Gastrocnemius is a superficial muscle, lying near the surface at the back of the lower leg, that forms much of the visible calf. It extends from the lower end of the thigh bone to the heel through the calcaneal tendon, crossing both the knee and ankle joints.
Where is gastrocnemius located?
Gastrocnemius lies behind the tibia and fibula, the bones of the lower leg. It occupies the superficial posterior compartment, the group of muscles nearest the surface at the back of the leg. Skin, fatty tissue and fascia, a sheet of connective tissue that encloses muscles, cover it.
Soleus, another calf muscle, lies deep to gastrocnemius, meaning farther from the skin. Gastrocnemius covers much of the upper part of soleus, while soleus extends farther down the leg. Together, these muscles form the triceps surae, the main calf muscle group within the muscular system.
At the knee, the two heads of gastrocnemius form the lower borders of the popliteal fossa, the hollow behind the joint. The tibial nerve and popliteal blood vessels pass through this region, deep to the tissues forming its roof. Farther down, the broad gastrocnemius muscle narrows towards its tendon.
What are the two heads of gastrocnemius?
A head of gastrocnemius is a distinct upper portion of the muscle with its own attachment to the femur, or thigh bone. Gastrocnemius has medial and lateral heads: medial means towards the body's midline, while lateral means away from it.
The medial head of gastrocnemius forms the inner part of the calf and generally extends farther down the leg than the lateral head. The lateral head forms the outer part. Their fleshy portions converge as they descend, contributing to the characteristic rounded upper calf.
The two heads are parts of one muscle, not separate muscles with unrelated functions. Each contributes force to the shared tendon below, and both act across the knee and ankle.
Where does gastrocnemius originate and insert?
For gastrocnemius, the origins are the proximal attachments to the femur; the insertion is the distal attachment to the calcaneus through the calcaneal tendon. Both heads originate from the lower femur, close to the knee. A condyle is a rounded bony prominence at the end of a bone.
| Part or attachment | Anatomical location |
|---|---|
| Medial head of gastrocnemius | Posterior surface of the femur immediately above the medial condyle of femur |
| Lateral head | Lateral surface of the lateral condyle of the femur |
| Common insertion | Posterior surface of the calcaneus through the calcaneal tendon |
Fibres from the heads attach to an aponeurosis, a broad, flat sheet of tendon on the deep surface of the muscle. This continues downwards and joins the tendon of soleus to form the calcaneal tendon, commonly called the Achilles tendon. The tendon attaches to the calcaneus, the heel bone.
The attachments place gastrocnemius behind both the knee and ankle. This arrangement explains why contraction can influence both joints rather than only moving the foot.
What does gastrocnemius do?
Gastrocnemius produces plantarflexion at the ankle: it points the foot downwards or raises the heel when the foot is planted. It also assists knee flexion, which means bending the knee. Its main actions can therefore be summarised as:
- At the ankle: pulling on the heel through the calcaneal tendon to produce plantarflexion.
- At the knee: drawing its attachments towards each other to help bend the joint.
During walking, gastrocnemius contributes to raising the heel and pushing the body forwards as the foot leaves the ground. It also contributes to movements such as running and jumping, alongside soleus and other lower-limb muscles.
Knee position affects its mechanical action because gastrocnemius crosses the knee. Bending the knee shortens the muscle at its upper end, reducing its ability to contribute to forceful plantarflexion. Soleus does not cross the knee, so knee position does not shorten it in the same way.
What supplies gastrocnemius with nerves and blood?
The tibial nerve, a peripheral nerve of the nervous system, supplies gastrocnemius. Its motor fibres, which carry signals that activate muscle contraction, originate principally from motor neurons in the S1 and S2 spinal cord segments. They pass through the corresponding anterior spinal nerve roots, which connect the spinal cord to the spinal nerves.
Blood reaches gastrocnemius mainly through the sural arteries, muscular branches of the popliteal artery behind the knee. Branches enter the deep surfaces of the muscle heads. Accompanying veins carry blood away from the muscle.
How can you find gastrocnemius in the 3D model?
The atlas entry beside this article is anchored to the medial head of gastrocnemius, which is one part of the whole gastrocnemius described here. Its side-specific entries are the medial head of left gastrocnemius and the medial head of right gastrocnemius.
Rotate the model to a posterior view, looking from behind, and zoom towards the calf. Select the medial head, then isolate it or fade neighbouring structures to examine its position. Switching layers on and off can help distinguish the muscle's location from the surrounding skeletal structures.
Follow its position from the inner side of the knee towards the calf. Keep the distinction between part and whole in mind: selecting a medial head identifies that portion, not both heads of gastrocnemius.