1. Calf Muscle Anatomy

A human calf is the back portion of the lower leg. It is a skeletal muscle and is attached behind the shin bone. The calf muscle is made up of two muscles - the powerful and two-headed gastrocnemius and the smaller muscle lying just beneath it is the soleus.

1.1. Gastrocnemius Anatomy

Based on scientific and anatomical observations and research (published in PubMed research archive), the gastrocnemius is the muscle responsible for most of your movements in the lower leg. It originates from the back of the knee and although it is a single muscle, its two heads make it seem that the gastrocnemius is made of two separate muscles. The heads of the gastrocnemius are attached to the femur or thigh bone.

The muscle then runs down the lower leg till it attaches to the soleus – a smaller muscle beneath it – which forms the Achilles tendon.

The gastrocnemius is a superficial muscle. You can see it easily and also touch it. This large muscle gets its blood supply from the sural artery and it is innervated by the tibial nerves (a branch of the sciatic nerve that extends from the back of the leg and ends at the foot).

The presence of the tibial nerve allows signals to reach the muscles and thus makes locomotion possible. Furthermore, it also helps detect sensations on your skin.

1.2. Soleus Anatomy

The soleus muscle is a small yet powerful muscle in the lower leg. The muscle extends all the way down the lower leg and is present beneath the larger gastrocnemius. The soleus originates from the back of the tibia or shin bone and extends to the back of the calcaneus – the heel bone. At the calcaneus, the soleus joins with the gastrocnemius and forms the Achilles tendon. According to some anatomists, the two heads of the gastrocnemius along with the soleus muscle form a single muscle group called the triceps surae.

The soleus is also innervated (supplied with nerves) by the tibial nerves.

2. Function

The calf muscle is responsible for all of your leg movements. It helps you control the movement of your lower leg, feet, and ankles. It allows you to flex your feet, jump, walk briskly, stand straight, and workout in the gym. It helps you maintain your balance and supports all of your body weight, too.

The gastrocnemius and soleus have distinct functions.

2.1. Gastrocnemius Function

The gastrocnemius is mainly responsible for plantarflex, i.e. flexing your feet and toes towards the sole or walking on the tips of your toes. However, gastrocnemius acts as a plantar flexor when your legs are straight.

As you walk, run, jump or climb the stairs, the gastrocnemius contracts. This causes your ankles to flex and propel you forward. When you stand with your soles pressed firmly to the ground, the gastrocnemius supports your body and helps you maintain balance.
The gastrocnemius is exerted along with the quadriceps and gluteus muscles when you raise your body upwards against the pull of gravity. Due to this function, it is also called the “anti-gravity” muscle.

Since this muscle originates from the back of the knee, it not only controls ankle movement but also acts on the knees. The gastrocnemius and hamstrings work together to flex and bend the knee.

2.2. Soleus Function

The soleus is also responsible for plantar flexion. When you bend your knee, the gastrocnemius muscle contracts. At this point, it is difficult for the muscle to help flex the ankle as well. Thus, the soleus plays a vital role here.

When you stand on one foot, the soleus helps you maintain your balance and is active in all sorts of weight-endurance activities.

2.3. Calf Muscle – Second Heart?

The soleus calf muscle has another important function. Due to this function, the calf muscle is called the “second heart” by medical experts.

As the name suggests, the soleus pumps blood from the feet and lower leg back to the heart. The veins have a one-way valve that prevents the backflow of deoxygenated blood, pumping it effectively towards the heart. The soleus aids in this process, acting as a sponge and pushing blood through the veins. This muscle function is often termed the “skeletal muscle pump” or the “peripheral heart muscles.”

3. Common Conditions Affecting Calves

Calf muscles are used so frequently that they can be overworked. This may lead to health problems that adversely affect the calves. Some common conditions are as follows:

3.1. Cramps

Cramps are painful involuntary muscle contractions that can last for some time but usually get better with a massage or a stretch. It is one of the most common lower leg conditions. It is estimated that 75% of people ages 50 or above are prone to getting cramps. Leg cramps can happen during the day or at night. You can also get cramps after exercise and even while you are sleeping. Certain factors such as dehydration, medication, vitamin deficiency, and pregnancy can be the underlying cause of cramps.

3.2. Spasm

Spasms are sharp involuntary convulsions of the muscle. They occur sporadically and can last for a few seconds. It may feel like your muscle is being squeezed tightly on its own when you have a spasm. It is extremely common among the masses and may be a result of dehydration or electrolyte imbalance.

3.3. Medial Gastrocnemius Strain (MGS) or Tear

The gastrocnemius strain or tearing of the muscles occurs when they are subjected to overuse, overstretched, or your muscles have to support weight beyond their endurance. The gastrocnemius being a  larger muscle is more prone to tearing. These tears occur in the bulk of the muscle and result in excruciating pain, swelling, bruising, and weakness. Strains mostly occur due to strenuous activity.

3.4. Achilles Tendonitis

Repeated, incorrect foot movements and overburdening the ankle irritate the Achilles tendon, which causes  Achilles tendonitis. The condition can be identified with throbbing pain in the tendon at the back of the heel bone. Swelling in the tendon may occur, hindering you from walking or running properly.

3.5. Achilles Rupture

Just like a calf muscle tear, subjecting your lower leg to unbearable force can cause tearing in the Achilles tendon, a condition known as an Achilles rupture. The rupture in the tendon can be partial or full. Signs of a  rupture include severe pain, swelling, bruising, and difficulty walking. Much like all muscle ruptures, an Achilles rupture is fixed through surgical intervention.

3.6. Compartment Syndrome

An injury to the muscle due to trauma, a fracture, or strenuous exercise can cause a fatal condition called “compartment syndrome.” In this condition, the blood supply to the muscle is decreased, leading to insufficient availability of oxygen.

3.7. Baker’s Cyst in Calf

A baker’s cyst is a fluid-filled cyst that forms in the back region of the knee, causing a bulge and intense pain. In some cases, the cyst can burst, leaking the synovial fluid in the calf area which can cause pain and swelling in the calf muscles.

3.8. Blood Clot in Calf Muscles

The large vein coursing through your calf muscles is the main site where a blood clot forms. The medical term used for this serious condition is – Deep Vein Thrombosis (DVT).

According to the Centers for Disease Control and Prevention (CDC), a clot in the muscle blocks the flow of blood in the vein and causes pain, redness, swelling, and a warm sensation in the calf muscles. Not moving enough, injury to your calves, and surgery increases the risks of blood clots.

4. How to Prevent These Conditions?

Maintaining the health of your calves and preventing these conditions is not as difficult as it might seem. Abiding by a few fundamental health rules should be enough to keep these problems at bay :

1. Lose extra weight: People who are obese are more prone to cramps and complain about pulled muscles more often. This is because the extra kilos put excess pressure on your calves. You can calculate a healthy weight through body mass index BMI or consult a healthcare provider. Following a certain diet plan may speed up the weight loss process.
2. Hydrate: According to Medical News Today - medically reviewed by Jillian Kubala, MS, RD, Nutrition - human muscle cells contain about 75% water content.  Therefore, you must drink enough water so they can function properly.
3. Warm-Up: Exercising can be taxing on your muscular health. Do warm-ups and light stretching to prepare your muscles before you do any exercises.