Gastrocnemius: The gastrocnemius is a very potent superficial bipennate muscle that is in the back part of the lower leg muscles. It moves from its two heads just over the knee to the heel, a two joint muscle.
Origin: Lower posterior surface of the femur above the medial condyle. Lateral head from the lateral surface of the femoral lateral condyle.
Insertion: The two heads unite into a broad aponeurosis which eventually unites posterior surface of the calcaneus via the Achilles tendon, inserting in the middle 1/3 of the posterior calcaneal surface.
Function: Powerful plantar flexor of the ankle joint.
Nerve Supply: Tibial nerve (S1, S2).