This Is What Happens To Your Heart When You Dive Into The Sea

    James Nestor, author of DEEP: Freediving, Renegade Science, and What the Ocean Tells Us About Ourselves, takes us on a transformative journey into the ocean.

    The next time you're at the beach your body will undergo the most profound transformation you can naturally experience. This is not a psychic prophecy; I don't have precognition. The transformation I am describing will be physical, and it will be real. It's the result of millions of years of human evolution, a trigger of ancient genes which you and all other humans share with billions of other deep-diving animals.

    It looks something like this: You will be lying on the sand. Your skin will be warmed by the sun. You will become hot and thirst for a swim in the ocean. You will pick yourself up and stroll to the water's edge, wade calmly into the lapping waves, and jump in. The moment your face submerges in the sea's salty waters, a Hulk-like metamorphosis will trigger. Blood will begin rushing from your hands and feet, up your legs and arms, and into your core; your heart rate will reflexively lower 25% its normal rate; your mind will enter a meditative, almost dreamlike-state. If you choose to dive deeper, the transformation will grow more profound until you bear only a passing resemblance to your terrestrial form. You will become a water animal — a fish, essentially.

    Scientists call this transformation the mammalian dive reflex or, more lyrically, the Master Switch of Life. They've been researching it for the past 50 years.

    The term Master Switch of Life describes not one but many switches, or reflexes, that are spurred when we enter the water. These reflexes affect the brain, lungs, and heart, among other organs, they work in concert with other triggers in the body to protect us from the immense underwater pressure of deep water and turn us into efficient deep-sea-diving animals. The equivalent pressures of such a deep dive on land would kill or injure us, but not in the ocean. The ocean has different rules, and often requires a completely different mindset to truly comprehend.

    Freedivers — those athletes who dive without the aid of any mechanisms, using only a single breath of air — understand the Master Switch better than anyone. In the past decade, they've used these reflexes to dive down to unthinkable depths. In the 1950s, scientists predicted that the deepest a human could dive and survive was 100 feet. Any deeper and the lungs would suffer a fatal collapse. Since then, freedivers have dived more than 700 feet; competitive freedivers regularly plummet to 300 feet. After just an hour or two of instruction, many beginners can plummet down 60, 70, even 100 feet. These divers aren't special; each of us is imbued with the Master Switch. We need only get in the water and dive and let our bodies do the rest.

    Here's what happens when we dive deep.

    In the first 30 or so feet underwater, the lungs, full of air, buoy your body toward the surface, forcing you to paddle as you go down. You feel the pressure on your body double at 33 feet underwater. At this depth, the contracting air will shrink your lungs to half their normal size. As you keep diving, at about 40 feet, you enter a gravityless area in the water column that freedivers call the "doorway to the deep." Here, the ocean stops pulling you up the surface and begins pulling you down. You place your arms at your sides in a skydiver pose, relax, and effortlessly drift deeper.

    At 100 feet, the pressure triples. The Master Switch kicks in harder. Your heart rate reflexively beats even slower. This will help you conserve oxygen, which will allow you to dive deeper for longer. Heart rates of freedivers below 100 feet can plummet below half their normal resting rates. Some divers have recorded heart rates as low as 14 beats per minute, about a third the rate of a person in a coma; some freedivers have even reported heart rates as low as seven beats per minute. (The average resting heart rate for most humans is between about 60 to 100 beats per minute.) According to physiologists, a heart rate this low can't support consciousness. And yet, somehow, deep in the ocean, it does.

    Around 300 feet, a depth reached often by freedivers, the walls of your organs and vessels, working like pressure-release valves, allow the free flow of blood and water into the thoracic cavity. Your chest collapses to about half its original size. During a dive in 1996, Cuban freediver Francisco Ferreras-Rodriguez's chest shrank from a circumference of 50 inches at the surface down to 20 inches by the time he reached his target depth of 436 feet. The Master Switch shifts into overdrive.

    As you ascend to 200 feet, 150 feet, 100 feet, the Master Switch slowly reverses its effects: The heart rate increases, and the blood that flooded into your thoracic cavity now floods back out into your veins and arteries and organs. Your lungs reinflate with air. You become a land animal again.

    When diving under your own power, in your natural state, the human body cannot get decompression sickness. The "bends" and other ailments like oxygen toxicity often associated with deep diving are the result of modern technologies. There are no "deco" stops in freediving; a freediver in her natural form, using no additional equipment, can ascend from depth as quickly as she wants and remain perfectly healthy. The human body reflexively processes the uptake of dangerous gases that occur at depth; we've known how to do this for, perhaps, millions of years. We are all born with this ability. We are, truly, born to dive.

    We're also born of the ocean. Each of us begins life floating in amniotic fluid that holds a 99% similar chemical composition to seawater. Our earliest characteristics are fishlike. The month-old embryo grows fins first, not feet; it is one misfiring gene away from developing fins instead of hands. At the fifth week of a fetus's development, its heart has two chambers, a characteristic shared by fish.

    Human blood has a chemical composition 98% similar to seawater. An infant will reflexively breaststroke when placed underwater and can comfortably hold his breath for about 40 seconds, longer than many adults. We lose this ability only when we learn how to walk.

    Dolphins, whales, seals, and other marine mammals also share the Master Switch, and use it to dive to astounding depths. Sperm whales, for instance, can plummet to more than 9,000 feet on dives that last about 90 minutes; some seals can hold their breath for over an hour and dive to depths of 2,500 feet. Scientists witnessed that these animals seem to gain oxygen the deeper and longer they dive; according to our understanding of physics and mammal physiology, this is impossible. And yet these animals do it all the time. And still, nobody quite understand how. (Again, the ocean has different rules, requires a different mind-set to comprehend.)

    Ancient human cultures knew all about the Master Switch and employed them for centuries to harvest sponges, pearls, coral, and food hundreds of feet below the surface of the ocean. European visitors to the Caribbean, Middle East, Indian Ocean, and South Pacific in the seventeenth century reported seeing locals dive down more than one hundred feet and stay there for up to 15 minutes on a single breath. These reports were considered exaggerations or outright fabrications for the last few hundred years.

    Today, the world record underwater breathhold is now more than 12 minutes, just three minutes shy of the "fabricated" reports of ancient sailors. If we continue at our current rate, humans will break the 15-minute mark by 2017.

    The ocean not only changes us physically, but psychically.

    In a world of 7 billion people, where every inch of land has been mapped, much of it developed, and too much of it destroyed, the sea remains the final unseen, untouched, and undiscovered wilderness, the planet's last great frontier. There are no mobile phones down there, no emails, no tweeting, no car keys to lose, no terrorist threats, no birthdays to forget, no penalties for late credit card payments, and no dog shit to step in before a job interview. All the stress, noise, and distractions of life are left at the surface. The ocean is the last truly quiet place on Earth.

    Those who dive deep in the ocean get a glassy look in their eyes when they describe their experiences; it's the same look one sees in the eyes of Buddhist monks or emergency room patients who have died and then been resuscitated minutes later. Those who have made it to the other side. And best of all, the divers will tell you, "It's open to everyone."

    Literally everyone — no matter your weight, height, gender, or ethnicity. In Japan, women in their seventies dive deep in the ocean to harvest urchins, seaweed, and abalone for hours a day, every day. The women, called ama, have been diving this way since their early teens, carrying on tradition of freediving that is many thousands of years old. Diving deep in the ocean does not sap their energy; the ama believe it gives them life. Some ama dive into their eighties.

    You don't need to dive to 300 feet, hold your breath for 12 minutes, or be 80 years old to feel the human connection to the ocean. You simply need to get wet. A two-second jump into the ocean triggers the Master Switch. You will feel the effects immediately — your body will relax, pulse will soften, and stress will dissipate. You will feel changed. This is the feeling of your body reacting to the life-changing energy of the largest living mass on the planet.

    It's a reminder that you've made it back home.


    James Nestor is a San Francisco-based journalist and author of DEEP: Freediving, Renegade Science, and What the Ocean Tells Us About Ourselves.

    For more about DEEP, click here.