Deep: Freediving, Renegade Science, and What the Ocean Tells Us About Ourselves

by James Nestor

Scholander noticed something else: Once his volunteers were underwater, the blood in their bodies began flooding away from their limbs and toward their vital organs. He’d seen the same thing happen in deep-diving seals decades earlier; by shunting blood away from less important areas of the body, the seals were able to keep organs like the brain and heart oxygenated longer, extending the amount of time they could stay submerged. Immersion in water triggered the same mechanism in humans. This shunting is called peripheral vasoconstriction, and it explains how Bucher could dive to below one hundred feet without suffering the lung-crushing effects that Boyle’s law had predicted. At such depths, blood actually penetrated the cell walls of the organs to counteract the external pressure. When a diver descends to three hundred feet—a depth frequently reached by modern freedivers—vessels in the lungs engorge with blood, preventing them from collapse. And the deeper we dive, the stronger the peripheral vasoconstriction becomes.

Scholander found that a person need submerge only his face in water to activate these life-lengthening (and lifesaving) reflexes. Other researchers tried sticking a hand or a leg in the water in an attempt to trigger the reflex, but to no avail. One researcher even put volunteers into a compression chamber to see if pressure alone would trigger a similar diving reflex. No dice. Only water could trigger these reflexes, and the water had to be cooler than the surrounding air. As it turns out, the tradition of splashing cold water on your face to refresh yourself isn’t just an empty ritual; it provokes a physical change within us.

Scholander had documented one of the most extreme transformations ever discovered in the human body, a change that occurred only in water. ...

Prinsloo insisted that there was more to freediving than descending along ropes and trying to beat your opponents. “It offers a stillness,” she told me on the boat, a kind of full-body meditation that could be found nowhere else. And there was no need to force yourself down to three hundred feet to find it. The most incredible transformation, she said, happened at around forty feet down. There, the force of gravity seemed to reverse; the water stopped buoying your body toward the surface and instead started pulling you deeper. This was the “doorway to the deep,” where everything changed, and anyone could pass through it—even

I ask about the convulsions. She explains that the body responds to extreme breath-holding in three stages. Convulsions are the first-stage response. “You start reacting not from the lack of oxygen, but from the buildup of carbon dioxide,” she says. “When that starts, it’s just a caution that you’ve only got a few minutes to go before you really need to breathe.” The second-stage response occurs when the spleen releases up to 15 percent more fresh, oxygen-rich blood into the bloodstream. This usually occurs only when the body goes into shock, an extreme state whose symptoms include low blood pressure, rapid heartbeat, and organ shutdown. But it also happens during extreme breath-holding. A freediver anticipates the spleen’s delivery of fresh blood, feels it happen, and uses it as a turbo-charge to dive even deeper.

The third-stage response is the blackout, which happens when the brain senses that there’s not enough oxygen for it to support itself and so shuts off, like a light switch, to conserve energy. Though the brain represents only about 2 percent of the body’s weight, it uses 20 percent of the body’s oxygen. The presence of liquid in the mouth or throat triggers another reflexive line of defense: the larynx automatically closes, stopping water from entering the lungs. Freedivers learn to sense the arrival of convulsions and spleen release, and they know exactly when to head back to the surface so the third-stage blackout won’t occur. A freediver survives by understanding and respecting these mechanisms.

The “doorway to the deep,” he said, was open to everybody. Those who’d reached the doorway described it in quasireligious terms—transcendent, life-changing, purifying. A new and shimmering universe. Getting there didn’t require rupturing lungs or tearing a larynx. All you needed was a little training. All you needed was faith. All you needed was a certain level of comfort with voluntary asphyxiation.

In 1958, during one of his first dolphin experiments, Lilly recorded a click-and-whistle conversation between dolphins and played it back at a slower rate. When he adjusted the frequency and speed of these dolphin sounds in water to match human speech in air, he found the ratio worked out to 4.5:1. This was a remarkable discovery. Sound travels 4.5 times faster in water than in air.

Humans share this electricity. Every cell in your body contains an electrical charge. Any time you look at something, hear a sound, feel, taste, or think, a storm of electrical discharges explodes inside your cells, going back and forth from your brain to different areas in your body at four hundred feet per second.

This electricity travels by way of a series of circuits called ion channels, tiny proteins in the membranes of cells. These channels can permit or block the flow of electrically charged ions through them.

Think of your nerves as rivers, and your brain as a lake into which all those rivers empty. Ion channels work like little dams to control the flow and direction of signals to and from the brain. You have somewhere in the neighborhood of thirty-five trillion cells in your body, each with its own ion channel, opening and closing in synchronicity to give you a se...

When a nerve fires an impulse, a significant amount of electricity is produced. According to Oxford University geneticist and author Frances Ashcroft, the electric field through the ion channel is ...

A human body generates around 100 millivolts (a measure of potential energy). If all the electricity in a person’s body could be harnessed and converted to light, the human body would be sixty thousand times brighter than a comparable mass of the sun. Pound for pou...

In Chinese medicine, the body’s electric energy is referred to as chi; the Japanese call it ki, and Indians know it as prana. The medical traditions of these eastern cultures are, in large part, based on adjusting the amount of energy in certain areas of the body to promote or restore health.

That nagging, need-to-breathe feeling you get holding your breath is triggered not by oxygen deprivation but by buildup of CO2. Comfort with this buildup is what separates good freedivers from great ones, or good ones from guys like me. Freedivers condition their bodies to tolerate high levels of CO2 using timed breath-hold exercises called static tables. Essentially, it’s interval training. Breathe two minutes, take four huge breaths, hold breath for two minutes; breathe one and a half minutes, take four huge breaths, hold for two and a half minutes, and so on.

One of the best surface-training methods is so-called walking apnea, which involves holding your breath and walking over a soft surface (in case you pass out) for extended distances. The idea is that the oxygen your muscles use when you’re walking slowly is about the same amount of oxygen muscles use during a freedive. You start by holding your breath while standing still for about thirty seconds until you feel your heart rate decrease, then you walk slowly in a straight line, turn around when you feel you’ve reached your halfway point, and walk back to your starting place. The distance you travel is about how far you’d be able to hold your breath during a deep dive.

When the average person tries to equalize his ears, he puffs out his cheeks and blows hard, so that compressed air enters the sinus cavities that lead to the ears. This method, called the Valsalva maneuver, is used by about 99 percent of the population, and it’s usually effective. But it doesn’t work when you’re freediving past around forty feet. As you dive deeper, air becomes more and more compressed in the lungs, until there isn’t enough left to push into the ears. The Valsalva method becomes useless.

Over ten minutes, he guides me through some exercises that include coughing a T sound and groaning with my mouth shut. Both act on the epiglottis, the fleshy flap that covers the windpipe, so that I can open and shut it at will. Next, Harty shows me how to “puke” air up from my stomach and “jackhammer” it with my tongue into the sinus cavities. By trapping air in my head (instead of the Valsalva method of pushing it up from the lungs), I’m able to shuffle air back and forth between the sinus cavities and release pressure in a fraction of a second. Once I get it, it works every time. The maneuver is as awkward as it sounds and nearly impossible to explain if you don’t have someone showing it to you, which is why Harty offers his private Skype sessions.

As we ride, Prinsloo shares some maxims, a kind of Ten Commandments of freediving: Freediving is more than just holding your breath, it’s a perception shift. Don’t kick down the doorway to the deep; slide in on your tiptoes. Never, ever dive alone. Always enter the ocean in peace with yourself and your surroundings.

The freediving I learned from Prinsloo, Buyle, Schnöller, Gazzo, and the ama was the opposite of this egocentric, numbers-driven approach. To this group, freediving was about connecting with the underwater environment, looking more keenly at your surroundings, focusing on your feelings and instincts, respecting your limits, and letting the ocean envelop you—never forcing yourself anywhere for any reason. This was a spiritual practice, a way of using the human body as a vessel to explore the wonders in the Earth’s inner space.