biped

A biped is an organism or machine that moves primarily by means of two legs. The term combines the Latin bi- meaning two and pes or pedis meaning foot. In biology, bipeds include habitual walkers such as humans and many birds, as well as animals that stand or move on two legs at times. In engineering, a biped refers to a two‑legged robot or other device designed to walk on two legs.

Biological bipedalism has evolved in several lineages. In humans and other hominins, upright two‑leg locomotion arose in the Miocene–Pliocene, with early candidates about 6 million years ago. Birds are extant bipeds whose legs support body weight during walking, while their forelimbs have become wings. Theropod dinosaurs, such as Tyrannosaurus and Velociraptor, also used hind legs for bipedal movement. Bipedal posture often frees the forelimbs for manipulation or flight but places distinctive stresses on the pelvis, spine, knees, and ankles.

Biomechanics and energy use: A biped's center of mass is controlled by alternating leg stance and pelvic and knee movements. Walking tends to be energy‑efficient over distance, while running involves different muscle activation and balance strategies. Advantages include a greater field of view and the ability to carry objects; disadvantages include higher joint loading and a greater fall risk on uneven terrain.

Robotics and applications: Two‑legged robots, such as Atlas and other humanoid prototypes, illustrate ongoing work in biped locomotion. Challenges include maintaining balance on varied surfaces, planning stable gaits, and conserving energy. Progress relies on sensing, actuation, and control algorithms to achieve robust, versatile walking and running.