In humans, the gastrocnemius muscle ( /ˌɡæstrɒkˈniːmiəs/ or /ˌɡæstrəˈniːmiəs/; Latin, from Greek γαστήρ “stomach” and knēmē “leg”; meaning “stomach of leg”, referring to the bulging shape of the calf) is a very powerful superficial pennate muscle that is in the back part of the lower leg.