Leg muscles: types, location, characteristics and functions.

A summary classification of the leg muscles and their function in the body.

The locomotor system is composed of the osteoarticular system (bones and joints) and the skeletal muscles of the body, i.e. those that respond to voluntary actions.. To give you an idea of the biomechanical masterpiece we have in our body, suffice it to say that we have 206 bones, 360 joints (86 of them in the skull) and more than 600 skeletal muscles, all of them with a common task: that we can maintain our shape and move.

The voluntary musculature (skeletal or striated) makes up approximately 40% of the weight of an adult male, so its functionality counts for itself. If we look at the legs, the third lower pelvic segment between the knee and the ankle, it is estimated that a human being walks about 3.5 billion kilometers in a lifetime. For this reason, the leg musculature must be prepared for light but continuous exercise throughout our existence.

For all these reasons, it is also common to see how overweight and obese people have serious problems with lower body movement. One kilogram of body weight added is equivalent to 7 kilograms more in the knee portion, so that an increase of 10 kilograms of mass, theoretically, is associated with 70 kilograms more pressure on this joint.

With all this data in hand, it is more than clear that the leg is an essential anatomical section of the human being, both for locomotion and for supporting our weight in a three-dimensional environment. In honor of these structures, today we present to you all the muscles of the legs and their particularities..

The muscles of the legs

As we have already said, the term "leg" refers to the lower extremity of the human body, which goes from the trunk to the foot.. In some contexts it is considered to include also the foot, and in others the thigh is excluded. In any case, we will perceive the structure as a "whole" at the anatomical level, ranging from the base to the tips of the toes. We begin by naming the muscles in the anterior compartment of the leg.

1. Muscles in the anterior compartment of the leg

Here we find 4 well differentiated Muscle groups: tibialis anterior, extensor digitorum longus muscle, extensor hallucis muscle and the third peroneus muscle. We will tell you about their particularities.

1.1 Anterior tibial

The tibialis anterior, as its name suggests, accompanies the tibia on its lateral surface.. The contraction of the tibialis anterior stabilizes the ankle, especially at the moment when the sole of the foot makes contact with the surface of the ground in the action of walking.

In general, its function is to keep the leg stable during walking, regardless of the condition of the ground or its inclination.

1.2. Extensor digitorum longus muscle (EDL)

This is a penniform muscle (feather-like shape) innervated by the peroneus profundus. It is an important dorsiflexor and therefore has the function of producing the simultaneous extension of almost all the toes, except for the big toe.except the great toe.

It originates from the lateral condyle of the tibia and the medial surface of the fibula. The fibers of this musculature converge in a tendon, which travels along the dorsal surface of the foot, to split into 4 units that insert into each toe.

1.3. Extensor hallucis extensor muscle

As you can imagine, this is the muscle responsible for the extension of the big toe, but also for the dorsiflexion of the sole of the foot (together with the extensor digitorum longus). It originates on the medial surface of the shaft of the fibula and inserts on the phalanx of the big toe..

1.4. Third peroneal muscle

This is a small muscle belly, located between the anterior and external portion of the leg. It originates with the EDL on the medial surface of the fibula, and runs with it for a certain distance, until it reaches the dorsal surface of the foot. Here, the third peroneal muscle divides and anchors to the fifth metatarsal. Together with other muscles, it is responsible for flexion and eversion of the foot..

2. Muscles in the lateral compartment of the leg

We continue on our tour, this time in the lateral leg, paying attention to the following muscle groups: the peroneus longus and peroneus brevis. Let's go with them.

2.1. Peroneus longus

This muscle is located on the lateral and external surface of the leg. It originates on the external aspect of the fibula and the tibial condyle, merging along its course into a tendon that inserts on the medial cuneiform and the base of metatarsal I. Its main function is to extend the foot over the leg, to carry it outwards and to allow it to perform a rotational movement..

2.2. Peroneus brevis

Located on the outside of the leg and below the knee, this muscle is responsible for allowing eversion of the foot. It is inserted on the anterolateral surface of the shaft of the fibula and is anchored on a tubercle associated with the V metatarsal..

Muscles in the posterior compartment of the leg.

Let's speed up the process, because in this last section, a total of 7 muscles await us to be described, at least in a cursory manner, which in turn are organized into two sides (superficial and deep, divided by a fascia). Let us move on.

3.1. Gastrocnemius

We are entering familiar territory, since this muscle divided into two halves is what is popularly known as "the twins". First of all, it should be noted that it has two "heads", one medial and one lateral, which converge in the ventral section. It is located over the soleus muscle and occupies a large part of the posterior aspect of the leg, from the knee to the ankle.. It is the main motor of the onset of physical walking.

3.2. Plantar

The plantaris muscle is in a deeper plane than the calf and is much smaller in size, with a thin diameter. It is absent in 10% of the world's population and its function is very weak, so we will not dwell on it any further.It is absent in 10% of the world's population and its function is very weak, so we will not dwell on it any further.

3.3. Soleus

As mentioned above, it is located below and behind the gastrocnemius. Curiously, it is called soleus because of its flattened and circular formwhich makes it resemble a soleus (sole in English).

3.4. Popliteus

The muscles we have named so far (gastrocnemius, plantaris and soleus) form the external aspect of the posterior compartment of the leg. From now on, the following muscle groups are located in the deep section of the same.

The popliteus is located at the top of the leg, "above the knee.". It is located in front of the gastrocnemius and is short, flattened and triangular in shape. Its function is to rotate, laterally, the femur on the tibia, thus allowing flexion of the knee joint.

3.5. Posterior tibial

Elongated in shape, this muscle is located between the flexor digitorum longus and the flexor digitorum greatorum, old acquaintances that we have already discussed.The posterior tibialis posterior muscle, old acquaintances that we have already discussed. Its function is to allow adduction of the foot, stabilize the plantar vault and allow plantar flexion of the foot.

3.6. Long flexor toe muscle

This muscle originates from the medial aspect of the posterior aspect of the tibia. While the extensor digitorum longus (EDL) muscle was in charge of the extension of the 4 toes, this is the one that allows their flexion.This is the one that allows their flexion.

3.7. Flexor digitorum longus muscle of the big toe

The same premise as in the previous case, but with the big toe. As simple as that.

Summary

As you may have noticed, we have counted a total of 13 muscles: 4 in the anterior compartment, 2 in the lateral compartment and 7 in the posterior compartment. Undoubtedly, the posterior side is the one we are all most familiar with, since this is where the calf, soleus or popliteus muscles are found, muscle groups that many of us have had to learn during a biology lesson.

With the exception of the plantaris, all of these muscles play an essential role in the functioning of the leg and feet alike. Thanks to them, we are able to move effectively at different speeds and on different terrains.

Bibliographic references:

• Jacobs, R., Bobbert, M. F., & van Ingen Schenau, G. J. (1996). Mechanical output from individual muscles during explosive leg extensions: the role of biarticular muscles. Journal of biomechanics, 29(4), 513-523.
• Joseph, J., & Nightingale, A. (1952). Electromyography of muscles of posture: leg muscles in males. The Journal of physiology, 117(4), 484-491.
• Muscles of the leg, teach me anatomy. Recogido a 11 de abril en https://teachmeanatomy.info/lower-limb/muscles/leg/
• Valentino, B., & Melito, F. (1991). Functional relationships between the muscles of mastication and the muscles of the leg. Surgical and Radiologic Anatomy, 13(1), 33-37.