Check out our freediving glossary

The deeper you dive, the harder it is for the sun’s rays to penetrate the water, so the environment naturally becomes darker. The level of light gradually declines to about 200 metres, where you are in total darkness. But you have to dive that deep first. And if you see any light or movements, then you might have stumbled across the lost city of Atlantis!

An international flag used by boats to indicate the presence of divers, spearfishermen or freedivers.

In medical terms, this simply means that your ventilation stops. It can be deliberate, for example to observe the seabed, or not, as in the case of the sleep apnoea syndrome.

Apnoea freediving refers to a water sport that consists of holding your breath and diving underwater, without any breathing apparatus other than your own lungs. Just like underwater snorkelling!  

As its name indicates, barotrauma is due to the difference in pressure between the ambient environment and the cavities or lesions in the body. Barotrauma can occur when descending or returning to the surface if the correct balance is not restored.

Buoyancy varies from one body to another due to the mass per unit volume and density. On the surface, divers tend to float, because their buoyancy is superior to their weight. At a given depth, their mass per unit volume is reduced by the pressure. At this point, their buoyancy is interior to their weight. Their buoyancy becomes negative and the diver sinks.

Ballast adds more to the diver and his equipment until buoyancy becomes negative and the diver descends. Ballast usually takes the form of weights attached to a belt or placed in the pockets of a buoyancy jacket.

In simple terms, gaseous exchanges between the air in the lungs, then between the blood and the various organs. We need to intake oxygen and to reject the carbon dioxide (CO2) produced.

When freediving, these exchanges still occur, but at a lower speed and they are disrupted, resulting in particular in hypercapnia and gradual hypoxia.

A discipline considered by certain divers as the purest form of freediving. It consists of diving as deeply as possible, using only the force of your legs, with or without fins. Divers must equalise head first, while controlling variations in buoyancy.

You probably don’t fancy diving in water at 10°C in your swimsuit! Even if this can be an invigorating experience, we fully understand! Diving suits help to protect the body from the cold. Their composition, thickness and watertightness are variable according to your needs.

Duck diving is a means of being quickly immersed underwater vertically. It consists of moving from lying on your belly to the vertical position. Fold your legs against your thighs, then raise your complete lower limbs against your torso. This technique can be used to descend without expending much energy, which is very important in freediving.

An apnoea discipline that consists of swimming horizontally as far as possible in a swimming pool, with or without fins. The record is 300 m!

A pool measuring up to 6 to 40 m in depth. Ideal for practising freediving all year round, even a long way from the coast. There are several freediving pools in France. Subea has tested the deepest diving pool in the world, in Italy. The Y40 !

In deep freediving, the goal is to dive as deep as possible. This discipline can be broken down into several categories:     - no limits: this is the most dangerous and best known form of freediving, because it featured in the film Le Grand Bleu. The divers dive using weights and return to the surface using a lift bag. The record is held by Herbert Nitsch: - 214 m in 2007.     - Free immersion: the diver pulls on a dive line with his arms to dive and return to the surface. All you need is a mask and a wetsuit!    - constant weight: the diver descends and ascends with or without fins, using on the force of his arms and legs.    - variable weight: the diver descends using weights and returns to the surface using fins or by pulling on the cable.

Equalisation consists of restoring the balance between the outer and middle ears. This equalisation is due in particular to the variation in depth. The Vasalva and Frenzel manoeuvres are two equalisation techniques.

An ecosystem is made up of the fauna and dense flora in the same natural environment. Coral reefs are a good example of an ecosystem. Plants and animals live in harmony, thanks to their interdependence and the exchanges of materials, energy and information.

Who has never felt that unpleasant sensation of blocked ears? Sometimes, the problem can be solved simply by yawning or swallowing. Doing this equalises your air spaces. When freediving, it is important to regularly equalise the pressure in the air cavities and the external pressure. Doing so prevents barotrauma, in particular in the ears. There are numerous techniques, including the Valsalva, Frenzel and Toynbee manoeuvres.

The eustachian tube is a bone and fibrocartilaginous duct linking the outer ear or rhino pharynx. When freediving, this duct tends to close due to the effect of the pressure, which is the reason why it is necessary to equalise with techniques like the Vasalva or Frenzel manoeuvre.

This equalisation technique consists of equalising the pressure between the inner and middle ears. Here’s what to do. Push air in the direction of the eustachian tubes in order to open them and equalise by moving your tongue rearwards and upwards. Pinch your nose, open your mouth, with your glottis closed, put your tongue on your palate and say “K”.

Using our own feet is not a very efficient means of moving around in water. It is much easier to move through water using fins, which take inspiration from fish fins.

A ventilatory technique that reduces CO2 levels in the body in order to delay the occurrence of hypercapnia and the desire to breathe. Not to be used, because when divers no longer feel the need to breathe, they are in danger of suffering from severe hypoxia and, consequently, syncope.

You start off diving in clear water where the visibility is good, when suddenly... The water becomes murky. Don’t worry. This natural phenomenon occurs when salt water meets fresh water. This saline mixture usually reduces visibility for a short distance.

A higher than normal level of carbon dioxide in the blood, for example when ventilation stops. Freedivers have to learn how to control this increase in the level of CO2, because it makes them want to breathe.

A lower than normal level of oxygen in the blood. Below a given threshold, a lack of oxygen can cause syncope.

The heart rate is the number of heart beats per unit of time. The heart rate tends to rise as the oxygen reserve in our tissues drops.

A Marseillaise is a type of weighted belt that allows the diver to adjust his buoyancy. A Marseillaise is a quick-release belt. It must allow the weights to be released quickly in an emergency.

Masks work like waterproof glasses with a wide vision, so that you can see clearly underwater.

A single large fin operated by both feet that are joined together at the ankle.

A component used to make most diving suits that provides thermal protection and freedom of movement.

This is the most impressive of all the freediving disciplines. It consists of diving to a greater depth than anyone else. Divers usually descend using weights and return to the surface with a parachute. At these depths, safety teams and SCUBA divers are necessary. Today, very few freedivers practise no-limits diving.

Nose clips pinch the nostrils to keep them closed. Divers can then balance their ears using the Vasalva manoeuvre, without even using their hands!

Neck weights are used in two freediving disciplines: dynamic and deep freediving.In dynamic freediving, the diver looks for a horizontal hydrodynamic position. The large volume of air in the lungs makes the upper body very buoyant. Neck weights help the diver to maintain the right position.When descending, freedivers try to adopt a hydrodynamic position during their free fall. Neck weights help them to do this.

In mathematical terms, pressure is a force that is applied to a surface. Expressed in kg/m2 or bar, pressure is due to the mass of liquid above the diver. This pressure modifies our physiology and explains why, for example, divers have to balance their ears when descending, or do not feel the same need to breathe when at depth.

Relaxation is essential for freedivers. It allows them to relax physically and mentally by reducing their muscular tone and lowering their heart rate and their nervous tension.

Buoys float on the surface to indicate the presence of freedivers. They are brightly coloured, usually yellow, orange or red. They are attached to the swimmers by a snap ring on their belt and have a line that is slightly longer than the operating depth.

A loss of consciousness caused by severe hypoxia. This is one reason why you should never dive alone, avoid hyperventilation and allow recovery times that are much longer than the duration of the apnoea.

Holding one’s breath for as long as possible, without moving. The world record: More than 11 minutes!

Swimming on the surface with a mask, fins and a snorkel. At Subea, we make the distinction between freediving and snorkelling. Snorkellers only swim on the surface. But they are usually quickly tempted by the ocean depths and the call of freediving!

A site where freediving possible. A spot can be a creek, a headland, the Blue Hole in Dahab, etc. Subea has selected of the top 10 spots for the beauty of their underwater scenery!

A simple but practical accessory that allows you to breathe when swimming on the surface with your head underwater.

This is the zone of transition between the warmer water close to the surface and the cold water at greater depths.

A long- or short-sleeved top of variable thickness that provides additional thermal protection under your wetsuit.

Voluntary tubal opening is an equalisation technique that restores the balance between the outer and middle ear. It consists of deliberately yawning, or making a jaw movement that opens the ducts. This technique is a difficult but more gentle way of equalising the ears.

This discipline consists of diving as deep as possible using weights. They then return to the surface using fins or the weights.

The mechanical action of filling and emptying the lungs. When we stop ventilating by holding our breath, we do not actually stop breathing.

A technique used to equalise the ears when diving or freediving. Named after its inventor, this technique consists of pinching your nose, opening your mouth and breathing out at the same time in order to inject air into the middle ear.

This is the most common type of diving suit. Wetsuits are made of neoprene and vary between 0.5 and 8 mm in thickness. They create a thermal barrier between your skin and the exterior.

Divers use weights to reach depths without having to swim, but just by holding onto a weight that descends to a given depth.