The lungs work harder to absorb this oxygen out of the air. You get out of breath. If you count breaths in and out and discover you are breathing with a different rhythm, don't worry about it. Adjusting your breathing pattern will not make you a better runner. The same with whether you breathe through your nose or your mouth.
Most runners naturally breathe through both.
Breathe through your nose. Suck the air in through your ears, if you can. Your jaw should be relaxed, your mouth slightly open. The oxygen will come through your nose and mouth to your lungs, to your blood and to your muscles without you needing to give it a lot of thought. We'd like to send you a FREE weekly email newsletter.