Well, the answer to the initial question is kind of obvious I think: running is less efficient (for the same speed) because when running more of your energy goe

Well, the answer to the initial question is kind of obvious I think: running is less efficient (for the same speed) because when running more of your energy goes into vertical motion (jumping from one foot to the other) than into horizontal motion. Of course, above certain speeds walking just isn't "feasible" anymore, but running will never be as efficient as walking at the optimal speeds for walking. ...but if you want the most efficient way to travel only with the power of your own muscles, you need a bicycle :)