Freediving Glossary
37+ terms covering disciplines, physiology, techniques, and equipment. Cross-linked to relevant pages.
Apnea
Voluntary breath hold; the core skill of freediving.
Apnea (from Greek: ἄπνοια) means 'without breathing.' In freediving, it refers to the voluntary suspension of breathing. All freediving disciplines are apneic by nature — the diver holds their breath for the entire dive.
AIDA
Association Internationale pour le Développement de l'Apnée — the global freediving body.
AIDA International is the primary governing body for competitive freediving worldwide. It standardizes rules, runs World Championships, and accredits instructors and judges. AIDA certification levels run from 1★ (introductory) to 4★ (instructor).
Blood Shift
Blood moves from the periphery into the lungs to prevent barotrauma at depth.
At extreme depths, the lungs compress to below residual volume. To prevent a lung squeeze, blood plasma floods into the pulmonary vasculature, maintaining pressure. This mammalian diving reflex allows humans to dive well beyond the theoretical lung compression limit.
Bradycardia
A slowing of the heart rate during a dive.
Dive bradycardia is a reduction in heart rate triggered by the mammalian diving reflex. Elite freedivers can reach heart rates below 20 bpm during deep dives, dramatically reducing myocardial oxygen consumption and extending breath-hold time.
BO — Blackout
Loss of consciousness due to hypoxia.
Blackout (BO) is a loss of consciousness caused by hypoxia (low oxygen). Shallow-water blackout typically occurs during ascent in the last 10 m as blood oxygen continues to drop despite reduced pressure. It is silent and sudden — the diver appears to be gliding normally. Always requires a safety diver.
Bifins
Standard two-fin configuration used in DYN and CWT.
Bifins are the standard two-fin setup (one per foot) used in DYN and CWT disciplines. They use a flutter kick and are generally easier to learn than monofin. Long-blade bifins (70–80 cm) are preferred for freediving.
CWT — Constant Weight
Vertical open-water dive to depth and back using fins.
Constant Weight (CWT) is the most popular open-water discipline. The diver descends and ascends along a dive line using bifins or a monofin, without touching the rope except at the bottom to turn. Weight remains constant throughout.
CNF — Constant Weight No Fins
Vertical dive to depth using only arms and legs.
Constant Weight No Fins (CNF) is the most prestigious open-water discipline. The diver uses only arm and leg movements (a modified breaststroke) to descend and ascend. No fins, no wetsuit in competition, no rope except to turn.
CO₂ (Carbon Dioxide)
The primary trigger for the urge to breathe in freediving.
It is rising CO2 — not falling O2 — that triggers the urge to breathe. In freediving, tolerating CO2 build-up (via CO2 tables) trains the diver to resist the urge to breathe longer, while maintaining full oxygen stores. Never suppress CO2 via hyperventilation.
CO₂ Table
A training protocol of repeated breath-holds with decreasing recovery intervals.
CO2 tables train tolerance to carbon dioxide build-up by keeping recovery short (the CO2 never fully clears). Typically: 8 rounds with the same hold duration and recovery times decreasing each round. This builds resilience to the urge to breathe.
DYN — Dynamic Bifins
Horizontal underwater swim for maximum distance using bifins.
Dynamic with bifins (DYN) is a pool discipline where the diver swims horizontally underwater for as far as possible on a single breath. Bifins (two separate fins) are used, as opposed to a single monofin in DYNB.
DNF — Dynamic No Fins
Horizontal underwater swim for maximum distance without fins.
Dynamic No Fins (DNF) is arguably the most physically demanding pool discipline. The diver swims horizontally underwater using only a modified breaststroke or dolphin-kick technique, with no fins and no wetsuit.
DYNB — Dynamic Monofin
Horizontal pool swim with a single monofin.
Dynamic with Monofin (DYNB) allows a single large monofin for the dolphin kick, producing the fastest and longest pool swims in competition. World records regularly exceed 300 m.
Dive Line
Vertical rope anchored at the bottom, used as a guide for open-water dives.
The dive line is a weighted vertical rope the freediver follows down and up. It provides a reference for depth, equalizes in one direction, and is the rescue route if a safety diver needs to retrieve an unconscious diver.
Equalization
The process of equalizing ear and sinus pressure as depth changes.
As a diver descends, increasing water pressure compresses air spaces. Equalization balances this pressure in the ears and sinuses. Freediving equalization techniques include Valsalva, Frenzel, and mouthfill in order of depth applicability.
FRC — Functional Residual Capacity
Lung volume after a normal passive exhale.
FRC is the volume of air remaining in the lungs after a relaxed exhale. FRC dives start from this mid-lung volume, creating negative buoyancy earlier in the dive and placing greater compression stress on the lungs. Used by advanced freedivers to train for deep diving physiology.
Frenzel Equalization
Advanced equalization using the tongue as a piston rather than the diaphragm.
Frenzel equalization uses the tongue, jaw, and throat muscles to push air into the Eustachian tubes, equalizing ear pressure. Unlike Valsalva (which uses the diaphragm), Frenzel works passively and is more efficient at depth where the diaphragm is compressed. Most freedivers transition to Frenzel after AIDA 2.
Freefall
The neutral-to-negative buoyancy phase of a deep dive where the diver sinks without finning.
Freefall begins around 10–15 m (depending on the diver's weight and lung volume) when the compressed air in the lungs and wetsuit is no longer sufficient to maintain positive buoyancy. The diver relaxes completely and sinks — the most meditative phase of a deep dive.
Hypoxia
Insufficient oxygen reaching the tissues.
Hypoxia in freediving is caused by excessive breath-hold duration or hyperventilation-induced CO2 washout before a dive. Symptoms progress from tingling and euphoria to tunnel vision, LMC, and blackout.
Hyperventilation
Over-breathing that lowers CO2, delaying the urge to breathe — extremely dangerous.
Hyperventilation washes CO2 out of the blood, which suppresses the urge to breathe without increasing oxygen stores. A diver who hyperventilates can lose consciousness from hypoxia before feeling any urge to breathe. It is the leading cause of preventable freediving deaths. Never hyperventilate before a breath-hold.
LMC — Loss of Motor Control
Involuntary muscle spasms/convulsions from hypoxia, diver still conscious.
LMC (Loss of Motor Control), also called 'Samba,' occurs when oxygen levels drop enough to affect motor control but the diver remains conscious. The diver experiences uncontrolled muscle spasms. A safety diver must be present. LMC is a serious warning before a full blackout.
Lanyard
Safety line connecting the freediver to the dive line.
A lanyard is a coiled wrist-to-line safety tether used in deep freediving. If a diver blacks out at depth, the lanyard prevents them from sinking. Competition divers are required to wear a lanyard that clips to the dive line.
Mammalian Diving Reflex
Suite of physiological responses triggered by breath-hold and cold water.
The mammalian diving reflex includes bradycardia (heart rate slowing), peripheral vasoconstriction, spleen contraction (releasing stored red blood cells), and blood shift. These responses conserve oxygen and allow extended and deep dives. Triggered by cold water on the face and breath-hold.
Mouthfill
Advanced deep-diving equalization; a charge of air is held in the mouth and metered into the Eustachian tubes.
The mouthfill technique (developed by Eric Fattah) stores a charge of air in the oral cavity before the glottis closes at depth. The tongue then meters this air into the Eustachian tubes for equalization well beyond the point where the lungs are too compressed to assist. Enables dives beyond 60–70 m.
Monofin
A single large fin straddling both feet, used in DYNB and deep CWT.
A monofin is a single wide fin connecting both feet, enabling a powerful dolphin kick. It generates more thrust than bifins but requires significant technique development. Used in DYNB and advanced CWT.
Molchanov / Molchanovs
A freediving education agency founded by Natalia Molchanova's family.
Molchanovs is a growing freediving education system founded by the family of Natalia Molchanova (the greatest competitive freediver of all time). Their Wave program provides structured progressive freediving education, now popular worldwide including India.
Negative / Negative Entry
Starting a dive by exhaling before submersion to accelerate descent.
A negative dive starts with an exhale before entering the water, reducing buoyancy immediately. This technique (common in competitive No-Limits and CWT training) allows faster freefall and reduced effort in the first phase of the dive.
Neoprene
Synthetic rubber foam used to make wetsuits.
Neoprene is a closed-cell synthetic rubber whose gas-filled bubbles trap heat. In open-cell wetsuits the inner surface is left raw (open cells exposed) for skin contact; the outer surface is lined with nylon for durability.
O₂ Table
Training protocol with increasing hold durations and constant short recovery.
O2 tables push the diver closer to their maximum breath-hold limit by progressively increasing hold duration while keeping recovery constant (typically 2 minutes). They train hypoxic tolerance. O2 tables are more dangerous than CO2 tables — always train with a buddy.
RV — Residual Volume
Air remaining in the lungs after a complete exhale.
Residual Volume is the minimum air volume in the lungs — the volume that cannot be exhaled. Depth limit for CWT is theoretically reached when the diver's RV equals the compressed lung volume at depth. World-class freedivers can dive well beyond their 'theoretical' RV limit via blood shift.
STA — Static Apnea
Face-down breath hold on the surface with no movement.
Static Apnea is the discipline of holding your breath while floating motionless, face-down, in the water. It is the purest test of breath-hold capacity and is the foundation discipline for all other freediving.
Spleen Contraction
The spleen squeezes stored red blood cells into circulation during a dive.
The spleen stores a reservoir of oxygen-rich red blood cells. During a breath-hold dive, it contracts and releases these cells, boosting blood oxygen capacity by up to 10%. Freedivers who train regularly develop larger spleens and a stronger contraction response.
Shallow-Water Blackout
Blackout occurring during ascent, typically in the last 10 m.
During descent, high pressure partially raises blood oxygen levels, masking the true depletion. On ascent, pressure drops rapidly, causing PO2 to plummet. The critical phase is the last 10 m where this effect is most pronounced. This is why one-up-one-down is the fundamental buddy safety rule.
Samba
Colloquial term for Loss of Motor Control (LMC).
Samba is the informal term for LMC — named for the involuntary body movements that resemble dancing. It occurs on surfacing and indicates severe hypoxia. A safety diver should immediately support the diver and perform the recovery protocol.
TLC — Total Lung Capacity
The maximum volume of air the lungs can hold.
TLC is the total air volume after a maximum inhalation. Most freediving breath-holds begin at TLC — a full breath. TLC dives provide maximum oxygen stores and positive buoyancy in shallow water.
Valsalva Equalization
Basic equalization by closing the nose and blowing gently.
Valsalva is the most commonly taught equalization technique — pinch the nose and gently blow. It works well at shallow depths but becomes unreliable below 20–30 m as the diaphragm compresses. Freedivers eventually replace it with Frenzel technique.
Wetsuit (Open-Cell)
Freediving wetsuits are made of open-cell neoprene for warmth and flexibility.
Freediving wetsuits use open-cell neoprene on the interior, which creates a suction seal against skin for excellent insulation. They are softer and more flexible than scuba wetsuits but more fragile and must be lubricated to don. Typical thickness in India: 1.5–3 mm.
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