Are you a new runner? Are your legs just fine, but you just can't seem to control your breathing? Are you frustrated by more experienced runners who appear to run with little effort and with unlabored breathing that seems as normal as if they were standing still? You’re not alone. Most new runners experience the same frustration. Just know that many experienced runners also struggled with the same breathing issues when they first started.
Your body needs a good deep inhalation in order to get oxygen deep into the lungs where it can be transpired from the alveoli into the bloodstream. Better oxygenated blood means more oxygen getting to the muscle where it's used to make energy. More energy means more endurance.