User:Cornyon/Walking

Origins of human walking
Data in the fossil record indicate that among hominin ancestors, bipedal walking was one of the first defining characteristics to emerge, predating other defining characteristics of Hominidae. [Judging from footprints discovered on a former shore in Kenya, it is thought possible that ancestors of modern humans were walking in ways very similar to the present activity as many as 3 million years ago.]

Today, the walking gait of humans is unique and differs significantly from bipedal or quadrupedal walking gaits of other primates, like chimpanzees. It is believed to have been selectively advantageous in hominin ancestors in the Miocene due to metabolic energy efficiency. Human walking has been found to be slightly more energy efficient than travel for a quadrupedal mammal of a similar size, like chimpanzees. The energy efficiency of human locomotion can be accounted for by the reduced use of muscle in walking, due to an upright posture which places ground reaction forces at the hip and knee. When walking bipedally, chimpanzees take a crouched stance with bent knees and hips, forcing the quadricep muscles to perform extra work and consequently costs more energy. Comparing chimpanzee quadrupedal travel to that of true quadrupedal animals has indicated that chimpanzees expend one-hundred and fifty percent of the energy required for travel compared to true quadrupeds.

In 2007, a study further explored the origin of human bipedalism, using chimpanzee and human energetic costs of locomotion. They found that the mass-specific energy costs expected for human walking travel is less than what would be expected for an animal of similar size and approximately seventy-five percent less costly than that of chimpanzees. Chimpanzee quadrupedal and bipedal energy costs are found to be relatively equal, with chimpanzee bipedalism costing roughly ten percent more than quadrupedal. The same 2007 study found that among chimpanzee individuals, the energy costs for bipedal and quadrupedal walking varied significantly, and those that flexed their knees and hips to a greater degree and took a more upright posture, closer to that of humans, were able to save more energy than chimpanzees that did not take this stance. Further, compared to other apes, humans have longer legs and short dorsally oriented ischia (hipbone), which result in longer hamstring extensor moments, improving walking energy economy. It was thought that hominins like Ardipithecus ramidus, which had a variety of both terrestrial and arboreal adaptions would not be as efficient walkers, however, with a small body mass A. ramidus had developed an energy efficient means of bipedal walking while still maintaining arboreal adaptations. Humans have long femoral necks, meaning that while walking, hip muscles do not require as much energy to flex while moving. These slight kinematic and anatomic differences demonstrate how bipedal walking may have developed as the dominant means of locomotion among early hominins based off of energy savings.

Biomechanics
[Human walking is accomplished with a strategy called the double pendulum. During forward motion, the leg that leaves the ground swings forward from the hip. This sweep is the first pendulum. Then the leg strikes the ground with the heel and rolls through to the toe in a motion described as an inverted pendulum. The motion of the two legs is coordinated so that one foot or the other is always in contact with the ground.] While walking, the muscles of the calf contract, raising the body’s center of mass, while this muscle is contracted potential energy is stored. Then gravity pulls the body forward and down onto the other leg and the potential energy is then transformed into kinetic energy. The process of human walking is able to save approximately sixty-five percent of the energy used by utilizing gravity in forward motion.