Gastrocnemius

The gastrocnemius, also known as the leg tricep, refers to the large muscle on the posterior calf of the leg. It is the leg's most superficial muscle and forms most of the calf muscle. Its name is derived from the Greek words “gaster”, meaning stomach or belly, and “kneme”, meaning leg. Together, the phrase refers to the belly of the leg or the bulk of the calf.

The gastrocnemius is located at the posterior of the lower leg. It has two heads, or components, with separate origins; the lateral head comes from the posterior aspect of the lateral condyle of the femur (i.e., the thigh bone), and the medial head originates from the posterior surface of the medial condyle of the femur and the popliteal surface of the femoral shaft. Both heads also originate from the capsule of the knee joint. The two heads of the gastrocnemius converge with the soleus and plantaris muscles at the popliteal fossa, which is the diamond-shaped space behind the knee joint. These three muscles are collectively referred to as the triceps surae muscle. 

Both heads to the gastrocnemius and the soleus muscle fuse to attach to the posterior surface of the calcaneus (i.e., heel bone) via the calcaneal tendon, also referred to as the Achilles tendon. The gastrocnemius muscle is innervated by the tibial nerve, primarily from the first sacral (S1) nerve root, with some contribution from the fifth lumbar (L5) nerve root.  

The gastrocnemius functions by lifting the heel upward and extending the foot downward (i.e., plantar flexion), which is essential during walking, running, and jumping. While walking, the quadriceps muscle and the gastrocnemius activate, particularly during the first phase, where the foot lifts and swings forward, and the knee extends. At the knee joint, the gastrocnemius also functions in leg flexion. 

The gastrocnemius is mainly used during fast, powerful leg movements and is less utilized when standing stationary. Therefore, it is predominantly white muscle fibers (i.e., fast twitch fibers). This is in contrast to the soleus muscle, which is active when standing still and has more red muscle fibers (i.e., slow twitch fibers).

The gastrocnemius can be injured, mainly while playing sports, such as tennis or squash. During both sports, the muscle can be overstretched by overextending the knee and dorsiflexing the ankle (i.e., bringing the toes of the foot up). This occurs more frequently with sudden ballistic movements involving the lower extremity, such as during sprinting or jumping. Rupture of the tendon at the medial head of the gastrocnemius and, less commonly, the plantaris muscle can occur. Those with gastrocnemius injuries will feel a sudden, sharp pain at the back of the calf, which may be described as a sudden tearing sensation or pop, accompanied by limping, and swelling of the posterior calf.

The gastrocnemius muscle is also prone to muscle spasms, colloquially known as “charley horses”. These are painful, involuntary contractions of the muscle that may last several minutes and are triggered by dehydration, muscle overuse, and electrolyte imbalances. The gastrocnemius muscle may also be strained, most commonly a medial gastrocnemius strain, during a strong ankle dorsiflexion force and typically presents with severe, acute pain. 

The gastrocnemius may also be involved in an injury at its insertion point at the Achilles tendon. Achilles tendon tendonitis refers to the overuse and repetitive strain of the gastrocnemius muscle and is more likely to occur in older adults. Repetitive strain leads to thickening of the Achilles tendon and resultant cartilaginous and bony metaplasia. A bony enlargement can typically be observed at the back of the foot, where the tendon inserts into the heel. Pain may also be localized to the area. The Achilles tendon can also fully rupture due to intense recreational sports. The individual will usually hear a popping sound, followed by pain when extending up their leg and an inability to plantar flex against resistance. Lastly, calcaneal bursitis refers to excessive friction caused by the movement of the calcaneal tendon, leading to inflammation and pain in the posterior heel. This is common in individuals who partake in long-distance running, basketball, and tennis. 

In the case of gastrocnemius injury, the treatment in the first 24 to 48 hours typically consists of the RICE protocol (Rest, Ice, Compression, Elevation), which helps to avoid the aggravation of the injury and reduces inflammation. Muscle relaxants (e.g., cyclobenzaprine) and analgesics (e.g., acetaminophen) can be taken if the pain is severe. Physical therapy and massage may also be helpful. If the area is weakened after injury, a clinician may recommend basic weight-bearing exercises, such as double and single leg calf raises, to rehabilitate the muscle. 

The gastrocnemius is the muscle that forms most of the calf, soleus, and plantaris muscles. It has two origin points, medially emerging from the medial condyle of the femur and laterally emerging from the lateral condyle of the femur. It joins with the other muscles of the triceps surae to attach to the calcaneal tendon. The gastrocnemius is responsible for plantar flexion of the foot and leg flexion at the knee. It is necessary for proper running and walking. The gastrocnemius can be injured while playing sports or with overuse. The muscle can be strained or overstretched by excessive foot dorsiflexion. Muscle strain treatment includes the RICE protocol, physical therapy, and rehabilitation.