The gastrocnemius muscle is a muscle located on the back of the lower leg, being one of the two major muscles that make up the calf. The other major calf muscle, the soleus muscle, is a flat muscle that lies underneath the gastrocnemius. Both the gastrocnemius and the soleus run the entire length of the lower leg, connecting behind the knee and at the heel. A third muscle, the plantaris muscle, extends 2.8 to 3.9 inches down from the knee and lies between the gastrocnemius and the soleus. The gastrocnemius branches at the top behind the knee, the two branches being known as the medial and lateral heads. The flexing of the muscle during walking and bending of the knee pulls on the femur, pulling it toward the tibia in the lower leg and causing the knee to bend. Both the gastrocnemius muscle and the soleus join to the Achilles tendon, the strongest and thickest tendon in the human body. The tendon starts approximately 5.9 inches above the heel, running down the center of the leg to connect to the heel below the ankle.
Written and medically reviewed by the Healthline Editorial Team
In Depth: Gastrocnemius