Swollen Calf Muscles – Causes of Swelling at Back of Leg

The calf is the back fleshy part of the lower leg. In order to understand the causes of swelling of the calves, it is important to first understand the anatomy of the area.

The lower leg is defined as the region between the knee and the ankle. This area of the leg is built up around two thin yet strong bones known as tibia and fibula. The muscles that cover these bones are divided into the following four compartments by thick sheets of connective tissue (known as fascia):

  • Anterior compartment: This is the compartment covering the front surface of the leg (also known as the shin region).
  • Lateral compartment: This compartment forms the outer side of the lower leg.
  • Posterior compartments: The back of the lower leg is formed by two posterior compartments, called the superficial compartment and the deep compartment.

The superficial posterior compartment of the lower leg contains two muscles – the gastrocnemius and the soleus muscles. Together, these are known as the calf muscles. The gastrocnemius muscle is a large muscle that is easily visible as a bulge at the back of the lower leg. The deep posterior compartment contains popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucus longus muscles. All these muscles make it possible to move the lower legs and the feet.

The calf muscles also have a critical role to play in returning the blood from the lower limbs back to the heart. Due to gravitation, blood has a tendency to pool in the lower limbs. To prevent the backflow of blood, the superficial and deep veins present in the lower legs have valves in them. In addition, the calf muscles squeeze these veins and act as pumps to facilitate the return of blood to the heart. When circulation problems do arise in these veins, they become apparent as varicose veins and deep vein thrombosis.

Why does swelling occur?

Sometimes, the back of the leg may appear swollen. The swelling usually affects all the regions at the back of the leg: the calf, the ankles and the feet. At other times, only the calf muscle may appear swollen. Most of the causes of swelling in calf muscles involve the veins and the lymphatic vessels that drain the entire region of the lower leg. Therefore, even when swelling is initially restricted to the calf muscles, it may eventually spread to the ankles and the feet.

A swelling in the calf muscle could indicate a localized problem in the area. However, the cause of swollen calf muscles cannot be determined without taking into account other accompanying signs and symptoms such as redness of skin, numbness, pain and muscular weakness.

Read more on leg swelling.

Causes of Swollen Calf Muscles

Swelling in calf muscles may occur due to various reasons. The most common causes include inflammation of the structures of the lower leg, and accumulation of fluid in the lower regions of the leg. The following are some of the most common conditions associated with swollen calf muscles.

Overuse and injury

Injury to any part of the lower leg can cause inflammation and swelling in the calf region. Inflammation is the body’s protective response to an injury, and serves to limit the tissue damage to the injured region. Redness, pain, warmth, and swelling are the characteristic features of inflammation in any part of the body.

Some of the injuries that may result in swollen calf muscles include blunt force trauma, trauma caused by sharp objects, fracture of leg bones, muscular strain, tendonitis, tear in calf muscle, inflammation of a leg vein after injury (phlebitis), leg surgery and compression of the leg. In addition to injury, overuse of leg muscles and tendons (such as in professional athletes) may also cause inflammation and swelling in calf muscles.

Compartment syndrome

The connective tissue fascia that forms the compartments of the leg is a tough sheet that does not expand easily. In case of inflammation and swelling within any leg compartment, the fascia does not stretch. Instead, it compresses the tissues within the compartment. This causes compression of the blood vessels leading to compromised circulation in the leg. In addition, compression of the nerves in the leg may result in pain, numbness, and even paralysis.

This is referred to as compartment syndrome, which can be a cause of swollen calf muscles. Acute compartment syndrome is caused by the same factors that cause injury and overuse of the leg muscles. Chronic compartment syndrome is most likely seen in professional athletes who train long and hard, and are at risk of overusing their leg muscles.


Bacteria are the most common causes of infections of the lower leg. Infectious bacteria may gain access to the deeper tissues of the leg through penetrating skin injuries caused by sharp objects. Infections of the leg may also be secondary, with the bacteria reaching the leg from other parts of the body through the bloodstream. This is, however, a rare occurrence. Infections of the lower leg are more likely to be found in persons with weak immune systems, diabetics, and those with sluggish blood and lymph circulation in the lower legs.

Infections causing swelling in the lower leg and the calf may affect any of the tissues of the lower leg. Examples include skin infections (such as erysipelas, impetigo, staphylococci), subcutaneous infections (such as cellulitis), bone infections (such as osteomyelitis), and vein infections (such as septic thrombophlebitis).

Blood vessels

Problems with the veins of the lower legs are also commonly associated with swollen leg and calf muscles. These problems may affect the entire venous system of the leg. Alternatively, only the superficial or the deep veins may be affected. Examples of venous problems in the lower legs include deep vein thrombosis, varicose veins, and phlebitis.

Deep vein thrombosis refers to the presence of blood clots in the deep veins of the lower legs. Dilation and twisting of the superficial leg veins is referred to as varicose veins. Phlebitis refers to inflammation of the veins. All these conditions result in venous insufficiency or poor blood circulation in the lower leg.

Read more on swollen leg veins.

Peripheral edema

Swelling in lower legs could also be due to accumulation of fluid within the tissue spaces of the leg. This is technically referred to as peripheral edema, and is caused by inadequate drainage of tissue fluid through the lymphatic system of the legs. Peripheral edema usually affects the entire lower leg, rather than just the calf region. Swelling due to peripheral edema may occur due to kidney disease, liver disease, heart failure, inflammation of lymphatic vessels (lymphangitis), and venous insufficiency.

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