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Bipedal locomotion is walking, running, and standing on two legs (as opposed to four). It is a process requiring complex interaction of mechanical and control-system characteristics. Humans are capable of performing such motion because their spines are s-curved and their heels are round. Whether such a system has evolved in an animal species or been engineered in a robot, many of the same issues are inevitably involved.
Energy-efficient means of standing bipedally involve constant adjustment of balance, and of course these must avoid overcorrection.
Efficient walking complicates these issues, as it entails tipping slightly off-balance forward and to the side, and correcting balance with the right timing.
Running is an inherently continuous process, in contrast to walking; a bipedal creature or device, when efficiently running, is in a constant state of falling forward, that is maintained as relatively smooth motion only by repeatedly "catching oneself" with, again, the right timing, but in the case of running only delaying the nearly inevitable fall for the duration of another step.
The phenomenon of "tripping" is also informative in this regard. One popular way to think of it is as having one's leg pulled out from under them. In fact, however, merely stopping the movement of one leg of a walker, and merely slowing one leg of a runner, is sufficient to amount to tripping them. They were already falling, and preventing the tripped leg from aborting that fall is sufficient to literally "drop them like a sack of dirt".
Engineers who study bipedal walking describe it as a repeatedly interrupted fall.
Many animals, including humans, have evolved bipedalism, with anatomical adaptations constituting the required mechanical systems and neurological adaptations the control-system ones.
As to anatomy, contrast in domesticated poultry the meaty drumstick and thigh, against measures like the assertive flavors that Buffalo-wing recipes use to "dress up" the small and bony wing. The technique of power-lifters highlights the similar difference in dimensions, even in untrained humans, between the muscleskeletal muscle Muscle is one of the four tissue types. The other three types are: epithelium, connective tissue and nervous tissue. The primary purpose of muscle tissue is to contract. Muscle contraction is used to move parts of the body, as well as to ms of the thigh and the upper arm. This difference is extreme: the large muscle in the human upper arm is the bicepsBiceps is a Latin term that means two heads''. It describes muscles that are made up of two distinct parts. In general usage, biceps usually refers to biceps brachii. The biceps brachii is the prominent muscle on the upper arm, and are associated with str, which bends the arm at the elbow; few people know the name of, or pay any attention to, the muscle that is used to straighten the arm; the quadricepsThe quadriceps femoris commonly the 'quadriceps', is a large muscle in the thigh, composed of the sections rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. External link . and hamstringIn human anatomy, the hamstrings are a group of muscles on the underside (posterior aspect) of the thigh. They are responsible for flexion of the knee, and all attach proximally to the ischial tuberosity. Because they attach to part of the hip, they also muscles of the thigh are both so crucial to bipedal activities, that each alone is much larger than even a well-developed biceps.
The famous knee jerk (or patellar reflexThe patella or kneecap is a thick, triangular bone which articulates with the femur and covers and protects the front of the knee joint. It develops from the tendon of the Quadriceps femoris muscle, which contracts to straighten the leg. The patella incre) emphasizes the necessary bipedal control system: the only function served nerves involved being connected as they are is to ensure quick response to imminent disturbance of erect posture; it not only occurs without conscious mental activity, but also involves none of the nerves which lead from the leg to the brain.
A less well-known aspect of bipedal neuroanatomyNeuroanatomy is the anatomy of the nervous system. In vertebrate animals, the routes that the myriad nerves take from the brain to the rest of the body (or "periphery") and the internal structure of the brain in particular are both extremely elaborate. can be demonstrated in human infants who have not yet developed toward the ability to stand up. They can nevertheless run with great dexterity, provided they are supported in a vertical position and offered the stimulus of a moving treadmill beneath their feet.
Human walking is composed of several separate processes: