Breath literally indicates how much oxygen you have to work with. Breath
differs from movement in that it indicates how much air you are getting in
proportion to how fast you're moving. The faster you move, the more oxygen
you require. At some critical point your muscles will be consuming more
oxygen than you are able to take in. If this happens your breath will
reach 0, and you will have to slow down. Note that breath regenerates
much faster than movement.
Mounts will allow you to move faster as horses and the like have very large
lungs and are built for moving quickly. If you move too fast and run totally
out of breath you will fall.
See Also: MOUNTING PROMPT