Brainiac on the human gait

OK, so I had to call Brainiac anyway for some help with the upcoming quiz. Could he kindly answer a question that came up Saturday?

"What now?" he growled. Brainiac clearly doesn't think much of the topics that consume us as we swill our post-run beers.

"Is it true that humans are more efficient at walking than running?" I asked.

"Of course it is, you moronic humanoid. Who would have thought otherwise?"

"Well, since you ask, it was Stick Insect."

"Bah," he sputtered. "He's the one not drinking any alcohol this month?"

"That's right." I said.

"Then tell him to get back on it. He's losing it."

For a more precise answer, here is a graph showing energy consumption during walking and running at various speeds. The vertical axis is calories expended per mile per 100 lbs. of body weight. As you can see, the most efficient way to cover ground is walking at a pace of around 3.5 mph (roughly 5.5 kph).

This of course is opposite to most other large mammals, and is attributed mainly to the geometry of human feet. As one study put it, "the human gait adapted for efficient walking at the cost of efficient running."

And bicycles? On level ground, anywhere from three to five times more energy-efficient than walking.