Human Anatomy (with the fundamentals of dynamic and sports morphology) - Ivanitsky M. F. 2008

Special Dynamic Morphology
Anatomical characteristics of body positions. Preliminary remarks

Body positions are characterized by their spatial orientation (vertical, horizontal, inclined, upside down, etc.), posture (the relative arrangement of individual body segments to one another), and their relation to the support surface.

Body positions are classified as static when external forces (gravity and the support reaction force) are mutually balanced. Equilibrium conditions depend on the mutual arrangement of body segments and the area of the support base. Since body segments typically do not lie in a single plane, and angles and torque moments are formed between them, maintaining any posture requires muscular tension. Furthermore, the greater the gravitational torque of the body segments, the greater the load placed on the Muscles responsible for maintaining them in a specific position. Depending on how the load is distributed between the right and left halves of the body, postures are divided into symmetrical and asymmetrical.

In symmetrical body positions, the motor apparatus works equally on both the right and left sides of the body, which promotes harmonious physical development. Asymmetrical positions (such as the stance of a boxer or fencer) are characterized by an unequal involvement of the right and left halves of the motor apparatus, which can lead to disharmony in body Structure and development.

Relative to the support surface, body positions are distinguished by lower support (standing, bridge, splits), upper support (hangs, excluding the arch hang), and mixed support (support on parallel bars).

According to the type of equilibrium, body positions are divided into unstable equilibrium and limited-stable equilibrium.

Depending on The Nature of the support, external forces may act in compression, tension, bending, or torsion. This determines specific features in the operation of the motor apparatus, as well as the functioning of Internal Organs, The Cardiovascular system, and other body systems.

In positions with lower support, gravity exerts a compressive effect on the underlying body segments that counterbalance the overlying ones. Therefore, the lower the segment, the greater the force acting upon it, and the more intensely the muscles must contract.

Conversely, in body positions with upper support, the Muscles of the underlying segments experience less tension than those of the overlying segments. For example, in a standing position, the muscles of the ankle joint counterbalance the weight of the entire body, whereas in a hang, these same muscles counterbalance the weight of only one FOOT. The degree of body mobility varies across different upper-support positions (depending on the distance from the body's center of gravity (CG) to the support and the size of the support area). Mobility decreases as the distance from the CG to the support decreases and the support area increases. Movements of body segments in both lower- and upper-support positions are accompanied by additional (compensatory) movements in other segments and joints. For instance, to maintain balance when holding a load in front of the body, the torso leans backward; when holding a load in the right hand, it leans to the left. Pulling up on a pull-up bar triggers a compensatory movement of the legs.

Standing Position

The standing position is a natural, habitual human posture developed through a long process of evolution. It can serve as a working posture, as well as the starting and ending position for movements and physical exercises. When standing, the body is vertical, the arms hang relaxed along the sides of the torso, the HEAD is held straight, and the soles of the feet are in full contact with the support surface. Gravity is directed downward, exerting a compressive force on the body segments. The closer a segment is to the support surface, the greater the gravitational moment. Consequently, the lower extremities, especially the foot, bear the heaviest load. The support reaction force is equal to the force of gravity but directed in the opposite direction.

One of the conditions for maintaining a human's balance in a standing position is that the body's center of gravity (CG) must be located directly over the support area. If the vertical line of this center falls outside the support boundaries, equilibrium is disrupted and the body falls. Moreover, a standing position can only be maintained when the movable segments of the body are held securely in place through the tension of muscles and ligaments.

Standing is classified as a body position with lower support. The support area is formed by the plantar surface of the feet and the space enclosed between them. The primary weight-bearing points of the foot are the lower surface of the calcaneal tuberosity, the heads of the metatarsals, and potentially the toes. The support area with closed heels is larger when the feet are angled slightly relative to each other, measuring approximately 250–350 cm².

In the standing position, pressure is distributed predominantly onto the heel and to a lesser extent onto the region of the metatarsal heads, primarily the 2nd and 3rd. Approximately 3/4 of the body weight falls on the rear part of the foot and 1/4 on the front part. If the torso is shifted backward or forward while standing, the pressure distribution between the forefoot and rearfoot changes. In the first case, the pressure on the forefoot decreases while the rearfoot pressure increases, and vice versa In the second case. Furthermore, the vertical line of the body's CG shifts closer to either the posterior or anterior edge of the support area, altering the muscular load. The so-called active support surface of the foot is significantly smaller than the footprint visible in prints, because the soft Tissues of the foot cannot serve as a rigid support for the body.

When a person stands in shoes, especially rigid boots, the "active" surface of the foot is larger than when barefoot, as the soft tissues at the edges of the foot offer greater resistance to gravity in the former case.

In a symmetrical standing posture, body weight is distributed evenly across both feet, and the vertical line of the body's CG passes approximately through the middle of the support area. However, balance can be disrupted if this vertical line moves beyond the BOUNDARIES OF THE support area. For this reason, the standing position is categorized as a limited-stable type of equilibrium.

Depending on whether the vertical line of the body's CG is closer to the posterior or anterior edge of the support, Three types of standing postures are distinguished (Fig. 169):

1) anthropometric,

2) relaxed,

3) tense.

The anthropometric position is one that serves as a baseline for various measurements (typically for determining body height using a vertical stadiometer). In this posture, the body is straightened and slightly shifted backward. The body's CG lies approximately in the same frontal plane as the transverse axes of the principal limb joints (shoulder, elbow, hip, knee, and ankle) and the centers of gravity of individual body segments (head, torso, and limbs).

The anthropometric posture is rather inconvenient because the support area behind the frontal plane is very small, and even a slight external force can cause the body to fall. Additionally, uneven Development of the muscles located anterior and posterior to the transverse axes of rotation in the joints leads to rapid fatigue in those that are insufficiently strong (for example, the muscles of the anterior leg). A certain degree of tension must be maintained by both the muscles located anterior to the transverse joint axes and those located posterior to them—namely, the flexors and extensors.

The relaxed position is characterized by the entire body being in an unconstrained state (such as the "At ease!" military stance). While symmetrical, the upper body is positioned slightly back, while the pelvis is shifted forward. The frontal plane passing through the body's CG lies posterior to the transverse axis of the hip joint and anterior to the axes of the knee and ankle joints, running roughly through the middle of the support area. The stability angles at the front and back, as well as the lateral ones, are equal. In this position, a person can perform movements within the support area without losing balance.

Because the moment arms of gravity in the hip, knee, and ankle joints are small, as are their torques, the relaxed standing posture involves minimal muscular tension. Meanwhile, backward movement of the body (driven by gravity) is prevented by the tension of the iliofemoral ligament, although the hip flexor muscles that stabilize the pelvis maintain some degree of tension.

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Fig. 169. Muscle tension in various standing positions:

1 — anthropometric posture (muscles contracted on both the anterior and posterior surfaces of the body); 2 — relaxed posture (slight tension in the muscles of the posterior trunk, the anterior thigh muscle group, and the posterior lower leg muscle group); 3 — tense posture (increased muscle tension across the entire posterior surface of the body).

Knee joint stability—where the line of the body's center of gravity (CG) passes anterior to the transverse axis—is reinforced by the tension of ligaments located on its posterior surface and within the joint itself. Ankle joint stability is ensured by the anatomical design of the joint. The trochlea of the talus is slightly wider anteriorly than posteriorly; therefore, when the lower leg is inclined forward, it is wedged more securely between the malleoli of the Tibia and Fibula than in the anthropometric posture. In a relaxed posture, with the trunk slightly leaning backward, only minimal muscle tension is required to stabilize both the Hip and knee joints.

Relative to the transverse axis of the atlanto-occipital joint, the body's CG line passes anteriorly, meaning that the muscles of the nuchal region must maintain tension to prevent the head from tipping forward. The upper trunk is prevented from falling forward by the back muscles, most notably the erector spinae. Because the upward PROJECTION OF THE body's CG line passes fairly close to the transverse axes of the joints connecting the head and trunk, relatively little muscular effort is required to keep these body parts in equilibrium. The ligamentous apparatus also plays a significant role in this process.

A tense body posture is characterized by an upright trunk shifted slightly forward, so that the body's CG line runs close to the anterior boundary of the support area, ahead of the transverse axes of all major lower limb joints: the hip, knee, and ankle. Consequently, the muscles located on the posterior aspects of these joints must remain in a state of constant contraction to prevent the body from falling forward.

In a tense posture, the primary load falls on the muscles located opposite to the side where the body's CG line passes. For instance, the head and trunk are supported by posterior muscles (trapezius, splenius, erector spinae, etc.). The Abdominal muscles also exhibit some degree of tension. Especially heavy work is performed by the muscles of the posterior hip joint (gluteus maximus, etc.), the posterior and lateral muscle groups of the lower leg, and the plantar muscles of the foot.

The "Attention!" (Smirno!) stance used in physical education practice represents a compromise between a tense and a relaxed body posture. It provides a high degree of stability; thus, much like in the relaxed state, the body's CG line passes anterior to the transverse axes of the ankle joints and approximately through the center of the support area. Unlike the tense posture, however, the "attention" stance does not feature an abruptly forward-shifted trunk or significant muscular strain.

Any standing posture must meet certain aesthetic criteria: avoiding postural defects (such as slouching), excessive muscle tension, and so forth. Comparing the anthropometric, relaxed, and tense postures alongside the athletic standing stance, the latter appears most advantageous, although fully satisfying all these criteria simultaneously is virtually impossible for any standing posture. Indeed, while a tense posture makes the transition to walking or running the easiest, it fails to meet other requirements fully. Meanwhile, the relaxed posture is best suited for minimizing the Organism's Energy Expenditure in maintaining equilibrium.

Handstand

In a handstand, the body assumes a vertical, upside-down position. This exercise represents a body posture with inferior support, where the upper body segments are balanced by the lower ones. Consequently, the lower a segment is located, the greater the tension in its muscles, and vice versa. For example, in a standard standing position, the ankle muscles experience the highest tension because they balance the entire body mass relative to the feet; conversely, in a handstand, these same muscles experience the least tension because they only balance the moment of force of a single foot (Fig. 170).

The degree of muscle tension depends on the magnitude of the resistance moment and the leverage (moment arm) of the muscle force: the greater the resistance moment, the heavier the load on the muscles; the larger the muscle's moment arm, the more mechanically advantageous its position (conversely, muscles that originate closer to the joint must exert greater tension due to their shorter moment arm).

The support area in a handstand is relatively small, comprising the surface area of the hands and the space between them. In terms of the relationship between the body's CG and the support area, a handstand is classified as a conditionally stable form of equilibrium: the body's CG is positioned quite high (in the region of the sacral vertebrae), the stability angles are small, and directional stability is limited in all directions.

It is well known that the equilibrium of any body segment is maintained provided the moments of two forces are equal: the force of gravity and the force of the muscles spanning the joint around which the segment can rotate. Therefore, muscle tension increases with greater body mass and a longer gravity moment arm.

The gravitational force acting on a foot in a plantarflexed position with a pointed toe is counterbalanced by the plantar muscles of the foot and the posterior lower leg muscles—excluding the bi-articular gastrocnemius, whose tension could induce an unwanted movement: knee flexion. This movement is also favored by the fact that the line of gravity for the foot and lower leg passes posterior to the knee joint. However, the gravitational moment is counteracted by the action of the rectus femoris and its heads. In a hollow-back (arched) handstand, the tension in this muscle is greater than in a straight handstand, since in the latter, the gravity moment arm is minimal, with the line of gravity passing almost directly through the center of the joint.

The CG of the "foot–lower leg–thigh" system is located approximately in the distal region of the thigh, and the vertical line dropped from this center passes slightly behind the transverse axis of the hip joint, favoring hip extension. The counteracting force that balances the superior segments is the moment generated by the hip flexor muscles and the tension of the iliofemoral ligament.

In the lumbar spine, the gravitational moment tends to produce extension, while the abdominal muscles counterbalance the mass of all superior body segments. In the thoracic region, conversely, the gravitational moment promotes spinal flexion, which is resisted by the trunk extensors. The tension of these extensors in a vertical handstand is greater than in an arched handstand because the gravity moment arm exceeds the muscle's moment arm.

Fig. 170. Diagram of gravitational moments (I) and muscle tension moments (II) in a handstand;

A — side view; B — rear view

The lower limb muscles operate with a proximal base of support.

In the upper extremity, all forearm and hand muscles are under tension in the wrist joint region. The flexors of the wrist and fingers are tense and elongated, which can sometimes lead (due to insufficient flexibility) to the flexion of the finger Phalanges. In the elbow joint, the triceps brachii is under tension because the line of gravity passes anterior to the joint's transverse axis. In the shoulder joint region, tension affects not only the stabilizing muscles but also the muscles of the Pectoral Girdle that anchor its skeletal framework. Scapular stabilization is facilitated by the upper and middle sections of the trapezius, the rhomboids, the deltoid, and all shoulder joint muscles attaching to the scapula. The back and chest muscles—specifically the teres major, pectoralis, and posterior deltoid—experience particularly high tension.

Minor body oscillations forward and backward during a handstand are counterbalanced by the tension of the pectoral muscles or latissimus dorsi. Contracting simultaneously, they prevent the body from swaying around the sagittal axis. When the body tilts to the right, the muscles on the left side of the body tense up; when it tilts to the left, the muscles on the right side do. Unlike lower limb muscles, upper limb muscles operate with a distal base of support.

The head is balanced by the muscles that extend it at the atlanto-occipital joint and by the extensor muscles of the cervical spine. Because the pectoral girdle is an open bony ring, the trunk along with the superior body segments tends to slip downward between the scapulae. This is resisted by the muscles that elevate the pectoral girdle in a standard standing position while working with a inferior support base (sternocleidomastoid, levator scapulae, upper fibers of the trapezius, etc.).

Respiration during a handstand is impaired. The upper and middle sections of The thoracic cage are fixed by the muscles of the pectoral girdle, shoulder joint, and abdomen. Upper chest breathing is almost entirely suppressed, while lower chest breathing is somewhat apparent. Abdominal breathing is also hindered by the tension of the abdominal muscles, which prevent the descent of the Diaphragm and resist the pressure exerted by internal organs.

Blood Circulation is likewise somewhat impaired in a handstand. Venous return from the head is slowed down because blood must flow upward against gravity rather than downward. The absence of Valves in the cerebral Veins causes blood pooling, leading to dilation of the Vessels of the Head and Neck, elevated vascular pressure, and facial flushing.

The handstand exercise promotes The Development of muscle strength in the upper extremities, abdomen, and back, and exerts a training effect on the diaphragm and the coordination apparatus. At the same time, approach this exercise progressively due to the restrictions it places on external respiration and blood flow.

Hang with straight arms

In a straight-arm hang, the body is in a vertical position, the hands are fixed to the gymnastic apparatus (rings, bar), the head is held straight, the torso is extended, and the legs are straight. There is extension at the hip and knee joints, and flexion at the ankle joint and the JOINTS OF THE foot (Fig. 171).

The arms may be pronated, with the thumbs turned toward each other, or supinated, when they are turned outward in opposite directions.

The support area in a straight-arm hang is represented by the area of the Contact surfaces of the palms touching the apparatus and the space enclosed between them. Gravity, directed downward, acts as a tensile force, striving to separate the lower PARTS OF THE body from the upper ones.

This is counteracted by the muscles, and the load on them is greater the higher their anatomical Location.

The COM of the body is located below the support area, which makes the equilibrium in this position stable.

The greatest load falls on the muscles of the upper extremity, which must not only keep the fingers in a flexed position on the bar (rings, trapeze, etc.), but also protect the joint structures from overstretching and tearing. The finger flexors of the forearm and hand are contracted, while in the area of the elbow and shoulder joints, all the surrounding muscles—which possess great strength—are in a less tense state compared to the finger flexors. In the elbow joint, Muscle Action is facilitated by The structure of the joint itself: the olecranon process of the ulna hooks around the trochlea of the humerus. In the shoulder girdle region, the muscles that depress the shoulder girdle from the starting position are contracted, as are the muscles that prevent the scapula from shifting forward and upward. In this position, the head of the humerus is held within the glenoid cavity of the scapula by the tension of the long head of the triceps brachii. Other muscles running near the shoulder joint (pectoralis major, latissimus dorsi, coracobrachialis, biceps brachii, subscapularis, infraspinatus, and teres muscles) also participate in the work. The deltoid muscle (especially its middle part) and the supraspinatus cannot play a major role in fixing the shoulder joint in this position. The scapula is fixed primarily by the tension of the rhomboid muscles, which (especially their lower sections) are in a heavily stretched state, as well as by the trapezius muscle and the latissimus dorsi, which presses the inferior angle of the scapula against the chest wall.

The muscles of the torso and lower extremities bear a somewhat lesser load. The foot is held by the strength of its plantar muscles, as well as the posterior and lateral muscle groups of the leg; the leg is held by the tension of the quadriceps femoris, and the thigh by the gluteus maximus. In the torso area, the extensor and flexor muscles (particularly the abdominal muscles) are tense, fixing the pelvis. All of these operate with a proximal base of support.

Due to the fact that the muscles elevating the Ribs (specifically the pectoralis minor, partly the pectoralis major, and the subclavius) are heavily stretched during a hang, the entire rib cage becomes expanded. Consequently, its respiratory excursions are hindered, and inhalation occurs primarily through the action of the diaphragm. However, the downward movement of the diaphragm is also impeded: the lumbar lordosis is increased, while the abdominal muscles are stretched and thus offer significant resistance to the Displacement of the abdominal viscera. The increase in lumbar lordosis is associated with the fact that the vertical line of the center of gravity of the lower extremities and pelvis passes anteriorly to the lumbar spine, as well as with the compression of internal organs onto the pelvis. In addition, the tension of the iliopsoas muscle contributes to the increase in lumbar lordosis. However, thanks to the contraction of the abdominal muscles—mainly the rectus abdominis—this lordosis decreases. When their contraction becomes especially pronounced (for example, in the L-hang position), it may be completely smoothed out because the pelvis shifts from an inclined position to an almost vertical one. The flattening of the lumbar lordosis occurs despite the increased pull of the iliopsoas muscle, because the rectus abdominis has a greater leverage relative to the transverse axes of Rotation of the spine than the iliopsoas muscle.

The most efficient grip in a straight-arm hang is one where the hands are spaced shoulder-width apart. With a very wide grip, fixing the scapula requires much greater work from the rhomboid and trapezius muscles, which draw it toward the spine. The narrower the grip, the greater the vertical component of the muscular force counteracting gravity, and the smaller the force tending to displace the inferior angle of the scapula laterally.

With a grip that is too narrow, the support area is greatly reduced, making equilibrium less stable, the glenoid cavities of the scapulae face more steeply upward, and the muscles stabilizing the shoulder girdle are stretched further. All of this creates disadvantages compared to a standard shoulder-width grip.

A straight-arm hang promotes the development of the muscles of the free upper extremity and shoulder girdle, as well as the back and abdominal muscles, and helps prevent and correct posture defects while developing diaphragmatic breathing.

Hang with bent arms

This position is characterized by the forearm flexors being in a contracted and heavily strained state. Specifically, the brachialis, brachioradialis, and several other muscles perform so much work that one can remain in this position for only a relatively short time. The biceps brachii is relaxed, apparently due to the fact that its origin and insertion points are brought closer together. In this hang, flexion occurs at the shoulder relative to the forearm, rather than vice versa (Fig. 172, 173).

In the bent-arm hang, a significant role is also played by the muscles that adduct and flex the shoulder: the latissimus dorsi, teres major, and pectoralis major. Simultaneous shoulder extension—i.e., its backward movement—occurs with the participation not only of the latissimus dorsi, infraspinatus, and teres major muscles, but also of the long head of the triceps brachii, whose tension is closely linked to the flexion of the arm at the elbow joint. The greater the degree of this flexion, the greater the tension in the triceps brachii, as its insertion point moves further away from its origin with progressive bending.

Fig. 172. Bent-arm hang

In the bent-arm hang, the body is not in a vertical position, as in the straight-arm hang, but in an inclined one. This position is the only one possible for maintaining equilibrium, because only in this posture is the COM of the body located directly beneath the support area.

Respiration is hindered to an even greater extent in the bent-arm hang than in the straight-arm hang. This is explained by the fact that the muscles running from the shoulder girdle to the chest, as well as the abdominal press muscles, are contracted significantly more than in a straight-arm hang.

Inverted arched hang

In this hang, the body assumes an upside-down vertical position. The arms are positioned along the torso and fixed to the gymnastic apparatus, the torso is extended, the legs are straight and raised upward, with the toes pointed (Fig. 174).

The work of the free upper extremity muscles is similar to that performed in a straight-arm hang. However, the action of the shoulder girdle muscles and the muscles running from the torso to the humerus is different. While in a straight-arm hang the muscles that depress the shoulder girdle are contracted, in the inverted arched hang, conversely, those that elevate it are active. In this case, the work of the muscles boils down essentially not to depressing the shoulder girdle relative to the torso, but to elevating and supporting the torso relative to the shoulder girdle.

Fig. 173. Muscle action during a pull-up:

A — electromyograms: 1 — biceps brachii; 2 — triceps brachii; 3 — erector spinae; 4 — rectus abdominis; 5 — pectoralis major; 6 — latissimus dorsi; 7 — quadriceps femoris; 8 — biceps femoris; K — movement chronogram: numbers 21–89 indicate film frame numbers (after E. G. Kotelnikova)

Due to its weight, the torso—which in this position is a more mobile body part than the upper extremities fixed to the shoulder girdle—tends to drop. At the same time, the free upper extremities and the shoulder girdle remain relatively stationary. When performing this exercise, the greatest load is borne by the following muscles: the trapezius (its upper portion), the levator scapulae, and the sternocleidomastoid. In addition, muscles that prevent the scapula from shifting by fixing the shoulder girdle relative to the torso are actively engaged (the serratus anterior, particularly its upper and middle slips, as well as the muscles that adduct the scapula toward the spinal Column — the rhomboids and the trapezius).

The contraction of the pectoralis major and latissimus dorsi observed during the arched hang helps prevent the torso from tilting forward and backward relative to the upper extremities.

As in Other types of hangs, the body in an arched hang appears to be in a state of stable equilibrium. Indeed, if one views the entire body as a single unit, its COM is located below the base of support. However, once the torso and extended legs are deflected from the upper extremities, returning to the initial position becomes extremely difficult. This is because the HEAD AND TORSO are in a state of conditionally stable equilibrium relative to the upper extremities, as the centers of gravity of the head, torso, and legs are positioned considerably higher than the shoulder girdle. Therefore, maintaining bodily equilibrium requires substantial muscular effort. The further the torso deviates forward or backward from the extended arms, the greater the gravitational torque relative to the transverse axis passing through the shoulder joint, and consequently, the harder it is to return to the starting position.

In the arched hang, certain internal organs assume an unusual position. Affected by gravity, they shift downward, press against the diaphragm by displacing it toward the head, and hold it in an exhalation state. Inhalation is severely impaired because shifting the diaphragm toward the pelvis and increasing the vertical dimension of the thoracic cavity requires the diaphragm to lift the abdominal viscera pressing upon it. Thus, respiration during the arched hang is carried out primarily through the Movements of the lower ribs (the upper ribs cannot move as they are fixed to the shoulder girdle).

Fig. 174. Arched hang on rings

No less significant changes occur in the Circulatory system. Blood outflow from the lower extremities and the lower half of the body is facilitated, whereas outflow from the head and neck is hindered. This occurs because blood from the head and neck must flow against the force of gravity. Valves that prevent the backflow of blood in veins are almost entirely absent here. This explains why the veins dilate severely and become engorged with blood during an arched hang. Capillaries also expand, leading to blood stagnation, which causes the Skin to flush or even turn cyanotic. Blood stasis is associated not only with impeded outflow but also with the Elastic properties of the capillary walls. With high elasticity, capillaries may change so little that neither redness nor cyanosis occurs (for example, in children). With low capillary elasticity (in adults), facial flushing or even cyanosis may persist even after assuming a normal body position. Of course, this does not mean that this exercise should be recommended for children and adolescents. Rather, out of caution, one should avoid exercises that place vital organs under unusual conditions and cause undesirable effects. These exercises are also contraindicated for individuals with vascular wall abnormalities or those who poorly tolerate blood surges to the head.

During the arched hang, not only the diaphragm, but also The Heart, Stomach, and Large Intestine are displaced toward the head.

Hang on the feet

In a hang on the feet, the dorsal surfaces of the feet serve as the point of support. Maintaining the feet and toes in an extended position requires strong tension from the anterior crural muscle group and the muscles of the dorsal foot. The demands placed on the foot extensors are exceptionally high, as these muscles (the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and especially the short toe extensors located on the dorsum of the foot) are relatively weak for supporting the entire body weight. Moreover, in this position, this force operates with a longer extensor moment arm. It is safe to say that there is no other gymnastic exercise in which these muscles experience such a heavy load. Therefore, this hang can only be successfully performed

by individuals with exceptionally well-developed lower limb muscles, particularly in the lower leg.

Hang with bent legs

Holding the body in a bent-leg hang requires keeping the lower legs flexed at approximately a right angle relative to the thighs. This presents no difficulty, as the knee flexors form an extremely powerful muscle group comprising not only the Posterior Thigh Muscles but also the gastrocnemius. The lifting force of these muscles is around 500 kg.

Support on parallel bars

During support on parallel bars, the body is in a vertical position with straightened arms aligned with the torso and fixed to the apparatus. The shoulder girdle is secured alongside them. This exercise falls under mixed-support movements. The lower base of support is provided by the upper extremities, represented by the surface area of the hands and the space between them. The head, torso, and lower extremities have an upper support—the shoulder girdle.

The body's COM relative to the upper extremities is located above the base of support, resulting in a conditionally stable type of equilibrium. Relative to the rest of the body, it lies below the base of support, ensuring stable equilibrium. Gravity exerts a compressive effect in the upper extremity region, increasing from top to bottom. In the torso region, it acts in tension, just like in a hang, attempting to separate the lower body segments from the upper ones while increasing from bottom to top (the heaviest load falls on the shoulder girdle muscles).

The work of the motor apparatus during parallel bar support mainly boils down to counteracting gravity, keeping the arms extended, and securing the shoulder girdle relative to the torso.

The hand is in an extended position, which occurs completely passively under the action of gravity. Consequently, the finger flexors are stretched, their tension rises, and gripping strength on the support increases. The most "critical" area of the hand through which weight is transferred to the bars is the wrist and the Base of the metacarpus.

The radiocarpal joint is stabilized by the surrounding muscles; lateral hand movements are prevented by the flexor and extensor muscles of the wrist and fingers, while forward and backward movements are checked by the hand abductors and adductors.

At the elbow joint, gravity causes the arm to tend to flex relative to the forearm. Resistance to flexion is provided by the tension of the active, contracted triceps brachii. Occasionally, individuals with poorly developed musculature (especially women) may exhibit some hyperextension at the elbow joint. Excessive arm extension and elbow joint injury are prevented by muscles located on its anterior surface (biceps brachii, brachialis, brachioradialis, pronator teres, etc.).

During this exercise, the shoulder girdle rests on the head of the humerus. The shoulder joint is stabilized by the surrounding muscles, particularly those that adduct the humerus (pectoralis major, latissimus dorsi, subscapularis, infraspinatus, teres Major and minor, and the long head of the triceps brachii).

Downward displacement of the torso relative to the shoulder girdle under METABOLISM/18.html">The Influence of gravity is resisted by the shoulder girdle depressors. These include the pectoralis minor, lower part of the trapezius, subclavius, lower slips of the serratus anterior, as well as the muscles that fix the scapula and keep its medial border parallel to the spinal column: the rhomboids and the middle part of the trapezius.

When performing the support on parallel bars, a heavy load falls on the lower portions of the pectoralis major and latissimus dorsi, as they help pull the torso upward, thereby reducing The impact of its mass transmitted via the scapula to the humeral head.

Maintaining good posture in the support position requires the action of muscles that straighten the spinal column and hold the lower limb in a straight and slightly extended position with a pointed toe. The largest of these muscles, besides the previously mentioned trapezius and rhomboids, include the erector spinae, gluteus maximus, quadriceps femoris, triceps surae, toe flexors, tibialis posterior, peroneals, and several other smaller muscles.

During a front support, the chest is kept in a slightly stretched, inhalation-like position because the major rib-elevating muscles are contracted. Breathing relies primarily on the movement of the diaphragm, which faces no significant mechanical obstacles in this position.

When a support is performed on rings rather than parallel bars, the muscular load increases significantly, as the muscles must actively prevent the rings from drifting apart. The muscles that brake the abduction of the arms away from the torso are primarily the shoulder adductors.

Among these, the pectoralis major and latissimus dorsi play the most prominent role. Working together, they form a sort of parallelogram of forces with a resultant vector directed toward arm adduction.

As the gymnast gradually moves the rings apart into a cross position, the tension in the muscles resisting this movement increases even further. As the arms abduct, the leverage of body weight lengthens and its rotational torque increases. Therefore, maintaining this position requires exceptionally well-developed upper-limb girdle musculature.

The support exercise strengthens the muscles of the shoulder girdle, the upper extremities, and the back, thereby helping to prevent posture disorders.

The Gymnastic Bridge

In the bridge position, the body forms a curved, arc-like shape with a greater or lesser radius of curvature. Alongside gravity, friction plays a crucial role: the magnitude of the frictional force dictates both the muscular tension required and the feasibility of the exercise itself. The base of support is defined by the contact area of the palms and the soles with the supporting surface, as well as the space enclosed between them (Fig. 175).

The body's COM lies above the base of support, outside the body, slightly below the spinal column and approximately above the center of the support area.

Equilibrium is conditionally stable; the anterior, posterior, and lateral angles of stability are wide, and the overall degree of stability is considerable.

The arrangement of body segments is as follows: flexion occurs in the ankle and knee joints, while extension takes place in the hip joint and the joints of the spinal column. Thoracic Kyphosis is reduced, whereas lumbar and cervical lordosis are increased. The lumbar intervertebral discs are stretched anteriorly and compressed posteriorly.

When performing this exercise on a slippery surface, the spinal curves are considerably less pronounced, and the bridge is lower than on a standard, slightly textured surface (such as a floor, carpet, or mat). On a horizontally secured ladder, the bridge can be executed with a deeper spinal arch than on the floor. On very slippery surfaces, the bridge position can only be maintained if the feet and hands are placed close together, or even if the hands grasp the feet. This requires exceptional spinal flexibility and hip mobility.

Fig. 175. The bridge:

A — on the floor; B — on the mat

In the bridge position, the shoulder girdle is shifted toward the head, the inferior angle of the scapula is rotated laterally, and the head of the humerus abuts the acromion. Maximal extension is observed in the shoulder, elbow, and wrist joints. The abdominal muscles (especially the rectus abdominis), pectoralis major and minor, serratus anterior, latissimus dorsi, biceps brachii, coracobrachialis, and the flexors of the wrist and fingers are in an extremely stretched state. The plantar flexors of the foot and the quadriceps femoris are stretched to a slightly lesser degree. These muscles, along with the intervertebral discs, spinal ligaments, and iliofemoral ligament, generate elastic forces that tend to pull the supporting body parts apart. Muscular tension counteracts gravity and elastic recoil, thereby stabilizing the body in this position.

The most active muscular work occurs in the extremities and along the spinal column. Furthermore, the load on these muscles increases from the apex of the arch toward the periphery (commensurate with the buildup of elastic forces within the arched structure).

In the lower extremities, the primary workload is borne by the plantar muscles of the foot, the posterior and lateral muscle groups of the leg, the anterior thigh group (which prevents knee flexion—i.e., the thigh moving closer to the leg), and the posterior hip muscles. The gluteus maximus, together with the spinal extensors, Supports the torso. Extension of the hip in the hip joint is restricted by the iliofemoral ligament, as well as by the tone of the muscles crossing anterior to the transverse axis of the hip joint (sartorius, rectus femoris, iliopsoas, and pectineus).

Because the shoulder girdle is anchored via the upper extremities, the head and trunk are supported by its elevating muscles, which run from the skeletal base of the head and neck to the BONES OF THE shoulder girdle. The pectoralis major and latissimus dorsi fix the humerus to the upper limb girdle.

Stabilization of the humeral head relative to the glenoid cavity of the scapula is achieved primarily through the Muscles surrounding the shoulder joint. The thin and roomy Joint Capsule lacks ligamentous thickenings and cannot play a significant role in stabilizing the shoulder joint in this position. The most critical role here is played by the triceps brachii (via its long head), latissimus dorsi, subscapularis, infraspinatus, and the teres major and minor muscles.

In the arm, the triceps brachii bears the heaviest load; it prevents elbow flexion—meaning it Functions not to extend the forearm at the elbow, but rather to extend the shoulder.

Apart from muscles and ligaments, the intrinsic design of the articular surfaces AIDS in locking the bones at the elbow: the trochlear notch of the ulna embraces the trochlea of the humerus, and the olecranon process of the ulna locks into the corresponding fossa of the humerus.

When supporting the body not on the entire SOLE OF THE foot, but only on the toes, the tension in the posterior leg compartment and the plantar muscles (triceps surae, tibialis posterior, long toe flexors, etc.) as well as the quadriceps femoris increases sharply, since the contraction of the gastrocnemius further accentuates knee flexion.

Because the spine is strongly hyperextended and the head is tilted back, the rib cage is stretched and elevated, the intercostal spaces (especially the lower ones) are widened, the costal arch and lower ribs protrude markedly, and the subcostal angle is enlarged. The chest remains in an inhalation position, with its vertical dimension slightly augmented by the flattening of the thoracic kyphosis. The lower ribs are the most mobile, driving respiration—meaning the expansion and reduction of thoracic volume. The abdominal muscles are stretched and taut, which impedes diaphragmatic movement. The diaphragm remains in an exhalation position, displaced toward the head due to pressure from the abdominal viscera (Liver, stomach, Spleen), which also restricts its excursion. Due to this high elevation of the diaphragm, the vertical dimension of the thoracic cavity is reduced, despite the vertical elongation of the rib cage.

The bridge exercise enhances mobility across nearly all body segments. It improves the elastic properties of muscles, intervertebral discs, and the Ligamentous apparatus of the limb joints, fosters coordination and spatial orientation, serves as a corrective exercise for postural defects, and exerts a conditioning effect on the diaphragm.

At the same time, this exercise places many vital organs under unusual conditions that hinder their normal functioning. For instance, respiratory excursion is restricted in the bridge position, the suction action of the chest on BLOOD AND Lymph is diminished, venous drainage from the head and neck is impeded, and The Heart and abdominal viscera are displaced toward the head, creating unfavorable conditions for their operation (food transit from The Stomach to the duodenum and Bile outflow from the Gallbladder are impaired). Therefore, maintaining this position for extended periods, especially for children, is not recommended.