Mechanism of movement: muscles involved in walking. Body position Muscles responsible for the vertical standing of a person
The vertical position of the human body, its movement in space, various types of movements (walking, running, jumping) developed in the process of long evolution along with the formation of man as a species. In the process of anthropogenesis, in connection with the transition of human ancestors to terrestrial conditions of existence, and then to movement on two (lower) limbs, the anatomy of the entire organism, its individual parts, organs, including the musculoskeletal system, changed significantly. Upright walking freed the upper limb from musculoskeletal function. The upper limb turned into an organ of labor - the hand - and could further improve its dexterity of movements. These changes, as a result of a qualitatively new function, were reflected in the structure of all components of the belt and the free part of the upper limb. The shoulder girdle not only serves as a support for the free upper limb, it significantly increases its mobility. Due to the fact that the shoulder blade is connected to the skeleton of the body mainly through muscles, it acquires greater freedom of movement. The scapula is involved in all movements that the collarbone makes. In addition, the scapula can move freely independently of the collarbone. In the multi-axial spherical shoulder joint, which is surrounded by muscles on almost all sides, the anatomical features of the structure allow movements along large arcs in all planes. The specialization of functions was especially noticeable in the structure of the hand. Thanks to the development of long, very mobile fingers (primarily the thumb), the hand has turned into a complex organ that performs subtle, differentiated actions.
The lower limb, having taken on the entire weight of the body, adapted exclusively to the musculoskeletal function. The vertical position of the body and upright posture affected the structure and functions of the girdle (pelvis) and the free part of the lower limb. The girdle of the lower extremities (pelvic girdle), as a strong arched structure, has adapted to transfer the weight of the torso, head, and upper extremities to the heads of the femurs. The pelvic tilt of 45-65°, established during the process of anthropogenesis, facilitates the transfer of body weight to the free lower limbs in the most favorable biomechanical conditions for the vertical position of the body. The foot acquired an arched structure, which increased its ability to withstand the weight of the body and act as a flexible lever when moving it. The muscles of the lower limb have greatly developed, which have adapted to performing static and dynamic loads. Compared to the muscles of the upper limb, the muscles of the lower limb have greater mass.
On the lower limb, the muscles have extensive surfaces for support and application of muscle force. The muscles of the lower limb are larger and stronger than those of the upper limb. On the lower limb, the extensors are more developed than the flexors. This is due to the fact that the extensors play a large role in holding the body in an upright position and during movement (walking, running).
In the arm, the flexors of the shoulder, forearm, and hand are concentrated on the anterior side because the work done by the arms is done in front of the torso. Grasping movements are produced by the hand, which is affected by more flexors than extensors. There are also more rotating muscles (pronators, supinators) in the upper limb than in the lower limb. In the upper limb they are much better developed than in the lower limb. The mass of the pronators and supinators of the arm relates to the rest of the muscles of the upper limb as 1:4.8. In the lower limb, the ratio of the mass of the rotating muscles to the rest is 1:29.3.
Due to the greater manifestation of force under static and dynamic loads, the fascia and aponeuroses of the lower limb are much better developed than those of the upper limb. The lower limb has additional mechanisms that help keep the body in an upright position and ensure its movement in space. The girdle of the lower limb is almost motionlessly connected to the sacrum and represents a natural support for the body. The tendency of the pelvis to tilt posteriorly on the heads of the femoral bones is prevented by the highly developed iliofemoral ligament of the hip joint and strong muscles. In addition, the vertical gravity of the body, passing in front of the transverse axis of the knee joint, mechanically helps to maintain the knee joint in an extended position.
At the level of the ankle joint, when standing, the area of contact between the articular surfaces of the bones of the tibia and talus increases. This is facilitated by the fact that the medial and lateral malleoluses cover the anterior, wider part of the trochlea of the talus. In addition, the frontal axes of the right and left ankle joints are set to each other at an angle that is open posteriorly. The vertical gravity of the body passes anteriorly in relation to the ankle joints. This leads, as it were, to pinching of the anterior, wider segment of the talus block between the medial and lateral ankles. The joints of the upper limb (shoulder, elbow, wrist) do not have such braking mechanisms.
The bones and muscles of the body, especially the axial skeleton - the spinal column, which is the support for the head, upper limbs, and organs of the thoracic and abdominal cavities, have undergone profound changes in the process of anthropogenesis. In connection with upright walking, curves of the spine were formed, and powerful dorsal muscles developed. In addition, the spine is almost motionlessly connected in a paired strong sacroiliac joint with the girdle of the lower extremities (with the pelvic girdle), which biomechanically serves as a distributor of the weight of the body onto the heads of the femoral bones (to the lower extremities).
Along with anatomical factors - structural features of the lower limb and torso, developed during the process of anthropogenesis to maintain the body in an upright position, ensure stable balance and dynamics, special attention should be paid to the position of the body's center of gravity.
The general center of gravity (GC) of a person is the point of application of the resultant forces of gravity of the parts of his body. According to M.F. Ivanitsky, the GCT is located at the level of the I-V sacral vertebrae and is projected onto the anterior surface of the body above the pubic symphysis. The position of the GCT in relation to the longitudinal axis of the body and spinal column depends on age, gender, skeletal bones, muscles and fat deposits. In addition, daily fluctuations in the position of the GCT are observed due to shortening or lengthening of the spinal column, which arise due to uneven physical activity day and night. In elderly and old people, the position of the central circulation also depends on posture. In men, the GCT is located at the level of the III lumbar - V sacral vertebrae, in women it is 4-5 cm lower than in men, and corresponds to the level from the V lumbar to the I coccygeal vertebra. This depends, in particular, on the greater deposition of subcutaneous fat in the pelvis and thighs than in men. In newborns, the GCT is at the level of the V-VI thoracic vertebrae, and then gradually (until 16-18 years) drops down and moves somewhat posteriorly.
The position of the GCT of the human body also depends on the body type. In individuals with a dolichomorphic body type (asthenics), the GCT is located relatively lower than in individuals with a brachymorphic body type (hypersthenics).
As a result of the research, it was found that the GCT of the human body is usually located at the level of the II sacral vertebra. The plumb line of the center of gravity passes 5 cm behind the transverse axis of the hip joints, approximately 2.6 cm posterior to the line connecting the greater trochanters, and 3 cm anterior to the transverse axis of the ankle joints. The center of gravity of the head is located slightly anterior to the transverse axis of the atlanto-occipital joints. The common center of gravity of the head and torso is at the level of the middle of the anterior edge of the X thoracic vertebra.
To maintain stable balance of the human body on a plane, it is necessary that the perpendicular lowered from its center of gravity fall on the area occupied by both feet. The stronger the body is, the wider the support area and the lower the center of gravity. For the vertical position of the human body, maintaining balance is the main task. However, by straining the corresponding muscles, a person can hold the body in various positions (within certain limits) even when the projection of the center of gravity is moved beyond the support area (strong tilt of the body forward, to the sides, etc.). At the same time, standing and moving the human body cannot be considered stable. With relatively long legs, a person has a relatively small area of support. Since the overall center of gravity of the human body is located relatively high (at the level of the second sacral vertebra), and the supporting area (the area of the two soles and the space between them) is insignificant, the stability of the body is very small. In a state of balance, the body is held by the force of muscle contractions, which prevents it from falling. Parts of the body (head, torso, limbs) occupy the position corresponding to each of them. However, if the relationship of body parts is disturbed (for example, stretching the arms forward, bending the spine when standing, etc.), then the position and balance of other parts of the body will change accordingly. Static and dynamic moments of muscle action are in direct connection with the position of the body’s center of gravity. Since the center of gravity of the entire body is located at the level of the second sacral vertebra behind the transverse line connecting the centers of the hip joints, the desire of the torso (together with the pelvis) to tip back is opposed by highly developed muscles and ligaments that strengthen the hip joints. This ensures the balance of the entire upper body, which is kept on the legs in an upright position.
The tendency of the body to fall forward when standing is due to the vertical passage of the center of gravity in front (3-4 cm) from the transverse axis of the ankle joints. Fall is resisted by the action of the muscles on the back of the lower leg. If the vertical line of the center of gravity moves even further anteriorly - to the toes, then by contracting the posterior muscles of the lower leg, the heel is raised, torn off from the plane of support, the vertical line of the center of gravity moves forward and the toes serve as support.
In addition to supporting limbs, the lower limbs perform a locomotor function, moving the body in space. For example, when walking, the human body makes a forward movement, alternately leaning on one or the other leg. In this case, the legs alternately make pendulum-like movements. When walking, one of the lower limbs at a certain moment is a support (back), the other is free (front). With each new step, the free leg becomes the supporting leg, and the supporting leg is brought forward and made free.
Contraction of the muscles of the lower limb during walking noticeably increases the curvature of the sole of the foot and increases the curvature of its transverse and longitudinal arches. At the same time, at this moment, the torso leans forward somewhat along with the pelvis on the heads of the femurs. If the first step is started with the right foot, then the right heel, then the middle of the sole and the toes rise above the plane of support, the right leg bends at the hip and knee joints and moves forward. At the same time, the hip joint of this side and the torso follow forward with the free leg. This (right) leg, with an energetic contraction of the quadriceps femoris muscle, straightens at the knee joint, touches the surface of the support and becomes the supporting one. At this moment, the other, left leg (until this moment the back, supporting leg) breaks away from the plane of support, moves forward, becoming the front, free leg. At this time, the right leg remains behind as a supporting leg. Together with the lower limb, the body moves forward and slightly upward. So both limbs alternately perform the same movements in a strictly defined sequence, supporting the body first on one side or the other and pushing it forward. However, during walking there is no moment when both legs are simultaneously torn off the ground (support plane). The front (free) limb always manages to touch the support plane with the heel before the back (support) leg is completely separated from it. This is how walking differs from running and jumping. At the same time, when walking, there is a moment when both legs simultaneously touch the ground, the supporting leg touching the entire sole, and the free leg touching the toes. The faster the walk, the shorter the moment of simultaneous contact of both legs with the support plane.
By tracking changes in the position of the center of gravity while walking, one can note the movement of the entire body forward, upward and sideways in the horizontal, frontal and sagittal planes. The greatest displacement occurs forward in the horizontal plane. The displacement up and down is 3-4 cm, and to the sides (lateral swings) - 1-2 cm. The nature and degree of these displacements are subject to significant fluctuations and depend on age, gender and individual characteristics. The combination of these factors determines the individuality of gait, which can change under the influence of training. On average, the length of a normal quiet step is 66 cm and takes 0.6 s.
Body Balance. The vertical position of the multi-link human body in space is associated with finely coordinated movements that ensure its balance at rest and in dynamics. This was developed and consolidated as a result of long evolution, during which complex changes occurred in the structure of the body of human ancestors, the distribution of its mass, the establishment of relationships between individual parts of the body, the development of muscles, ligaments, nerves, etc.
Despite the evolutionary path of development, the uprightness of the body in space, both at rest and in motion, is developed at the beginning of a person’s life, that is, during the period of the child’s familiarization with his relationship with the environment. The omission of this age period for introducing upright walking in the future is almost irreparable. The equilibrium of a body, according to the laws of statics, is ensured provided that the sum of the forces acting on it is equal to the sum of the reactions of these forces, and the resulting moment of all forces (acting and reaction) is equal to zero, i.e. when the action is equal to the reaction. However, it is known that the vertical position of the human body is quite unstable. Almost all joints of the body links have static moments that are not balanced due to the constant displacement of its individual parts relative to each other. This is obviously due to the fact that all joints of the body at rest are characterized by a flexion position. Therefore, the vertical position of the body depends on the stretching of the flexor muscles. For example, when a person stands in a comfortable position, the ankle joint is at an angle of ~88°. The constant tension of the muscles in the flexion position of the body is explained by the fact that the total length of the antagonist muscles (flexors - extensors) is slightly less than the total distance between their points of attachment. Therefore, when straightening the body into a standing position, large muscle moments develop in the knee and hip joints and in the spine.
The possibility of long-term balance in space, due to continuous fluctuations in the general center of gravity of the body, is associated with the work of the muscular-ligamentous apparatus. But the degree and nature of the participation of various muscle groups in maintaining the balance of the body, as well as in its dynamic functions, are not the same. To determine the degree of muscle activity, electromyography, stabilography and other methods are used. Since the preservation of body balance over time is associated with continuous fluctuations of the general center of gravity (GC) and relative displacements of body parts, even when a person is standing, there is not peace - static balance, but dynamic balance, determined mainly by the functions of systems that regulate balance.
Despite the fact that many works of domestic and foreign researchers have been devoted to determining the position of the human center of gravity of the body and the characteristic posture, until now there is no generally accepted method for studying a comfortable stable body posture when standing, the position of the center of gravity, and there is no single device. This explains the different interpretations of the position of the body's central center, the location of its projection and a comfortable standing posture.
To study the biomechanics of walking, the Central Research Institute of Prosthetics and Prosthetic Manufacturing (TsNIIPP) has developed methods for studying individual kinematic and dynamic parameters of walking using electrical methods for recording mechanical quantities. Using them, the following biomechanical features of normal human standing were identified. When a person is in a comfortable position, all the main joints of the lower extremities (knee, hip) and torso (shoulder) are located anterior to the plumb line passing through the ankle joints. The curves of the spine are well defined. The vertical, lowered from the central center of the body, passes in front of the axis of the ankle joints by 4-6 cm, in front of the knee joints by 0.5-1.5 cm and 1-3 cm behind the axis of the hip joint. In this case, the shins are deviated from the vertical by 4-5°, and the legs are bent at the knee joints by 2-3° (Fig. 7). As a rule, the projection of the GCT of the body is located asymmetrically with respect to the sagittal and frontal planes, and the positions of the GCT of the body and limbs do not remain constant over time. The load on the right and left limbs can vary between 3-6% of the total body weight. But often this difference can be greater.
Rice. 7. Schemes of the position of the projection of the body’s central core in a comfortable position:
a - in relation to the joints and head (Gl); b - in relation to the projections of the axis of the joints; Pl - Shoulder; T - hip; K - knee; G - ankle
It is believed that a person’s vertical posture is stable when the projection of the body’s central gravity oscillations does not extend beyond the contour of the supporting area of the feet. But in all cases, the determining factor in the stability of the body is the functional state of the nervous system.
When standing in a comfortable position, the muscles associated with the ankle joint are most active: the tibialis anterior, the peroneus longus and the gastrocnemius. The closer the muscles of the joints (knee, hip) are located to the body’s central core, the less active they are in maintaining a comfortable standing posture. Biomechanical studies have shown that the static moment in the ankle joint in relation to the static moments in the knee and hip joints is maximum, which is explained by the significant distance from the axis of this joint to the projection of the GCT of the body (see Fig. 7).
It is believed that in the processes of walking and standing, muscles work without fully using their capabilities. For example, the calf muscle, which is particularly active when the body is in an upright position, expends only 1/9 of its strength. Consequently, to ensure a vertical position, a person has a multiple reserve of power, which is spent on quickly restoring the disturbed balance. The stability of the body in space when it is orthograde is actually determined by the biomechanical and reflex interaction of all the muscles of the trunk and limbs. This is explained by the fact that in order to maintain a vertical position of the body, despite the multi-link structure of the skeleton, which has dozens of degrees of freedom, a person has a fairly limited number of them. It is believed that under normal conditions a person realizes only 2-4 degrees of freedom. The passage of the vertical line of the projection of the body's central gravity (the line of action of the force of gravity of the body) in front of the axes of the knee and ankle joints determines the straightened state of the knee joint when standing. At the same time, the muscles of the back of the thigh and lower leg, acting together, prevent the body from falling forward. This passage and high position of the body's central center of gravity from the support (according to M.F. Ivanitsky, the body's center of gravity is located from the plane of support at a height of 55±1.5% of a person's height) cause constant tension in the entire muscular system, and not just the muscles of the lower extremities of a person.
Extension and flexion of the torso are carried out around the frontal axis. The main muscles that provide extension of the torso are the erector spinae muscle and the transverse spinalis muscle.
The erector spinae muscle makes up the bulk of the back muscles. This muscle has a wide origin from the sacrum, from the iliac crest, from the spinous processes of the lumbar vertebrae. It is further divided into 3 parts: external (iliocostal), middle (longest) and internal (spinous). The iliocostalis muscle is attached to the transverse processes of the thoracic vertebrae and the angles of the ribs. The longissimus muscle is attached to the transverse processes of the thoracic and cervical regions and to the mastoid process. The spinous muscle is attached to the spinous processes of the thoracic vertebrae. The erector spinae muscle is a powerful extensor of the torso and neck and tilts the head back. With unilateral contraction, together with contraction of the abdominal muscles of the same side, it produces an accelerated tilt of the torso in its direction. The muscle holds the human body in an upright position, preventing the body from falling forward under the influence of gravity. A large load on this muscle falls when the torso is extended during lifting. At the same time, the muscle contracts, performing overcoming work.
The spinospinalis muscle is located under the erector spinae muscle. The bundles of the transverse spinalis muscle are directed obliquely and lie in 3 layers. They start from the transverse processes of the vertebrae and attach to the spinous ones (the adjacent vertebra, after one vertebra, after 5-6 vertebrae). With bilateral contraction, the muscle produces extension of the torso; with unilateral contraction, together with the abdominal muscles, it provides an accelerated tilt of the torso in its direction, as well as rotation of the torso in its own direction.
The main muscles that provide flexion of the torso during accelerated movement are the rectus abdominis muscle, the external oblique abdominal muscle, the internal oblique abdominal muscle, and the iliopsoas muscle when supported on the femur.
The abdominal muscles form the anterior and lateral walls of the abdominal cavity.
The rectus abdominis muscle is located in the thickness of the anterior abdominal wall (Fig. 12). It starts from the cartilage of the lower ribs and attaches to the pubic bone. The muscle ensures flexion of the torso during its accelerated forward (downward) movement.
The external oblique muscle is located superficially on the side wall of the abdomen. It begins with teeth from the lower ribs, is directed obliquely inward downwards and is attached to the iliac crest and to the pubic bone. With bilateral contraction, the muscle bends the torso as it moves forward rapidly; with unilateral contraction, turns the body in the opposite direction; contracting together with the back muscles of the same side, tilts the body in its direction during its accelerated movement.
The internal oblique muscle of the abdomen is located under the external oblique muscle. Its fibers are directed perpendicular to the outer one. It starts from the iliac crest and attaches to the lower ribs. With bilateral contraction, it bends the torso as it accelerates forward; with unilateral contraction, together with the back muscles of the same side, it tilts the torso in the same direction during its accelerated movement, and also turns the torso in its own direction.
The iliopsoas muscle starts from the bodies and transverse processes of the XII thoracic and all lumbar vertebrae, as well as from the fossa of the pelvic bone, and is attached to the lesser trochanter of the femur. When supported on the spine, the hip flexes and supinates. When supported on the hip, contracting on both sides, it bends the torso as it moves forward at an accelerated rate.
In a standing position, with unilateral contraction of the muscle with support on the thigh, the torso is rotated in the opposite direction. With the joint contraction of the abdominal and back muscles of the same side, an accelerated tilt of the body in one direction is ensured.
When slowly bending the torso, the listed muscles do not tense, since the forward movement is carried out under the influence of the weight of the torso, and the torso is kept from falling forward by the erector spinae muscle, which at the same time stretches, performing yielding work.
The body is tilted to the right and left around the sagittal axis.
Bending of the torso occurs with simultaneous contraction of the flexors and extensors of one side. Thus, an accelerated tilt of the torso to the right is produced by contraction of the rectus abdominis muscle (right), external oblique abdominal muscle (right), erector spinae muscle (right), transverse spinalis muscle (right), internal oblique abdominal muscle (right).
When bending the body slowly, the driving force is the heaviness of the body. It is counteracted by the flexor and extensor muscles of the same name on the opposite side, which, when stretched, produce yielding work. Return to the starting position is ensured by the same stretched muscles, which, contracting, will already perform overcoming work.
The body turns to the right and left around the vertical axis. Torso turns are produced by muscles with oblique direction of fibers during their unilateral contraction. Thus, turning the torso to the right is achieved by contracting the external oblique abdominal muscle (left), internal oblique abdominal muscle (right), transverse spinalis muscle (right) and iliopsoas muscle (left).
M. Devyatova
The main muscles that provide movement of the lumbar region and other materials on neurology.
The muscles responsible for a straight vertical position hold the spine, maintain its curves, move the legs and support the head.
1. Feet and Lower Legs: The muscles in front of the lower legs that point or raise the toes and move the foot upward are constantly aligned with the body's center of gravity so that the body does not lose its foundation.
Stand with your eyes open and then close them. Lower the focus of consciousness to the lowest, setting point. Feel the state of dynamic muscular balance necessary to maintain balance.
2. Hips: The lumbar muscles are the most important for holding the spine in the vertical position characteristic of humans. The psoas muscle connects the legs to the torso, linking the transverse processes of the lumbar vertebra to the smaller of the femoral trochanters (upper and outer femur) on each side. It is this muscle that gives the lower back its characteristic forward bend, shifting the center of gravity of the torso forward and placing it between the feet. The psoas muscle is designed to help the body maintain position in space. It constantly contracts and relaxes, adjusting the position of the body. The psoas muscle also takes part in the process of body movement.
The psoas muscle changes its action under the influence of the movement of the diaphragm, a thin plate of horizontal muscle responsible for breathing. The lower fibers of the diaphragm emphasize the curve of the lumbar spine (low back) to bring it forward. The diaphragm contracts with each exhalation and thereby affects the psoas muscles, posture and balance of the body. We can easily imagine how sensitively and subtly these muscles have to control the body. And it is easy for us to understand that tension that prevents these muscles from working at their full potential will inevitably change posture, creating too much of a curve in the lower back, stiffening the pelvis, or causing other structural, and ultimately functional, problems.
3. Trunk: The quadratus lumborum muscle originates from the iliac crest (hip) and the iliopsoas ligament (pelvic girdle) and connects to the lowest rib and the four upper lumbar vertebrae. The quadratus lumborum muscle regulates the position of the center of gravity of the body on the legs.
4. Spine: the short and deep transverse spinous muscles rise at an angle upward from the transverse processes of the underlying vertebrae and are attached to the spinous processes of the overlying vertebrae. Exactly these
muscles play a major role in maintaining the spinal column in a straight and vertical state. And they are supported by intertransverse, small muscles located between the transverse and spinous processes of the vertebrae, which are placed in pairs between the crests of adjacent vertebrae. In addition to this, the transversospinalis muscles send nerve signals to other postural muscles that are located in front and behind the spinal column to maintain continuous muscle contraction to keep the torso in a strictly upright position.
5. The head is supported by the splenius, middle and posterior scalene muscles. They support the cervical vertebrae, balance the head on the body and allow it to move back and forth.
These muscles, which hold the body upright, work in all standing postures. We will not particularly highlight their function when describing the asanas of surya namaskara, unless they play a special role in some specific position.
More on the topic Direct position:
- Episode 16. Standing poses and standing forward bends
- APPROVED by the order of the Ministry of Health of Ukraine dated June 19, 1997 No. 359 REGISTERED with the Ministry of Justice of Ukraine dated June 14, 1998 No. 14/2454 REGULATIONS on the procedure for certification Likariv I. REGULATIONS
Walking is the main way to move in space and navigate in it. When walking, space is perceived through visual, auditory, skin, proprioceptive and vestibular sensations.
When walking, the main role in children’s orientation in space, especially at a young age, belongs to vision.
The role of vision in orientation in space when walking is detected in healthy children when walking in a straight line with their eyes closed. It turned out that preschool children and even children 7-8 years old deviate significantly to the sides when walking with their eyes closed. From 9-10 years of age, these deviations decrease significantly and at 13-14 years of age they reach relatively constant values. At 15-17 years of age, gait asymmetry no longer decreases.
Hence, orientation in space when walking, it is not only preserved, but also improved with age after vision is turned off. After vision is turned off, it is carried out due to the receipt of impulses into the nervous system from the vestibular apparatus and from the receptors of muscles, joints and tendons - proprioceptors, the role of which increases with age.
Rice. 39. Age-related changes in the orientation of movements in space:
/ - fluctuations when standing, 2 - asymmetry of walking, 3 - jump accuracy, 4 - fluctuations in tempo
Thus, with age, the importance of the muscular sense in orientation in space increases.
Deviations when walking with eyes closed in preschoolers on the right and left sides are observed equally often. With age, preschoolers tend to deviate to the right when walking with their eyes closed more often than to the left. It turned out that at 3-7 years old children place their feet more straight in the sagittal plane, and the older school-age children are, the more they turn their feet to the sides. The angle of rotation of the feet in preschool children is not constant. Stereotype of steps increases with age. If the foot is turned more to the right side, then the deviation from the straight line occurs to the right, and vice versa. The decrease in deviations to the sides when walking with eyes closed in children with age depends on the decrease in the difference in the turn of the right and left feet. Blind children deviate to the sides from a straight line when walking more than sighted children. The greatest deviations are observed in blind children at a young age. In blind children of middle and high school age, walking is stereotypical and perfect.
Children with vestibular apparatuses disabled by disease when walking with their eyes closed deviate significantly more to the sides from a straight line than healthy ones. This difference is especially pronounced from 11 to 14 years. Consequently, for children’s orientation in space with their eyes closed, not only impulses from proprioceptors, but also from the vestibular apparatus are essential. When the vestibular apparatus is turned off, improvement in orientation in space occurs due to the receipt of impulses from proprioceptors. Deaf children, when walking with their eyes closed, spread their legs wider than normally hearing and blind children, and sway more from side to side and stumble more often. Consequently, in orientation in space, in addition to vision and impulses from the vestibular apparatus and proprioceptors, hearing is also essential.
While walking, children learn to measure time intervals.
Orientation in space during high jumps is determined mainly by impulses from the proprioceptors and vestibular apparatus, and not from the receptors of the retina.
Orientation in space during long jump is determined mainly by vision.
With age, in children from 14 to 16 years old, the accuracy of long jumps over a certain distance increases by more than 5 times.
At 9-10 years of age, the magnitude of the error in distance sharply decreases, and then it decreases more gradually. The smallest error in determining the jump distance is observed in children 13-14 years old, in whom the accuracy of the jump becomes almost the same as in adults. At 15-16 years old, the accuracy of the jump decreases somewhat. Despite the fact that jumps are made with open eyes, control of the distance of the jump before it is completed is carried out not only by the receptors of the retina of the eyes, but also thanks to impulses from the proprioceptors of the eye muscles, and during flight this control is carried out mainly thanks to impulses from the proprioceptors of the skeletal muscles involved in jump.
Children's orientation in space during standing long jumps increases 2-3 times from 4 to 12 years old, and changes slightly from 12 to 16 years old. When vision is turned off, the accuracy of orientation when standing long jumps decreases by 2 times, and when jumping high does not change compared to jumping with open eyes.
Thus, with age, the importance of vision increases relatively only during forward movements made with a lift off the ground, and during vertical movements, it is not vision that is decisive, but centripetal signaling from the motor system.
Pose. The standing pose is the starting point for changing the position of the body in space. When standing and sitting, a person takes a position that is comfortable for him.
Standing upright is carried out reflexively due to muscle contractions that overcome the force of gravity of the Earth. In this postnotonic reflex, the main role belongs to the proprioceptors of the leg muscles. The upright posture is difficult to maintain. The general center of gravity of an adult's body is located in the 2nd sacral vertebra, 4-5 cm above the transverse axis of the hip joints. Depending on gender, age and muscle development, the position of the center of gravity when standing ranges from 1 to 5 sacral vertebrae. Women have a lower center of gravity than men. When standing, a person rests on the lower surfaces of the heel tuberosities, the heads of the metatarsal bones and the toes.
When lying on your back, the center of gravity is approximately 1 cm above the promontory - the protrusion at the junction of the 5th lumbar vertebra with the 1st sacral vertebra. When an adult stands in a comfortable position with a forward bend, all the main joints of the torso and legs (shoulder, hip and knee) are located in front of the vertical line, passing from the general center of gravity of the body in front of the axis of the ankle joints by 4-5 cm.
Rice. 40. Scheme of contraction of some muscles when standing upright, A - anthropometric position; B - calm position; B - tense position
When standing quietly, this vertical line runs 4-5 cm in front of the axis of the ankle joints, 0.4-1.5 cm in front of the axis of the knee joints and 1-3 cm behind the axis of the hip joints. When standing, the muscles of the ankle joint are reflexively tense: the tibialis anterior, the peroneus longus and especially the gastrocnemius. The muscles of the knee joint area are less active, and even less are the hip and longissimus dorsi muscles. The body is kept from falling forward by contraction of the lower leg muscles, especially the gastrocnemius, and from falling backward by contraction of the iliopsoas and rectus femoris muscles.
The muscles involved in maintaining the standing posture use only a negligible part of their tension reserve (no more than 1/20 of the possible maximum tension). This power reserve indicates the relative efficiency of a comfortable standing posture and ensures its stability when the center of gravity of the body shifts.
In healthy people (right-handed), the load on the right leg when standing is 3-5% more of the total body weight than on the left leg.
The center of gravity of the head is 0.5 cm in front of the atlanto-occipital joint (between the 1st cervical vertebra and the occipital bone). Therefore, the head is held in an upright position by the tension of the neck muscles.
The stability of the body position when standing is recorded by the number and magnitude of head vibrations over a certain period of time. A recording of these oscillations (cephalogram) showed that the greater the height, the greater the oscillation of the head from front to back. Therefore, in children, head oscillations increase with age, but with increasing strength of the back muscles, the magnitude of these oscillations decreases.
Fatigue caused by arm work or squats dramatically increases body sway when standing (up to 90%). Exercising improves standing stability.
Maintaining an upright body position is not innate. In rare cases, when children lived among animals, they did not acquire the ability to maintain an upright body position. It is known that prolonged stay in bed in a horizontal position leads to the loss of this ability. Consequently, the postnotonic reflex of the vertical position of the body is the result of a complex combination of conditioned and unconditioned reflexes of self-regulation of tension in certain muscle groups.
Vision is involved in maintaining a standing posture. Closing the eyes when illuminated increases the amplitude of body vibrations by an average of 45%. Closing the eyes in the dark additionally increases the amplitude of oscillations of the body's center of gravity by an average of 1.3-1.5 times. The vestibular apparatus, which interacts with vision and proprioception, is also involved in maintaining a standing posture. After switching off the vestibular apparatus, while maintaining vision and proprioception, the standing posture is not noticeably disturbed. However, the participation of the vestibular apparatus together with proprioception in maintaining a standing posture is beyond doubt. It should be taken into account that reflexes from the vestibular apparatus to the redistribution of muscle tension, causing straightening of the body, as well as tonic reflexes of the neck muscles, are sharply inhibited with age in children. This inhibition occurs in most healthy children by the age of two, and in rare cases in some by the age of five. Fast reflex self-regulation of standing posture with the influx of proprioceptive impulses is carried out by the spinal cord, medulla oblongata and cerebellum, and slower - by the cerebral hemispheres and the nearest subcortical centers.
Children 6-7 years old cannot yet stand upright for a long time. With age, this ability continues to improve unevenly, and the body's stability when standing increases.
In children 7-13 years old, body vibrations when standing are greater than in adults: at 7-10 years old, body stability when standing is less than at 10-13 years old, and within this age it almost does not change. The greatest increase in stability occurs from 10 to 13 years. At 13-14 years of age, stability is the same as in adults. When schoolchildren maintain a standing posture, the activity of the hip extensor muscles is 12 times less than when they contract voluntarily.
When standing on a fixed horizontal support, pelvic vibrations in children 7-15 years old in the frontal and sagittal planes are significantly greater than vibrations of the head and torso. Body vibrations in children aged 7-11 years are greater in the frontal plane than in the sagittal plane.
When standing, the body oscillates in the sagittal and frontal planes more in boys than in girls. With increasing growth, the amplitude of oscillations increases. In girls, body stability when standing is greater due to lower height and a lower center of gravity of the body. The participation of vision in maintaining an upright posture increases with age.
When standing on a displaced support, the posture reflex increases as the support tilts. The greater the inclination, the greater the straightening of the body. The faster the tilt changes, the smaller the magnitude of the upright reflex. With age, the tilt reflex decreases more and more. At a certain speed of tilting the support, children 7-8 years old stand straighter with their eyes closed than 14-15 year olds. The upright posture in children 14-15 years old differs little from adults under these conditions. With age, the number of children who feel tilted increases.
When comparing the upright standing reflex with open and closed eyes, it turned out that when the eyes are closed, the postnotonic upright standing reflex decreases even when the support is displaced.
The role of vision in this reflex increases with age. In older children, the postnotonic reflex when bending over with eyes open is significantly greater than in younger children, compared with the same reflex with eyes closed.
When the torso is tilted, the greatest muscle tone is observed on the side opposite to the tilt. At the moment of tilting, the muscles on the side in which the body is leaning are excited, and then, when maintaining the tilting position, on the opposite side due to the reflex stretching of the skeletal muscles caused by irritation of the proprioceptors located in them (myotatic reflex).
When sitting, the longissimus dorsi muscles are symmetrically tense in the area of kyphosis at the level of the thoracic spine, and the tension in the cervical and lumbar muscles is insignificant.
The reflex of holding the body in an upright position when sitting is much smaller than when standing, and in some cases is absent. In older children (14-15 years old) it is completely absent, and in younger children (7-8 years old) it is weakly expressed.
The decisive role in the implementation of the vertical body position reflex belongs to impulses from the proprioceptors of the legs and receptors of the skin of the soles. When sitting, the correct assessment of the inclination of the support is felt more often than when standing. This is probably explained by an increase in the area of irritation of the receptors in the skin of the ischium compared to the area of the skin of the soles.
In school-age children, when lying on their backs and sides, rhythmic vibrations of the body are observed, the frequency of which coincides with that observed when standing. When the vestibular apparatus is irritated, these rhythmic movements of the body are inhibited.
The magnitude of static force and dynamic work of the arm muscles depends on the posture. When sitting, the tension in the arm muscles is much greater than when standing. This can be explained by the fact that when standing, the nerve centers of the leg muscles, which also carry out static efforts aimed at combating gravity, inhibit the nerve centers of the arm muscles. On the contrary, when standing, the dynamic work of the arm muscles is performed more coordinatedly and economically than when sitting.
Posture. Individual characteristics of body position are called posture. Basically, it is formed by the age of 6-7 years. For each person, posture changes depending on the structure of the skeleton, the state of the nervous system, muscle tone and development. There are very good, good, average and poor posture. With very good posture, the convex chest is slightly in front of the flat or retracted abdomen, and the physiological curves of the spine are moderate. With good posture, the chest is located at the level of the front wall of the abdomen, and the curves of the spine are more pronounced. With average posture, the chest is flat and the anterior wall of the abdomen is slightly pushed forward, the lumbar lordosis is more pronounced. With poor posture, the head is tilted forward, the chest is flat or sunken, the stomach protrudes strongly forward, and thoracic kyphosis and lumbar lordosis are pronounced. Good posture is natural, does not require special muscle contraction, therefore, is not tiring and provides good conditions for the development and activity of the organs of the chest cavity: the heart and lungs. Rational physical exercises, such as balancing with a ball on your head, strengthen the spinal muscles and help develop good posture.
To form correct posture, the development of the trunk muscles is of great importance. The tension of these muscles forms and maintains posture, and a decrease in their tension disrupts it. In children of preschool and primary school age, these muscles are not yet tense, so their posture is unstable.
In children, deviations from normal posture are caused by skeletal diseases, for example, rickets, low mobility, poor development of muscles that counteract the force of gravity, improper sitting at a desk or work table, carrying heavy objects in one hand, which causes the torso to tilt, etc.
In the formation and development of scoliosis in the absence of spinal diseases, the decisive role is played by the unevenness of the tone and contractions of the skeletal muscles on both sides of the spine. At the beginning of the development of scoliosis on the concave arch of the spine, muscle tone is increased and their contractility is increased compared to the convex side of the spine. But as scoliosis develops, as a result of a protective reaction that prevents a further increase in the curvature of the spine, on the contrary, on its convex side, muscle tone and contractions increase, and on the concave side they weaken. Corrective gymnastics at the beginning of the development of scoliosis should be aimed at equalizing the tone and contractility of the muscles on both sides of the spine, and with developed scoliosis - at strengthening the tone and contraction of the muscles on the convex side.
The formation and development of pronounced kyphosis in a healthy spine depends on improper sitting at a desk or desk and on decreased tone and contraction of the back muscles that hold the torso in an upright position. A decrease in muscle strength and insufficient general physical development contribute to the development and increase in kyphosis.