One of my pet theories is that regular exercise strengthens your core muscles and allows you to recruit those core muscles more effectively. This is what allow

One of my pet theories is that regular exercise strengthens your core muscles and allows you to recruit those core muscles more effectively. This is what allows the diaphragm to expand more and thus facilitates deeper breathing. More oxygen per breath, and fewer heartbeats required to circulate it through the bloodstream. Could be total rubbish, but I'd be interested to see a study either way.