Freediving is natural diving, the way we are meant to dive. Free from mechanical scuba equipment, our safe little atmospheres packaged up into a can that we can take underwater, ancient genetic memories start to surface and our bodies start to react differently.

Monica Ganame from Argentina and her Spanish partner, Eusebio Saenz de Santamaria, run Apnea Total, a freediving school on the island of Koh Tao in the Gulf of Thailand. We signed up for the 5-day Advanced Freediver course from F.R.E.E. (Freediving Regulation and Education Entity) and this is a report on those five days that changed my views on diving completely.

Day One - Technical Snorkelling

Day one starts with the usual form filling and then some videos on the different disciplines in freediving. Freediving has no back-up or bail out, the air you put in your lungs is all you have so safety procedures are paramount. There are some basic procedures: always dive with someone else and always use a surface float (to rest on, to warn boats, to give a visual reference, to support you during breathe ups).

The biggest dangers are a shallow water blackout (SWB) and the less serious "samba", a pre-SWB convulsion. Carbon dioxide triggers warning in the body that we are running low on oxygen. On a normal breath-hold dive, carbon dioxide in the blood trips the instinct to ascend before oxygen levels drop too low. However, if we start the dive with our carbon dioxide threshold artificially lowered (either through deliberate hyperventilation or poor breathing techniques) then we can run low on oxygen long before CO2 levels ring the warning bells. Water pressure at depth can be enough to keep the ppO2 high enough to maintain conciousness but the pressure drops on ascent so in the shallows the diver may black-out.

To avoid SWBs (or the less serious samba), freedivers should never hyperventilate. Monica and Eusebio begin by teaching proper breathing techniques instead that make the lungs more efficient. The basic technique is two stage breathing: filling the lower lungs and then the chest. The diaphragm and stomach are pushed out to get air deep into the lungs and only then is the chest inflated, breathing through pursed lips so as to gauge how much and how fast air is going in. This gets a lot more air into the body than normal, the added pressure on the organs can increase blood pressure. Exhaling straight away can cause a dangerous blood pressure drop (at best making you dizzy, at worse causing unconciousness) so instead they teach you to make a little pop with the lips to relieve pressure before making a full exhale. The basic pre-dive breathe up is sixteen breath cycles, taking four to six minutes. The final breath is held and then the dive is made.

After the dive, Monica and Eusebio explain, the body has an imbalance of gases, high CO2 and low O2. The urge is to breathe deep and fast but again this can cause unconciousness. Monica teaches using recovery breathing. Recovery breathing is a shallow but forceful breathing pattern, like repeatedy sighing. "Breathe using 50% of your lungs," says Eusebio. "Not 60% or 40% or you'll die." he grins. "Mmmmm," agrees Monica, raising an eyebrow.

Freediving equipment is different from what most divers are used to. Most of us use low volume masks, but compared to freediving masks we might as well be using buckets over our heads. On a dive, the mask is an airspace that will need to be equalized. The only air available is what is in your lungs so the smaller the airspace the less air wasted. Monica and Eusebio do point out though that air breathed into the mask on the way down can be inhaled again on the way up. Other options are scleral contact lenses, huge lenses that are specially made to compensate for vision in water and cover the whole front of the eye. The other is fluid goggles. These are like normal swimming goggles curved in such a way that if they are flooded with either water or saline that they form a lens that allows the diver to see. Neither scleral lenses or fluid goggles have airspaces that need equalised. Snorkels are still used to allow divers to do their breathe up with their faces immersed in the water but they are never attached to the mask (more later). Because they aren't attached, straight, simple snorkels need to be used, ones with flexible bores would just flop into the water. Full foot fins are used rather than pocket fins with heel straps as they give the foot more power and control. Blades are usually longer and stiffer to give more power per kick. Alternatively, monofins (a huge, plastic triangle with a foot pocket for both feet) can be used to swim like a dolphin. Some freediving events use no fins at all. Wetsuits are always used on freedives, even in the warmest water because it will still leach energy from the diver. With a hood it creates a temperature difference between the face and the water which can trigger the mammalian diving reflex (more later too). Wetsuits fit very closely, usually smooth lined like neoprene drysuit seal material, to keep out any water. This makes the suit as warm as a very thick regular wetsuit but without the bulk or buoyancy but can be easily damaged. Finally weightbelts are different too, made from rubber straps rather than webbing. As the diver descends the rubber contracts and keeps the belt tight while the body is crushed, a regular webbing belt will become very loose.

In the afternoon we hitch a ride on a diveboat out to one of the local dive sites. While everyone else is loading cylinders, stab jackets, regulators and clutter, we have a mask, fins and snorkel. It feels like we have forgotten something. When we reach the site, Monica rigs the float and a descent line in the water. First we work on entry technique, the traditional duck dive: floating face down, bend at the waist, raise the legs straight into the air and slide silently into the water. Monica does it gracefully and without effort, like an eel. Telling her that was a big mistake: "I hate eels," she replies with a glare. We do it with thrashing, frothing and spluttering. "Mmmm," Monica says. She says that a lot. The big urge is to start kicking as soon as you are head down, but for a second or two your feet are sticking up in the air so you aren't actually achieving anything other than looking daft. A bit more work and she is satisfied.

There is no relief from Monica, once you have mastered one skill she adds another on top of it, putting you right back to the start again. "Mmmm," she says, "try again". One major difference between freediving taught by Monica and traditionally taught snorkelling is the way the snorkel is used. You do the 16 cycle breathe up with the snorkel, hold your breath and remove the snorkel completely, holding it in your hand, either by your side or pointed straight down for streamlining. A very common cause of snorkelling accidents is diving with the snorkel in the mouth: only the epiglottis keeps the airway closed and as the diver descends pressure builds and eventually forces water down the snorkel and past the epiglottis. On ascent with the snorkel in the mouth, it must be cleared before you can breathe. Blast clearing can cause a massive drop in ppO2 and black out. Exhaling on the way up leaves you without a breath if it goes wrong.

The big limit to the depth of a freedive is being able to equalise. Monica and Eusebio teach equalisation by pinching the bridge of the nose rather than the nostrils, another small but significant air saving. The first equalisation, they say, is the most important. If you miss it then the rest become harder and harder. Both of us found this out for ourselves and limited what we were able to do until we find something that worked for us. "Mmmm," Monica would say. "Perfect entry but equalise sooner". She misses nothing. We do as she say. "Mmmm, good equalisation. But keep your elbow in". No-one ever teaches you that but it's obvious. Diving instructors always teach skills in big, sweeping movements for emphasis, equalisation is no different. So you get into the habit of equalising with your arm sticking out. There is no need, keeping your arm tucked in keeps you streamlined.

Again, once we get everything perfect, Monica throws something else in. Freedives, especially deep freedives, are impossible without a descent line. Simply as a visual reference, it is very hard to swim perfectly vertical without it. More importantly, if your are next to the line then your buddy on the surface knows where you are and you will surface next to the float for support. Monica is very strict in following the line but it isn't as easy as it sounds. Our first attempts we get tangled in the line, we swim away from the line, we don't even manage to break the surface or miss the line completely. My instinct is to look where I am going but Monica knocks that out of me. Always look at the line, don't tilt your head back and look down. She sees looking where you are going as a distraction, you either keep swimming or you turn back, depth is only relevant afterwards. She has us watch the surface, this keeps the chin tucked and our faces right on the line. Again Monica's advice has us doing perfect freedives, and I am starting to feel like the people I've only seen in documentaries. As our technique gets better, so does our depth. Already our depths are hitting at least 10m on each dive. The day before on the beach 2-3m was as far as I got. But again, she keeps us on our toes. "Keep swimming," Monica advises after watching my lazy, drifting ascent, "even on the ascent when you know you are floating up, sometimes you might need it".

Finally, Monica has us doing the full four minute pre-dive breathe up. She moves the line into deeper water and has us dive, giving us her depth gauge (but warning us not to look at it). Without effort I swim down, my eyes watching the shimmering surface disappear and seeing the bright red line going upwards until I reach the end of the line. I roll round in a cartwheel and kick up, eyes on the line, keep kicking. In ten years of mixed-gas diving and cave diving I've grown used to having more regulators and gases than I know what to do with, suddenly I feel very alone and aware that I have nothing to back me up and very aware of being alive. It is a long way back up the line and just as I'm feeling the urge to breathe I see a black, rippling shadow from the corner of my eye and I know this is Monica, watching everything. "Recovery breathing," she reminds me when I break the surface. She shows me the gauge, 16m. After a week of scuba diving on Koh Tao, we have just done the deepest dive of the holiday on a lungful of air each.

Later in the afternoon the dive boat moved on to the next dive site, throwing heavily laden divers into the sea with huge splashes. Monica gives us the float and tells us to go and play. We move out over the reef, practicing everything she has taught us (knowing that she is probably watching constantly). Sticking to the procedures we have been taught, Shona and I take it in turns to dive, the other breathing up on the surface, following the diver below. We had dived this reef four or five times on scuba but this time seemed different. Both of us noticed how much more we saw and felt the reef ws different to the place we had dived so many times. Almost effortlessly we dived down into water that was 7-12m, swimming alongside seemingly mechanical scuba divers without them even noticing. On one dive a girl with a camera just stopped and stared at me, for the first time ever on a dive I felt like I was part of the sea, looking at the crowds of divers I felt like for a minute or two I was no longer one of them.

That night we fell asleep at about 8pm. For an island with bars and clubs everywhere, this would prove to be a very sad pattern for the rest of the course.