A British woman pushed the boundaries of human endurance to new levels yesterday as she dived 96 metres (314ft) below the surface of the Atlantic and back again on a single, very deep, breath.

Sara Campbell — “part woman, part fish” — broke the world record in the extreme sport of freediving, whose participants dice with death by submerging themselves to lung-crushing depths without breathing apparatus.

Holding her breath for three minutes 36 seconds, she went deeper than any female freediver has gone before without weights or equipment to hasten her descent, or an airbag to speed her back to the surface.

“The dive felt great and I’m just feeling fantastic,” she said last night. “At one point I started feeling negative thoughts — ‘Do I really want to do this?’ — but then I told myself not to be ridiculous, just get it done, go for the bottom.

“For me, that’s really what the personal battle was all about — fighting my demons and overcoming my doubts.”

Ms Campbell, 37, caught the freediving community by surprise in 2007 when she broke three world records in 48 hours while still a novice, having taken up the sport only nine months earlier.

The death of her mother forced her to drop out of competition last year, allowing her Russian rival, Natalia Molchanova, to take her titles.

Last night, at the Vertical Blue competition off Long Island in the Bahamas, Ms Campbell snatched back her crown in the constant weight discipline, which requires freedivers to descend and return using only the power of their own bodies and a mermaid-like fin attached to their feet.

“My mother died ten days before I was due to attempt two more world records last year. I was with her when she died and one of the last things she said to me was, ‘Go back out there and get those records’,” Ms Campbell said.

“I know I made her ridiculously proud and of course there’s a part of me that wanted to continue to make her proud and to finish off a promise I made to her.” The former PR woman and yoga instructor from Wandsworth, South London, reclaimed her constant weight record at a 202-metre underwater cavern off Long Island known as Dean’s Blue Hole — the deepest “blue hole”, or sinkhole, in the world. Her feat outstripped beat Ms Molchanova’s performance last year by one metre.

Also known as Mighty Mouse because of her diminutive 4ft 11in frame, Ms Campbell has been studied by doctors to try to understand her extraordinary physiology. Her lungs are 25 per cent larger than an average person of her size and weight, allowing her to pack more air into her system before she descends.

She also relies on a natural physical instinct called the mammalian dive reflex, which sustains the body under water by helping respiration and withstanding the pressures of the deep. Coupled with strength and breathing techniques — Ms Campbell does special breathing exercises for four minutes before she dives — freedivers can use the reflex to plunge deeper, and for longer, than others. The world record for a person holding their breath under water while static is 10 minutes 12 seconds.

The heartbeat slows, which reduces the amount of oxygen required by the body. As the diver pushes deeper, and the water pressure increases, the blood vessels constrict, diverting blood away from the extremities, pushing it harder to the lungs, brain and heart. That helps to prevent the lungs from total collapse as they are crushed to the size of oranges by the external pressure, although by the time the diver nears the surface again the lungs are screaming for air.

“Before I started freediving I had the same fear of deep water that a lot of people have,” Ms Campbell said.

“The idea of suddenly being at 50 metres without air, of course that’s a terrifying prospect, like finding yourself at the top of a ski-jump when you have never even put skis on before. But it’s a gradual progression — you train your mind and your body and it can be done safely.”

Ms Campbell will return to the water in four days’ time in an attempt to conquer her record with a 100-metre plunge. “It’s a big number, but I believe I have it in me,” she said.

Even the best freedivers can suffer blackouts as they near the surface and the blood vessels return to normal, suddenly slowing the flow of oxygen to the brain. “About 15 metres from the top I was starting to feel like I might be drifting off and I had to really focus on contracting my body, trying to keep the oxygen supply to my brain going, just trying to keep that grip on reality,” she said.

In 2002 the world record holder for weight-assisted freediving, Audrey Mestre, of France, died after she was stuck under water for more than eight minutes at a depth of 171 metres in the Caribbean when an air balloon that should have shot her back to the surface malfunctioned.

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