LEG MUSCLES: CLASSIFICATION AND FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2024

The muscles of the leg or muscles of the lower limbs are the largest and most powerful in the entire human body, since they must not only carry the weight of the whole body, but also mobilize it. The lower limb does not have as wide a range of movements as the upper limb.

However, the muscles of the lower limbs are no less specialized, since the functions they must fulfill require not only power but also coordination and even finesse in some movements; otherwise, a classical dancer would not achieve that characteristic graceful displacement.

As in the upper limb, in the leg there are two types of muscles: some are short and very powerful, they are located at the level of the hip joint and their function is to keep the coxofemoral joint stable (where the limb bottom joins the trunk).

On the other hand, there are the long and powerful muscles responsible for locomotion, which take insertion in the bone structures, from the pelvis to the fibula (fibula) and the tibia, and their function is to mobilize the legs.

Classification

According to their shape, the muscles of the lower limb are divided into two large groups:

- The short muscles, which stabilize and rotate the hip.

- The long, powerful and very large muscles, responsible for the set of movements that the legs can perform.

Depending on their anatomical location, the leg muscles can be divided into:

- Muscles of the anterior compartment, if they are in front of the bone, looking towards the back of the foot.

- Muscles of the posterior compartment, located behind the bone, looking towards the heels.

- Muscles of the medial compartment or of the adductors, if they are only in the thigh, facing the crotch.

- Muscles of the lateral compartment, which are those that are only in the leg, looking outwards.

Short muscle function

These muscles are located between the pelvis, specifically surrounding the obturator fossa and the femur. They are very short and strong muscles whose function is to stabilize the coxofemoral joint and keep the legs aligned in their correct position.

They are located in very deep planes and are covered by larger and superficial muscular structures that literally cover them, thus making access to them during surgeries quite laborious.

Long muscle function

Long muscles go from one bone structure to another, passing in most cases over a joint.

They are strong and voluminous muscles capable of mobilizing the entire weight of the body and conferring flexion-extension and abduction-adduction movements on the lower limb, as well as internal and external rotation.

In order to facilitate their understanding when they are studied, they are divided according to the region in which they are found, so that in the lower limb we find: muscles of the gluteal region, muscles of the femoral (or crural) region, muscular structures of the leg (below the knee) and intrinsic muscles of the foot.

Description of the leg muscles

A detailed and detailed description of all the muscles of the lower limb would take several volumes and dozens of illustrations.

However, a basic understanding of the lower limb muscles will aid in a better understanding of the biomechanics of standing and locomotion.

Once these leg muscle basics are mastered, hitting the gym becomes a lot of fun as you are aware of exactly what each muscle group is doing.

The most important details of the muscles of the lower limb according to each region are described below:

Muscles of the hip and gluteal region

It encompasses all the short muscles that go from the pelvis to the femur and whose function is the internal rotation of the leg. In turn, these are covered in the posterior region by the muscles of the gluteal region, which extend the thigh back and rotate the lower limb outwards.

The deepest of all are the hip muscles, which include:

Pyramidal

It goes from the sacrum to the femur, occupying the deep plane of the gluteal region. Rotate the thigh outward and assist in abduction (separation from the midline) of the thigh.

Internal and external shutter

They are muscles that arise from the ischiopubic branches and attach to the femur. Its function is to rotate the thigh outward.

Gemini

They are a pair of small and rudimentary muscles that are practically fused with the internal obturator, thus sharing its functions.

Crural square

It is larger than the previous ones and covers them in their entirety, inserting into the ischial tuberosity on the inside and the femur on the outside. Its function is the external rotation of the thigh.

Above the hip muscles (also considered the deepest muscles in the gluteal region) is the gluteal muscle complex (buttock muscles), which includes:

Gluteus minus

It is the deepest of the gluteal muscle complex and is located in the same plane and depth as the obturators. It goes from the iliac fossa to the greater trochanter of the femur and functions as an abductor of the thigh (separates the legs).

Gluteus medius

It is located on a more superficial plane with respect to the gluteus minimus and the rest of the hip muscles. It goes from the iliac fossa to the femur and its main function is as an abductor of the thigh.

However, when partially contracted it assists in external rotation of the thigh; Likewise, when it takes its fixed point on the femur, the contraction of the gluteus medius projects the pelvis forward.

Gluteus maximus

It is the largest, most voluminous and known in the region, given that it gives it its characteristic shape and is usually the site where intramuscular injections are placed.

It is a very powerful muscle that goes from the iliac crest to the femur, inserting itself in the cephalic portion of the linea aspera and completely covering all the muscles in the region.

Its main function is the extension of the thigh, although it also functions as an external rotator, working as an agonist for the deepest muscles in the region.

At this point, mention must be made of the iliopsoas, a large and powerful muscle that originates from the anterior aspect of the lumbar vertebrae and the inner aspect of the iliac wing. From there they exit the abdomen, passing through the crural arch (in its outer portion) to cover the anterior aspect of the hip and insert into the femur.

It is a very powerful muscle whose function is to flex the thigh on the abdomen (when it takes its fixed point in the spine and pelvis), as well as to lean the trunk forward (sign of reverence) when it takes its fixed point in the femur.

Thigh muscles

Thigh

The thigh muscles are divided into three large groups: the anterior, responsible for extending the knee; the posterior ones, whose function is to flex the knee; and the medial or internal ones, which function as thigh adductors (bring the leg closer to the midline).

Furthermore, there is a fourth group represented by a single muscle (tensor fascia lata) that originates in the gluteal region and ends in the knee, occupying the entire lateral aspect of the thigh.

The muscular structures that make up each of these groups are:

Previous compartment

- Crural quadriceps, which includes four different muscles: crural, vastus medialis, vastus medialis, and rectus anterior thigh. The latter is sometimes accompanied by an accessory muscle known as the subcrural.

- Sartorio, which is a very particular muscle since it runs from top to bottom and from outside to inside giving the unique ability to flex the thigh over the hip, simultaneously rotating the thigh outwards. It is the muscle that allows one leg to cross over the other when we sit down.

The muscles that make up the anterior compartment are the following:

- Flexor carpi radialis muscle.

- Long palmar muscle.

- Flexor carpi ulnar muscle.

- Superficial flexor muscle of the fingers.

- Deep flexor muscle of the fingers.

- Long flexor muscle of the thumb.

Medial compartment

- Adductor major.

- Adductor minor.

- Pectineus.

- Middle adductor.

- Internal rectum.

Rear compartment

- Semimembranous.

- Semitendinosus.

- Crural biceps.

Leg muscles

These muscles are essential for balance and standing; take their insertion into the leg bones (tibia and fibula or fibula) exerting their action on the ankle joint.

They are divided into three groups: anterior, posterior, and lateral (or fibular). The former function as flexors of the foot on the leg (they bring the tips of the fingers up) and extensors of the toes.

The posterior muscles serve as extensors of the foot (allowing us to stand on our toes) and as flexors of the fingers. The last group of muscles stabilize the ankle, allow a slight external tilt, and rotate the foot outward.

The muscles in these groups include:

Previous compartment

- Tibial anterior.

- Extensor proper of the first toe (hallux).

- Common extensor of the fingers.

- Fibular or anterior fibula.

Rear compartment

- Popliteus.

- Long common flexor of the fingers.

- Posterior tibial.

- Long flexor of the first toe (hallux).

- Soleus (more superficial than the previous ones, covers them almost entirely).

- Plantar thin (tendinous in almost all its extension, separates the soleus from the most superficial muscles).

- Gastrocnemius (calf muscles or calf muscles), are the largest and most superficial in the region. They are the only ones visible and fully cover the muscles of the deep planes. They are inserted into the heel via the Achilles tendon.

Side or external compartment

- Fibular or short fibula.

- Fibular or long fibula.

Intrinsic muscles of the foot

It includes the lumbricals and interossei, as well as a number of specialized muscle structures, such as the short plantar flexor. Their complex interaction and biomechanics require a separate chapter for a more detailed study.

References

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