I really identify with the phases and experience you describe above. The act of being engaged as your body moves through them is powerful.

Writer Haruki Murakami, a distance runner, was asked by an interviewer what we thinks about when he runs. Murakami responded that he basically doesn't think of anything. He runs not to think, but to _not_ think. That He runs specifically to create a void. (from his book "What I Talk About When I Talk About Running")

I would also encourage anyone who hasn't experienced this before: find an activity that demands this from you. You will learn a lot about yourself.