0:00:23 > 0:00:26In my quest to find real-life superhumans,
0:00:26 > 0:00:28I've taken to the depths.
0:00:30 > 0:00:33Human beings like you and me are able to explore this amazing
0:00:33 > 0:00:37underwater world using breathing equipment, like this scuba gear.
0:00:38 > 0:00:42But imagine being able to be down here for minutes at a time
0:00:42 > 0:00:44without any breathing equipment at all.
0:00:47 > 0:00:52You'd need incredible abilities underwater - huge lungs,
0:00:52 > 0:00:57amazing swimming skills, fish-like streamlining.
0:00:57 > 0:01:01You'd need the powers of a real-life superhero,
0:01:01 > 0:01:04a superhero like Aquagirl,
0:01:04 > 0:01:06perfectly at home underwater,
0:01:06 > 0:01:10and with unbelievable swimming ability.
0:01:10 > 0:01:14Well, I've heard of a real-life Aquagirl.
0:01:14 > 0:01:17Sara Campbell is one of the world's greatest freedivers.
0:01:17 > 0:01:20With just one breath, Sara can dive to crushing depths
0:01:20 > 0:01:23few ordinary humans could survive.
0:01:23 > 0:01:25She's broken four world records,
0:01:25 > 0:01:27and won the Freediving World Championships.
0:01:30 > 0:01:33Freediving is what we call diving underwater
0:01:33 > 0:01:36without any special breathing equipment, for example, scuba gear.
0:01:36 > 0:01:39With the right training and experience,
0:01:39 > 0:01:41freedivers can dive very, very deep.
0:01:41 > 0:01:43But without the right training and supervision,
0:01:43 > 0:01:46it can be very, very dangerous.
0:01:48 > 0:01:51Tim has travelled all the way to Dubai to meet this superhuman.
0:01:52 > 0:01:55And here she is, Sara.
0:01:55 > 0:01:58- How amazing to meet you, hi. - Hi, lovely to meet you too.
0:01:58 > 0:02:01Now, tell me, what is the longest you've ever held your breath?
0:02:01 > 0:02:03Me personally? Just over five minutes,
0:02:03 > 0:02:06which, to the average person, it sounds like a big number.
0:02:06 > 0:02:08That's amazing. What is the attraction for you
0:02:08 > 0:02:09of not wearing scuba gear?
0:02:09 > 0:02:13The freedom of how I can move in the water, and then also the challenge.
0:02:13 > 0:02:16You know, scuba is not really a sport, whereas freediving,
0:02:16 > 0:02:19learning to hold your breath, pushing your body...
0:02:19 > 0:02:22Every time I jump in the water, it's like I'm learning about myself
0:02:22 > 0:02:26and learning really what's possible. So far, I haven't found the limit.
0:02:26 > 0:02:29With scuba diving, there's a depth which you can get to, basically,
0:02:29 > 0:02:33- but you're going below that, are you?- Yes, I dive a lot deeper than
0:02:33 > 0:02:35- most scuba divers.- Wow, right, wow.
0:02:36 > 0:02:38You have the most incredible abilities.
0:02:38 > 0:02:40We would love to put you to the test.
0:02:40 > 0:02:44We've set up three Super Tests designed to help us examine you
0:02:44 > 0:02:47and to try and help us understand what makes you unique.
0:02:47 > 0:02:50We've searched high and low to find somebody to measure up
0:02:50 > 0:02:52against you, but we couldn't find anyone.
0:02:52 > 0:02:54So I'm going to have to do. Is that OK?
0:02:54 > 0:02:59- That sounds brilliant. - OK, let's go.- Let's go.
0:02:59 > 0:03:02This is Dr Megan John. She's an expedition doctor
0:03:02 > 0:03:05and has kept people alive while they attempt some of the most
0:03:05 > 0:03:07dangerous activities you can imagine.
0:03:09 > 0:03:12She's created three Super Tests to find out how Tim
0:03:12 > 0:03:15and Sara's bodies react differently.
0:03:18 > 0:03:21For Super Test One, I've brought the two of you here
0:03:21 > 0:03:24to the Ambassador Lagoon, Dubai. Because here,
0:03:24 > 0:03:30- they've got one of the biggest aquariums in the world.- Wow.
0:03:30 > 0:03:34In my Super Test One, you'll both be wearing scuba equipment.
0:03:34 > 0:03:37I'm going to be looking at how long you can each make
0:03:37 > 0:03:40the air in a tank last you.
0:03:40 > 0:03:44Inside this tank, there are 60,000 fish.
0:03:44 > 0:03:47Are you two ready to take the plunge and join them?
0:03:47 > 0:03:49- I can't wait.- Are there sharks?
0:03:49 > 0:03:52- Wait and see. - OK. This is brilliant!
0:03:52 > 0:03:55Scuba diving is different from freediving.
0:03:55 > 0:03:59Scuba divers breathe underwater using tanks full of air,
0:03:59 > 0:04:00which get used up during the dive.
0:04:01 > 0:04:05Sara and Tim will be using scuba tanks in Super Test One,
0:04:05 > 0:04:09so Dr Megan can measure how much air they use while they swim about.
0:04:09 > 0:04:12It's important they don't stop to admire the fish, though,
0:04:12 > 0:04:15so Dr Megan has organised a game that they have to play.
0:04:15 > 0:04:19She's hidden 20 coloured marbles in the fish tank. Sara has to find
0:04:19 > 0:04:21the ten yellow ones, and Tim the ten red ones,
0:04:21 > 0:04:25and they have to put them in a tray to get counted.
0:04:25 > 0:04:27So, Sara, do you have any tips that might help me?
0:04:27 > 0:04:31Yes, absolutely. The most important thing when you're in the water,
0:04:31 > 0:04:34whether it's freediving or scuba diving, is to remain calm.
0:04:34 > 0:04:36And the way that we remain calm,
0:04:36 > 0:04:38the best way is to manage how we breathe.
0:04:38 > 0:04:43Make sure that you keep it calm, keep it slow, relatively deep.
0:04:43 > 0:04:46If you find that you're breathing very shallowly and rapidly,
0:04:46 > 0:04:50that means that you're getting into a panic state and that is going to
0:04:50 > 0:04:53have an effect, not only on keeping your mind nice and calm, so stopping
0:04:53 > 0:04:56you getting too excited while you're looking for those marbles,
0:04:56 > 0:05:00but it's also going to keep your heartrate low, which means
0:05:00 > 0:05:03you're going to use less of the air in your tank as you swim around.
0:05:03 > 0:05:06Oh, right, so not only does it stop me from getting panicky,
0:05:06 > 0:05:08- it also helps me to save air.- Yes.
0:05:08 > 0:05:11Very clever. So long, slow, deep breaths
0:05:11 > 0:05:13Yes, absolutely.
0:05:15 > 0:05:19Long, slow, deep breaths? Easier said than done.
0:05:19 > 0:05:22Once Sara and Tim start looking for the marbles in Super Test One,
0:05:22 > 0:05:25there's a good chance they'll forget all about their breathing.
0:05:25 > 0:05:29Sara, Tim. I've set you both up with tanks filled with identical
0:05:29 > 0:05:32amounts of air, 200 bar. They've each got a gauge
0:05:32 > 0:05:33which will start at 200,
0:05:33 > 0:05:36and the needle will go down as you use up the air inside.
0:05:36 > 0:05:39Don't worry, I've made sure there's more than enough in each tank
0:05:39 > 0:05:41to last you both 20 minutes.
0:05:41 > 0:05:44You've also got these specially adapted masks, which will
0:05:44 > 0:05:46allow you to talk to me while you do the challenge.
0:05:46 > 0:05:49- But I would suggest you don't talk too much.- Cos it uses lots of air.
0:05:49 > 0:05:53- Exactly.- So, like, "Wow, a fish! Wow, a marble! Wow, a thing!
0:05:53 > 0:05:54"Wow, this!" would not be good.
0:05:54 > 0:05:58- There's 60,000 fish down there.- That would take a lot of air.- That would.
0:05:59 > 0:06:02Scuba diving can be very dangerous,
0:06:02 > 0:06:06and even experienced scuba divers can get into difficult situations.
0:06:06 > 0:06:09Diving deeper can cause you to sink faster
0:06:09 > 0:06:12and not knowing how to get back to the surface can cause you to panic.
0:06:12 > 0:06:16Panic causes you to use more oxygen, meaning the air level
0:06:16 > 0:06:18in your tank will start to drop faster.
0:06:18 > 0:06:21If you try to swim to the surface too quickly, the change
0:06:21 > 0:06:25in water pressure can cause earache and your ears could start to bleed.
0:06:25 > 0:06:27You may get decompression sickness.
0:06:27 > 0:06:30Decompression sickness can cause sore joints and breathing problems.
0:06:30 > 0:06:33In severe cases, it can cause dizziness, confusion,
0:06:33 > 0:06:36unconsciousness and death.
0:06:36 > 0:06:38To make sure Sara and Tim are as safe as possible
0:06:38 > 0:06:41during Super Test One, they've had training beforehand,
0:06:41 > 0:06:45and a team of safety divers will be in the water with them at all times.
0:06:45 > 0:06:47OK, then, guys. You get your kit on.
0:06:47 > 0:06:49I'm going to head down to the observation window.
0:06:49 > 0:06:51When you're ready, you head over there
0:06:51 > 0:06:54and I'll give you a cue on the walkie-talkie. OK?
0:06:54 > 0:06:56- Yep. Ready?- Good luck. - Brilliant, let's do this.
0:06:56 > 0:06:59Sara doesn't normally use scuba gear.
0:06:59 > 0:07:02With her freediving abilities, she doesn't need it.
0:07:02 > 0:07:05But by using it today, Dr Megan can see how much air
0:07:05 > 0:07:07her and Tim use during the 20-minute test.
0:07:07 > 0:07:09OK, then, guys, are you ready?
0:07:11 > 0:07:15Three, two, one, dive!
0:07:19 > 0:07:22It's a massive tank, full of moving fish.
0:07:22 > 0:07:25How on earth are they going to find any marbles?
0:07:25 > 0:07:27I did notice that some of the fish have been pushing
0:07:27 > 0:07:31the marbles around - that could make it even harder for them.
0:07:31 > 0:07:33Sara and Tim are trying to stay relaxed
0:07:33 > 0:07:36and swim as efficiently as possible in this test,
0:07:36 > 0:07:38just like a freediver has to
0:07:38 > 0:07:41when trying to make one breath of air last.
0:07:41 > 0:07:43It's interesting, Sara's body language,
0:07:43 > 0:07:44keeping her arms very still.
0:07:44 > 0:07:46It'll be interesting when Tim comes back round
0:07:46 > 0:07:48to see how he's managing.
0:07:48 > 0:07:51Early in the test, and Tim seems to be doing quite well,
0:07:51 > 0:07:53keeping relaxed while he swims around.
0:07:58 > 0:08:01So they've not found any yet.
0:08:01 > 0:08:04Nearly four minutes.
0:08:04 > 0:08:06At the end of the 20-minute test,
0:08:06 > 0:08:08Dr Megan will read the gauges in their tanks
0:08:08 > 0:08:11to see how well they've managed to make their air last.
0:08:11 > 0:08:14I've got one, hurray!
0:08:14 > 0:08:17Oh! I've found my first one too.
0:08:19 > 0:08:22There we go. Sara, the first marble in the basket.
0:08:24 > 0:08:26Tim's got one too.
0:08:28 > 0:08:30Just seconds apart.
0:08:32 > 0:08:35This is a great way of testing how the guys use their air.
0:08:35 > 0:08:38Because it's very distracting - this is a competition,
0:08:38 > 0:08:41this is a game for them, so they can't think about just technique.
0:08:45 > 0:08:46Yeah, that's my second.
0:08:49 > 0:08:51There we go, Sara's coming in with her second now.
0:08:51 > 0:08:54Ha-ha, look at that!
0:08:54 > 0:08:565 minutes and 30 seconds.
0:09:00 > 0:09:02I have lost my marbles.
0:09:11 > 0:09:15Number three, so three to one. Nearly seven minutes.
0:09:15 > 0:09:17Remember, I'm not interested, really,
0:09:17 > 0:09:18in how many marbles they get.
0:09:18 > 0:09:21I'm using that as a distraction to keep them both swimming
0:09:21 > 0:09:24so I can record how much air they use in the 20 minutes.
0:09:26 > 0:09:30The more Tim and Sara move round, the more oxygen they'll use up.
0:09:30 > 0:09:34This is because everything in your body is made up of tiny cells.
0:09:34 > 0:09:37There are lots of different types of cells - skin cells,
0:09:37 > 0:09:40muscle cells, nerve cells, and even bone cells.
0:09:40 > 0:09:44Every single cell needs oxygen and sugars from your body
0:09:44 > 0:09:45to work properly.
0:09:45 > 0:09:48They use the oxygen and sugars in a chemical reaction
0:09:48 > 0:09:52to make energy, and this is called respiration.
0:09:52 > 0:09:56Respiration also makes water and another gas called carbon dioxide.
0:09:56 > 0:09:59You don't NEED carbon dioxide, so you get rid of it when you breathe out.
0:09:59 > 0:10:02The harder your cells work, the more oxygen they need
0:10:02 > 0:10:04and the more oxygen you breathe in.
0:10:04 > 0:10:07Sara's doing well not getting stressed out,
0:10:07 > 0:10:10considering where some of the marbles have been hidden.
0:10:10 > 0:10:12I've found another ball, but it's in here.
0:10:14 > 0:10:17I don't know if my arms are long enough to get it.
0:10:17 > 0:10:22If I were freediving now, I could get inside here easily.
0:10:22 > 0:10:25But with all this breathing equipment, I can't.
0:10:26 > 0:10:30Tim is struggling to keep his breathing under control.
0:10:30 > 0:10:32It's really hard down here to try
0:10:32 > 0:10:37and concentrate on breathing slowly. Way overexcited.
0:10:37 > 0:10:39And the more excited Tim is,
0:10:39 > 0:10:42the more oxygen his body will be demanding.
0:10:42 > 0:10:45Oxygen gets into your body through your lungs.
0:10:45 > 0:10:49Your lungs are made of lots of tubes that branch out like a tree.
0:10:49 > 0:10:53At the end of the tubes are tiny air sacs called alveoli.
0:10:53 > 0:10:56The average human body has 700 million alveoli,
0:10:56 > 0:11:00and if they were all laid flat, they'd cover half a tennis court.
0:11:00 > 0:11:04When you breathe in, air goes right down into the alveoli.
0:11:04 > 0:11:08Alveoli are covered in blood vessels, and oxygen from the air goes through
0:11:08 > 0:11:12the walls of the alveoli into your blood to be carried round your body.
0:11:12 > 0:11:14The faster you breathe, the more
0:11:14 > 0:11:16oxygen your lungs will take in from the air.
0:11:20 > 0:11:22I just found two.
0:11:24 > 0:11:28Sara's just showing the cameraman she's got two marbles in her hands.
0:11:28 > 0:11:30I wonder if Tim noticed.
0:11:30 > 0:11:34Sara's got another one there, look, I can see that.
0:11:34 > 0:11:36I really have no idea where they are.
0:11:39 > 0:11:42So that's five marbles to Sara, three to Tim...
0:11:43 > 0:11:47..at 13 minutes and 45 seconds.
0:11:47 > 0:11:50A big part of Sara's amazing ability as a freediver
0:11:50 > 0:11:53is keeping calm whilst diving.
0:11:53 > 0:11:57In general, watching Sara is more peaceful, she's more relaxed,
0:11:57 > 0:12:00she moves a lot less and she doesn't use her arms at all.
0:12:02 > 0:12:04With all his flapping about in the water,
0:12:04 > 0:12:06Tim must be using more air than Sara.
0:12:07 > 0:12:10As the time goes on, they both seem to be working harder.
0:12:15 > 0:12:18So that's five marbles for Sara, four for Tim,
0:12:18 > 0:12:20with three minutes to go.
0:12:25 > 0:12:28What's really important is not how many marbles they get,
0:12:28 > 0:12:31but how much air they've used by the end of the test.
0:12:35 > 0:12:39Obviously, we know that Sara is much more experienced in the water
0:12:39 > 0:12:41and much more comfortable in the water than Tim is.
0:12:41 > 0:12:44Because of that, she's using a lot less movement,
0:12:44 > 0:12:48she's more confident. And Sara's coming in with another one.
0:12:50 > 0:12:54That's 20 minutes. If you can both finish now.
0:12:54 > 0:12:56The two of them are heading back up to the surface.
0:12:56 > 0:12:58I want to find out how much air they've both used.
0:13:00 > 0:13:04With the test over, Sara's right to look happy.
0:13:04 > 0:13:05I'm OK!
0:13:05 > 0:13:08She collected six marbles while Tim only had five.
0:13:08 > 0:13:10Fresh air!
0:13:10 > 0:13:13But it's not the marbles they've collected that's important.
0:13:13 > 0:13:14Good, you're out.
0:13:14 > 0:13:16It's how much air they used.
0:13:16 > 0:13:19And Dr Megan's looking at the results now.
0:13:19 > 0:13:24Tim, during the 20 minutes, you used up 110 bar of air.
0:13:24 > 0:13:27But, Sara, I'm completely blown away.
0:13:27 > 0:13:29You only used 60 bars of air.
0:13:29 > 0:13:32You would have been able to last almost double
0:13:32 > 0:13:33the length of time that Tim did.
0:13:33 > 0:13:36I know you're a bit smaller than Tim, so I might have expected him
0:13:36 > 0:13:40to use a LITTLE bit more, but that difference is phenomenal.
0:13:41 > 0:13:44I used up a lot of air searching for marbles,
0:13:44 > 0:13:47but long ago in the Middle East, people searched the ocean floor
0:13:47 > 0:13:51for a different prize, using just one breath.
0:13:51 > 0:13:56For hundreds of years, diving for pearls was a popular job in Dubai.
0:13:56 > 0:13:59Pearl divers would freedive up to as 40m down to the seabed
0:13:59 > 0:14:01to collect oysters which make pearls.
0:14:01 > 0:14:05The divers collected as many oysters in one dive as they could,
0:14:05 > 0:14:09holding their breath for up to five minutes at a time.
0:14:09 > 0:14:11When they ran out of air, they'd tug on a rope
0:14:11 > 0:14:13and be pulled to the surface.
0:14:13 > 0:14:17They dived all day, risking their lives among poisonous jellyfish
0:14:17 > 0:14:20and sharks for the valuable pearls.
0:14:22 > 0:14:25Freediving has always existed.
0:14:25 > 0:14:27Many cultures around the world
0:14:27 > 0:14:30have relied on swimming while holding their breath to find food,
0:14:30 > 0:14:33long before scuba-diving equipment was ever thought of.
0:14:34 > 0:14:38Most mammals can dive for brief periods under water. In fact,
0:14:38 > 0:14:41some mammals went from spending a short time underwater
0:14:41 > 0:14:42to living full-time there.
0:14:44 > 0:14:47Sara's a world champion, and with all her training,
0:14:47 > 0:14:52she can hold her breath for around five minutes underwater. Amazing.
0:14:52 > 0:14:55But some mammals, like whales, can dive for 90 minutes
0:14:55 > 0:14:56on just one huge breathe.
0:14:59 > 0:15:02All mammals have a special trick that lets them dive
0:15:02 > 0:15:06so well underwater. It's called the mammalian dive reflex,
0:15:06 > 0:15:08and it starts as soon as your face hits the water.
0:15:10 > 0:15:13Most people can hold their breath for a short while,
0:15:13 > 0:15:16but underwater, you can hold your breath for a bit longer.
0:15:16 > 0:15:20This is because nerve cells on your face send information
0:15:20 > 0:15:23to your brain, telling it that you're underwater.
0:15:23 > 0:15:25Your brain then sends signals round your body.
0:15:25 > 0:15:28This causes less blood to flow to your arms and legs
0:15:28 > 0:15:33so they use less oxygen, and your heartrate slows down.
0:15:33 > 0:15:36Using less oxygen means that the air in your lungs will last longer
0:15:36 > 0:15:39and this means you can hold your breath for a bit longer.
0:15:39 > 0:15:42With years of training, this automatic dive reflex helps
0:15:42 > 0:15:46top freedivers, but it will not save the average human from drowning
0:15:46 > 0:15:47if they run out of air.
0:15:47 > 0:15:50You must never fight your body's natural need to breathe.
0:15:50 > 0:15:52You really could drown.
0:15:53 > 0:15:56To be able to be a great freediver like Sara, you need to be able
0:15:56 > 0:15:58to stay under the water for as long as possible.
0:15:58 > 0:16:02To do this really well, you'll need to take as much air as possible
0:16:02 > 0:16:04down with you in your lungs.
0:16:07 > 0:16:10In Super Test Two, I want to look at how much air
0:16:10 > 0:16:13you can hold in your lungs. I'm going to do that using a spirometer.
0:16:13 > 0:16:14How does it work?
0:16:14 > 0:16:17Well, I'll be asking the two of you to take a deep breathe in,
0:16:17 > 0:16:20and then out and back in again though the tube.
0:16:20 > 0:16:23The computer will then give me a readout about the total amount
0:16:23 > 0:16:25of air you can fit into your lungs.
0:16:25 > 0:16:28- Great.- Shall we try it? - Yeah, let's have a go.- OK.
0:16:28 > 0:16:33- Right then, Tim, you're up first. - OK.- When you're ready.
0:16:35 > 0:16:39Tim's filling his lungs with as much air as he can.
0:16:39 > 0:16:41Breathing right out...
0:16:41 > 0:16:43Whoa, Tim, don't hurt yourself.
0:16:44 > 0:16:47Don't forget to breathe back in again.
0:16:47 > 0:16:50The machine can now measure how much his lungs can hold
0:16:50 > 0:16:52compared with the average man of his size.
0:16:52 > 0:16:56- Let's have a look.- Did that work? - You went purple.
0:16:56 > 0:16:58- Did I?- Yes.- I tried really hard.
0:17:02 > 0:17:04You might think that it's your lungs
0:17:04 > 0:17:06that make you breathe in and out, but it's not.
0:17:06 > 0:17:08It's done by a very clever muscle.
0:17:08 > 0:17:11Your diaphragm is a stretchy muscle
0:17:11 > 0:17:14that sits right underneath your lungs.
0:17:14 > 0:17:17When it moves down, it pulls air into your lungs
0:17:17 > 0:17:20and when it moves up, it pushes air out of your lungs.
0:17:20 > 0:17:25Your brain controls your diaphragm, making it move 12 times every minute.
0:17:25 > 0:17:28When you're breathing at rest, you will only fill around a quarter
0:17:28 > 0:17:30of your lungs with air.
0:17:30 > 0:17:33But if you pull your diaphragm as low as you can,
0:17:33 > 0:17:35you can fill your lungs completely with air.
0:17:37 > 0:17:40The maximum amount your lungs hold is called your lung capacity.
0:17:40 > 0:17:44With training, you can make your lung capacity bigger.
0:17:44 > 0:17:48- OK, Sara, you're up next. When you're ready.- Yep.
0:17:51 > 0:17:54A deep, controlled breath from Sara.
0:17:54 > 0:17:56She looks like she knows what she's doing.
0:18:05 > 0:18:08That's amazing, you actually become a square.
0:18:08 > 0:18:11You know, like normally, you're a normal person-shape
0:18:11 > 0:18:14and then suddenly you go... and you inflate yourself.
0:18:14 > 0:18:16- You inflate yourself. - I'm a pufferfish.
0:18:19 > 0:18:21Now, Tim, you did better than I expected.
0:18:21 > 0:18:24- 10% better than average.- OK. - Really well done.
0:18:24 > 0:18:26Thanks. That's really exciting.
0:18:26 > 0:18:31Sara, however, you achieved 3.82 litres.
0:18:31 > 0:18:35That's over 22% more than we would have expected for your size.
0:18:35 > 0:18:36Phenomenal.
0:18:36 > 0:18:41With an incredible 22% more than the average lung capacity,
0:18:41 > 0:18:44Sara has a lot of breath to use during a dive.
0:18:44 > 0:18:48It's no wonder she's one of the best freedivers in the world.
0:18:48 > 0:18:49So, how does Sara do it?
0:18:49 > 0:18:53Sara's lungs might not be bigger than the average person,
0:18:53 > 0:18:57but years of training have made her diaphragm superstrong, so Sara can
0:18:57 > 0:19:02stretch her lungs to make them even bigger and hold even more oxygen.
0:19:02 > 0:19:06Sara uses mental exercises to keep herself calm and relaxed,
0:19:06 > 0:19:08and moves as little as she can.
0:19:08 > 0:19:10This slows down her heartrate and uses less oxygen.
0:19:10 > 0:19:12Sara is also quite small,
0:19:12 > 0:19:14and smaller bodies use less oxygen than bigger ones.
0:19:14 > 0:19:17All this means that when Sara dives, not only does she hold more air
0:19:17 > 0:19:21than an average person, but she uses it up more slowly.
0:19:21 > 0:19:24This allows her to dive for a long, long time on just one breath.
0:19:29 > 0:19:31Holding your breath's hard enough when you're relaxed.
0:19:31 > 0:19:34But imagine trying to do it with a shark in the water.
0:19:36 > 0:19:39On Reunion Island near Madagascar, there have been
0:19:39 > 0:19:42so many shark attacks that swimming was banned.
0:19:42 > 0:19:46Luckily, freediver Fred Buyle came to the rescue.
0:19:46 > 0:19:49He can hold his breath calmly at the bottom of the ocean
0:19:49 > 0:19:50without disturbing the sharks.
0:19:50 > 0:19:55Incredibly, when Fred plays music, the sharks come to investigate.
0:19:55 > 0:19:58When they get close, he puts a tracker on them
0:19:58 > 0:20:01without hurting them. Now, people can swim safely
0:20:01 > 0:20:04because lifeguards know exactly where the sharks are.
0:20:09 > 0:20:13For the final Super Test, Dr Megan has taken Sara and Tim
0:20:13 > 0:20:16off to the coast of Fujairah, in the Gulf of Oman.
0:20:17 > 0:20:19Super Tests One and Two, to control the environment,
0:20:19 > 0:20:21we carried them out in an aquarium.
0:20:21 > 0:20:25But to really see what Sara can do with her freediving,
0:20:25 > 0:20:29I've had to find somewhere a lot deeper - the ocean.
0:20:29 > 0:20:32The team have come to a deep-water location
0:20:32 > 0:20:35and dropped a line an incredible 50 metres down.
0:20:35 > 0:20:38This line will mark the depth and keep Sara and Tim on course.
0:20:38 > 0:20:42With one breath, they will attempt to swim all the way to the bottom
0:20:42 > 0:20:45and return. 100 metres - that's like swimming
0:20:45 > 0:20:47the length of a football pitch with one breath.
0:20:47 > 0:20:50Because it's such a risky challenge that we're undertaking,
0:20:50 > 0:20:52I've put together my largest ever safety team.
0:20:52 > 0:20:55I've got a lot of medical experts here on standby.
0:20:55 > 0:20:57We've got specialist safety scuba divers in the water
0:20:57 > 0:20:59and some specialist safety freedivers.
0:20:59 > 0:21:01If Sara and Tim get into trouble,
0:21:01 > 0:21:03we need to get them out straight away.
0:21:03 > 0:21:06The two of them could black out or sustain pressure injuries.
0:21:06 > 0:21:09One factor that the team hadn't reckoned on was the bad weather.
0:21:09 > 0:21:11There's a strong current today,
0:21:11 > 0:21:14which is dragging the weighted safety line to one side.
0:21:14 > 0:21:17This could mean that Tim and Sara get pulled away with the line
0:21:17 > 0:21:20and have to waste precious air swimming against the current.
0:21:20 > 0:21:22In that case, they might not make it all the way down
0:21:22 > 0:21:24to the target 50 metres.
0:21:24 > 0:21:27So here we are. The boats are in position.
0:21:27 > 0:21:31Before I set you off, I've done a little bit of an experiment.
0:21:31 > 0:21:34- Have a look at this metal bottle. - Yeah.
0:21:34 > 0:21:36See if you can crush it.
0:21:36 > 0:21:38Oh, it's really strong, isn't it?
0:21:38 > 0:21:41- Not really making any inroads, are you, Tim?- No. None at all.
0:21:41 > 0:21:45I sent an identical bottle down to the sort of depths
0:21:45 > 0:21:47that Sara's going dive to.
0:21:47 > 0:21:49Dr Megan has placed cameras on the bottle
0:21:49 > 0:21:52to show what the pressure does at just 30 metres.
0:21:55 > 0:21:57Oh, my word.
0:22:00 > 0:22:03- And look what happened.- Whoa!
0:22:03 > 0:22:07That's the effect of the pressure down at depths, crushing in.
0:22:07 > 0:22:10It's what would happen to your body if we sent you down.
0:22:10 > 0:22:13The deeper you dive, the more your body gets
0:22:13 > 0:22:16squashed by the pressure of water around you.
0:22:16 > 0:22:20The pressure is so strong, it can burst your eardrums.
0:22:20 > 0:22:24The deeper you go, the more your body gets squeezed, and soon your lungs
0:22:24 > 0:22:27get squashed so they'll only be the size of oranges.
0:22:27 > 0:22:29Blood and bodily fluids get pushed into your lungs
0:22:29 > 0:22:32and they can start to bleed.
0:22:32 > 0:22:35When you dive below ten metres, you will stop being able to float
0:22:35 > 0:22:37and you'll be sucked down towards the bottom.
0:22:37 > 0:22:40And if you try to come back up, the sudden change in water pressure
0:22:40 > 0:22:42can make you pass out.
0:22:42 > 0:22:45Then you'll run out of oxygen and die.
0:22:46 > 0:22:49I'm afraid, Tim, I've got some bad news.
0:22:49 > 0:22:53Because of that, the BBC safety authorities have decided
0:22:53 > 0:22:55you just can't try this challenge.
0:22:55 > 0:22:59Whoa, OK. I mean, Sara, it's really that dangerous?
0:22:59 > 0:23:00With no training, absolutely.
0:23:00 > 0:23:04There are many, many risks involved with freediving.
0:23:04 > 0:23:06If you don't know what you're doing,
0:23:06 > 0:23:08you should never, ever have a go on your own.
0:23:08 > 0:23:12So I appreciate that possibly today is not your day.
0:23:14 > 0:23:16But today might not be Sara's day, either.
0:23:16 > 0:23:19Although she's dived twice as deep to over 100 metres,
0:23:19 > 0:23:22setting her own personal record in the past,
0:23:22 > 0:23:25the choppy sea conditions today are still a cause for concern.
0:23:25 > 0:23:28It could cause her big problems in the dive.
0:23:28 > 0:23:30OK, we've set the rope,
0:23:30 > 0:23:33and we do have quite a bit of current today, actually.
0:23:33 > 0:23:36So the rope is kind of at this angle, which isn't ideal.
0:23:36 > 0:23:38It's also less than ten metres' visibility.
0:23:38 > 0:23:41So these are both conditions that I'm really not used to diving in.
0:23:41 > 0:23:45For Sara's dive, I'll be fitting her with this specialist dive computer.
0:23:45 > 0:23:47It'll give me readouts of her heartrate
0:23:47 > 0:23:48as she goes through the dive.
0:23:48 > 0:23:51It'll be really interesting to see what story that tells.
0:23:51 > 0:23:53Are you happy with that, guys?
0:23:55 > 0:23:58Before each dive, Sara goes through a preparation routine.
0:24:00 > 0:24:03She takes controlled breaths and relaxes her body, ready to begin
0:24:03 > 0:24:07the attempt to make the incredible 50-metre dive in one breath.
0:24:09 > 0:24:12Sara's done all her breathing exercises and warm-up,
0:24:12 > 0:24:14she's ready to go. Good luck, Sara.
0:24:18 > 0:24:19She's away!
0:24:21 > 0:24:24For safety, Sara is tethered to the rope.
0:24:24 > 0:24:27Without it, she might drift off course and get lost.
0:24:27 > 0:24:30Amazing, she's like a massive big fish, isn't she? Beautiful,
0:24:30 > 0:24:34stunning, willowing through the water with the big fins coming out
0:24:34 > 0:24:38- behind her. It's amazing.- She's like a beautiful silver mermaid, Tim.
0:24:39 > 0:24:43As the air in her lungs is squashed, she becomes less buoyant.
0:24:43 > 0:24:47If she passes out now, she'll just carry on sinking.
0:24:47 > 0:24:51She's just gone past the point where she doesn't need to paddle any more,
0:24:51 > 0:24:55because your body suddenly gets heavier and you get sucked down.
0:24:55 > 0:24:59Sara is at the point now that the bottle crushed in the experiment.
0:24:59 > 0:25:01From years of training, Sara can withstand the pressure,
0:25:01 > 0:25:03being able to equalise her ears,
0:25:03 > 0:25:07and her amazing diaphragm stretching to allow the shrinking of her lungs.
0:25:11 > 0:25:15She just seems so very relaxed in the water. That's amazing, isn't it?
0:25:15 > 0:25:18She uses a lot less oxygen so she needs a lot less air,
0:25:18 > 0:25:20so she can keep going for longer.
0:25:20 > 0:25:24With every metre she goes down, the pressure crushes her more.
0:25:24 > 0:25:27and she has less and less oxygen left in her lungs.
0:25:27 > 0:25:30So she's getting to the bottom now. She's nearly 50 metres down.
0:25:30 > 0:25:35- It's incredible. 50 metres is a really long way.- It's phenomenal.
0:25:35 > 0:25:38She's reached the bottom. It's amazing!
0:25:38 > 0:25:4150 metres down with just one breath of air -
0:25:41 > 0:25:43and all under crushing pressure.
0:25:43 > 0:25:47A normal person would be in agony as the water pressure
0:25:47 > 0:25:50squeezed on their chest, and they would suffer burst eardrums.
0:25:52 > 0:25:55The pressure on her body, the squeezing must be incredible.
0:25:55 > 0:25:57Her heartrate's now down at 46,
0:25:57 > 0:25:59that's less than half what it was at the surface.
0:25:59 > 0:26:01But, unbelievably,
0:26:01 > 0:26:04the most dangerous part of the test is still ahead of her.
0:26:06 > 0:26:08Her body would have a huge amount of pressure on it,
0:26:08 > 0:26:12squishing her lungs in, squishing in on her ears and her head.
0:26:12 > 0:26:14She could start to get light-headed if she doesn't come up.
0:26:14 > 0:26:17Only Sara's awesome abilities
0:26:17 > 0:26:20and years of training allow her to make an attempt like this.
0:26:20 > 0:26:23Don't ever try something like this yourselves.
0:26:24 > 0:26:27Sara has been down for nearly two minutes.
0:26:28 > 0:26:31So far, she is fighting the body's natural desire to breathe,
0:26:31 > 0:26:34but there's still a long way to go.
0:26:37 > 0:26:41The most dangerous part of this dive is the last ten metres.
0:26:41 > 0:26:44This is usually the point that freedivers black out
0:26:44 > 0:26:48from lack of oxygen. And it's happened to Sara herself before.
0:26:48 > 0:26:52For that reason, it's essential that a safety freediver is waiting
0:26:52 > 0:26:54to guide her up for the last stretch.
0:26:54 > 0:26:57If she blacks out now, he'll need to save her.
0:27:08 > 0:27:11Sara, that was truly one of the most magical things I've ever seen.
0:27:11 > 0:27:14You are one of the most incredible people I've ever met.
0:27:14 > 0:27:17It's just been a pleasure sharing this wonderful sport with you.
0:27:17 > 0:27:20I came to the Emirates to find a real-life superhuman,
0:27:20 > 0:27:25a person who could dive deeper and longer than any normal human.
0:27:25 > 0:27:30I found one. Sara Campbell, you are superhuman.
0:27:33 > 0:27:36Sara Campbell is one of the world's top freedivers,
0:27:36 > 0:27:38with years of training and experience.
0:27:38 > 0:27:42Do not attempt any of the activities shown in this programme.
0:27:42 > 0:27:44You will be putting your life in danger.
0:27:51 > 0:27:54Subtitles by Red Bee Media Ltd