ScienceDaily (Sep. 16, 2005) — Despite having the bones and muscles to perform a variety of gaits, human beings have developed an overwhelming preference for just two: walking and running. Now, computer analysis that allows simulation of infinite two-legged locomotions has shown our favored modes of bi-pedal travel use the least amount of energy.

Indeed, in an article published in the current online edition of the British journal Nature, Cornell engineers Andy Ruina and Manoj Srinivasan compare the mechanics of walking and running with "many other strange and unpractised gaits." They used a set of computer models that simulated physical measurements such as leg length, force, body velocity and trajectory, forward speed and work.

"We wish to find how a person can get from one place to another with the least muscle work," they report. "Why do people not walk or even run with a smooth level gait, like a waiter holding two cups brim-full of boiling coffee?"

The engineers' computer simulations conclude that walking is simply most energy efficient for travel at low speeds, and running is best at higher speeds. And, they report, a third walk-run gait is optimal for intermediate speeds, even though humans do not appear to take advantage of it.

The findings help to explain why the possible--but preposterous--gaits in the Monty Python sketch, "Ministry of the Silly Walks," have never caught on in human locomotion. The researchers add that extensions of this work might improve the design of prosthetic devices and energy-efficient bipedal robots.

Human gaits can vary a great deal. This animation shows the two most common human gaits, walking and running. Movement of the center of body mass (superimposed) is shown in simplified versions of the two gaits. Cornell's Manoj Srinivasan and Andy Ruina used computer simulations to compare movement of the center of body mass in multiple other strange gaits with that of the human walk and run. They found walking to be the most energy efficient at low speeds and running the most efficient at high speeds. (Credit: Zina Deretsky, National Science Foundation)

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