Imagine yourself exercising: running, hiking, dancing, lifting weights — whatever you like to do. Picture yourself pushing to a maximum intensity. Now, ask yourself: Are you breathing out of your nose or your mouth?

If you are like most exercisers, you breathe through your mouth, especially as the intensity of the exercise mounts. But experts are learning that breathing through the mouth may not be as efficient or effective as breathing through the nose.

The nose is built with a specific purpose: to support our respiratory system (the primary purpose of the mouth, on the other hand, is to start the digestive process). The nostrils, hair and nasal passageways are designed to assist in filtering allergens and foreign bodies from entering the lungs. The nose also adds moisture and warmth to inhaled air for smoother entry to the lungs.

Nasal breathing, as opposed to mouth breathing, has another important advantage, especially for effective and efficient exercise: It can allow for more oxygen to get to active tissues. That is because breathing through the nose releases nitric oxide, which is necessary to increase carbon dioxide in the blood, which, in turn, is what releases oxygen. Mouth breathing does not effectively release nitric oxide, which means the cells are not getting as much oxygen as through nasal breathing, which could lead to fatigue and stress.

A recent study demonstrated this. The study tested 10 runners, male and female alike, who for six months had used nasal-only breathing while exercising. Participants were put through standardized testing, once with nasal breathing and then with mouth breathing, to compare their maximum oxygen intake rates. They were also tested for various other respiratory and exercise markers, including oxygen and carbon dioxide levels while exercising.

Their maximum rate of oxygen consumption did not change from nasal to mouth breathing. But the study found that the runners’ respiratory rate, breaths per minute and ratio of oxygen intake to carbon dioxide output decreased during nasal breathing. The researchers said this is probably because of the lower breath rate used during nasal breathing, which allows more time for oxygen to get to the bloodstream.

Hyperventilation through the mouth, i.e., the quick and hard breaths through the mouth that so many of us take when exercising at high intensity or feeling stressed, causes the body to offload more carbon dioxide, making it harder to oxygenate our cells. In intense moments, nasal breathing is the ideal way to oxygenate our systems.

Nasal breathing also activates the part of the nervous system that supports rest, recovery and digestion, rather than the part of the nervous system that is responsible for survival or stress states, such as flight or freeze. That means that, even if the body is in a stressful state of high-intensity exercise, nasal breathing can provide a sense of calm and allow us to function better.

“It’s incredibly difficult to learn or process anything in survival mode,” says Brian Mackenzie, author, athlete and founder of the Art of Breath, a program that teaches how to use breathing to optimize athletic performance. “We are now understanding some of the deeper layers to managing stress, which has direct impact on not only the general population, but is at the heart of how elite performers can optimize performance.”

So, if nasal breathing helps us stay relaxed and improves our athletic performance, how can we do more of it?

First, pay attention. Do you more often breathe through your nose or mouth during the day? What about while exercising, especially as the workouts get more difficult? Notice what is happening with the breath as well as what it feels like to pay attention to the breath.

Now consider practicing nasal breathing. Close the mouth and relax the tongue and jaw. Start by simply nasal breathing during warmups and cool-downs with workouts. Then try experiencing daily life while breathing through the nose.

Some people who mouth-breathe during sleep try “mouth taping,” putting specially designed tape over their lips to assist with nasal breathing.

Once you have your groove and are consistently nasal breathing, check for potential differences in these areas.

Emotional state: Nasal breathing should lead to a more relaxed state. (When life is stressful, and you note that you are mouth-breathing, try switching to nasal breathing and inhaling slowly and deeply.)

Exercise performance: At first, high-intensity exercise may feel more difficult with nasal breathing. The body needs to adapt to a different approach to the respiratory process, and if it is used to hyperventilation during exercise, nasal breathing may feel a bit slow at first. Things will shift. Be patient.

Exercise recovery: Because nasal breathing is more efficient, recovery should be smoother.

Immune system: Nasal breathing is a major line of defense against airborne pathogens. The mouth has no defense system. You may experience improvements with overall breathing and decreasing allergies or colds.