Gastrocnemius

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.  

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. Both muscles are referred to as triceps surae, which literally translates to “three-headed muscle of the calf” in Latin. 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 for posture, when standing stationary, in contrast to the soleus muscle. Indeed, the gastrocnemius is made of more type II muscle fibers (i.e., fast-twitch fibers), as opposed to the soleus muscle, which is made of more type I 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 is related 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 seen 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, along with early introduction of movement and exercise, depending on the type and severity of the injury. Muscle relaxants (e.g., cyclobenzaprine) and analgesics (e.g., acetaminophen, ibuprofen) 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.