Death-defying free dives push boundaries

In an extreme sport in which divers reach great depths on one breath, records are being broken and doctors are surprised by feats never thought possible

The following script is from "Free Diving" which aired on Jan. 13, 2013, and was rebroadcast on Aug. 18, 2013. Bob Simon is the correspondent. Michael Gavshon, producer.

Ever tried to hold your breath for as long as you can? Most of us have. Well this is a story about people who hold their breath for a really long time and dive down to depths never even approached before.

As we reported last January, the sport is called free diving and it involves going down hundreds of feet into cold and dark waters on one single breath. It's considered an extreme sport because it is very dangerous. It's an experimental sport because it is revealing human capabilities which had never even been imagined, forcing medical scholars to rewrite their textbooks on human physiology. It's becoming more popular every year and our story might encourage more people to try it. Or not.

Free diving has been around a very long time. Homer and Plato wrote about it. It was how the ancient Greeks went down for sponges. Without so much as a snorkel, they'd dive to around 100 feet. Today's free divers go down a lot further for fun and sport. They want to join the sea world without disturbing it. No tanks, no bubbles, no noise. Yes, that is a shark but it seems friendly enough. The diver, New Zealander William Trubridge has become just another guy in the neighborhood.

Trubridge is also a world champion in the competitive sport of free diving. Here, he is getting ready to dive 331 feet, twice the height of the Statue of Liberty on a single breath. He'll be doing this just with his arms and legs no fins to help him.

This film -- with the music -- was produced by his team. Going down is the easy part. After 70 feet, he's loses buoyancy and gets pulled down by gravity alone.

He reaches his target, collects a tag to prove that he got there and goes into reverse for the hard part: getting back up.

His body is craving oxygen but he goes up slowly and gracefully as if he were doing a water ballet.

He was underwater four minutes and 10 seconds.

A new world record: 331 feet. That's 101 meters. Five years ago the record was 80 meters.

Bob Simon: Five years ago, did anyone think it was possible to go down 100 meters?

William Trubridge: When the record was 80? I don't think so. I don't think anyone realistically thought it was going to happen or at least not soon.

Bob Simon: Isn't there a certain limit of underwater that's just-- you can't go beyond it without dying?

William Trubridge: Definitely. It's out there but there's no way of kind of knowing exactly where it is. It's just deeper than we are now, we know that much.

And because of free diving, scientists now know that humans are closer to dolphins than had been thought. Just like dolphins, when we go into cold water a reflex kicks in which slows down our pulse; shifts blood from our extremities to our heart and to our brain. Our spleen contracts releasing oxygen rich blood into our arteries.

Is under the water a place humans belong? Free divers think so. They point out that the amniotic fluid in the womb where a fetus lives for nine months is very similar to seawater. That if a newborn is immediately submerged in a pool it will swim the breaststroke and be able to hold its breath for 40 seconds. It will retain this ability until it learns how to walk. Then it's all over.

Tanya Streeter: We're physiologically designed to hold our breath underwater. We're not designed to breathe underwater.

During her career as a free diver Tanya Streeter held 10 world records. She had gone down deeper than any man. The key to her success, she says, is her ability to equalize the pressure underwater so her eardrums don't burst.

Tanya Streeter: As you dive, the pressure of the weight of water around you increases. And it pushes your eardrums in and in and in. And you have to push air into the Eustachian tubes to be able to pop the eardrums out to equalize that pressure. I mean it hurts. I've described it as an elephant sitting on my chest, stabbing hot pokers in my eardrums.