Gastrocnemius: origin, insertion, action and innervation

The gastrocnemius is the most superficial calf muscle. Its two bellies form the bulge of the calf, and it joins the soleus to form the Achilles tendon.

Where it is

It lies at the back of the leg. Its two heads start just above the knee, frame the lower part of the popliteal fossa (the hollow behind the knee), then merge into a broad tendon halfway down the leg.

Origin and insertion

• Medial head: the back of the femur, just above the medial condyle.
• Lateral head: the outer surface of the lateral condyle of the femur.
• Insertion: the back of the calcaneus, through the calcaneal (Achilles) tendon, shared with the soleus.

Gastrocnemius and soleus together are called the triceps surae.

What it does

1. Plantar flexion of the ankle: rises onto the toes, pushes off when walking, running and jumping.
2. Knee flexion: because it crosses the knee, it helps bend it.

Since it crosses two joints, it's most effective as an ankle plantar flexor when the knee is straight. With the knee bent, the soleus does more of the work.

Innervation and blood supply

The tibial nerve (S1–S2) supplies it, in the popliteal fossa. The sural arteries, branches of the popliteal artery, supply its blood.

How to remember it

• "Gastro" = belly: the two bellies of the calf.
• Two joints, two heads: knee and ankle, medial and lateral.
• Calf raises with straight knees train gastrocnemius; with bent knees, soleus.

Frequently asked questions

What does the gastrocnemius do?

It plantar flexes the ankle and helps flex the knee.

Where does the gastrocnemius insert?

On the calcaneus, through the calcaneal (Achilles) tendon.

Which nerve supplies the gastrocnemius?

The tibial nerve, from S1 and S2.

Sources

• OpenStax, Anatomy and Physiology 2e, 11.6 Appendicular muscles of the pelvic girdle and lower limbs
• Z-Anatomy, the libre 3D atlas of anatomy