Only time I'm satisfied with the 'nature intended us to' argument is some combination of walking/running. The way a good, smooth runner's body flows when they hit a fast jog screams to me "my skeletal and muscular structure was built for this!" Otherwise, yeah, as best I can tell adaptability is our only real designed-in-feature.

We're not as fast as most animals out there, but I don't think that means we didn't run a lot in prehistory.