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

Myology
Muscles of the Lower Extremity

The Muscles of the Lower Limb produce movements in the hip, knee, ankle, and FOOT joints.

Muscles producing movements at the hip joint

Corresponding to the three mutually perpendicular axes of rotation passing through the center of the hip joint, Movements of the thigh (with the pelvis fixed, and consequently the entire leg) can occur in the following directions:

1) flexion and extension, i.e., forward and backward movement;

2) abduction and adduction;

3) pronation and supination;

4) circumduction.

When the thigh or the entire leg is fixed, the muscles move the pelvis: forward, backward, sideways, and in right and left rotations. To perform these movements, the hip joint features six functional Muscle groups.

Hip flexion

The Muscles responsible for flexing the thigh at the hip joint are those that cross the transverse axis of this joint and lie anterior to it. These include:

1) the iliopsoas;

2) the sartorius;

3) the tensor fasciae latae;

4) the pectineus;

5) the rectus femoris (see p. 152).

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Fig. 57. Muscles of the lower limb (anterior view):

1 — iliacus m.; 2 — psoas major m.; 3 — psoas minor m.; 4 — inguinal ligament; 5 — pectineus m.; 6 — adductor longus m.; 7 — gracilis m.; 8 — adductor magnus m.; 9 — sartorius m.; 10 — vastus medialis m.; 11 — gastrocnemius m.; 12 — soleus m.; 13 — superior extensor retinaculum; 14 — inferior extensor retinaculum; 15 — extensor hallucis longus m.; 16 — extensor hallucis brevis m.; 17 — extensor digitorum longus m.; 18 — fibularis tertius m.; 19 — extensor digitorum brevis m.; 20 — tibialis anterior m.; 21 — fibularis brevis m.; 22 — fibularis longus m.; 23 — patellar ligament; 24 — Patella; 25 — vastus lateralis m.; 26 — rectus femoris m.; 27 — tensor fasciae latae

The iliopsoas Muscle consists of three parts: the psoas major, the iliacus, and the psoas minor (Fig. 57).

The psoas major originates from the bodies and transverse processes of the five lumbar vertebrae and the body of the twelfth thoracic vertebra, lying lateral to them. Passing downward, this muscle merges with the iliacus. The iliacus is situated within the iliac fossa, which serves as its origin. Both muscles (the psoas major and iliacus) insert via a common tendon into the lesser trochanter.

The psoas minor originates from the bodies of the XII thoracic and I lumbar vertebrae and inserts into the pelvic fascia, which it acts to tense. This muscle is inconstant.

Fig. 58. Muscles of the lower limb (posterior view):

1 — gluteus maximus m.; 2 — gluteus medius m.; 3 — tensor fasciae latae; 4 — iliotibial tract; 5 — biceps femoris m. (long HEAD); 6 — biceps femoris m. (short head); 7 — plantaris m.; 8 — gastrocnemius m. (lateral head); 9 — soleus m.; 10 — fibularis longus m.; 11 — fibularis brevis m.; 12 — calcaneal (achilles) tendon; 13 — abductor digiti minimi m. of the foot; 14 — flexor digitorum brevis m.; 15 — gastrocnemius m. (medial head); 16 — popliteal fossa; 17 — semitendinosus m.; 18 — semimembranosus m.; 19 — gracilis m.; 20 — adductor magnus muscle

The iliopsoas muscle passes from the trunk onto the thigh inferior to the inguinal ligament through the muscular lacuna, being separated from the vascular lacuna by a ligament.

This muscle lies directly adjacent to the anterior surface of the hip joint. Its function is to flex and supinate the thigh. When the thigh is fixed, it flexes the spinal Column and the pelvis relative to the thigh (for example, when rising from a supine to a seated position). When standing on one leg, it not only flexes the pelvis but also rotates it around the vertical axis of the hip joint.

When the torso is rotated to the right and left while standing on both legs, the contralateral iliopsoas muscle works by stretching on the same-sided (homolateral) side. The iliopsoas muscle plays a crucial role in forming the lumbar lordosis. When it relaxes, the lordosis decreases (in a seated position); when it contracts, it increases. If this muscle contracts simultaneously with a strong contraction of the rectus abdominis, it can lead not only to a reduction of the lumbar lordosis but even to The formation of a general thoracolumbar Kyphosis (for example, in the "L-sit" position on parallel bars).

Fig. 59. Muscles of the lateral surface of the lower extremity:

1 — gluteus medius m.; 2 — sartorius m.; 3 — tensor fasciae latae; 4 — rectus femoris m.; 5 — vastus lateralis m.; 6 — tibialis anterior m.; 7 — extensor digitorum longus; 8 — extensor hallucis longus; 9 — superior and 10 — inferior extensor retinaculum; 11 — peroneus tertius m.; 12 — calcaneal (Achilles) tendon; 13 — peroneus brevis m.; 14 — peroneus longus m.; 15 — soleus m.; 16 — gastrocnemius m.; 17 — plantaris m.; 18 — biceps femoris m.; 19 — semimembranosus m.; 20 — fascia lata; 21 — gluteus maximus m.

The sartorius muscle (see Fig. 57) is the longest muscle in The Human Body. It originates from the anterior superior iliac spine, runs anterior to the hip joint downward and medially—initially along the anterior and then the Medial surface of the thigh—and inserts into the tibial tuberosity. Being a two-joint muscle, it flexes both the thigh and the leg. Its spiral course also allows it to participate in the supination of the thigh. While flexing the leg, it also pronates it. The sartorius muscle is clearly visible beneath the Skin along its entire length when the thigh is flexed, abducted, and supinated, and the leg is extended, appearing as a cord-like Structure between the quadriceps on one side and the adductors on the other. When the thigh is fixed, the sartorius participates in tilting the pelvis and rotating it around the vertical axis.

The tensor fasciae latae (Fig. 58) originates from the anterior superior iliac spine, passing downward and slightly backward between two layers of the fascia lata, to which it is anchored. The continuation of this muscle's tendon is known as the iliotibial tract, which forms the thickened portion of the fascia lata of the thigh and inserts into the lateral condyle of the Tibia. This muscle Functions not only as a flexor of the thigh but also as its pronator. In addition, it abducts the thigh. When the thigh is fixed, it participates in the Rotation of the pelvis. The muscle is particularly well-defined when the straightened leg is flexed at the hip joint at a right angle to the torso. In this position, two elevations become clearly contoured on the lateral side of the thigh: the gluteus medius and the tensor fasciae latae (Fig. 59).

The pectineus muscle (see Fig. 57) is located on the anterior surface of the thigh. It originates from the superior ramus of the pubic bone, extends downward and laterally, and inserts into the linea aspera of the Femur. The pectineus flexes, adducts, and supinates the thigh, and, together with other muscles, participates in the forward tilt of the pelvis.

The rectus femoris muscle (see Fig. 57) is one of the heads of the quadriceps femoris (see p. 185).

THE CONTRIBUTION OF all these muscles to thigh flexion varies. The primary role in this movement belongs to the iliopsoas muscle. Due to its origin being distant from the joint and its insertion being relatively close, even a slight contraction causes flexion with a large amplitude. The action of the rectus femoris and sartorius muscles can manifest when the point of force application is on the tibia with a fixed lower leg. The flexing function of the pectineus muscle becomes more pronounced when its adductor function is blocked by the contraction of the abductor muscles.

Thigh Extension

Thigh extension involves muscles that also cross the transverse axis of the hip joint but are located posterior to it. These muscles run either from the pelvis to the thigh or from the pelvis to the leg. They include:

1) gluteus maximus;

2) biceps femoris;

3) semitendinosus;

4) semimembranosus;

5) adductor magnus (see p. 181).

The gluteus maximus muscle (see Fig. 58) is located on the posterior surface of the hip joint. It originates from the sacrum, the posterior region of the ilium, and the sacrotuberous ligament, and inserts into the gluteal tuberosity of the femur and the fascia lata. In humans, this muscle is well developed because its contraction maintains an upright posture. Its physiological cross-section is approximately 30 cm². It has a coarse-fibered structure, with Connective Tissue layers located between its individual bundles.

The function of the muscle is to extend and supinate the thigh. It also performs extension of the pelvis relative to the thigh (extending the torso from a flexed position).

The biceps femoris muscle (see Fig. 58) is located on the lateral side of the posterior surface of the thigh. It has two heads: the long head originates from the ischial tuberosity, while the short head originates from the lower part of the linea aspera of the femur and the lateral intermuscular septum. The biceps femoris has a common tendon which, after passing behind the transverse axis of the knee joint, inserts into the head of the Fibula.

The function of the biceps femoris is to extend the thigh when the pelvis is fixed, and to flex and supinate the leg when the thigh is secured. As the leg bends, the tendon of this muscle shifts posteriorly, thereby increasing its leverage (moment of force). The muscle is easily palpable on the lateral side of the popliteal fossa.

The semitendinosus muscle (see Fig. 58) is located on the posterior surface of the thigh on the medial side. It shares a common origin with the long head of the biceps femoris on the ischial tuberosity, runs past the knee joint, and inserts into the tibial tuberosity. The function of this muscle is to extend the thigh, and to flex and pronate the leg. Pronation of the leg is most achievable when the leg is flexed.

The semimembranosus muscle (see Fig. 58) originates from the ischial tuberosity. Located posterior to the semitendinosus, it inserts into the medial condyle of the tibia. The muscle extends the thigh, flexes the leg, and also participates in the pronation of the leg as it bends. When the leg is fixed, the semimembranosus tilts the pelvis backward and also secures it to the thigh, preventing a forward tilt.

The biceps femoris (long head), semitendinosus, and semimembranosus are two-joint muscles. They can extend the thigh when the lower leg is fixed at the knee joint. When the leg is flexed (for example, during walking), these muscles cannot perform hip extension because they are occupied with stabilizing the lower leg. The primary muscle responsible for extension at the hip joint is the gluteus maximus, especially during uphill walking, stair climbing, and rising from a chair.

Thigh Abduction

The hip abductor muscles cross the sagittal axis of the hip joint and are located on its lateral side. They attach primarily to the greater trochanter. These muscles include:

1) the gluteus medius;

2) the gluteus minimus;

3) the piriformis;

4) the obturator internus;

5) the gemelli;

6) the tensor fasciae latae (p. 176).

The gluteus medius muscle (see Fig. 58) is partially covered by the gluteus maximus. It originates from the outer surface of the ilium and the fascia lata, and inserts into the greater trochanter. During leg swinging movements, the muscle is clearly contoured under the skin of the thigh (see Fig. 59). Its primary function is hip abduction. Because the anterior fibers of the muscle run downward and backward, while the posterior fibers run downward and forward, it participates in both pronation (anterior bundles) and supination (posterior bundles) of the thigh. The physiological cross-sectional area of the gluteus medius is 21 cm2. In terms of generated force, it is slightly inferior to the gluteus maximus.

The gluteus minimus muscle lies deep to the gluteus medius. It originates from the ilium and inserts into the greater trochanter. The function of this muscle is similar to that of the gluteus medius.

The piriformis muscle originates on the anterior surface of the sacrum, passes through the greater sciatic foramen into the gluteal region, and inserts onto the apex of the greater trochanter. This muscle abducts the thigh. Because its resultant force line passes posterior to the vertical axis of the hip joint, it also assists in hip supination.

As it passes through the greater sciatic foramen, the piriformis muscle divides it into two openings: the supra- and infrapiriform foramina. Blood Vessels and nerves pass through these passages.

The obturator internus muscle is located within the lesser pelvis. It originates from the obturator membrane, courses laterally, loops around the lesser sciatic notch, enters the gluteal region, and inserts into the trochanteric fossa.

The superior and inferior gemelli muscles, which lie superior and inferior to the tendon of the obturator internus, attach to it as it emerges from the lesser pelvis. These two small muscles originate from the ischial spine (superior muscle) and the ischial tuberosity (inferior muscle).

The function of the obturator internus and gemelli muscles is to abduct the thigh when the pelvis is fixed, and, when standing on one leg, to prevent the pelvis from tilting toward the opposite side. Additionally, these muscles participate in hip supination.

The gluteus medius plays the primary role in hip abduction, with its anterior and middle sections producing greater abduction than the posterior section. With distal attachment fixed, the gluteus medius and minimus tilt the pelvis laterally.

In the first case, the gluteus medius sacrifices force for a greater variety of movements; In the second case, it gains mechanical advantage in force at the expense of a smaller range of joint motion. This is due to the different ratios between the muscle force arm and the resistance force arm. With a proximal attachment—when the pelvic bones are fixed and the muscle acts on the thigh—its force arm is small, whereas the resistance arm (and consequently the moment of force generated by the weight of the lower extremity) is substantial. A large force is required to perform this movement. With a distal attachment—when the lower extremity is fixed (standing on one leg)—the muscle force arm is larger than the resistance force arm. Consequently, the muscle is capable of exerting considerable force to support the weight of the opposite half of the body and prevent the pelvis from tilting toward the unsupported leg.

Hip Adduction

Hip adduction is performed by muscles that cross the sagittal axis of the hip joint and are located medially to it. These include:

1) the pectineus (see p. 177);

2) the gracilis;

3) the adductor longus;

4) the adductor brevis;

5) the adductor magnus.

The gracilis muscle (see Fig. 57) originates from the inferior ramus of the pubis, descends as a relatively slender muscle strap, and inserts into the tibial tuberosity. Among all the adductor muscles, this is the only two-joint muscle. Passing near the knee joint slightly posterior and medial to its transverse axis, it adducts the thigh and assists in flexing the leg at the knee joint.

At the insertion site on the tibia, the sartorius, semitendinosus, and gracilis muscles converge to form the pes anserinus (superficial goose's foot).

The adductor longus muscle (see Fig. 57) originates from the anterior surface of the superior ramus of the pubis, expands inferiorly, and inserts into the middle third of the linea aspera of the femur. The function of the muscle is to adduct the thigh.

The adductor brevis muscle originates from the inferior ramus of the pubis, runs inferiorly and laterally, and inserts into the linea aspera of the femur. Its function is similar to that of the preceding muscle. In addition, together with the adductor longus and pectineus muscles (on one side), and the sartorius and tensor fasciae latae (on the other), it forms a force couple involved in hip flexion.

The adductor magnus muscle (see Fig. 57) is the largest of the hip adductors. It originates from the ischial tuberosity and the ramus of the ischium, and inserts into the linea aspera of the femur, extending down to the medial epicondyle of the femur. This muscle also plays a major role in hip extension when the pelvis is fixed, or in pelvic extension when the thigh is fixed. This action of the muscle increases as the hip flexes, because its lever arm and torque become greater. With the hip extended, the line of action of the resultant force of the muscle almost coincides with the transverse axis of the hip joint, causing its torque relative to this axis to approach zero. As a hip adductor, it acts with particular force when the hip is abducted. The physiological cross-sectional area of the adductor magnus is 20 cm².

Tension in the adductor muscles creates conditions for the manifestation of their flexion function. Specifically, the adductor longus flexes the thigh up to an angle of approximately 70° and then becomes its extensor. The adductor brevis flexes the hip only up to an angle of 50°. As for the adductor magnus, its anterior part also flexes the hip up to an angle of 50° and then acquires an extensor function. The posterior part of this muscle, which originates from the ischial tuberosity, extends the hip in all of its positions.

The transition to bipedalism had a major impact on The Development of the hip adductors. Taking into account human evolutionary history, Z. I. Katsitadze subdivides them into the oldest (pectineus, gracilis); old (adductor longus); and new (adductor brevis and adductor magnus).

Hip Supination

Except for the iliopsoas, the muscles that supinate the hip cross the obliquely vertical axis of the hip joint. The iliopsoas supinates the hip due to the specific position of the lesser trochanter (located both anteriorly and medially). The muscles that supinate the hip include:

1) the iliopsoas (see p. 174);

2) the quadratus femoris;

3) the gluteus muscles, of which the gluteus medius and gluteus minimus supinate the hip only with their posterior fibers (see p. 179);

4) the sartorius (see p. 176);

5) the obturator internus (see p. 179) and obturator externus muscles;

6) the piriformis (see p. 178);

7) the gemelli (see p. 179).

The quadratus femoris muscle originates from the ischial tuberosity, runs laterally, lies posterior to the hip joint, and inserts into the greater trochanter.

The obturator externus muscle originates from the external surface of the obturator membrane and adjacent areas of the pubic and ischial bones, runs laterally, and inserts into the trochanteric fossa and the Joint Capsule of the hip.

Hip Pronation

The group of hip pronators is relatively small. It includes:

1) the tensor fasciae latae muscle (see p. 176);

2) the anterior fibers of the gluteus medius muscle (see p. 178);

3) the anterior fibers of the gluteus minimus muscle (see p. 180);

4) the semitendinosus, semimembranosus, and gracilis muscles (see pp. 178, 180).

The adductor muscles also assist in the pronation of a strongly supinated hip.

It should be noted that when an extended leg rests on the heel, both pronation and supination of the hip can be performed more intensely than when the hip is suspended. This is explained by the fact that in the former case, the muscles that elevate the hip are relaxed, whereas in the latter, they are contracted and their tone impedes rotation of the hip around the vertical axis of the hip joint.

Circumduction of the hip in the hip joint is performed by all the muscle groups located around it, acting sequentially. From the list of muscles provided, it is evident that the same muscle can participate in different movements. Furthermore, under different initial positions, the same muscle can perform different work. For example, the adductor magnus extends the hip from a flexed position and adducts it from an abducted position. Therefore, the involvement of muscles in a particular movement can only be characterized by taking into account the initial body position. In addition, individual bundles of large muscles can contract in isolation. For instance, if the gluteus minimus contracts entirely, it abducts the hip; however, if only its anterior fibers contract, it rotates the hip inward. All muscles that move the hip simultaneously participate, when the hip is fixed, in movements of the pelvis along with the torso. Thus, when the thigh is fixed, the iliopsoas flexes the pelvis and the lumbar spine, moving the torso forward; with the torso flexed, the adductor magnus performs the reverse action—it extends the torso at the hip joint.

Hip mobility depends on THE POSITION OF the lower leg (shank). When the leg is extended, active flexion in one hip joint without associated movements in the other generally does not bring the thigh to a horizontal position in untrained individuals. This is because the tightening biceps femoris, semitendinosus, and semimembranosus muscles restrict the movement (see Fig. 59). Conversely, when the knee is flexed—removing the braking effect of these muscles—flexion can exceed the horizontal plane. During hip extension, the opposite occurs: when the knee is bent, the hip can be extended through fewer degrees than when the knee is straight, since in the former case the rectus femoris is stretched more tightly than in the latter.

Mobility in the hip joint can be significantly increased by applying external force. For instance, the thigh can be sharply flexed until it touches the front of an upright torso, provided the knee is simultaneously bent. This primarily requires stretching the muscles located at the back of the hip joint, whose resistance is relatively easy to overcome. It is more difficult to increase the range of hip extension (such as in the split, where body weight acts as the external force increasing mobility in this direction). The primary restraints for this movement are the iliofemoral ligament and, to some extent, muscles such as the iliopsoas, rectus femoris, sartorius, and tensor fasciae latae.

Significant hip abduction is hindered by the greater trochanter, which abuts the upper rim of the acetabulum and halts the movement. This resistance can be overcome by laterally rotating (supinating) the thigh. In this position, only the hip adductor muscles act as restraints, and they are relatively easy to stretch. The ischiofemoral ligament offers little resistance to hip abduction. Therefore, during movements like the grand battement side, the gesturing leg must be significantly supinated; otherwise, the exercise is impossible to execute.

Just below the inguinal ligament, the thigh muscles form the femoral triangle. Its upper boundary is formed by the inguinal ligament, the medial boundary by the adductor longus muscle, and the lateral boundary by the sartorius muscle. The floor of the triangle is formed by two muscles: the iliopsoas and the pectineus. Inferiorly, the triangle transitions into the anterior femoral sulcus, which is covered by the sartorius muscle.

In the lower third of the thigh, between the vastus medialis and the adductor magnus, a Cytology/practical/45.html">Dense connective tissue plate spans across to enclose the anterior femoral sulcus into the adductor canal, which leads into the popliteal fossa.

Muscles producing movements in the knee joint

With the thigh fixed (proximal support), the Muscles surrounding the knee joint perform flexion, extension, pronation, and supination of the lower leg; with the lower leg fixed (distal support), they produce forward and backward movement, pronation, and supination of the thigh.

Flexion of the lower leg

The flexor muscles of the lower leg cross the transverse axis of the knee joint and are located posterior to it. These include the following muscles (see Figs. 38, 58):

1) biceps femoris (see p. 178);

2) semitendinosus (see p. 178);

3) semimembranosus (see p. 178);

4) sartorius (see p. 176);

5) gracilis (see p. 180);

6) popliteus;

7) gastrocnemius (part of the triceps surae) (see p. 187);

8) plantaris (see p. 187).

The popliteus is a short, flat muscle directly adjacent to the posterior wall of the knee joint. It originates from the lateral femoral condyle and the joint capsule, passes downward, and inserts into the tibia. Upon contraction, it promotes not only flexion of the lower leg but also its pronation. Because this muscle partially attaches to the knee joint capsule as well, it helps pull the capsule backward as the lower leg bends.

Extension of the lower leg

Extension of the lower leg is performed by the quadriceps femoris, which crosses the transverse axis of the knee joint anteriorly (see Figs. 37, 57). This is one of the most massive muscles in the human body. Located on the anterior surface of the thigh, it has four heads:

1) rectus femoris;

2) vastus lateralis;

3) vastus medialis;

4) vastus intermedius.

Of all the heads, only the rectus femoris is biarticular, spanning both the Hip and knee joints, while the others are uniarticular. The rectus femoris originates from the anterior inferior iliac spine, runs downward, and merges in the lower third of the thigh with the remaining heads—the vastus muscles.

The three broad muscles of the thigh originate from the anterior, lateral, and medial surfaces of the femur. All four heads of the quadriceps femoris insert into the patella. Extending from the patella to the tibial tuberosity is the patellar ligament, which is a continuation of the quadriceps femoris.

The quadriceps femoris extends the leg at the knee joint. In addition, the rectus femoris assists in flexing the thigh at the hip joint.

All heads of the quadriceps femoris are clearly visible beneath the skin, especially when rising onto the toes from a standing position with weight distributed across the entire foot. The quadriceps femoris has a pennate structure, which increases its lifting power. The physiological cross-sectional area of the muscle is 56 cm².

As a sesamoid bone, the patella helps increase the leverage (moment of force) of the quadriceps.

Pronation of the leg

Pronation of the leg at the knee joint is only possible as the leg bends—that is, as the collateral ligaments (tibial and fibular) relax. The muscles responsible for leg pronation are all those located posteriorly and medially to the knee joint:

1) semitendinosus (see p. 178);

2) semimembranosus (see p. 178);

3) sartorius (see p. 176);

4) gracilis (see p. 180);

5) medial head of the gastrocnemius (see p. 187);

6) popliteus (see p. 185).

Supination of the leg

Supination of the leg at the knee joint (like pronation) is only possible as the leg bends. The supinators of the leg are the muscles located on the lateral side of the knee joint:

1) biceps femoris (see p. 178);

2) lateral head of the gastrocnemius (see p. 186). Thus, the pronator muscle group is considerably stronger than the supinator group.

Muscles producing foot movements

The following movements of the foot are distinguished: flexion, extension, slight adduction and abduction during flexion, pronation, and supination.

Flexion of the foot

The flexor muscles of the foot cross the transverse axis of the ankle joint and lie posterior to it on the posterior and lateral surfaces of the leg. These muscles include:

1) triceps surae;

2) plantaris;

3) tibialis posterior;

4) flexor hallucis longus;

5) flexor digitorum longus;

6) fibularis longus (see p. 191);

7) fibularis brevis (see p. 191).

The triceps surae (Fig. 38, 58) consists of three heads. Two of them (lateral and medial) form the gastrocnemius, while the third is the soleus. All three heads converge into a single common calcaneal tendon (Achilles tendon), which attaches to the calcaneus. The Water/144.html">Origin of the gastrocnemius is the medial and lateral femoral condyles.

The soleus arises from the posterior surface of the upper third of the tibial shaft and from the tendinous arch located between the BONES OF THE leg. This muscle lies deeper and slightly inferior to the gastrocnemius. Passing posterior to the ankle and subtalar joints, the soleus acts as a plantar flexor of the foot.

The triceps surae is clearly visible beneath the skin and is easily palpable. The calcaneal tendon projects significantly posterior to the transverse axis of the ankle joint, giving the triceps surae a large moment of arm relative to this axis. The two heads of the gastrocnemius flex not only the foot at the ankle joint but also the leg at the knee. The action of the gastrocnemius on the knee joint is minor, as its origin is located very close to the axis of rotation of the knee. As the knee flexes, the muscle's moment arm increases, enhancing its action as a knee flexor.

The soleus is a monoarticular muscle, acting solely on the ankle joint. It plays a major role in standing by stabilizing the leg and preventing the body from falling forward. The calcaneal tendon is extremely strong, withstanding loads of up to 549 kg in adults. At ages 13–14, its tensile strength is 245–375 kg. The safety factor of the tendon is approximately 3 to 5 times. However, loads exceeding this threshold can result in tendon injury.

The medial and lateral heads of the gastrocnemius form the BOUNDARIES OF THE popliteal fossa. It is diamond-shaped, bounded superiorly and laterally by the biceps femoris, superiorly and medially by the semimembranosus, and inferiorly by the two heads of the gastrocnemius and the plantaris. The floor of the fossa is formed by the femur and the capsule of the knee joint.

The plantaris (see Fig. 58) originates from the lateral femoral condyle. It has a very long tendon that merges with the calcaneal tendon shared by the preceding muscles. This muscle is vestigial in nature (absent in 12% of cases) and cannot exert a significant effect on movements at either the ankle or the knee joint.

Fig. 60. Muscles of the Plantar Surface of the Foot:

1 — flexor hallucis longus; 2 — abductor digiti minimi; 3 — flexor digiti minimi brevis; 4 — flexor digitorum brevis; 5 — lumbricals; 6 — flexor hallucis brevis; 7 — abductor hallucis

The tibialis posterior originates from the posterior surface of the interosseous membrane of the leg and the adjacent areas of the tibia and fibula. Passing posterior to the medial malleolus, it inserts into the tuberosity of the navicular bone, all cuneiform bones, and the bases of the Metatarsal Bones. Its function is to plantarflex, adduct, and supinate the foot.

The flexor hallucis longus (Fig. 60) is the strongest of all Deep Muscles of the posterior leg. It arises from the lower portion of the posterior surface of the fibula and the posterior intermuscular septum. On the plantar surface of the foot, this muscle runs between the heads of the flexor hallucis brevis and inserts onto the plantar surface of the Base of the distal phalanx of the hallux. Its function is to flex the big toe and the entire foot. Because its tendon partially blends with the tendon of the flexor digitorum longus, it also exerts some influence on the flexion of the 2nd and 3rd toes. The flexor hallucis longus plays a crucial role in supporting the medial part of the longitudinal arch of the foot. The presence of two large sesamoid bones on the plantar surface of the first metatarsophalangeal joint increases the moment of force of this muscle relative to the transverse axis of the joint.

The flexor hallucis longus is involved not only in plantarflexion of the foot but also in its supination and adduction. The force of this muscle acting on the big toe is quite substantial, averaging 18.1 kg in men and 14 kg in women. In ballet dancers, this muscle, together with the extensor hallucis longus, stabilizes the big toe when performing on pointe.

The flexor digitorum longus (see Fig. 60) originates from the posterior surface of the tibia and passes onto the foot posterior to the medial malleolus within a canal situated beneath the flexor retinaculum. On the PLANTAR ASPECT OF the foot, this muscle crosses the tendon of the flexor hallucis longus and, after receiving fibers from the quadratus plantae, divides into four tendons that insert into the bases of the distal Phalanges of the 2nd–5th toes.

The function of the muscle is to plantarflex and supinate the foot, as well as to flex the toes. It should be noted that the quadratus plantae, which attaches to the tendon of this muscle, helps to "average" its action. Specifically, as the flexor digitorum longus passes posterior to the medial malleolus and diverges fanwise toward the phalanges, it produces not only toe flexion but also a degree of foot adduction and supination. Because the quadratus plantae pulls the tendon of the flexor digitorum longus laterally, adduction is somewhat reduced, and toe flexion occurs predominantly in the sagittal plane.

The last three muscles form the deep muscle group of the posterior leg. The strongest of them is the triceps surae, which has a physiological cross-sectional area of approximately 41 cm2. Between these muscles and the soleus lies the cruropopliteal canal, through which Blood Vessels and nerves pass.

Dorsiflexion of the foot

The dorsiflexors of the foot, like the plantar flexors, cross the transverse axis of the ankle joint, but are located anterior to it, forming the anterior muscle group of the leg. These include:

1) tibialis anterior;

2) extensor digitorum longus;

3) extensor hallucis longus.

The tibialis anterior (see Fig. 57) lies directly adjacent to the lateral surface of the tibia, from which it originates. In addition, this muscle arises from the interosseous membrane and the crural fascia. Descending inferiorly, the muscle passes beneath the superior and inferior extensor retinacula—specialized thickenings of the Fascia of the leg and foot located in the ankle region—reaches the medial cuneiform and the base of the 1st metatarsal bone, and inserts into the medial margin of the foot. The tibialis anterior is easily palpable beneath the skin throughout its length, particularly at the transition from the leg to the foot. Here, its tendon stands out during dorsiflexion of the foot, i.e., when lifting the toes. The muscle contributes not only to dorsiflexion but also to supination and adduction, although its contribution to the latter movement is minor. During standing and walking, it pulls the leg forward and, together with its antagonists, stabilizes the ankle joint.

The extensor digitorum longus (see Fig. 57) is located lateral to the previous muscle in the upper part of the leg; it originates from the upper end of the tibia, the head and anterior border of the fibula, the interosseous membrane, and the crural fascia. Passing onto the foot, it divides into five tendons: four of these travel to the 2nd, 3rd, 4th, and 5th toes and insert into their distal phalanges, while the fifth, known as the fibularis tertius, inserts into the base of the 5th metatarsal bone.

As a multiarticular muscle, the function of the extensor digitorum longus consists not only in extending the toes but also in dorsiflexing the foot. Because the fifth tendon of this muscle attaches to the lateral margin of the foot, it produces both dorsiflexion and slight pronation of the foot. Thus, in its position and function, the extensor digitorum longus of the foot corresponds to the extensor digitorum of the hand.

The extensor hallucis longus (see Fig. 57) originates from the medial surface of the fibula and the interosseous membrane in the lower half of the lower leg. This muscle is weaker than the two preceding ones, between which it lies. Inserting into the base of the distal phalanx of the big toe, it acts as an extensor not only of this toe but of the entire foot as well. In addition, this muscle assists in the supination of the foot. Its tendon is readily palpable.

Adduction of the foot

There are no dedicated muscles exclusively involved in the adduction of the foot; this movement is governed by the parallelogram of forces through the simultaneous contraction of the following muscles:

1) the tibialis anterior (see p. 188);

2) the tibialis posterior (see p. 188).

Abduction of the foot

The muscles involved in the abduction of the foot are located on the lateral side of the vertical axis of the ankle joint. These include:

1) the peroneus brevis (see p. 192);

2) the peroneus longus (see p. 191).

Pronation of the foot

Pronation of the foot is performed by muscles located lateral to the sagittal axis around which this movement takes place. The foot is pronated by the following muscles:

1) the peroneus longus;

2) the peroneus brevis;

3) the peroneus tertius (see pp. 188, 195).

The peroneus longus muscle (see Figs. 57, 59) has a pennate structure. It lies on the lateral surface of the fibula, forming, together with the peroneus brevis, the Lateral Muscle Group of the lower leg. The peroneus longus originates from the fibular head, the crural fascia, the lateral condyle of the tibia, and the lateral surface of the fibula in its upper two-thirds. The tendon of this muscle curves posterior and inferior to the lateral malleolus. Across the lateral surface of the calcaneus, the muscle is held in place by the superior and inferior peroneal retinacula. Passing onto the plantar surface, the tendon runs through the groove on the Inferior surface of the cuboid bone, reaches the medial margin of the foot, and inserts into the tuberosity of the base of the 1st metatarsal bone, the 1st cuneiform bone, and the base of the 2nd metatarsal bone. Among the pronating muscles of the foot, the peroneus longus is the strongest. It flexes, pronates, and abducts the foot. Furthermore, together with the tibialis anterior, it forms a musculotendinous sling that Supports the transverse arch of the foot.

The peroneus brevis muscle (Figs. 57, 59) originates from the lateral surface of the fibula and the intermuscular septa of the lower leg. The tendon of this muscle curves inferior and posterior to the lateral malleolus and inserts into the tuberosity of the 5th metatarsal bone. The muscle flexes, pronates, and abducts the foot.

Supination of the foot

Supination of the foot involves muscles that intersect the sagittal axis around which this movement occurs and are situated medially to it. The foot is supinated by the following muscles:

1) the tibialis anterior (see p. 189);

2) the extensor hallucis longus (see p. 190). The alternative contraction of muscle groups passing near the JOINTS OF THE foot and descending to it from the lower leg produces circular motion of the foot.

Muscles producing movements of the toes

The movements of the toes involve both muscles extending from the lower leg to the foot and intrinsic muscles of the foot. The muscles located on the plantar surface of the foot flex the toes, whereas those on the dorsal surface extend them. The intrinsic muscles of the foot are those that both originate and insert within the foot. They are quite numerous and can be divided into two groups: the muscles of the plantar surface of the foot and the muscles of the dorsal surface of the foot.

Muscles of the plantar surface of the foot

The muscles of the plantar surface of the foot (see Fig. 60) can be divided into three groups: 1) medial, 2) lateral, and 3) middle.

The medial group is located in the region of the medial part of the longitudinal arch of the foot; it attaches to the 1st toe and constitutes the intrinsic muscles of this digit. These include the abductor hallucis, the flexor hallucis brevis, and the adductor hallucis.

The lateral group attaches to the 5th toe and consists of two muscles: the abductor digiti minimi and the flexor digiti minimi brevis.

The intermediate group is the most substantial one. It includes the flexor digitorum brevis, the quadratus plantae, four lumbricals, and the interosseous muscles (three plantar and four dorsal).

The function of these muscles is evident from their names. In addition, the lumbricals flex the phalanges, the dorsal interossei abduct the toes, and the plantar interossei adduct them. The short muscles of the plantar surface account for approximately 25% of the total mass of all muscles attaching to the Bones of the foot.

The abductor hallucis muscle (see Fig. 60) originates from the calcaneal tuberosity and the plantar aponeurosis, inserting into the base of the proximal phalanx of the hallux. This superficial muscle has a pennate structure, which provides it with significant lifting power. It fuses with the flexor hallucis brevis and acts together with it to flex and abduct the big toe.

The flexor hallucis brevis (see Fig. 60) originates from the ligaments of the plantar skeletal surface of the foot and inserts into the sesamoid bones and the base of the proximal phalanx of the hallux. This muscle flexes the proximal phalanx of the big toe.

The adductor hallucis has two heads: oblique and transverse. The oblique head originates from the long plantar ligament, the cuneiform bones, and the plantar surface of the bases of the 2nd and 3rd metatarsals, whereas the transverse head arises from the joint capsules of the metatarsophalangeal joints of the 3rd, 4th, and 5th toes, running transversely to the base of the proximal phalanx of the hallux. Both heads share a common tendon that attaches to the lateral sesamoid bone and the base of the proximal phalanx of the big toe. The function of the muscle is not only to adduct the big toe but also to flex it. The transverse head helps maintain the transverse arch of the foot.

The abductor digiti minimi (see Fig. 60) originates from the calcaneus and the plantar aponeurosis. Extending anteriorly, it attaches to the tuberosity of the 5th metatarsal bone and the base of the proximal phalanx of the little toe. Its function is to flex and abduct the toe.

The flexor digiti minimi brevis (see Fig. 60) originates from the base of the 5th metatarsal bone and the long plantar ligament, inserting into the base of the proximal phalanx of the little toe, which it flexes.

The flexor digitorum brevis (see Fig. 60) originates from the calcaneal tuberosity and the plantar aponeurosis. It forms four tendons extending to the 2nd–5th toes. Each tendon lies within a synovial sheath alongside the tendon of the flexor digitorum longus. Near their insertion points, the tendons of the flexor digitorum brevis are split (perforated) by the tendons of the flexor digitorum longus. The flexor digitorum brevis inserts into the bases of the middle phalanges of the 2nd–5th toes and flexes them.

The quadratus plantae originates from the calcaneus and inserts into the lateral margin of the flexor digitorum longus tendon. It essentially acts as an accessory head of the flexor digitorum longus. By pulling on its tendon, this muscle aligns the direction of pull According to the parallelogram of forces. Furthermore, it increases the contractile force of the flexor digitorum longus.

The four lumbricals (see Fig. 60) are located between the tendons of the flexor digitorum longus. They originate from these tendons, pass along the medial side of the proximal phalanges, and insert into their dorsal aponeurosis. The lumbricals function to flex the proximal phalanges, adduct them, and extend the middle and distal phalanges.

Because these muscles originate on the tendons of the flexor digitorum longus, their tone increases when the latter contracts.

The interosseous muscles of the foot are divided into dorsal (four muscles) and plantar (three muscles) groups.

The dorsal interossei originate from the opposing surfaces of two adjacent metatarsals and insert into the bases of the proximal phalanges of the three middle toes, partially continuing into the dorsal aponeurosis of these toes. The first dorsal interosseous pulls the 2nd toe medially, whereas the second, third, and fourth muscles pull their respective toes laterally. Additionally, all dorsal interossei flex the proximal phalanges and extend the middle and distal phalanges.

The plantar interossei originate from the medial surfaces of the 3rd–5th metatarsals and insert into the bases of the proximal phalanges of the corresponding toes. They also partially blend into the dorsal aponeuroses of these toes. The plantar interossei flex the proximal phalanges, extend the middle and distal phalanges, and pull the 3rd–5th toes medially.

The action of the plantar interossei, much like their position, is comparable to that of their hand counterparts. The plantar interossei adduct the toes toward the sagittal plane passing through the 2nd toe, whereas the dorsal interossei abduct them away from this plane.

On the plantar surface of the foot, between the intermediate, medial, and lateral muscle groups, lie two plantar grooves: the medial and lateral plantar grooves.

Muscles of the dorsal surface of the foot

The dorsal surface of the foot contains several small muscles that act as extensors of the toes, alongside the tendons of the anterior leg compartment.

The extensor digitorum brevis originates from the calcaneus. It gives rise to three thin tendons running to the 2nd–4th toes. The muscle extends these toes.

The extensor hallucis brevis (see Fig. 57) shares a common origin with the preceding muscle and inserts into the base of the proximal phalanx of the big toe. It extends the hallux.

Additionally, an inconstant peroneus tertius muscle (see Fig. 57) may be found on the dorsal surface of the foot, representing an accessory tendon of the extensor digitorum longus that attaches to the base of the 5th metatarsal bone.

Comparing the plantar and dorsal muscles of the foot clearly shows that the former are significantly stronger than the latter. This is due to the difference in their functions. The plantar muscles help maintain the arches of the foot and largely provide its spring-like Shock-absorbing properties. Conversely, the dorsal muscles participate in extending the toes during forward movement of the foot (e.g., while walking and running). These muscles are so weak that they cannot prevent the body from falling backward if the toes are fixed and the vertical line of the body's center of gravity shifts beyond the rear boundary of the support base.

Connective tissue structures of the lower limb muscles

The Fasciae of the lower limb are divided into superficial and deep (or proper) layers. The latter is commonly referred to as the fascia lata of the thigh. The superficial fascia has a structure similar to that in other Regions of the body. It is well-developed only below the inguinal ligament, where a certain amount of fatty tissue lies between it and the proper fascia, containing cutaneous vessels and nerves, as well as Lymph Nodes.

The fascia lata (deep fascia of the thigh) is one of the toughest fascial structures in the human body. It originates from the inguinal ligament and iliac crest, extending superiorly and posteriorly into the gluteal fascia, and inferiorly into the popliteal fascia and the crural fascia (fascia of the leg).

Just beneath the inguinal ligament, the fascia lata splits into two layers. The deeper layer forms the floor of the femoral triangle, while the superficial layer overlies the femoral vessels and is perforated by numerous openings for the passage of blood vessels and nerves.

The fascia lata is most prominently developed on the lateral aspect of the thigh, where it forms a thick, broad band known as the iliotibial tract. This tract courses over the greater trochanter and descends to attach to the lateral condyle of the tibia as well as the femur. The fascia lata serves as an attachment site for the tensor fasciae latae and gluteal maximus muscles. By attaching to the linea aspera of the femur, the fascia lata forms the lateral intermuscular septum of the thigh, which gives origin to muscles of both the anterior and posterior compartments. The medial intermuscular septum, located between the vastus medialis and the adductor muscles, is significantly thinner and less pronounced than the lateral one. These intermuscular septa divide all thigh muscles into three main compartments: anterior, medial, and posterior.

The gluteal fascia originates from the sacrum and iliac crest, overlying the glutealis maximus muscle. While relatively thin, it sends fibrous septa inward between the muscle bundles of the gluteus maximus.

The popliteal fascia features well-developed transverse fibers and spans tightly across the popliteal fossa.

The fascia of the leg (crural fascia) is a direct continuation of the popliteal fascia on the posterior aspect of the leg. It attaches firmly to the bones and contributes to the Formation of the anterior and posterior intermuscular septa. Together with the rest of the crural fascia, these structures form osteofascial compartments for the three muscle groups of the leg: the anterior group (tibialis anterior, extensor hallucis longus, extensor digitorum longus), the lateral group (peroneus longus and brevis), and the posterior group (triceps surae, tibialis posterior, flexor hallucis longus, flexor digitorum longus).

In its distal portion, the crural fascia thickens to form retinacula that stabilize the underlying tendons: superiorly, the superior extensor retinaculum, and distally where the fascia transitions to the dorsum of the foot, the inferior extensor retinaculum. Beneath these retinacula lie fibrous tunnels enclosing the tendons of the anterior leg muscles, which are protected by synovial sheaths.

Between the medial malleolus and the calcaneus lies a groove transmitting the deep tendons of the posterior leg. As the crural fascia transitions into the plantar fascia, it thickens over this groove to form the flexor retinaculum. Beneath this band are additional fibrous canals: three transmit muscle tendons enclosed in synovial sheaths, while the fourth contains major blood vessels and nerves.

Inferior to the lateral malleolus, the crural fascia also forms a thickening known as the peroneal retinaculum (fibular retinaculum), which secures the fibular tendons in place.

The fascia of the foot. The foot possesses a superficial fascia, which is a continuation of the crural fascia, and a deep fascia that sends fibrous extensions—or intermuscular septa—deep toward the tarsal and metatarsal bones. On the plantar surface, the deep fascia thickens significantly to form the plantar aponeurosis, a robust, tendon-like structure up to 2 mm thick. In terms of position and embryological development, it corresponds to the palmar aponeurosis. The fibers of the plantar aponeurosis run in both longitudinal (anteroposterior) and transverse directions. Intermuscular septa divide the plantar side of the foot into three fascial compartments: the lateral compartment houses the muscles of the little toe (flexor digiti minimi brevis and abductor digiti minimi); the medial compartment contains the muscles of the great toe (flexor hallucis brevis, abductor hallucis, and adductor hallucis); and the central compartment encloses the flexor digitorum brevis, tendons of the flexor digitorum longus, lumbricals, quadratus plantae, as well as a considerable portion of the adductor hallucis.

The tendons crossing from the leg to the foot are enclosed in synovial sheaths at multiple locations. Around the ankle joint, these sheaths are organized into three groups: anterior (for extensors), medial (for flexors), and lateral (for fibular muscles). On the SOLE OF THE foot, the tendons lie within osteofascial tunnels surrounded by a synovial lining.