In humans, the gastrocnemius muscle (plural gastrocnemii; Latin, from Greek γαστήρ “stomach” and κνήμη (knēmē) “leg”; meaning “stomach of leg” (referring to the bulging shape of the calf) is a very powerful superficial bipennate muscle that is in the back part of the lower leg. It runs from its two heads just above the knee to the heel, a two joint muscle.