Human Anatomy (with Fundamentals of Dynamic and Sports Morphology) - Ivanitsky, M. F. 2008

General Dynamic Morphology
Morphokinetic Analysis of the Lower Extremity

The primary movements performed by the lower limb as an integrated organ during physical education and sports include the following:

1. Movements associated with the weight-bearing function, wherein the lower limb serves as a support for the entire body.

2. Movements through which the lower limb performs a Shock-absorbing function (in combination with weight-bearing) during various types of landing (in jumping, running, walking, etc.).

3. Locomotor movements (during walking, running, and jumping).

4. Striking an object (in soccer).

5. Moving the torso away from the point of support (in rowing, weightlifting, rising onto the toes, cycling, etc.).

6. Movements associated with the weight-bearing function in specific body positions (such as hanging by the toes or with flexed legs).

7. Pushing off from the surrounding aquatic environment (in swimming).

These principal Movements of the lower limb can be combined and complicated, particularly during asymmetric movements or body positions.

The work performed by the lower limb in each of the seven aforementioned primary groups of movements possesses distinct Anatomical Characteristics.

1. The weight-bearing function of the lower limb is manifested most prominently in a standing position supported by both legs or by a single leg. During normal standing, the lower limb is extended at the knee and hip joints, while the ankle joint is in a neutral position between flexion and extension (see p. 439).

Functionally, the JOINTS OF THE lower limb are interconnected; consequently, in many body positions, the stabilization of bones in one joint affects the degree of their fixation in adjacent joints. Thus, while standing, it is impossible to alter THE POSITION OF bones in any of the three joints (hip, knee, and ankle) without simultaneously changing bone alignment in the others. Therefore, factors that contribute to the stabilization of one joint indirectly influence the stability of another. It is well known that the iliofemoral ligament not only prevents extension at the hip joint but, when taut, also restricts femoral rotation around the vertical axis. Considering that the medial femoral condyle is larger than the lateral, knee flexion can be regarded as possible only when the lower leg is somewhat supinated. Consequently, by reinforcing the hip joint and restricting outward Rotation of the thigh, the iliofemoral ligament thereby indirectly contributes to the stabilization of the knee joint. However, stabilization of the hip joint depends not only on the iliofemoral ligament but also on the action of numerous Muscles. Therefore, the tone of the femoral pronator muscles indirectly affects the Stability of the knee joint.

⁸ F. Engels, Dialectics of Nature. - K. Marx, F. Engels, Collected Works, vol. 20, p. 488.

Viewing the lower limb as a whole, one can observe that the transverse axes of its major joints are not entirely parallel to one another and do not lie in the same plane. Furthermore, the longitudinal axes of the thigh and lower leg form an angle of approximately 170° with each other, opening laterally. This is also of great importance for the weight-bearing function of the lower limb, as it hinders simultaneous flexion across its joints, thereby facilitating muscular effort, for example, in the standing position.

2. The shock-absorbing (spring) function of the lower limb is crucial, as it mitigates shocks and jolts to the body during walking, running, and jumping. It is facilitated by the presence of the arches of the FOOT, muscles, and intra-articular ligaments. As noted in the Description of the Skeleton, the foot features an arched Structure in both longitudinal and transverse directions, which enhances its shock-absorbing properties (p. 104). The arches of the foot are maintained by passive and active forces.

Passive forces include the tension of the Ligamentous apparatus of the foot, which keeps the articular surfaces of the bones forming the arches in contact. The longest ligament of the foot is the long plantar ligament.

Active forces maintaining the arches of the foot include Muscle tension, which can be divided into two groups: 1) long muscles extending to the FOOT FROM THE lower leg, and 2) intrinsic Muscles of the foot itself (see p. 166). The long muscles include, first, the long toe flexors, whose tendons run in an anteroposterior direction along the PLANTAR ASPECT OF the foot. These muscles work synergistically with the intrinsic muscles of the foot located both in the middle part of its plantar surface and in the Regions of the hallux and little toe. Second is the peroneus longus muscle, which runs obliquely along the Inferior surface of the Tarsal Bones, helping to maintain the transverse arch. Together with the tibialis anterior muscle, it participates in forming a bone-tendon-muscular loop that Supports the arch of the foot from below. The intrinsic muscles of the foot include the adductor hallucis (its transverse HEAD, which runs transversely on the plantar side of the foot). It maintains the transverse arch of the foot in the region of the metatarsal heads. The Role of muscles in reinforcing the arches of the foot is immense. It was previously widely believed that when the foot is unloaded (e.g., suspended), its arches are more pronounced than when weight-bearing, at which point a certain flattening of the foot is observed. According to X-ray observations, the opposite is often the case. For example, in a standing person, the arch of the foot is somewhat more pronounced than in a seated person. This is explained by the fact that at the moment of weight-bearing, a reactive contraction of the muscles maintaining the arches occurs, which increases their prominence. If a person in a standing position is subjected to a load, a moment arrives when the foot arches can no longer withstand the pressure of the body and the additional weight, and they begin to descend. Temporary and rapidly resolving flattening of the foot, caused by muscle fatigue and stretching, may also occur under light but prolonged loads. The broadening of the plantar surface of the foot upon weight-bearing is due to the fact that its soft Tissues act as a cushion; when compressed from above, this cushion decreases vertically and increases transversely and anteroposteriorly, although direct linear measurements of the skeletal foot itself do not increase during standing, but rather decrease.

The shock-absorbing Properties of the lower limb depend on the Structural and functional features not only of the foot, but of the entire limb. Any landing on the foot involves the entire lower limb acting as a shock-absorbing apparatus. This is clearly demonstrated during landing from a jump. Such shock absorption occurs because all joints are slightly flexed at the moment of landing, and the muscles producing extension in them (or flexion in the ankle) contract reflexively, permitting eccentric work to carry out further movement in these joints without allowing them to reach their extreme ranges of motion.

The shock-absorbing function is performed through eccentric Muscle Action during landing (moving from bottom to top, i.e., in the direction of the transmission of resistance): in the foot — all muscles on the plantar surface; in the ankle region — muscles passing behind its transverse axis (triceps surae, tibialis posterior, flexor hallucis longus, flexor digitorum longus, fibular muscles); in the knee region — the quadriceps femoris; in the hip region — the muscles of its posterior surface, primarily the gluteus maximus, adductor magnus, biceps femoris, etc. When landing on the heel (e.g., in the long jump), the shock-absorbing properties of the foot can hardly be utilized, and all work related to the spring function of the lower limb falls upon its remaining segments (hence artificial shock absorbers are used on athletic fields, such as loose sand in the landing pit). The impossibility of utilizing the foot's shock-absorbing properties in this case is explained by the fact that pointing the toe requires overcoming the resistance of the anterior muscle group of the lower leg; furthermore, since the body approaches the ground at a shallow angle toward the end of flight, this plantarflexion would have to be very extensive, which is difficult to execute. In sprinting, pointing the toe is quite feasible because the limb approaches the supporting surface at an almost right angle. Here, this plantarflexion plays another role: it reduces The Effect of recoil and sometimes increases stride length. Utilizing the entire foot, starting from the toes, as a shock-absorbing apparatus always requires intense muscular effort. In walking, landing is typically performed on the heel, as is the case in most instances of long-distance running (for more details, see p. 455).

3. The locomotor function of the lower limb consists primarily in providing active Displacement of the entire body in space during walking, running, and jumping through pushing off from supporting surfaces. The work of the lower limb in this process reduces to the initial approximation of its proximal and distal ends, which then move apart due to movements in the joints. Consequently, the body receives an impulse that propels it through space. When analyzing the movements of the supporting leg, one should highlight plantarflexion of the foot, extension at the knee and hip joints, as well as pelvic movements at the hip joint.

4. During strikes performed by the lower limb, its distal end moves freely. Such movement is observed during the execution of various gymnastic exercises, as well as during running and walking (during the swing phase from the rear-stride to the front-stride position, etc.). In these movements, active and passive insufficiency of two-joint muscles (see p. 106) plays an important role, determining the mobility of individual limb segments.

Characteristically, when the hip is flexed, extension of the lower leg at the knee joint is hindered due to passive insufficiency of the hamstring muscles (biceps femoris, semitendinosus, semimembranosus) and partly due to active insufficiency of the quadriceps femoris. When the hip is extended, knee flexion may be hindered due to passive insufficiency of the rectus femoris and active insufficiency of the aforementioned hamstrings.

When the lower leg is extended at the knee joint, plantarflexion at the ankle joint is hindered due to passive insufficiency of the gastrocnemius muscles and active insufficiency of the anterior lower leg muscles. When the lower leg is flexed at the knee joint, plantarflexion may in some cases be somewhat hindered (especially in children) As a result of active insufficiency of the posterior lower leg muscles and passive insufficiency of its anterior muscles. However, age-related features are also significant in the latter case: children exhibit greater dorsiflexion mobility and lesser plantarflexion mobility at the ankle joint compared to adults, in whom the opposite is true.

When the foot is unfixed, movement occurs first at the hip joint, then at the knee, the ankle, and finally within the joints of the foot.

These movements occur almost simultaneously or sequentially; in most cases, hip movements conclude slightly before lower leg movements, and lower leg movements conclude before foot movements. The relative speed of movement of each segment is usually unequal.

5. When moving the torso away from the point of support, extension occurs at the Hip and knee joints, accompanied by flexion at the ankle joint.

The long flexors of the digits, particularly the hallux, when supported solely by the distal part of the foot, cause plantar flexion at the ankle joint and (due to resistance) passive extension at the metatarsophalangeal joints. The muscles of the posterior leg compartment—including the triceps surae, tibialis posterior, and digital flexors—as well as the muscles of the lateral leg compartment (the peroneals), when supporting the entire plantar surface, do not produce ankle flexion, but rather leg extension. Consequently, they indirectly participate in the extension of the knee joint.

When lifting a load, the plantar surface of the foot is fixed, but the pelvis is not fully fixed, allowing it to tilt backward. In this process, the tension of the Posterior Thigh Muscles assists in extending and stabilizing the pelvis, and consequently the entire torso, at the hip joint. Extension at the knee joint, meanwhile, is driven by the action of the quadriceps femoris. The peroneal, soleus, and deep calf muscles extend the leg at the ankle joint, which in turn facilitates its extension at the knee joint. From a terminological standpoint, it is more accurate here to speak of femoral extension at the knee joint relative to the lower leg rather than vice versa, since the lower leg serves as a less mobile body segment than the Femur.

During certain physical exercises (such as rowing or cycling), when the foot and forward-inclined pelvis are fixed, specific features in Muscle Function are observed. The posterior thigh muscles (biceps femoris, semitendinosus, and semimembranosus) can function as synergists to the quadriceps femoris, meaning they facilitate extension at the knee joint rather than flexion. When the lower leg and foot are unfixed, these muscles flex the leg at the knee and extend the thigh at the hip. When the lower leg is fixed, they flex the thigh at the knee relative to the lower leg, and when both the thigh and lower leg are fixed, they extend the pelvis at the hip joint. Additionally, during movements involving pressing the foot against an object, the action of the leg extensor muscles at the hip and knee joints, along with the flexors of the ankle and foot joints, is augmented by the force of gravity—acting not only on the leg itself, but on other body links as well. For example, during cycling, to increase the force of foot pressure on the pedal, contractions of several muscle groups are utilized, notably the muscles of the torso and upper limbs (as the cyclist grips the handlebars).

6. When performing movements associated with a supporting function in specific body positions, such as hanging by the toes or with bent legs, the function of the lower limb is characterized by the body being supported on the dorsal surface of the forefoot or the posterior aspect of the upper leg. In a toe hang, the muscles of the dorsal foot and anterior leg are in a state of intense tension: extensor hallucis brevis, extensor digitorum brevis, extensor hallucis longus, extensor digitorum longus, tibialis anterior, and peroneus tertius. These muscles are considerably weaker than those of the posterior leg, making this exercise quite challenging. In this regard, a hang with bent legs is much simpler, as it recruits the entire powerful group of knee flexors (sartorius, gracilis, biceps femoris, semitendinosus, semimembranosus, as well as the popliteus and gastrocnemius muscles).

7. When the body pushes off against the surrounding aquatic environment (in swimming), lower limb mechanics exhibit a range of distinct features depending on the swimming stroke. In the breaststroke on the chest, following the preliminary abduction and flexion of the legs at the hip and knee joints, a forceful adduction and extension is performed. Of the entire movement cycle, these phases demand the highest muscular exertion. They are executed with the involvement of all adductor muscles (adductor magnus, longus, and brevis, gracilis, pectineus), as well as the leg extensors and foot flexors. As a result of the initial leg adduction, the mass of Water situated between the limbs is effectively squeezed out, propelling the body away from this water mass.

During the front crawl stroke, alternating upward and downward movements of the thigh are performed at the hip joint relative to the horizontal plane passing through its center. The function of the muscles surrounding this joint is characterized by the fact that for the "upper" leg, peak contraction force is required during its downward movement toward the horizontal plane, whereas for the "lower" leg, it is required during its upward movement to that same plane. Subsequent movement of the lower limbs is largely driven by the "ballistic" action of the hip flexors and extensors.

During asymmetrical body positions and movements, the function of the lower limb as an integrated organ becomes more complex. For instance, in a single-leg stance, particularly with the torso flexed or leaning forward, relying solely on the muscles located on the anterior or posterior surfaces of the hip is insufficient to stabilize the pelvis; the engagement of muscles situated laterally or medially to the joint is also required, depending on the trajectory of the body's center of mass (COM) vertical relative to the sagittal axis of the joint. If this vertical line passes medially, stabilizing the pelvis requires the action of thigh abductors functioning under distal closure (gluteus medius and minimus, piriformis, obturator internus, and gemelli). However, these muscles are not strong enough to maintain a horizontal pelvic position, and consequently, a slight pelvic drop toward the opposite leg is typically observed in a single-leg stance. If the COM vertical line passes laterally to the sagittal axis of the hip joint, stabilizing the pelvis necessitates the engagement of the thigh adductors.

The range of mobility in the hip joint depends not only on The structure of the joint itself, but also on the position of the greater trochanter relative to the upper rim of the acetabulum, as well as the architecture of the ligamentous and muscular apparatus. Maximal thigh abduction requires a supinated position, in which the greater trochanter does not obstruct movement. Therefore, in the exercise *grand battement à la seconde*, the thigh is placed in supination. In an exercise such as the splits, where one leg is deeply flexed at the hip and the other correspondingly extended, the limiting factor is the tension of Ligaments and Muscles. A state is possible where the biarticular posterior thigh muscles are intensely stretched on one leg, while the iliofemoral ligament and the anterior hip muscle group (sartorius, rectus femoris, tensor fasciae latae, pectineus, iliopsoas) are stretched on the other. Such profound stretching of the ligamentous and muscular systems can be achieved through systematic training, and in some cases is determined to a certain extent by innate flexibility. Lateral pelvic tilt in the splits measures 16–18°, while the rotation of the pelvis around the body's longitudinal axis reaches 28–32°. Training in this exercise helps increase the range of motion for disciplines such as hurdling, soccer, and others. For executing a side split (straddle split), the greater trochanters act as the primary anatomical barrier, as previously noted, and individuals who successfully perform this movement typically exhibit specific anatomical variations in the STRUCTURE OF THE greater trochanter and hip joint.

During squatting and heel raises (performed on either both legs or a single leg), the exact same muscles contract, with the sole difference that during the former movement they perform overcoming (concentric) work, while in the latter they perform yielding (eccentric) work. The points of foot support during toe raises and descents include not only the heads of the metatarsals and the plantar surfaces of the toes, but also the sesamoid bones. Throughout these movements, the entire foot can be likened to a Class-two lever, although positions and movements of the foot are possible where it Functions as a class-one or class-three lever.