Gastrocnemius Muscle (Medial Head)

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The gastrocnemius muscle is the most superficial and prominent of the calf muscles. It is made of two muscular regions, the medial head and lateral head, which attach to the medial and lateral sides of the femur. The heads of the gastrocnemius muscle work together to plantarflex the foot at the ankle and to flex the leg at the knee.

Anatomy

The medial head of the gastrocnemius is a large, muscular belly located on the medial side of the calf next to the almost identical lateral head of the gastrocnemius. It is a superficial muscle, making it easy to palpate through the skin of the calf while pointing one's toes. Deep to the gastrocnemius are the soleus and plantaris muscles.

The medial head of the gastrocnemius muscle arises from the medial condyle of the femur just distal and medial to the popliteal fossa. From its origin it passes posterior to the knee joint and descends the leg parallel to the lateral head of the gastrocnemius. At about the middle of the calf, both heads merge together to form the calcaneal tendon, which is more commonly known as the Achilles tendon. The calcaneal tendon continues distally toward the ankle, where the soleus and plantaris muscles join the tendon. After passing posterior to the ankle joint, the calcaneal tendon inserts to the calcaneus, or heel bone.

Physiology

The gastrocnemius muscle crosses both the knee joint and the ankle joint, giving it a distinct function at each joint. At the ankle joint, the gastrocnemius pulls on the calcaneal tendon and calcaneus to plantarflex the ankle. Plantarflexion is a specific movement at the ankle, which moves the sole of the foot posteriorly and points the toe. The soleus and plantaris muscles, which also form the calcaneal tendon, assist the gastrocnemius in this motion, but the gastrocnemius is by far the most powerful plantarflexor. At the knee joint, the gastrocnemius pulls the calcaneus posteriorly toward the posterior of the femur, flexing the knee. The three hamstring muscles also work with the gastrocnemius to perform knee flexion.