How long can you hold your breath underwater? Humans have the smallest breath-holding capacity of all mammals and usually after three minutes of breath holding, most of us will pass out.
Free divers get a kick out of seeing how long they can stay down in the deep without the aid of breathing equipment. Free diver Tom Siestas holds the current world record for breath-holding a massive nine minutes and 58 seconds.
But what about the rest of us?
Dr Rochford has offered to learn the tricks of the trade from some of the best free divers in the business to discover their secret for staying underwater for so long.
Ernie Schultz is an old-timer at America's largest free diving club, the LA Fathomiers. If anyone can help, he can.
First, Andrew watches some pros to see how it's really done. They demonstrate a breathing technique where they build up oxygen in their body and then purge carbon dioxide out to allow them to extend their time underwater.
Both these guys would happily stay under for five minutes or more, but it takes years of training to get this good.
Dr Robert Banzett, a scientist at Harvard University, has been studying free divers for several years. His expertise is the field of breathlessness and he has done work with free divers to see if the way they hold their breath is to do with physiology or training.
"All of us have something called a maximum total lung capacity. When we breathe in and can't go any further, that's total lung capacity … these people [free divers] use their mouth to pump in more air after that," says Dr Banzett.
This breathing exercise allows free divers to add an additional one to two litres of air to their lungs so they can stay underwater for longer.
Before hitting the big seas, Andrew practices breath-holding in the training pool. Before Ernie's tips, Andrew could hold his breath for less than a minute.
First attempt:One minute.
Second attempt:A minute-and-a-half.
Third attempt:Two minutes.
"That's double what I did less than half an hour ago," says Andrew. "And my mind's convincing me I don't need to breathe."
Fourth attempt:Two-and-a-half minutes.
Ernie's tricks have made a huge difference, however the pool is relatively easy compared to open water.
Ernie and his crew take Andrew to Catalina Island, off the coast of Los Angeles, where dolphins surf and giant kelp float in the water it's a diver's paradise.
The water is only 15 degrees Celsius, so a wetsuit is definitely in order. Once the suit is on, there's only one thing left to do. Breathing, free diver style, before taking the plunge.
First dive:Free diving in the ocean, even at a depth of 10 metres, is nothing like the pool. Out there you have to tread water, the currents are playing havoc while at the same time you're trying to hold your breath.
Result: 45 seconds.
Second dive:On his second attempt, after warming up a bit to the cold, Andrew stretches his depth to 20 metres this time.
"It's so peaceful down here that I'm almost forgetting I need to breathe," Andrew says.
Result: one minute a 15-second improvement on last time.
It is possible to hold our breath for longer than three minutes with continued practice. Free divers all around the world hold their breaths for longer than three minutes.
While professional free divers have an increased tolerance for a huge drop in blood oxygen level, they also experience the same discomfort at the same time as untrained people when given increased doses of carbon dioxide.
"I have to say, this whole free diving thing has really blown me away. I think it also probably blows away the idea that humans have weak lungs and can only hold their breath for up to three minutes … yesterday, I was only holding my breath for a minute and then Ernie showed me a few tips and I was holding my breath for up to two-and-a-half minutes. It meant I could go down today and enjoy what was below the surface," says Andrew.
But please remember, the LA Fathomiers do everything under strict supervision and they're trained. So it's not something you should be trying by yourself.
- The problem for free divers is not actually holding their breath.
It's the risk of suffering a shallow water blackout losing consciousness from a carbon dioxide build-up in their blood and drowning as a result. According to Dr Banzett, "If you push it too far, you will run out of oxygen before you have the urge to breathe and that can cause brain injury or death, especially if you're underwater."
- Babies average over 50,000 breaths a day, for a 10-year-old, it's about 25,000, adults, about half as much again. The reason? It's all about size the smaller you are, the faster you breathe. Babies have faster metabolic rates than grown-ups as they need to take in more oxygen and breathe out more carbon dioxide.