How can you dive 700 feet in one breath?

Extreme Sports Image Gallery  Freedivers can hold their breath for minutes on end. See more pictures of extreme sports.
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Actually, if you're a confirmed landlubber, what you're probably wondering is: What would possess anyone to dive deep into the ocean without an oxygen tank in the first place? If humans were meant for such activity, we'd have gills and finned extremities, wouldn't we?

Well, what might seem like an impossible, watery nightmare to ordinary mortals is merely a challenge to an elite breed of aquatic athletes known as freedivers, who've trained their bodies and minds to function underwater for long periods without taking a breath. Freediving's Michael Phelps equivalent is a 39-year-old Austrian named Herbert Nitsch who is capable of going without a gasp of air for more than nine minutes straight and who has held 22 world records recognized by the International Association for the Development of Freediving (AIDA), the sport's governing body [source: Beyond Limits]. In 2007, Nitsch shattered his own world record in the ultimate "no-limits" category, in which divers are permitted to use a ballast to help them descend. He reached a depth of 702.1 feet (214 meters), according to AIDA stats. To get a sense of the magnitude of his feat, imagine submerging a 58-story skyscraper and then swimming down to the first-floor lobby.

But Nitsch isn't satisfied with being the closest thing we have to a real-life Aquaman. He hopes eventually to descend to 984 feet (300 meters). That's nearly as deep as the most accomplished scuba divers in the world are able to go -- with oxygen [source: Monroe].

So how is it that freedivers are able to dive so deep and last so long without taking a breath? One reason is the diving reflex, an evolutionary adaptation that enables seals and dolphins to dive deep and stay underwater for extended periods by slowing and/or shutting down some physiological functions. As scientists have discovered, even though humans evolved on land, we've retained a trace of that reflex, too. Freedivers have learned to push self-induced apnea -- the scientific term for going without breathing -- to new extremes through sophisticated mind-body control techniques similar to those employed by meditating yogis and martial artists.

So, what's the science behind holding one's breath? Are we really part dolphin?

Freediving History

People started diving into deep water and making like dolphins thousands of years ago, long before they understood exactly why they had the ability to do it. Ancient Greek divers weighted themselves down and descended to depths of 100 feet (30.5 meters) or more to pluck sponges from the sea bottom. In Japan and Korea, traditional female freedivers known as Ama have long collected edible seaweed and clams at depths of 65 feet (19.8 meters) or more [source: Hanna]. Because coastal dwellers have been freediving for many generations, you might suspect that they've developed special genetic traits that make them better at it than inlanders. But scientists who've studied them say there's no evidence of that [sources: Focazio].

All humans do share an evolutionary adaptation with air-breathing aquatic animals that makes it possible for them to dive and swim underwater for a while without taking a breath. In 1870, French physiologist Paul Bert observed that ducks had an amazing ability to slow their heart rate if they were forced to stay underwater. Scientists went on to discover that immersion in cold water -- or even simply holding your breath -- triggers something called the diving reflex, which the body uses to conserve life-giving oxygen. When the reflex kicks in, your pulse slows and your circulatory system constricts, and blood is shunted away from your muscles, skin and visceral organs, guaranteeing that your heart and brain get first dibs [source: Bove].

For years, scientists believed that humans were capable of enduring without oxygen for only a few minutes and that they couldn't dive deeper than 164 feet (50 meters), because the pressure would shrink their lungs and crush their rib cages. But in the 1960s and 1970s, divers disproved that myth. As it turns out, a phenomenon called blood shift causes the lungs to fill with plasma, preventing collapse [source: AIDA New Zealand]. Learn how freedivers put blood shift to work on the next page.

Freediving Today

In 1976, French diver Jacques Mayol became the first human to descend to (328 feet) 100 meters [source: Independent]. Mayol, who studied Indian yoga and the breathing techniques of kung fu-practicing Shaolin monks, adapted those mind-body control methods to slow his pulse from 60 to 27 beats per minute underwater, enabling him to dive deeper and longer. In doing so, he revolutionized freediving and paved the way for Herbert Nitsch's generation of divers to push the limits even further.

It's fairly easy to get into freediving. It doesn't require a lot of expensive equipment -- a wet suit for warmth, a mask and a set of special flippers designed for underwater efficiency can be had for less than $1,000. And according to freediving expert and author Terry Maas, with competent instruction and a little practice, novices quickly can learn to stay under for 45 seconds, long enough to descend as far as 30 feet (9.1 meters) and experience the ocean from a startlingly new angle [source: Maas].

But going without oxygen for longer periods and diving to serious depths isn't for dabblers. Elite divers must endure rigorous training to develop their lung capacity and control their pulse rates. They also utilize special safety equipment, such as balloon systems to help them return to the surface more quickly.

Even then, tragedies sometimes occur. In 2002, elite French diver Audrey Mestre was attempting to set a no-limits depth record off the coast of the Dominican Republic, when equipment malfunctions apparently kept her underwater too long. She lost consciousness during her ascent and perished [source: IAFD]. Another French champion freediver, Loic Leferme, died off the south of France in 2007 when his ascent rope became snagged [source: Dive Magazine].

Learn more about water sports and other adventurous activities by clicking through the links on the next page.

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