The breath was something I never really thought of until I started running and I found myself short of it. Once my legs were able to run continuously, I noticed that breathing controlled my experience of the run to a large extent. In the early days of running, I must have sounded like an elephant on fire as I huffed and puffed wondering if I was going to pass out of oxygen deprivation. Eventually, it started to get a little more settled. It is still the first thing to go when I am not watchful. In asana practice, I find myself holding my breath, especially when the poses are difficult. A constant refrain in class is to keep the throat passive and that is reminds me to breathe.
The act of breathing in yoga is widely different from that in running. It was easier to keep the two separate when I was running regularly. Breathing in asanas is through the nose and exhaling through the mouth while running gets me confused because my mind says one thing and the body demands another.
The more I am aware of my breath during the day, the more I see it as a dynamic and powerful force, something to be respectful of. Perhaps someday, some lifetime, I may be able to be one with the cosmic prana. Until then, it is practice, practice, practice.