Mathematics proves the walk

Manoj Srinavasan and Andy Ruina, researchers in applied mechanics at New York's Cornell University, drew up a geometrical model of human walking and running.They found that, in essence, each leg is a "telescoping actuator" that can change its length.In walking, the body vaults forwards in circular arcs, driven forward by the pendular swing of the legs, with the toe and heel providing the push-off and landing point for each movement. In running, though, the body travels from one parabolic arc to the next, with a bounce in between.Srinavasan and Ruina then factored in the metabolic cost of three drains on energy on both movements.These are the energy expenditure required to keep the body's basic functions ticking over; the cost of swinging the legs; and the cost incurred when a leg is in contact with the ground.Their equations showed emphatically that walking and running are the most energy-efficient gaits for our species, honed by millions of years of evolution.