What is the most energy efficient speed to walk at?

Most cars have a specific speed at which, all things being equal, getting from A to B uses up the least petrol. But what’s the optimum speed for human walking? I can imagine that there could be slight variations for each individual, but I’m still interested to know if in general walking extremely slowly is, for instance, more efficient than going at a normal pace…

My understanding is that it varies based on the length of your legs and it’s based on how your leg naturally swings as a pendulum. There’s probably a formula to determine it using on leg length.

So the short answer is it depends. I’ll let someone more knowledgeable give the long answer.

The Master speaks:

[QUOTE=Cecil Adams]
Analyses of the biomechanics of walking vs. running suggest that walking is a more efficient gait except at higher speeds. The crossover point is somewhere around 5 mph, varying with the individual.
[/QUOTE]

As fast as possible, if you consider being chased by a lion as expending all your energy into becoming food.