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.