Home » Freediving 101 » Terminology for Freediver

In the world of the Inner Space, people communicate with special words and expressions to describe a particular subject, activity, or situation in regards of freediving. If you find yourself lost in those alien conversations, don’t worry, FiDive provides a list of common freediving terminology to help you decode those conversations!

Top 50 Terminology in Freediving

*The list of freediving terminology below is quoted from selected third party websites and is in alphabetical order.


Freediving is NOT an anaerobic exercise. Freedivers DO USE their respiratory system to eliminate CO2, even though they are not breathing. The CO2 moves from the blood to the lungs, eliminating most of it from the blood.



Apnea is the cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged.



Barotrauma refers to injuries caused by increased air or water pressure, such as during airplane flights or scuba diving. Barotrauma of the ear is common. Generalized barotraumas, also called decompression sickness, affects the entire body. 


Beance Tubaire Volontaire (BTV)

Also known as hands free equalization.

This technique is difficult to teach and only approximately 30% of taught can perform it reliably. Muscles of the soft palate are contracted while upper throat muscles are employed to pull the Eustachian tube open. 

Beance Tubaire Volontaire (BTV)

Black Out (BO)

Freediving blackoutbreath-hold blackout or apnea blackout is a class of hypoxic blackout, a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold (freedive or dynamic apnea) dive. Shallow water black out occurs when a diver ascends to a shallow depth and falls unconscious from a lack of oxygen.

Blood Shift

Blood Shift allows a freediver to dscend without crushing their chest. The blood shunted from a diver’s extremities by vasoconstriction travels to organs in his chest cavity, occupying the space created when air in the lungs compresses.


Bi-fins (also known by its acronym, BF or as ‘stereo-fins’) is swimming on the surface of the water with mask, snorkel and a pair of fins using a crawl style. Both bi-fins and monofin are permitted in freediving and the technique is irrelevant. 

Bohr Effect

Hemoglobin’s oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide.

Increase in the carbon dioxide partial pressure of blood and decrease in blood pH results in the lower affinity of hemoglobin for oxygen, enhancing unloading of bound Oxygen by hemoglobin passing through the metabolically active tissue and thus improving oxygen delivery.

Boyle’s Law

As pressure changes, the volume of gases in the diver’s body and soft equipment changes too. The volume of gas in a non-rigid container (such as a diver’s lungs or buoyancy compensation device), decreases as external pressure increases while the diver descends in the water. 

Constant Weight (CWT)

Diving to depth and back, with bi-fins or a monofin, wearing the same amount of weight for the descent and ascent.

Constant Weight No Fins (CNF)

It is an AIDA International freediving discipline in which the freediver descends and ascends by swimming without the use of fins or without pulling on the rope or changing his ballast; only a single hold of the rope to stop the descent and to start the ascent is allowed. Constant weight without fins is the depth discipline of freediving that is most challenging, because of the physical effort needed to swim without assistance.


A diaphragm contraction is simply the movement of the diaphragm, which can be very subtle, almost like a little flutter, or a movement that seems to bend our entire body in half. Some freedivers say that they never ever get diaphragm contractions when they freedive and some people get them very early on.

CO2 Tolerance

CO2 tolerance is something that freedivers like to build up so that they can delay and reduce the onset of the urge to breathe. The more your CO2 tolerance, the less urge to breathe at the same CO2 level.

Dalton’s Law

Dalton’s law explains that the concentration of oxygen and nitrogen in a diver’s lungs increase independently of each other. The presence of nitrogen and carbon dioxide in the diver’s lungs in no way limits the concentration of oxygen.

Decompression Sickness

Decompression sickness (DCS) is a disorder in which nitrogen dissolved in the blood and tissues by high pressure forms bubbles as pressure decreases. Symptoms can include fatigue and pain in muscles and joints.

Getting DCS while freediving is uncommon. Unlike when breathing compressed gas, freedivers typically do not accumulate enough nitrogen to provoke DCS. 

Dynamic (DYN)

Swimming distance horizontally underwater, usually in a swimming pool, whilst wearing bi-fins or a monofin.

Diaphragmatic Breathing
(Abdominal Breathing, Belly Breathing, Deep Breathing)

Diaphragmatic breathing is a type of a breathing exercise that helps strengthen your diaphragm, an important muscle that helps you breathe.

Duck Dive

Duck diving is the technique used to get yourself underwater smoothly and efficiently without any splashing about on the surface. It’s very easy with a little practice. 

Duck Dive

(Ear Cleaning)

Ear clearing or clearing the ears or equalization is any of various maneuvers to equalize the pressure in the middle ear with the outside pressure, by letting air enter along the Eustachian tubes, as this does not always happen automatically when the pressure in the middle ear is lower than the outside pressure.


Finswimming is an underwater sport consisting of four techniques involving swimming with the use of fins either on the water’s surface using a snorkel with either monofins or bifins or underwater with monofin either by holding one’s breath or using open circuit scuba diving equipment. 

Frenzel Maneuver

The Frenzel Maneuver is named after Hermann Frenzel (German ear, nose and throat physician and Luftwaffe commander). The maneuver was developed in 1938 and originally was taught to dive bomber pilots during World War II

By performing this technique, the compressed air is forced into Eustachian tubes, and thus into the middle ear.

Frenzel Maneuver


Freediving, free-diving, free diving, breath-hold diving, or skin diving is a form of underwater diving that relies on breath-holding until resurfacing rather than the use of breathing apparatus such as scuba gear



Freefalling in freediving is the point where we stop moving completely and we assume a relaxed, yet streamlined position, and start to sink, or “freefall.”  Freefalling allows us to limit muscle activation and conserve oxygen, which lets us put more focus on relaxation and equalization. 

Free Immerison (FIM)

Free immersion training requires less energy and effort, and can be done in a head-down position. This enables you to use less energy, and makes equalization easier for newer freedivers.

Free Immerison (FIM)

Functional Residual Capacity (FRC)

The volume of air in the lungs at the end of a normal exhalation (FRC=RV+ERV).

Functional Residual Capacity (FRC)

Hook Breathing (Recovery Breathing)

Hook breathing is a particular recovery-breathing technique freedivers use when resurfacing after dives. Hook breathing rapidly shuttles more oxygen into your bloodstream than regular breathing and also boosts lung air pressure & blood pressure. For these reasons, hook breathing can be incredibly effective at preventing surface water blackouts.

Hook Breathing (Recovery Breathing)


Hyperventilation is a condition in which you start to breathe very fast. Healthy breathing occurs with a healthy balance between breathing in oxygen and breathing out carbon dioxide. You upset this balance when you hyperventilate by exhaling more than you inhale.



Hyperthermia and heat stroke are some of the heat challenges that can result from prolonged exposure to extreme temperatures. In this particular article we are going to focus on hypothermia, so read on, if you want to learn how to prevent, recognize and deal with it.

Lactic Acid

The amount of lactic acids in dynamics depends mostly on the mammalian diving reflex, as it reduces the blood flow to the muscles. When the muscles don’t get much blood, they don’t get much oxygen, so they have to use more anaerobic energy producing mechanisms which produce lactic acids.

fidive terminology lactic acid

Liquid Goggles

Fluid Goggles are swim goggles filled entirely with saline solution and fitted with special lenses so you can see underwater with no air space in front of your eyes.

fidive terminology liquid goggles

Loss of Motor Control (LMC)

LMC occurs when the diver has reached the surfce. It is caused by hypoxia. A diver suffering from an LMC is in the danger zone of low oxygen before losing consciousness. Sometines divers underwater will experience LMC before blacking out (BO).

fidive terminology LMC

Lung Squeeze

Thoracic squeeze, also called Lung Squeeze, compression of the lungs and thoracic (chest) cavity that occurs during a breath-holding dive under water. During the descent, an increase in pressure causes air spaces and gas pockets within the body to compress.

Lung Squeeze

Mammalian Diving Reflex (MDR)

The mammalian diving reflex is a unique set of evolutionary adaptations leftover from a time when all life developed in the oceans. The diving reflex, as well as the swimming reflex, are an inherent part of human nature and can be observed in newborns and infants when placed in an aquatic environment.

Mouthfill (MF)

Mouthfill is the technique that freedivers use to equalise on deep dives, normally beyond 40m. It is one of the trickiest techniques to master, but with conservative depth increase, is the single most effective way for you to dive deep and minimise the risk of lung or trachea squeeze.

Mouthfill (MF)


A monofin is a type of swimfin typically used in underwater sports such as finswimming, free-diving and underwater orienteering. It consists of a single or linked surfaces attached to both of the diver’s feet. The diver’s appearance is then reminiscent of a mermaid or merman.

fidive terminology mono-fin

Neutral Buoyancy

Neutral buoyancy occurs when an object’s average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink or rise. An object that has neutral buoyancy will neither sink nor rise. 

Neutral buoyancy should be at around 1/3 of the depth of your total dive, but no less than 10m (32ft).

fidive terminology Neutral Buoyancy

Nitrogen Narcosis

Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gases at high pressure.

Freedivers do get nitrogen narcosis. Nitrogen narcosis usually affects freedivers if they go deeper than about 85 feet ( 25 meters deep).

fidive terminology nitrogen narcosis

No Fin

Diving without fins is often considered the purest form of freediving.

fidive terminology No Fin

No Limits (NLT)

No Limits apnea is one of two, with Variable Weight, non-competition disciplines for which world records can be set. As the name suggests, the No-Limits freediver can use any means they like to descend as deep as possible and ascend to the surface again.


Lung packing is a method some freedivers use to inhale more air than their resting lung capacity can hold. Lung packing is a way of literally forcing more air than is normal into your lungs, so your body benefits from extra oxygen during a deep dive.

fidive terminology Packing

Personal Best (PB)

The deepest depth, longest distance or longest time achieved by a diver.

fidive terminology personal best

Residual Volume (RV)

The amount of air in the lungs at the end of a maximal exhalation.

fidive terminology residual volume

Reverse Block

If you feel pressure in your ear or sinuses while ascending from your dive, you are experiencing a reverse block. A reverse block is caused by mucus preventing air bubbles in your middle ear, tissues or sinuses from escaping our body.

fidive terminology reverse block

Reverse Lung Packing

Reverse lung packing is an advanced lung and diaphragm exercise for freedivers. It helps increase ribcage and diaphragm flexibility and get freedivers bodies used to the effects of extreme pressure at depth. Find out how to do it and what precautions you should take.

fidive terminology Reverse Lung Packing

Sinus Squeeze

Sinus squeeze, a condition where pressure inside a sinus cavity causes pain, commonly occurs when a diver cannot equalize sinus pressure due to nasal congestion. This is also called (sinus) barotrauma. There are four pairs of sinuses in the skull.

fidive terminology Sinus Squeeze

Static Apnea (STA)

STA, stands for Static Apnea, is a discipline in which a person holds their breath (apnea) underwater for as long as possible, and need not swim any distance. Static apnea is defined by the AIDA International and is distinguished from the Guinness World Record for breath holding underwater, which allows the use of oxygen in preparation. It requires that the respiratory tract be immersed, with the body either in the water or at the surface, and may be performed in a pool or open water (sea, lake, river, etc.).

Static Apnea (STA)

Spleen Effect

The spleen effect is another way your body can maximize oxygen efficiency. After repeated freediving, the spleen contracts, releasing more red blood cells into the blood. This increases the oxygen carrying capacity of the blood, enabling longer dives or breath holds. 

fidive terminology spleen effect

Surface Interval

The period between each dive is known as a surface interval. It is an important aspect that each diver should have in mind. The surface interval represents the period of time in which the diver has to rest before venturing back in the deeps. Diving can be stressful on the body and a rest period is required between each dive.

fidive terminology Surface Interval

Valsalva Maneuver

The Valsalva maneuver is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one’s mouth, pinching one’s nose shut while expelling air out as if blowing up a balloon.

fidive terminology Valsalva Maneuver

Variable Weight (VWT)

Diving to depth using weight, then leaving the weight at the bottom and ascending by finning and/or pulling on a dive line using the arms.

Vertical Blue

Vertical Blue is a freediving competition which has been held annually in The Bahamas at Dean’s Blue Hole since April 2008 by freediving world record holder William Trubridge. It is an AIDA International judged competition and has been the venue for multiple world and national records for athletes coming from countries all over the world.

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