I'm no athlete, just get around town on foot a lot. Even on sidewalks with no baggage, running at a medium pace with a springy step seems less tiring. If I'm w

I'm no athlete, just get around town on foot a lot. Even on sidewalks with no baggage, running at a medium pace with a springy step seems less tiring. If I'm wrong about that, at least it's obviously easier to run downhill. When walking, it can even take more effort vs flat. But when running, by definition both feet leave the ground at some points, so you have less friction and can let gravity do its thing.