Lying prostrate on the ground with the rifle in his hands, eyes narrowed on his mark, Steve Kardian concentrated on not moving a muscle. "I need complete control for long-range shots; even one micro flinch can send the bullet flying feet from your target," he says. The FBI defense tactics instructor had been called upon by a top military agency to take on a classified secret service–like assignment—if he failed these qualifying tests the job was gone. Just before stepping up to the line, Kardian performed a deep diaphragmatic breathing exercise taught to him by his respiratory guru of two years, Belisa Vranich. "It brought a calm over me. I was able to maintain my positions and hit all my targets."

Kardian was so impressed with the changes Vranich's instruction wrought ("it lowers my blood pressure and heart rate, allows nervous excitement to leave me") that he referred his son-in-law, Michael DeBiase, 30, a competitive jiu-jitsu fighter, to her. "I kept running out of gas with a couple rounds left in the match because of how I was breathing; in certain positions, I couldn't get enough air." DeBiase performed Vranich's exercises while running errands, walking down the street, and at work. "After a few months I entered the NAGA World Championships and beat several black belts—as a brown belt. My classmates said I made it seem effortless."

For the past 15 years, Vranich, Psy.D., a clinical psychologist, has been teaching CEOs, SWAT units, DEA officers, and Carnegie Hall musicians the most basic of human functions—breathing. "I look at your dysfunctional, subpar breathing and completely dismantle it," she explains. Indeed, Vranich's method (detailed below) goes beyond simple eyes-closed inhales and exhales. Her aim is to overhaul students' involuntary respiratory patterns (how one subconsciously takes in oxygen) in the name of consuming more O2, which in theory keeps stress at bay and increases overall stamina. Now, with her new group "lung workout" offered at New York City's Willspace fitness studio, she's bringing better breathing to the masses. In the 55- or 90-minute classes, Vranich wraps measuring tapes around clients' torsos, pushes their stomachs with her hands, and assures them it's okay if they pass out or cry. (Both have happened before.)

Vranich isn't the first mental health professional to use the science of respiration to lower anxiety. Doctors K.P. Buteyko, M.D., and Stanislav Grof, M.D., Ph.D., pioneered breathing methods—Buteyko Breathing Normalization, which trains against hyperventilation (one in 10 adults suffers from it), and Holotropic Breathing, which operates through marathon sessions (three-plus hours) of deep breathing, respectively—both of which are taught nationwide. And popular among meditation acolytes is Conscious Connected Breathing—a method that uses continuous, rhythmic inhaling and exhaling to eliminate negative emotions.

"You can perform on caffeine and sugar for a while, but then the rock bottom you hit later starts to feel worse and worse," says Vranich. "When you give your system a huge bucketful of oxygen, that's the purest energy you can get." Vranich holds that students leave her class feeling like they've been on a mini vacation. "The brain is clear and focused, you're even-keeled and optimistic, you stop yawning and sighing."

Her clients concur: "I'm constantly traveling the country for work, sleeping in crappy hotels," says Cliff Byerly, 46, a former Marine and LAPD officer who is now the lead instructor for Blauer Tactical Systems. "I'll go into the frequent flyers' club, lay down in a corner, and listen to a 20-minute audio recording of Vranich's instruction. In a couple of minutes, I feel like I've slept for hours."

Even with regular respiration practice, in high-pressure situations panic can set in. "Recently a market position I took was really going against me; by noon I was down $40,000," says Gus Graber, 37, founder of Chicago trading group V Derivatives, who's been taking private Conscious Connected Breathing lessons for two years. "Usually I'd try to get all the money back in one day—even one trade. Horrible idea. I stepped out of the pit, centered myself with some breathing exercises, and by the closing bell cut our losses in half."

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Waiting to Exhale: Do's and Don'ts
It's not as simple as "in through your nose, out through your mouth." Here's how you should be breathing all day, every day to perform at your highest potential:

What Not To Do
Take a deep breath. Chances are your traps tightened, your shoulders shrugged, and your chest puffed out. That's all wrong, says Vranich. "Oxygen is cell fuel. If you breathe in a shallow, erratic, unbalanced way, your cells aren't getting the single most important thing they need," she says. Problem is that stress, too much time spent sitting, and ill-fitting pants compress stomachs and get men in the habit of respirating through their chests. The result: an out-of-whack oxygen-to-carbon dioxide ratio, which can slow down your nervous system, bring on anxiety and brain fog, and contribute to chronic fatigue, insomnia, even cancer. Plus, lifting your chest every time you inhale spurs muscle imbalances and poor posture.

What To Do
Lower your diaphragm and engage your intercostals (the muscles between your ribs that help the ribcage expand). Humans are designed to breathe through their entire lungs—which reach into the abdomen—not just the top 20 percent situated in the chest, as most people do. This enables more oxygen to reach cells and more carbon dioxide to leave them. Breathing this way also helps maintain a steady heart rate and prevents it from rising too rapidly in an overwhelming situation.