The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.
Legs are used for standing, walking, jumping, running, kicking, and similar activities, and constitute a significant portion of a person's mass.
In human anatomical terms, the leg is the part of the lower limb that lies between the knee and the ankle, the thigh is between the hip and knee and the term "lower limb" is used to describe the colloquial leg. This article generally follows the common usage.
The leg from the knee to the ankle is called the cnemis /'niːmɪs/ or crus. The calf is the back portion and the shin is the front.
Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually guided manipulation and the lower limb's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. The human adaption to bipedalism is not limited to the leg, however, but has also affected the location of the body's center of gravity, the reorganisation of internal organs, and the form and biomechanism of the trunk.