If you want to run comfortably in middle and long distance running, it is most important to distinguish the running stage and speed. At the beginning of running, or when the speed is slow, the oxygen demand is small, and only breathing through the nose can meet the oxygen demand. If the temperature is low or you run against the wind, you should breathe through your nose, so that the gas entering your lungs can be heated and humidified by nose hair and nasal mucosa, thus avoiding diseases such as cough, tracheitis, abdominal pain (people often say it is a fork) and stomach cold caused by inhaling dust and bacteria.
When running for a long time or at a high speed, it is difficult for nasal breathing to meet the body's need for oxygen. If you only breathe through the nose, it is easy to make the respiratory muscles tired. At this time, open your mouth to cooperate with breathing and relieve the pressure on the respiratory muscles.
Of course, it is not good to open your mouth completely. It is best to open your mouth slightly, grind your teeth gently, roll up the tip of your tongue, and gently press your palate to let air in and out through your teeth. Pay attention to even and rhythmic breathing, exhale short and forcefully, inhale slowly and evenly, and the depth is appropriate.