This is the first in a series where Paul Charman looks at New Zealand freediver William Trubridge, his unusual sport and what he must do to set a world record – and cheat death.

William Trubridge, holder of 15 world freediving records and fast-emerging sports hero, enters a sinkhole in the Bahamas, descends the equivalent of 25 storeys into near total darkness, collects a token clipped to a rope, then gracefully frog-kicks up to the light.

His underwater swimming looks ethereal, even godlike. It's all there - symbolic death, burial and resurrection. Plus there's the tantalising prospect of setting a new world record.

Or maybe drowning.

On December 3, the former Hawkes Bay resident will attempt to add an extra metre to his unassisted 101-metre record set in 2010.

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But how does he do it - holding his breath underwater for an insane four-plus minutes; a time that would mean loss of consciousness and even death for most of us?

The answer is that there is both science and a touch of spirituality about the sport. When I called him, Trubridge was relaxing with wife Brittany at their home on rustic Long Island, in the Bahamas.
He'd turned my first call down as he was cooking the couple's dinner, mainly fish (speared by Trubridge) and vegetables out of the garden.

"No sugar, meat or processed foods," he says, pointing out that even his meals are geared towards his freediving. They'd just completed a special high alkaline meal (plenty of carbohydrates, no meat or sugar) designed to offset the acids which build up in Trubridge's body.

They stem from massive amounts of carbon dioxide which flood his bloodstream during dives. That is just one of the obstacles which freedivers must overcome through training and technique.

Trubridge admits surprise at his sport is growing so much in popularity; some claim it's now the fastest growing underwater sport. He has attracted mainstream sponsorship from Steinlager Pure for his world record attempt - with senior brand manager Michael Taylor pointing out that Trubridge is "an amazing New Zealander doing outstanding things on a world stage" as well as being a snug fit with Steinlager's brand values: "No unnecessary ingredients, just absolute simplicity at its best, from the world's purest place."

Trubridge moved to the Bahamas nine years ago, to train regularly in the sinkhole - Dean's Blue Hole, the best freediving spot in the world. At 202 metres, this is the deepest limestone shaft of its type, providing freedivers consistently warm, calm and clear water, free of sharks and jellyfish.

"It's hard for me to put myself in other people's shoes when they see freediving, I've been immersed in the sport for so long," says Trubridge. "I suppose there's something other-worldly about it all. I mean, we pretty much spend all our lives in the gas element. This is the only sport completely immersed in liquid, while not carrying the equivalent of an roomful of air strapped to your back.

"Maybe that's what makes it so alien to our normal concept of life, so fascinating to watch."

He got serious about extreme freediving in his mid-20s but the appeal began a lot earlier. Born in north England, he spent most of his boyhood sailing the world with his parents and brother, Sam, and, while passing through Vanuatu, the boys egged one another on to dive down 15 metres to the bottom of the reef.

"We wore that achievement like a badge of honour in front of the other kids."

Their heroes were their dad, who could clear an anchor chain at 20m, and a mysterious Tahitian sailor who could do 40m.

"You have to confront yourself, dealing with your instincts for survival and urge to breathe - and on a deep dive even more so. So you're in touch with self-preservation but with your environment as well.

"You're a natural participant in the underwater world and there's a great attraction for that these days. It helps people appreciate their environment and leads them to want to safeguard it and prevent doing large scale damage to the seas."

Getting started may not be hard as people assume, says Trubridge, who runs a freediving school for novices and advanced athletes. Assuming reasonable fitness and swimming ability, wannabe divers generally manage 20-25 metres, or more, after a week-long course.

"Most people can learn techniques of breathing, relaxation and equalising (pushing air into the middle ear so water pressure does not burst the ear drums)."

Most can swim with fins to get down to reasonable depths. After that it becomes a question of development techniques so divers swim more efficiently and use less oxygen.

"The next stage is about developing your resistance to high carbon dioxide levels and low oxygen, the mental aspects of it, staying relaxed and calm despite the urge to breathe."

Freedivers develop flexibility of lungs to accommodate the pressure changes. They cope with high levels of lactic acid in their muscles and the potential confusion of nitrogen narcosis at depth. More aspects are taught piece by piece as they confront greater depths. Trubridge does yoga and meditation to help him to slow his system down, and thus use less oxygen, during dives.

One key is "the breath up", time spent breathing before the dive. If done correctly, this maintains a safe level of carbon dioxide within the body, vital for retaining the urge to breathe.

The stakes are high, as hyperventilation which eliminates the carbon dioxide from the body, could lead to the diver blacking out and drowning.

Trubridge aims to maximise oxygen within his blood through relaxation ahead of each dive, while maintaining a healthy level of carbon dioxide.

He says guidance and training is essential: "In my view this sport is extremely safe, because of the knowledge and techniques we learn, the training we do and safety measures we have in place.
"But if you don't know what you're doing, it could be highly dangerous."