendons are stretched during muscle contraction. Located in the area of connection of striated muscle fibers with collagen fibers of tendons.
NEUROMUSCULAR SPINDLES - encapsulated formations located parallel to the course of muscle fibers, which are stretch receptors for striated muscles.
MOTOR PLAQUE contains the terminal branch of the axon of a motor neuron lying in the anterior horn of the spinal cord, in contact with the sheath of the striated muscle fiber.
By the age of 7-8, the innervation apparatus of skeletal muscles acquires the structure characteristic of an adult. During this period, the growth of muscle tendons increases, aponeuroses and fascia noticeably thicken, intramuscular connective tissue grows, the vascular bed of the muscles develops, the vascular network becomes denser, and new capillaries appear.
During puberty (11-15 years), there is an intensive increase in muscle mass, with the length of the muscles increasing more than their diameter. The improvement of connective tissue formations of muscles continues: in the endomysium and perimysium, fibrous structures predominate over connective tissue cells, and the number of elastic fibers increases.
The most intensive growth of muscle fibers and muscles in general occurs in childhood and adolescence. Sex hormones - androgens - play an important role in muscle development. In men they are produced in the gonads (testes) and adrenal cortex, in women - only in the adrenal glands. In males at any age, their concentration in the blood is higher than in females. The increase in muscle mass in the interval of 20-30 years goes in parallel with the increase in the production of androgens, which stimulate the synthesis of myosin and actin in skeletal muscles. The increase in muscle mass is also regulated by somatotropic hormone of the pituitary gland, pancreatic insulin, thyroxine, and 3-iodine thyronine of the thyroid gland.
In a newborn, skeletal muscles make up 20-22% of the total mass bodies. At the age of 1-2 years, muscle mass decreases to 15-16%. At 6 years old due to high motor activity In children, skeletal muscle mass increases, reaching more than 21% of the total body weight, and further continues to increase: in 8-year-olds - 27%, in 15-year-olds - 32%, in 18-year-olds - 44% of total body weight. At the age of 18-20 to 35-40 years, muscle mass fluctuates slightly, stabilizes, and subsequently decreases. In women, muscle mass is on average 33%, in men - 36-40% of total body weight.
In adults, the shape and size of skeletal muscles are relatively stable. Even in elderly people, their involutive changes are usually small. They consist only of a slight decrease in the diameter of muscle fibers, an increase in collagen fibers in the muscle, and the development of adipose tissue. In old age, involutive changes intensify, muscles undergo functional atrophy.
In the first years of a child's life, the muscles of the upper and lower extremities grow rapidly. In the period from 2 to 4 years, increased growth is observed long muscles back and big gluteal muscle. Muscles that provide vertical position bodies grow rapidly after 7 years, especially in adolescents 12-16 years old.
In newborns, the length of the belly of most muscles is relatively long, and the tendons are small compared to the muscles of adults. In the first years of life, muscles grow mainly due to lengthening of the tendons, and the muscle part grows in the area of the transition to the tendon, and therefore the pennation of the muscles becomes more pronounced, and the area of attachment of the tendons to the bones of the fascia increases.
During development, muscle mass is redistributed in the body. The muscles of the lower extremities grow faster than the muscles of the torso, and the latter, in turn, outstrip the muscles of the head in growth. In the first 8-9 years, the muscles of the hand and foot grow faster on the limbs.
Back muscles. In a newborn baby, the back muscles, especially the deep ones, are poorly developed. The development of the back muscles occurs gradually. Already in the first years, the belt muscles, muscles of the occipital group, and iliocostal muscles become more pronounced. Increased development of the back muscles occurs at 5-6 years, but its volume especially increases during puberty.
Chest muscles. By the time of birth superficial muscles The breasts are better developed than the deep ones. The intercostal muscles are poorly developed, especially the internal ones, and by the time the child is born they do not play a significant role in the act of breathing. The chest muscles differentiate gradually. At 5-6 years old, they are all clearly contoured. A significant increase in muscle mass and the manifestation of individual characteristics of muscle relief begin from 10-12 years.
Diaphragm. In a newborn, the diaphragm is relatively well developed. Its weight makes up 5.3% of the weight of all muscles (in adults - only 1%). This is explained by its participation in the act of breathing, in which weak intercostal muscles participate little. The differentiation of muscle fibers in the diaphragm of a newborn is not yet complete, but, compared to other muscles, the fibers here are more mature and thick, and all types of fibrous structures of loose connective tissue are richer. The diaphragm protrudes into the chest cavity in the form of two domes, the right of which is higher and wider. After the first respiratory movements, the dome descends from the level of the 5th rib to the 7th rib. Excursions of the diaphragm during inhalation and exhalation in a newborn - 3 ribs. With age, the position of the diaphragm changes and its structure improves. As the child grows, the proportions between its tendon and muscle parts change. How older child, the larger the tendon center.
In older people, the diaphragm is flat. After 60-70 years, signs of atrophy are found in its muscular part against the background of an increase in the tendon center.
Abdominal muscles. The anterior abdominal wall of a newborn is protruded; The abdomen is cone-shaped. Oblique and transverse muscles The abdomen is poorly developed, their aponeuroses are tender and wide. The rectus abdominis muscles are thin and narrow. Their transverse tendon bridges lie high and not always symmetrically. The fascia covering the oblique and transverse muscles is very thin, so the muscles are difficult to separate from one another. The linea alba in the upper part and the navel area has thinned areas with elongated narrow slits.
Intensive development abdominal muscles are observed from the time the child begins to walk. Aponeuroses are strengthened, muscle mass increases. Thus, the width of the rectus abdominis muscles doubles by the end of the 1st year of a child’s life. Protrusion of the abdomen is typical only for early childhood, with muscle development it gradually disappears. In 7-year-old children, the stomach is tucked. The fascia delimiting the muscles becomes denser. The linea alba expands slightly, and as the child grows, it lengthens. During puberty, the anterior abdominal wall becomes flat, its muscles, especially the rectus muscles, are clearly contoured, and the linea alba narrows.
Muscles shoulder girdle and free upper limb. By the time of birth, all the muscles of the belt and free upper limb are formed, but they are poorly developed. Their muscle part predominates over the tendon part. On the shoulder, the anterior and posterior muscle groups are separated by thin connective tissue septa. The shape of the muscles is almost rectangular. The muscles of the anterior surface of the forearm lie in 4 layers, on back surface- in 2 layers. The osteofibrous channels through which the muscles of the forearm are directed to the hand are mostly formed. The muscle tendons are covered with synovial sheaths. The hand muscles of a newborn are very delicate.
Differentiation of the muscles of the upper limb occurs gradually and at different speeds in various departments. The muscles of the hand differentiate most quickly. By the age of 5-6 years they increase significantly in size, and by 10-12 years they are practically no different from the muscles of an adult. The muscles of the forearm develop more slowly than the muscles of the hand, and the muscles of the shoulder and shoulder girdle - even more slowly. With age, not only the mass of muscles increases, but their tendons lengthen. The shoulder and forearm become characterized by a conical or spindle-shaped shape, in contrast to the cylindrical shape of a newborn. The mass of the muscles of the forearm, shoulder and shoulder girdle increases quite intensively at the age of 5-6 years, then the development of the muscles of these sections slows down, after which muscle relief the upper limb develops powerfully during puberty. In parallel with the development of muscles, the fascia thickens, and the amount of fatty tissue in the intermuscular spaces increases.
Muscles lower limb . The anterior, posterior and medial groups of thigh muscles in a newborn are formed and separated from one another by intermuscular connective tissue septa. The length of the tendons is short, so the shape of the femur is cylindrical. At birth, each calf muscle is characterized by a relatively large belly and a short tendon. The muscles of the anterior group of the lower leg are well demarcated; the peroneal muscles (lateral group) are initially almost the same width; calf muscle forms a single whole with the soleus (posterior group). The muscles of the deep layer also form a single layer. In area ankle joint due to the thickening of the fascia, bone-fibrous channels are formed for the tendons of the lower leg muscles, which are directed to the foot. The tendons in the canals are surrounded by synovial sheaths. With age, the muscles of the lower limb differentiate. On the foot, already in the 1st year of life, the initially isolated abdomens of the short, flexor and extensor fingers merge. The mass of the muscles of the plantar surface increases, the plantar aponeurosis thickens. The accelerated development of the foot muscles is caused by the need to strengthen it by the time the child begins to stand and walk, while the foot experiences a large axial load. By the age of 5-6 years, the muscles of the foot noticeably increase in size, and by 10-12 years they differ little from those of an adult.
By the age of 4-6 years, the development of the lower leg muscles intensifies, the size of the muscles of the anterior group increases, the long and short peroneal muscles of the lateral group are separated, in posterior group The gastrocnemius and soleus muscles are separated, and the deep muscles are demarcated. During this period, not only the muscle mass increases, but the tendons also lengthen, and the cylindrical shape of the lower leg is replaced by a conical or spindle-shaped one. At 10-14 years of age, the muscles of the lower leg are well developed, their diameter increases by more than 2 times compared to 5 years of age.
The muscles of the thigh and pelvis differentiate more slowly than the muscles of the leg and foot. Their development follows the path of increasing muscle mass and changing the ratio of muscle and tendon parts in favor of the tendon. Increased development of the thigh muscles occurs at 4-5 years, but the muscle mass of the thigh increases especially quickly at 12-14 years, when the muscular relief of the limb appears. In parallel with the development of the muscles of the limbs, the intermuscular septa thicken, the fascia thickens, and the synovial vagina and synovial bursae reach their final development.
Neck muscles. In a newborn baby they are relatively short due to the high standing chest, have a cylindrical shape and are poorly developed. Their peculiarity is the almost complete absence of tendons at the points of fixation. The development of the neck muscles is gradual. By the age of 5-7, all muscles are well expressed, among them the muscles of the anterior group, lying above and below the hyoid bone, stand out. Not only does muscle mass increase in them, but tendon elements become clearly visible. The mass of the scalene and prevertebral muscles increases. By the age of 10-14 years, the neck muscles are not much different from those of an adult. As muscles develop, the fascia becomes denser, and the size of the intermuscular and interfascial spaces increases. The amount of loose fiber in them increases by the age of 7 and during puberty.
Head muscles. By the time of birth, the muscles of the head are generally poorly developed, the degree of differentiation of individual muscle groups not the same. The epicranial muscle is quite well expressed. Its frontal and occipital parts are thin, and the tendon helmet is loosely connected to the skin, which is why the scalp is very mobile. All facial muscles are weakly defined and located close to one another. The muscles of the mouth circumference and the buccal muscles, which provide the act of sucking, are best differentiated. The fat pad of the cheek is well developed, having a thin connective tissue membrane and fixed to the buccal muscle. The lump prevents the soft tissues of the face from being drawn into the oral cavity during sucking. Chewing muscles poorly developed and have almost no tendon elements at the points of fixation.
With age, the muscles of the head develop unevenly. The supracranial muscle is characterized by a constant increase in the muscle mass of its frontal and occipital parts, thickening of the tendon helmet, which by the age of 5-7 years firmly fuses with the scalp. During the first year of life, the muscles around the mouth and cheeks develop very quickly. The rest are somewhat behind in development.
By the end of the preschool period, the facial muscles, with the exception of the muscles of the ear circumference, are sufficiently differentiated. In the future, its development is largely individual. Cheek fat pad with development facial muscles flattens and moves posteriorly.
The masticatory muscles differentiate in connection with the development of the dentofacial apparatus. Their intensive growth is observed from the age of 3 years. By the age of 7-8, not only the mass increases, but also the tendon sections of these muscles. The chewing muscles reach their definitive development by the time the permanent teeth erupt.
