Mind you, our backs and feet suck for pretty much everything.

I tend to think that apparent effect comes from habitual misuse of the body.

It's possible that millions of years of mammalian evolution could have just screwed-up and puked-out some creature that was mal-adapted everywhere but somehow took-over the earth. But I suspect that what's happening is that human are pretty adapted to many activities but we are so darn flexible to we put themselves in situations even beyond our adaptability.