Medial head of gastrocnemius

At a glance

English

Medial head of gastrocnemius

Latin (TA2)

Caput mediale musculi gastrocnemii

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the medial head of gastrocnemius

Gastrocnemius is the bulky, superficial muscle that gives the calf its rounded shape, and it has two heads. The medial head is the larger of the pair and reaches further down the leg, which is why the inner calf bulges lower than the outer. Its name, from Greek, means the belly of the leg. Together with the deeper soleus it forms the triceps surae, the main group that lifts the heel.

The medial head arises by a strong tendon from the back of the femur just above the medial condyle, on the popliteal surface, and from the adjoining capsule of the knee joint. It forms the lower inner border of the popliteal fossa. Its fibres run down to a broad tendinous sheet on the front of the muscle, which unites with the lateral head and then with the tendon of soleus to form the calcaneal (Achilles) tendon. That tendon attaches to the middle of the back of the calcaneus.

Crossing both knee and ankle, the head plantarflexes the foot and helps flex the knee, though it cannot do both fully at once. It is rich in fast-twitch fibres, so it works hardest in sprinting, jumping and pushing off, while the slow, postural soleus does most of the work in quiet standing. It is supplied by a branch of the tibial nerve in the popliteal fossa, and by the medial sural artery from the popliteal artery.

The medial head is the usual site of a calf strain, the injury once blamed on plantaris and called tennis leg. A sudden forced upward bend of the ankle with the knee straight tears fibres where the muscle meets its tendon, giving sharp pain in the inner calf. Painful cramps are also common in this muscle. An abnormal course of the medial head, or of the popliteal artery around it, can squeeze the artery and cause calf pain on exercise, known as popliteal artery entrapment.

Attachments, action and supply

Origin

Popliteal surface of the femur just above the medial condyle, and the adjacent capsule of the knee joint.

Insertion

Posterior surface of the calcaneus through the calcaneal (Achilles) tendon, shared with the lateral head and soleus.

Action

Plantarflexes the foot at the ankle and assists flexion of the knee.

Nerve supply

Tibial nerve (S1, S2).

Blood supply

Medial sural artery from the popliteal artery.