I read this somewhere on another forum...
If you're like most people, when you run, you exhale as your right foot hits the ground. This puts downward pressure on your liver (which lives on your right side), which then tugs at the diaphragm and creates a side stitch, according to The Doctors Book of Home Remedies for Men. The fix: Exhale as your left foot strikes the ground.
I've taught myself to breathe every 3rd stroke when swimming and inhale every 3rd step when running (taking two steps to exhale). By alternating sides it helps to prevent the side aches and is an excellent way to train your body to be more effecient with breathing.
However if you're tired enough to have to breathe every other step when running, make sure to exhale on the left foot.
