Fitness instructors, you may have noticed, are always nattering on about breathing: "Breathe through the nose," "Control the breath," "Push up on the exhale."
There's a reason for that.
"Your breathing matches the level of activity," says David Hryvniak, a physical rehabilitation and medicine fellow at the University of Virginia Health System and team physician for several of the school's sports teams. "If you run and jump you will breathe through both your mouth and nose to get the proper amount to oxygenate the body."
This is not just a matter of getting enough oxygen to the lungs and other organs; oxygenating the body (in addition to things like carbohydrates) supplies a building block to the muscle cells to create energy to refuel the muscles.
"But if you are relaxing and really taking those deep belly breaths, then you can breathe through the nose," says Hryvniak, who is also a long-distance runner.
In fact, breathing deeply and fully can be key when relaxing and releasing tension, says Elliot Greene, a psychotherapist.
"Humans don't tolerate anxiety very well," says Greene, who specializes in the interconnectedness of the mind and body and uses massage therapy in his practice. "One of the ways we cope is to shut down."
That means "putting a lid on" or "choking on" our feelings -- both apt expressions since they can involve partially holding our breath, tensing the diaphragm and relying on shallow breathing, Greene says.
When we do all this, it has ripple effects throughout the body and mind, Greene says. Our shoulders hike up and our throats constrict -- we feel stuck physically and mentally, hardly a relaxed state.
On the flip side, if we breathe deeply and can release some of the built-up tension -- physical and emotional -- we feel better, Greene says.
"Taking deep chest and belly breaths can help us become 'unstuck,' " he says.
From an athletic standpoint, Hryvniak says, belly breathing is recommended because the abdominal muscles are stronger than the diaphragm and can help supply the body with oxygen more efficiently if they are engaged.
"We preach belly breathing" to our athletes, Hryvniak says, adding that breathing is part of athletic conditioning these days.
In many yoga styles, nose-breathing is emphasized for the very reasons Greene mentions -- the calming, releasing, relaxing effects of deep breaths through the nose.
But in Bikram (26 set poses bookended by breath work done in a room heated to 104 degrees Fahrenheit), the breath work at the beginning and especially the end features mouth breathing.
"Bikram is an energizing practice," says Lara Atella, a Bikram yoga instructor at Hot Yoga Capitol Hill in Washington. "And breathing through the mouth is more energizing."
The practice starts with what's called pranayama breathing (in through the nose and out through the mouth) and ends with kapalabhati breathing (quick mouth breathing).
Learning how to be aware and eventually to control our breathing, Atella says, can help slow down the heart rate and inhibit the release of adrenaline and cortisol -- stress hormones that can age us prematurely.
In essence, the breath not only helps us get the most out of the physical practice -- whether it's yoga or running -- but also helps shape up our insides.
"We tone our nervous system by how we breathe," says Atella, who has a background in neurobehavioral science at Johns Hopkins University.
One way to start becoming more aware of breath is to make a slight oceanlike sound in the throat -- in some yoga practices called "ujjayi breathing" -- making the breath a more tangible focal point.
"Natural deep breathing is like a wave," Greene says. "You focus on the exhale and then the [in] breath rushes in."
For athletes, though, the in-breath and the out-breath are not necessarily the same length or quite as instinctive as Greene describes.
Instead, for U-Va. runners, Hryvniak recommends breathing in for two strides and breathing out for one stride -- a "two-to-one pattern," he calls it.
Seem like a lot to coordinate?
"I recommend starting with easy runs where it is easier to control the breath," he says. "You slowly introduce the pattern and then it becomes routine."
For weightlifters and other power athletes, breath plays an important role, too. If they hold their breath -- which can happen -- they risk building up too much pressure in the chest cavity, Hryvniak says. This can lead to everything from hernias to, in rare cases, heart attacks.
"We recommend that you breathe deeply throughout the entire rep," Hryvniak says. Usually, the push or top exertion happens on the exhale.
To recap: Breathe through the nose for calm and focus; through the mouth and nose for high energy; let the breath flow to avoid chest cavity pressure; and use deep belly breath for effective oxygenation and mental release.
Boston is a fitness trainer and freelance writer. She can be found at www.gabriellaboston.com.