 coming into your lungs and your brain is just being re-oxygenated the whole time. And the brain works much better if it's got oxygen. Every part of your body is working, but at a very low level. So it's not like running. Your brain is able to go another place. You're not having to think at all. Walking really lends itself to a more mindful state that I don't think you could do with any other form of physical movement.