HAMBURG — Nobody can take a deeper breath than Tom Sietas.
The 31-year-old German has blown away the competition in the nascent sport of “free diving,” in which people vie to see how long they can hold their breath underwater. Thanks to a large set of lungs and advanced training techniques, Sietas has pushed the boundaries of physical endurance far beyond what was thought possible.
Doctors once assumed brain damage was certain for anyone whose respiration stopped for more than three or four minutes. And yet, on June 7, in a swimming pool in Athens, Sietas submerged himself underwater for 10 minutes and 12 seconds, shattering the world record by more than a minute.
Sietas, a lanky fellow who stands 6-foot-4 and weighs 165 pounds, doesn’t appear any worse for the wear. “I’m a pioneer in my sport,” he said in an interview, relaxing at a cafe at this river city in northern Germany.
He’s taking a short break from training these days after a busy summer. In September, he sat in a plexiglass tank of water on the stage of “Live With Regis and Kelly” in New York and vied for the record in a slightly different category, in which he was allowed to soak up pure oxygen beforehand. This time, he held his breath for 17 minutes and 19 seconds before he bobbed to the surface.
“Tom, are you okay?” a nervous Kelly Ripa asked her German guest as he opened his mouth to gulp in fresh air.
“Much better,” he replied with a smirk.
In July in Hamburg, he set the world record for swimming the longest distance underwater without taking a breath: 700 feet, or almost nine lengths of the pool.
Like other extreme sports, free diving has exploded in popularity in recent years, attracting an estimated 10,000 competitors to organized events.
The sport draws on a long tradition of underwater breath-holding, including Asian pearl divers who swim to depths of 100 feet to harvest oysters and abalone. Even today, most free divers prefer to test their limits in the freedom of the ocean, instead of indoor pools.
Sietas discovered the sport in 2000 on a trip to Jamaica. He was scuba diving but was constricted from pain in his ears that got worse the deeper he went. Instructors taught him how to equalize the inner-ear pressure, a trick that worked so well he ditched his scuba tanks and began testing how deep he could go.
“I was so happy,” he said. “I could go down 15 to 20 meters” — 50 to 65 feet — “and the whole undersea world was just so wonderful.”
His scuba instructors noticed that he had a talent for holding his breath. They provided a little coaching. By the end of his vacation, Sietas was going without air for more than four minutes.
“I was like, ‘Whoa, if you put some effort into it, Tom, you could be really good,’ ” he recalled.
Back home in Hamburg, he began training with other free-diving aficionados. It wasn’t long before he was attracting attention. In 2004, he smashed the world record for underwater breath-holding (without extra oxygen) with a mark of 7 minutes 48 seconds.
Sietas attributes his success to a strict training regimen that he has developed himself. It is a combination of strength exercises, endurance workouts and concentration tactics. When he is submerged, he goes completely limp and blanks his mind to lower his heart rate and conserve energy.
“I have a strong will and a strong discipline,” he said.
Elite free divers also rely on an advanced technique called “lung packing,” by which they force extra air into their lungs by inhaling through the mouth and swallowing at the same time.
Sietas said he has developed other breathing patterns as well but is reluctant to divulge his secrets for competitive reasons. “I don’t want to share all my knowledge,” he said.
Sietas is also blessed with an above-average pair of lungs. But doctors who have examined him said they aren’t as large as you might expect: about 15 percent bigger than an average person of his height.
Kay Tetzlaff, a physician from Freiburg, Germany, who has examined Sietas and other free divers as part of an ongoing study, said they are able to expand their normal lung capacity by almost 50 percent through lung packing.
“That, of course, is enormous,” Tetzlaff said. “These guys have some features that make them come closer to diving birds and mammals.”
Some, like Sietas, also benefit from high levels of hemoglobin in their blood, which enables them to absorb oxygen more efficiently.
Although free diving can be a risky sport, especially for those who practice in the depths of the ocean, Tetzlaff said it is difficult to hurt yourself by holding your breath. Rising levels of carbon dioxide in the blood send signals to the brain that make it almost impossible to withstand the urge to breathe.
Overcoming that urge is the biggest challenge for free divers. Given that Sietas has exceeded the 10-minute mark for static apnea — the technical term for holding your breath without moving — Tetzlaff said it was hard to calculate the limits of what is humanly possible.
“I have to admit, I don’t know, honestly,” said Tetzlaff, who directs respiratory clinical research for Boehringer Ingelheim Pharmaceuticals. “Ten minutes is incredible. Maybe you could do another couple of minutes. I can guess that might be possible.”
Sietas said he is careful not to push himself too far when free diving. He said he has never lost consciousness, although he came close a couple of times early in his career.
For now, Sietas is thinking about shifting his focus to deep diving and is contemplating training in the Red Sea or Mediterranean.
But he is also fiercely protective of the records he has set and served notice that he would aggressively respond to any challengers.
For example, he said, he was interested in the notion of a televised competition with David Blaine, the American illusionist and stuntman who held his breath for 17 minutes 4 seconds on “The Oprah Winfrey Show” in April. That marked a world record in the category that allows entrants to breathe pure oxygen beforehand. Sietas broke it five months later.
“David, of course, is a showman, but he’s also a very great athlete,” Sietas said. “It would make very dramatic scenery if we went head-to-head, but I am the better diver. I am very sure of myself.”