Soleus Muscle

Soleus muscle Anatomy

The soleus muscle is a wide flat leg muscle found on the posterior leg. It runs from just below the knee to the heel and lays immediately deep into the gastrocnemius.

These two muscles, along with the plantaris muscle, belong to the group of superficial posterior compartment calf muscles.

They make up the trio of muscles known as the triceps surae, together with the gastrocnemius. They both function in numerous fundamental movements, including walking, running, and leaping, and they both insert on the calcaneus via the calcaneal tendon. The triceps surae muscle bellies’ size and shape affect the interindividual variations in human calves’ appearance, which ranges from slender to rather significant.

Origin

The soleus muscle arises from the soleal line on the dorsal surface of the tibia, medial border of the tibia, head of the fibula, and posterior border of the fibula.

Insertion

Soleus insert onto the posterior surface of the calcaneus via the calcaneal tendon. The calcaneal tendon, commonly called the Achilles tendon

Nerve supply

The soleus is innervated by the ventral rami of S1 and S2 spinal nerves, carried by the tibial nerve into the posterior compartment of the leg.

Blood supply

The superior branch arises from the popliteal artery while the inferior branch arises from a peroneal artery (fibular artery) or the posterior tibial artery.

Actions

Soleus contraction causes strong plantar flexion.

These strong muscles are essential for running, walking, and maintaining equilibrium. The soleus muscle is crucial for preserving upright posture; without it, the body would tip over front.

Additionally, while in an upright position, the soleus, also known as the skeletal muscle pump, peripheral heart, or sural (tricipital) pump, is in charge of returning venous blood from the periphery to the heart.

Compared to many other muscles, the soleus has slower muscle fibers. Some animals, including cats and guinea pigs, have soleus that are made entirely of sluggish muscle fibers. The proportion of slow fibers in human soleus varies, ranging from 60% to 100%.

The soleus, often known as the first gear muscle, is the muscle most useful for plantarflexion when the knee is bent. Because the gastrocnemius muscle originates in the femur, its effective tension is limited when the leg is bent. Because its slow-twitch fibers withstand exhaustion, the soleus is the major muscle used for plantarflexion during regular activity (e.g., walking).

Relations

The soleus muscle, which is located beneath the gastrocnemius, is closer to the skin, being superficial to it.

Between the two muscles lies the plantaris muscle, along with a section of its tendon.

The transverse intermuscular septum, which divides the leg’s superficial and deep posterior compartments, is located deeper into it (away from the skin).

The tibialis posterior muscle, flexor digitorum longus, flexor hallucis longus, posterior tibial vein, posterior tibial artery, and tibial nerve are located on the other side of the fascia.

The posterior compartment is the bulge of muscle medial to the tibia on the anterior side of the leg whereas the anterior compartment is lateral to the tibia. In the superficial center of the tibia is the soleus.

Synergists

Gastrocnemius
Plantaris
Tibialis posterior
Peroneus longus and Brevis
Flexor Digitorum Longus (FDL)
Flexor Hallucis Longus (FHL)

Antagonists

Tibialis anterior

Palpation

To make sure the gastrocnemius stays relaxed when palpating the soleus, plantarflex the ankle while flexing the knee to 90 degrees. The Achilles tendon’s lateral and medial sides can then be used to palpate the lateral and medial portions of the muscle. The majority of the muscle’s distal to proximal distance can be felt with palpation; however, if the gastrocnemius heads are large, it will be more challenging to feel the proximal attachments.

Accessory soleus muscle (ASM)

Between 0.7 and 5.5% of people have it. It typically manifests in the second or third decade of life and is 2:1 more common in girls than in males. For the most part, it is unilateral.

This supernumerary muscle is situated in the posterior upper third of the fibula, between the posterior portion of the tibia and the fibular head, in the oblique soleus line, underneath the gastrocnemius muscle. The ASM extends anteriorly and medially from its point of origin to the Achilles tendon.

Soleus muscle Strengthening exercise:

Double-Leg Calf Raise:

Calf raises are the classic calf-strengthening exercise. They use your body weight to strengthen and tone the gastrocnemius and soleus.

Starting position: Stand near a wall for balance. Place your feet hip-width apart, and make sure your ankles, knees, and hips are in vertical alignment to protect your joints.

Action: Press down into the balls of both feet to raise your body upward. Keep your abdominal muscles pulled in so that you move straight upward, rather than shifting your body forward or backward.

Single-Leg Calf Raise:

You can increase the intensity of the calf raise by doing it on one leg. That way you can strengthen your calf muscles even more.

Starting position: Stand on one leg near a wall for balance with the other leg bent behind you. Be sure the ankle, knee, and hip of the leg you’re working are in vertical alignment to protect the joints.

Action: Press down into the ball of your foot to raise your body upward. Keep your abdominal muscles pulled in so you avoid shifting forward or backward.

Stretching exercise of Soleus muscle:

• Stand about arm’s-length from the wall.
• Lean forward and place both hands on the wall about shoulder-width apart.
• Extend one foot (the side to be stretched) behind you with one heel on the ground, and the other foot closer to the wall.
• Lean into the wall with your hips until you feel a stretch in the calf of the extended leg.
• Hold this stretch for about 30 seconds, and then change sides.
• For a deeper stretch, move your foot farther back.
• This stretch is similar to the Achilles tendon and heel stretch; however, by keeping your knee straight, you focus the stretch on the calf rather than the Achilles tendon.

Clinical Importance:

Deformity:

Clubfoot is a birth defect where one or both feet are rotated inward and downward. The affected foot and leg may be smaller in size compared to the other. Approximately 50% of cases of clubfoot affect both feet. Most of the time, it is not associated with other problems. Without treatment, the foot remains deformed, and people walk on the sides of their feet. This may lead to pain and difficulty walking.

ACL Injury and Soleus Muscle:

A better understanding of the agonistic behavior of the soleus muscle on the anterior cruciate ligament may lead to the development of training and rehabilitation strategies that could reduce the incidence of injury and improve function in both patients with anterior cruciate ligament deficiency and patients who have undergone anterior cruciate ligament reconstruction.

Compartment Syndrome

Leg muscles have extensive fascia surrounding them, which makes them vulnerable to compartment syndrome. This condition is related to inflammation of the tissue that compresses nerves and alters blood flow. If compartment syndrome is not treated, it can result in neuropathy, blood clots, and muscular atrophy.

Soleus tear

In sports medicine and primary care clinics, strained calf muscles are often observed injuries. Overuse is a common cause of a soleus tear. Runners often sustain injuries as a result of overtraining and exhaustion. Because long-distance and endurance running and walking demand continuous soleus motion, athletes who specialize in these sports are more vulnerable to injury.

Some of the symptoms are:

Ache in the lateral leg on either side of the soleus
Calf weakness and poor plantar flexion, particularly when the knee is bent; dull calf pain from exercise; pain from foot dorsiflexion or pressure on the calcaneal tendon.

The RICE approach (rest, icing, compression, and elevation) is part of the treatment. It’s important to distinguish between a gastrocnemius tear and a soleus tear, as the latter is typically the result of abrupt trauma from rapid motions like jumping or running. The Cause of it has led to it being referred to as the tennis leg.

Soleus pain

A Soleus tear or overuse may be the cause of soreness in the soleus. Affected individuals usually claim that their pain starts during exercise and becomes better over time. Usually, the pain returns after the training. The lateral middle area, the head of the muscle, which may transmit pain all the way up into the sacroiliac area, or the calcaneal tendon and muscle belly transition are the three primary places where muscle discomfort usually arises. It may not always be easy to diagnose a soleus injury. To identify diseases inside the muscle, MRI or ultrasound are typically utilized in addition to clinical symptoms and physical examination.

A deep vein thrombosis (DVT), which poses a danger of pulmonary embolism (PE) and is a potentially fatal medical emergency, may also be the cause of sudden calf pain. In addition to calf pain, other common signs of DVT include calf swelling and redness. Heparin, warfarin, and factor Xa inhibitors are examples of pharmacotherapeutic drugs used in anticoagulation therapy. One preventive tactic is to use compression stockings.

FAQ

References

• Soleus. (n.d.). Physiopedia. https://www.physio-pedia.com/Soleus
• Jurkovicova, E. (2023, September 19). Soleus muscle. Kenhub.https://www.kenhub.com/en/library/anatomy/soleus-muscle