It’s late morning and I’m splayed out on a yoga mat on the parched lawn of a roadside public park in the foothills of the Sierra Nevada mountains. There’s a picnic table full of emergency medical technicians eating lunch to my right, an old man brown-bagging a tallboy beer on a bench to my left. Above me, the autumn sun is so clear and bright that it’s blinding, even through squinted eyes. I take a huge, heaving breath into the pit of my abdomen and let it out. I’ve been doing this for the past few minutes, and I can feel beads of sweat erupting on my forehead and face. I’ve got another half hour to go.

“Twenty more!” yells the man standing over me. I can barely hear him through the thunder of big rigs shifting gears on the highway behind us. His name is Chuck McGee III, and he’s a big dude with a sandy bowl cut, rainbow-lensed blade glasses, and cargo shorts that dangle just a few inches above white socks and dirt-baked sneakers. I’ve hired him for the day to help me redline my sympathetic nervous system with overbreathing.

So far it’s working. My heart is beating violently. It feels like there’s a rodent loose in my chest. I feel anxious and paranoid, sweaty and claustrophobic.

This must be the sympathetic overload. This must be Irritable Heart Syndrome coming on.

Breathing, as it happens, is more than just a biochemical or physical act; it’s more than just moving the diaphragm downward and sucking in air to feed hungry cells and remove wastes. The tens of billions of molecules we bring into our bodies with every breath also serve a more subtle, but equally important role. They influence nearly every internal organ, telling them when to turn on and off. They affect heart rate, digestion, moods, attitudes; when we feel aroused, and when we feel nauseated. Breathing is a power switch to a vast network called the autonomic nervous system.

There are two sections of this system, and they serve opposite functions. Each is essential to our well-being.

The first, called the parasympathetic nervous system, stimulates relaxation and restoration. The mellow buzz you get during a long massage or the sleepiness you feel after a big meal happens because the parasympathetic nervous system sends signals to your stomach to digest and to the brain to pump feel-good hormones such as serotonin and oxytocin into your bloodstream. Parasympathetic stimulation opens the floodgates in our eyes and makes tears flow at weddings. It prompts salivation before meals, loosens the bowels to eliminate waste, and stimulates the genitals before sex. For these reasons, it’s sometimes called the “feed and breed” system.

The lungs are covered with nerves that extend to both sides of the autonomic nervous system, and many of the nerves connecting to the parasympathetic system are located in the lower lobes, which is one reason long and slow breaths are so relaxing. As molecules of breath descend deeper, they switch on parasympathetic nerves, which send more messages for the organs to rest and digest. As air ascends through the lungs during exhalation, the molecules stimulate an even more powerful parasympathetic response. The deeper and more softly we breathe in, and the longer we exhale, the more slowly the heart beats and the calmer we become. People have evolved to spend the majority of waking hours—and all of our sleeping hours—in this state of recovery and relaxation. Chilling out helped make us human.

The second half of the autonomic nervous system, the sympathetic, has an opposite role. It sends stimulating signals to our organs, telling them to get ready for action. A profusion of the nerves to this system are spread out at the top of the lungs. When we take short, hasty breaths, the molecules of air switch on the sympathetic nerves. These work like 911 calls. The more messages the system gets, the bigger the emergency.

That negative energy you feel when someone cuts you off in traffic or wrongs you at work is the sympathetic system ramping up. In these states, the body redirects blood flow from less-vital organs like the stomach and bladder and sends it to the muscles and brain. Heart rate increases, adrenaline kicks in, blood vessels constrict, pupils dilate, palms sweat, the mind sharpens. Sympathetic states help ease pain and keep blood from draining out if we get injured. They make us meaner and leaner, so we can fight harder or run faster when confronted with danger.

But our bodies are built to stay in a state of heightened sympathetic alert only for short bursts, and only on occasion. Although sympathetic stress takes just a second to activate, turning it off and returning to a state of relaxation and restoration can take an hour or more. It’s what makes food difficult to digest after an accident, and why men have trouble getting erections and women often can’t experience orgasms when they’re angry.*

For all these reasons, it seems odd and counterintuitive to willingly place yourself in an extended state of extreme sympathetic stress, and to do this every day. Why make yourself light-headed, anxious, and flaccid? And yet, for centuries, the ancients developed and practiced breathing techniques that did just this.

The stress-inducing breathing method that brought me to this roadside public park is called Inner Fire Meditation, and it’s been practiced by Tibetan Buddhists and their students for the past thousand years. Its history begins around the tenth century AD, when a 28-year-old Indian man named Naropa got bored with domestic life. He divorced his wife, packed a bag, and walked northeast until he was surrounded by stone towers, pavilions, temples, and blue lotus trees. This dazzling place was Buddhist University Nalanda, and thousands of scholars from throughout the East gathered there to study astronomy, astrology, and holistic medicine. A few sought enlightenment.

Naropa excelled in his courses, mastering the lessons of Sutra and the secret techniques of Tantra, which had been handed down from one master to another over the millennia. He set out into the Himalayas to put everything he’d learned into practice, living inside a cave on the banks of the Bagmati River in what is now Kathmandu, Nepal. The cave was cold. Naropa harnessed the power of his breath to keep himself from freezing to death. The practice became known as Tummo, the Tibetan word for “inner fire.”

Tummo was dangerous. If used incorrectly, it could elicit intense surges of energy, which could cause serious mental harm. For that reason, it was reserved only for advanced monks and stayed in the Himalayas, locked up in the Tibetan monasteries for the next thousand years.

Fast-forward to the early 1900s, when a Belgian-French anarchist and former opera singer was making her way up to Tibet with soot on her face, yak fur woven into her hair, and a red belt around her head. Her name was Alexandra David-Néel, and she was in her mid-40s traveling alone through India—unheard-of at the time for a Western woman.

David-Néel had spent most of her life exploring different philosophies and religions. As a teenager, she’d hung out with mystics, starved herself, beaten herself, and followed diets used by ascetic saints. She was into Freemasonry and feminism and free love. But it was Buddhism that really fascinated her. She taught herself Sanskrit, then set out on a spiritual pilgrimage through India and Tibet that lasted 14 years. Along the way she happened into a cave high in the Himalayas, just as Naropa had done. It was there that a Tibetan holy man passed down the instructions for the superheating power of Tummo.

“[Tummo was] but a way devised by the Thibetan hermits of enabling themselves to live without endangering their health on the high hills,” wrote David-Néel. “It has nothing to do with religion, and so it can be used for ordinary purposes without lack of reverence.” David-Néel would rely on the practice over and over again to keep happy, healthy, and heated as she hiked for 19 hours a day in freezing temperatures without food or water, at elevations above 18,000 feet.

“Two more, make them good,” says McGee. I can’t see him—my eyes are still squinted—but I can hear him, heavy-breathing alongside me, cheering me on. I take another giant inhale, then roll the air up to my chest and exhale, like a wave. I’ve been doing this for what feels like five minutes. My hands are tingling and my intestines feel like they’re slowly uncoiling. I let out an uncontrolled moan.

“Yes!” McGee cheers. “Expression is the opposite of depression! Go for it!”

I moan a little louder, wiggle my body, and breathe a little harder. For a moment, I get self-conscious thinking about the EMTs and the ruddy-faced drunk nearby, who no doubt are watching the spectacle: the middle-aged city boys hyperventilating on a purple BPA-free yoga mat, both of us sounding like dedicated perverts.

This self-expression is an important part of Tummo, McGee said before we started. It reminds me that the stress I’m creating is different from the stress of, say, running late for an important meeting. It is conscious stress. “This is something you are doing to yourself—not something happening to you!” McGee keeps yelling.

The stress that Da Costa’s soldiers experienced was unconscious. The men had grown up in rural environments, outside the noise and crowds of the city. The more carnage they saw, the more their unconscious sympathetic responses kept building with no means of release. Eventually, their nervous systems were so overloaded that they short-circuited and collapsed.

I don’t want to short-circuit. I want to condition myself so I can remain flexible to the constant pressures of modern life.

“Keep going,” says McGee. “Get it all out!”

Professional surfers, mixed martial arts fighters, and Navy SEALs use Tummo-style breathing to get into the zone before a competition or black ops mission. It’s also especially useful for middle-aged people who suffer from lower-grade stress, aches and pains, and slowing metabolisms. For them—for me—Tummo can be a preventative therapy, a way to get a fraying nervous system back on track and keep it there.

Simpler and less intense methods of breathing slow, less, through the nose with a big exhale, can also diffuse stress and restore balance. These techniques can be life-changing, and I’d seen dozens of people changed by them. But they can also take a while, especially for those with long-standing chronic conditions.

Sometimes the body needs more than a soft nudge to get realigned. Sometimes it needs a violent shove. That’s what Tummo does.

That shove is still perplexing to the few scientists paying close attention to such phenomena. They ask: How exactly can conscious extreme breathing hack into the autonomic nervous system?

Dr. Stephen Porges, a scientist and professor of psychiatry at the University of North Carolina, has studied the nervous system and its response to stress for the past 30 years. His primary focus is the vagus nerve, a meandering network within the system that connects to all the major internal organs. The vagus nerve is the power lever; it’s what turns organs on and off in response to stress.

When perceived stress level is very high, the vagus nerve slows heart rate, circulation, and organ functions. This is how our reptilian and mammalian ancestors evolved the ability to “play dead” hundreds of millions of years ago, to conserve energy and deflect aggression when under attack by predators. Reptiles still access this ability, as do many mammals. (Imagine the limp body of a mouse in the jaws of a house cat.)

People “play dead,” too, because we share the same mechanisms in the primitive part of our brain stem. We call it fainting. Our tendency to faint is controlled by the vagal system, specifically how sensitive we are to perceived danger. Some people are so anxious and oversensitive that their vagus nerves will cause them to faint at the smallest things, like seeing a spider, hearing bad news, or looking at blood.

Most of us aren’t that sensitive. It’s much more common, especially in the modern world, to never experience full-blown, life-threatening stress, but to never fully relax either. We’ll spend our days half-asleep and nights half-awake, lolling in a gray zone of half-anxiety. When we do, the vagus nerve stays half-stimulated.

During these times, the organs throughout the body won’t be “shut down,” but will instead be half supported in a state of suspended animation: blood flow will decrease and communication between the organs and the brain will become choppy, like a conversation through a staticky phone line. Our bodies can persist like this for a while; they can keep us alive, but they can’t keep us healthy.

Porges found that patients who suffer Da Costa–like maladies such as tingling in their fingers, chronic diarrhea, rapid heart rate, diabetes, and erectile dysfunction are often treated for each of these symptoms with a focus on individual organs. But there’s nothing wrong with their stomachs, hearts, or genitals. What they often suffer from are communication problems along the vagal and autonomic network, brought on by chronic stress. To some researchers, it’s no coincidence that eight of the top ten most common cancers affect organs cut off from normal blood flow during extended states of stress.

Fixing the autonomic nervous system can effectively cure or lessen these symptoms. In the past decade, surgeons have implanted electrical nodes in patients that work as an artificial vagal nerve to restart blood flow and communication between organs. The procedure is called vagus nerve stimulation, and it’s highly effective for patients suffering from anxiety, depression, and autoimmune diseases.

But there is another, less invasive way Porges found to stimulate the vagus nerve: breathing.

Breathing is an autonomic function we can consciously control. While we can’t simply decide when to slow or speed up our heart or digestion, or to move blood from one organ to another, we can choose how and when to breathe. Willing ourselves to breathe slowly will open up communication along the vagal network and relax us into a parasympathetic state.

Breathing really fast and heavy on purpose flips the vagal response the other way, shoving us into a stressed state. It teaches us to consciously access the autonomic nervous system and control it, to turn on heavy stress specifically so that we can turn it off and spend the rest of our days and nights relaxing and restoring, feeding and breeding.

“You are not the passenger,” McGee keeps yelling at me. “You are the pilot!”

This was supposed to be biologically impossible. The autonomic nervous system, per its definition, was supposed to be autonomic, as in automatic, as in beyond our control. And for the past hundred years or so, this belief has held. In much of medicine, it still holds today.

When Alexandra David-Néel finally returned to Paris and wrote about Tummo and other Buddhist breathing techniques and meditations in her 1927 book, My Journey to Lhasa, few doctors and medical researchers believed the stories. Few could accept that breathing alone could keep a body warm in freezing temperatures. Fewer believed it could control immune function and heal diseases.

Through the twentieth century, interest in Tummo grew, and a flood of anthropologists, researchers, and seekers traveled to the Himalayas and came back reporting the same feats that David-Néel had been talking about. They told stories of monks wearing nothing but a single layer of clothes throughout the winter, heating themselves in frigid stone monasteries by day and melting circles in the snow around their bare bodies by night. Eventually, a Harvard Medical School researcher named Herbert Benson thought it might be time to put Tummo to the test.

Benson flew to the Himalayas in 1981, recruited three monks, hooked them up to sensors that measured the temperature in their fingers and toes, and then asked them to practice Tummo breathing. During the practice, the temperature in the monks’ extremities went up by as much as 17 degrees Fahrenheit and stayed there. The results were published the next year in the esteemed scientific journal Nature.

The videos and photographs taken during the Harvard experiments showed short men with satchels wrapped around flabby waists, their skin covered in a thick sheen of sweat, eyes half-closed and lost in a thousand-mile stare. The experiments added credence to what DavidNéel and Naropa and described, and yet Benson’s monks seemed even stranger than an anarchist opera singer or ancient mystic. It all seemed totally inaccessible to Westerners.

That would change by the early 2000s, when a Dutch man named Wim Hof ran a half-marathon through the snow above the Arctic Circle shirtless and in bare feet. Here was a Westerner who had a beard, thinning lead-colored hair, and a face pulled from a Bruegel painting. In short, he looked like every other middle-aged Northern European male. Hof hadn’t grown up in a cave in India or suffered from tuberculosis in a village hospital. He’d worked as a mail carrier and was a father of four.

Years earlier, Hof’s wife had taken her own life after years of depression. He had sought refuge from his pain by deepening his practice of yoga, meditation, and breathing practices. He unearthed the ancient technique of Tummo, honed it, simplified it, repackaged it for mass consumption, and began promoting its powers in a string of daredevil stunts that would have been quickly discounted if the media hadn’t been around to verify them.

Hof submerged himself in a bath filled with ice for an hour and 52 minutes, and he suffered no hypothermia or frostbite. Then he ran a full marathon in the Namib desert in temperatures that reached 104, without ever sipping a drop of water.

Over the span of a decade, Hof broke 26 world records, each more baffling than the last. These stunts earned him international fame, and his smiling, frost-covered face soon appeared on dozens of magazine covers, in flashy documentary specials, and in a handful of books.

“Wim violated the rules laid out in medical textbooks so drastically scientists had to pay attention,” said Andrew Huberman, a professor of neurobiology at Stanford University. Scientists paid attention.

In 2011, researchers at Radboud University Medical Center in the Netherlands brought Hof into a laboratory and started poking and prodding him, trying to figure out how he did what he did. At one point, they injected his arm with an endotoxin, a component of E. coli. Exposure to the bacteria usually induces vomiting, headaches, fever, and other flu-like symptoms. Hof took the E. coli into his veins and then breathed a few dozen Tummo breaths, willing his body to fight it off. He showed no sign of fever, no nausea. A few minutes later, he rose from the chair and got a cup of coffee.

Hof insisted he wasn’t special; neither were David-Néel or the Tibetan monks. Almost anyone could do what they all did. As Hof put it, we just had to “Breathe, motherfucker!”

He proved his point three years later, when Radboud University researchers brought in two dozen healthy male volunteers and randomly split them into two groups. Half the men spent the next ten days learning Hof’s version of Tummo while exposing themselves to cold, doing things like playing soccer shirtless in snow. The control group received no training. The two groups were brought back into the lab. Each was hooked up to monitors, then injected with the E. coli endotoxin.

The group trained by Hof were able to control their heart rate, temperature, and immune response, and stimulate the sympathetic system. This practice of heavy breathing along with regular cold exposure was later discovered to release the stress hormones adrenaline, cortisol, and norepinephrine on command. The burst of adrenaline gave heavy breathers energy and released a battery of immune cells programmed to heal wounds, fight off pathogens and infection. The huge spike in cortisol helped downgrade short-term inflammatory immune responses, while a squirt of norepinephrine redirected blood flow from the skin, stomach, and reproductive organs to muscles, the brain, and other areas essential in stressful situations.

Tummo heated the body and opened up the brain’s pharmacy, flooding the bloodstream with self-produced opioids, dopamine, and serotonin. All that, with just a few hundred quick and heavy breaths.

“One more,” says McGee. “Then let it all out and hold.”

I do as instructed, and listen as the rushing wind that was pouring through my lungs suddenly stops and is replaced by pure silence, the kind of jarring quietude a skydiver feels the moment a parachute opens. But this stillness is coming from inside. As I hold my breath longer, I feel a comforting heat spread across my body and face. I focus on my heart, rock to its vibrations. Each thump sounds and feels like the kick drum from the beginning of Black Sabbath’s “Iron Man.”

“Make the silence between your heartbeats last an eternity,” McGee says in a soothing voice.

After a minute or so, McGee directs me to take in a huge breath without exhaling, and to hold it again for 15 seconds, gently moving the air around my chest. At his order, I exhale and the cycle starts all over again “Three more rounds,” McGee says, his voice raising to a yell. “Be your own superpower!”

As I’m huffing again, I slide my focus to McGee, my cheerleader. He’d told me earlier how he’d been suddenly diagnosed with type 1 diabetes six years ago, at 33. His pancreas shut down and no longer produced insulin. Then he suffered chronic back pain, making him anxious and severely depressed. His blood pressure shot up.

McGee’s doctor gave him insulin injections to help stabilize his blood sugar, enalapril to lower his blood pressure, and Valium to ease the pain. “I was also taking four or five ibuprofen every day,” he said. But nothing really helped. He only got sicker.

McGee was like 15 percent of the American population—more than 50 million people—who suffer from an autoimmune disorder. In simple terms, these diseases are the result of an immune system that goes rogue and starts attacking healthy tissues. Joints become inflamed, muscles and nerve fibers waste away, rashes cover the skin. These ailments go by many names: rheumatoid arthritis, multiple sclerosis, Hashimoto’s disease, type 1 diabetes.

Pharmaceutical treatments, such as immunosuppressants, work by easing symptoms and keeping the patient more comfortable, but they do nothing to address the core malfunction in the body. Autoimmune diseases have no known cure, and even the causes are debated. An increasing body of research has shown that many are tied to dysfunction of the autonomic nervous system.

McGee’s awareness of alternative treatments began when a friend mentioned a short feature on someone named “the Ice Man” on Vice TV, the news and culture network. That night McGee tried Wim Hof’s heavy breathing technique. “For the first time in a long time, I slept peacefully,” he told me. He signed up for Hof’s ten-week video course, and within weeks watched as his insulin levels normalized, pain subsided, and blood pressure plunged. He quit taking enalapril and reduced his insulin intake by around 80 percent. He still took ibuprofen, but only a pill or two once a week.

McGee was hooked. He flew to Poland to attend an instructor retreat with Hof, where he and a dozen other students spent two weeks hiking up snowy mountains and swimming in freezing lakes. They breathed a lot. It never felt like a competition, McGee told me, or like some extreme fitness regimen. “Fight it. No pain, no gain. That’s all bullshit. That’s how you get hurt,” McGee explained. The point was to rebalance the body so that it could do what it is naturally adapted to do.

I’d heard dozens of these stories. Men, mainly in their 20s, who’d suddenly been diagnosed with arthritis and psoriasis or depression, who, weeks after practicing heavy breathing, no longer suffered any symptoms. Twenty thousand others in Hof’s community exchange blood work data and other metrics of their transformations online. The before-and-after results confirmed their claims. Some of these people were reducing inflammatory markers (C-reactive protein) 40-fold within just a few weeks.

“Doctors say this is more pseudoscience than science, that there’s no way any of this can be true,” McGee told me. And yet McGee and thousands of other heavy breathers kept showing profound improvements. They kept getting off medications they’d been on for years. They kept heating and healing themselves.

“You cannot copyright breathing, that’s part of it, and you can’t fault someone for the way they’ve learned,” said McGee. “All you can do is give information.”