[ultrarunner]

Imagine if your shoes had some sort of linear bearing system that would allow you to glide over the ground, preventing energy loss while allowing brief rest periods.

I don't know if I can even satisfactorily define running itself on the spot, but I'm pretty sure I know it when I see it.

[hermitdev]

I think you could succinctly define running as a motion similar to walking, except only one foot has contavt with the ground at the time.