In humans, the leg is the lower limb, which is attached to the trunk at the pelvis by the hip joint. Its major bones are the femur, passing from the hip to the knee, and the tibia and fibula, which pass from the knee to the ankle joint, where the leg articulates with the foot. The legs are concerned with maintenance of posture, walking, running, and jumping. The powerful muscles of the buttock, pelvis, and thigh act about the hip and knee joints, while calf muscles act via the Achilles tendon across the ankle on the foot.