alt=An 1887 stop-motion of a human walking.|thumb|upright=.65|Human walking cycle thumb|Computer simulation of a human walk cycle. In this model the head keeps the same level at all times, whereas the hip follows a sine curve. 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 can save approximately sixty-five percent of the energy used by utilizing gravity in forward motion.
alt=An 1887 stop-motion of a human walking.|thumb|upright=.65|Human walking cycle thumb|Computer simulation of a human walk cycle. In this model the head keeps the same level at all times, whereas the hip follows a sine curve. 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 can save approximately sixty-five percent of the energy used by utilizing gravity in forward motion