Freediving, free-diving, free diving, breath-hold diving, or skin diving, is a mode of underwater diving that relies on breath-holding until resurfacing rather than the use of breathing apparatus such as scuba gear.
Besides the limits of breath-hold, immersion in water and exposure to high ambient pressure also have physiological effects that limit the depths and duration possible in freediving.
Examples of freediving activities are traditional fishing techniques, competitive and non-competitive freediving, competitive and non-competitive spearfishing and freediving photography, synchronised swimming, underwater football, underwater rugby, underwater hockey, underwater target shooting and snorkeling. There are also a range of "competitive apnea" disciplines; in which competitors attempt to attain great depths, times, or distances on a single breath.
Historically, the term free diving was also used to refer to scuba diving, due to the freedom of movement compared with surface supplied diving.
See also: Sponge diving and Pearl hunting.
In ancient times freediving without the aid of mechanical devices was the only possibility, with the exception of the occasional use of reeds and leather breathing bladders. The divers faced the same problems as divers today, such as decompression sickness and blacking out during a breath hold. Freediving was practiced in ancient cultures to gather food, harvest resources such as sponge and pearl, reclaim sunken valuables, and to help aid military campaigns.
In Ancient Greece, both Plato and Homer mention the sponge as being used for bathing. The island of Kalymnos was a main centre of diving for sponges. By using weights (skandalopetra) of as much as 15kg (33lb) to speed the descent, breath-holding divers would descend to depths up to 30m (100feet) to collect sponges. Harvesting of red coral was also done by divers.
The Mediterranean had large amounts of maritime trade. As a result of shipwrecks, particularly in the fierce winter storms, divers were often hired to salvage whatever they could from the seabed. Divers would swim down to the wreck and choose the most valuable pieces to salvage.
Divers were also used in warfare. Defenses against sea vessels were often created, such as underwater barricades, and hence divers were often used to scout out the seabed when ships were approaching an enemy harbor. If barricades were found, it was divers who were used to disassemble them, if possible. During the Peloponnesian War, divers were used to get past enemy blockades to relay messages as well as supplies to allies or troops that were cut off, and in 332 BC, during the Siege of Tyre, the city used divers to cut the anchor cables of Alexander's attacking ships.[1]
In Japan, ama divers began to collect pearls about 2,000 years ago.For thousands of years, most seawater pearls were retrieved by divers working in the Indian Ocean, in areas such as the Persian Gulf, the Red Sea, and in the Gulf of Mannar (between Sri Lanka and India). A fragment of Isidore of Charax's Parthian itinerary was preserved in Athenaeus's 3rd-century Sophists at Dinner, recording freediving for pearls around an island in the Persian Gulf.
Pearl divers near the Philippines were also successful at harvesting large pearls, especially in the Sulu Archipelago. At times, the largest pearls belonged by law to the sultan, and selling them could result in the death penalty for the seller. Nonetheless, many pearls made it out of the archipelago by stealth, ending up in the possession of the wealthiest families in Europe. Pearling was popular in Qatar, Bahrain, Japan, and India. The Gulf of Mexico was also known for pearling.Native Americans harvested freshwater pearls from lakes and rivers like the Ohio, Tennessee, and Mississippi, while others dived for marine pearls from the Caribbean and waters along the coasts of Central and South America.
In 1940, Dottie Frazier pioneered freediving for women in the United States and also began teaching classes. It was also during this time that she began to design and sell rubber suits for Navy UDT divers.
Spearfishing is an ancient method of fishing that has been used throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks.
Today modern spearfishing makes use of elastic powered spearguns and slings, or compressed gas pneumatic powered spearguns, to strike the hunted fish. Specialised techniques and equipment have been developed for various types of aquatic environments and target fish. Spearfishing may be done using free-diving, snorkelling, or scuba diving techniques. Spearfishing while using scuba equipment is illegal in some countries. The use of mechanically powered spearguns is also outlawed in some countries and jurisdictions. Spearfishing is highly selective, normally uses no bait and has limited by-catch.
Some types of shellfish are collected by freediving. One example is the historical recreational collection of abalone in South Africa, before illegal harvesting reduced stocks to levels which resulted in recreational collection being banned indefinitely. This did not completely stop illegal harvesting because selling illegally harvested abalone remained lucrative.
Aquathlon (also known as underwater wrestling) is an underwater sport where two competitors wearing masks and fins wrestle underwater in an attempt to remove a ribbon from each other's ankle band in order to win the bout. The "combat" takes place in a 5-metre (16 ft) square ring within a swimming pool, and is made up of three 30-second rounds, with a fourth round played in the event of a tie. The sport originated during the 1980s in the former USSR (now Russia) and was first played at international level in 1993. It was recognised by the Confédération Mondiale des Activités Subaquatiques (CMAS) in 2008.
Competitive spearfishing is defined by the world governing body CMAS as "the hunting and capture of fish underwater without the aid of artificial breathing devices, using gear that depends entirely on the physical strength of the competitor." They publish a set of competition rules that are used by affiliated organisations.
Synchronized swimming is a hybrid form of swimming, dance, and gymnastics, consisting of swimmers (either solos, duets, trios, combos, or teams) performing a synchronized routine of elaborate moves in the water, accompanied by music. Synchronized swimming demands advanced water skills, and requires great strength, endurance, flexibility, grace, artistry and precise timing, as well as exceptional breath control when upside down underwater. During lifts swimmers are not allowed to touch the bottom.
Traditionally it was a women's sport, but following the addition of a new mixed-pair event, FINA World Aquatics competitions are open to men since the 16th 2015 championships in Kazan, and the other international and national competitions allow male competitors in every event. However, men are currently still barred from competing in the Olympics. Both USA Synchro and Synchro Canada allow men to compete with women. Most European countries also allow men to compete, and France even allows male only podiums, according to the number of participants. In the past decade, more men are becoming involved in the sport and a global biannual competition called Men's Cup has been steadily growing.
Swimmers perform two routines for the judges, one technical and one free, as well as age group routines and figures. Synchronized swimming is both an individual and team sport. Swimmers compete individually during figures, and then as a team during the routine. Figures are made up of a combination of skills and positions that often require control, strength, and flexibility. Swimmers are ranked individually for this part of the competition. The routine involves teamwork and synchronization. It is choreographed to music and often has a theme. Synchronized swimming is governed internationally by FINA (Fédération Internationale de Natation).
Underwater hockey (also called octopush, mainly in the United Kingdom) is a globally played limited-contact sport in which two teams compete to manoeuvre a hockey puck across the bottom of a swimming pool into the opposing team's goal by propelling it with a hockey stick. The sport originated in England in 1954 when Alan Blake, the founder of the newly formed Southsea Sub-Aqua Club, invented the game he called octopush to keep the club's members interested and active during the cold winter months, when open-water diving lost its appeal. Underwater hockey is now played worldwide, governed by the Confédération Mondiale des Activités Subaquatiques (CMAS). The first Underwater Hockey World Championship was held in Canada in 1980, after a planned championship in 1979 was scuttled by international politics and apartheid.
Underwater football is a two-team underwater sport that shares common elements with underwater hockey and underwater rugby. As with both of those games, it is played in a swimming pool with snorkeling equipment (mask, snorkel, and fins). The goal of the game is to manoeuvre (by carrying and passing) a slightly negatively buoyant ball from one side of a pool to the other by players who are completely submerged underwater. Scoring is achieved by placing the ball (under control) in the gutter on the side of the pool. Variations include using a toy rubber torpedo as the ball, and weighing down buckets to rest on the bottom and serve as goals.
It is played in the Canadian provinces of Alberta, Manitoba, Newfoundland and Labrador, and Saskatchewan.
Underwater rugby is an underwater team sport. During a match, two teams try to score a negatively buoyant ball (filled with saltwater) into the opponents’ goal at the bottom of a swimming pool. It originated from within the physical fitness training regime existing in German diving clubs during the early 1960s and has little in common with rugby football except for the name. It was recognised by the Confédération Mondiale des Activités Subaquatiques (CMAS) in 1978 and was first played as a world championship in 1980.
Underwater target shooting is an underwater sport that tests a competitors’ ability to accurately use a speargun via a set of individual and team events conducted in a swimming pool using free diving or apnea technique. The sport was developed in France during the early 1980s and is currently practised mainly in Europe. It is known as Tir sur cible subaquatique in French and as Tiro al Blanco Subacuático in Spanish.
Competitive freediving is currently governed by two world associations: AIDA International and Confédération Mondiale des Activités Subaquatiques (CMAS). Historically, there were two more organisations that regulated freediving records and activities — International Association of Freedivers (IAFD) and Freediving Regulations and Education Entity (FREE). Each organization has its own rules on recognizing a record attempt which can be found on the organization's website. Alongside competitive disciplines, there are record disciplines — disciplines that are not held in competitions, that are just for setting world records. There is a third organization, Guinness, which in addition to AIDA and CMAS presides over record disciplines.
Almost all types of competitive freediving are individual sports based on the best individual achievement. Exceptions to this rule are the bi-annual AIDA Team World Championship, where the combined score of the team members makes up the team's total points, and Skandalopetra diving competitions held by CMAS, the only truly ‘team’ event in freediving for which teams are formed by two athletes: one acting as the diver and the other acting as an assistant .
There are currently eleven recognized disciplines defined by AIDA and CMAS, and a dozen more that are only practiced locally. All disciplines can be practiced by both men and women, and only CMAS currently separates records in fresh water from those at sea. The disciplines of AIDA can be done both in competition and as a record attempt, with the exception of variable weight and no limits, which are both solely for record attempts. For all AIDA depth disciplines, the depth the athlete will attempt is announced before the dive; this is accepted practice for both competition and record attempts. Most divers choose monofin (MF) over bifins (BF) where there is a choice.
| Discipline | Measurement | AIDA | CMAS | Description | |||
|---|---|---|---|---|---|---|---|
| open water | pool | open water | pool | ||||
| Constant weight apnea (CWT) | depth | – | – | Maximum depth following a guide line. The line to act solely as a guide and only a single hold of the rope to stop the descent and start the ascent is permitted. Dropping dive weights is not permitted. Both bi-fins and monofin are permitted and the technique is irrelevant. | |||
| Constant weight bi-fins (CWT BF, CWTB) | depth | – | – | As for CWT above but monofins are not permitted and the athlete is prohibited to use a dolphin kick for his / her propulsion. | |||
| Constant weight without fins (CNF) | depth | – | – | As for CWT above but no swimming aids such as fins are permitted. This discipline is the most recently recognised discipline having been recognised by AIDA since 2003. | |||
| Dynamic apnea without fins (DNF) | horizontal distance | – | Maximum distance underwater, in a pool, no swimming aids such as fins are permitted (AIDA). | ||||
| Dynamic apnea with fins (DYN) | horizontal distance | – | Maximum horizontal distance on one breath in a pool. Monofin or bi-fins are permitted and the technique is irrelevant. | ||||
| Dynamic apnea with bifins (DYN BF, DYNB) | horizontal distance | – | – | Same as DYN above but monofins are not permitted and the athlete is prohibited to use a dolphin kick for his / her propulsion. | |||
| Free immersion apnea (FIM) | depth | – | – | Maximum depth following a vertical line. The line may be used to pull down to depth and back to the surface. No ballast or fins are permitted. It is known for its ease compared with the Constant Weight disciplines, while still not permitting the release of weights. | |||
| Jump blue (JB, also the cube) | horizontal distance | – | Maximum distance covered around a 15-metre square at a depth of 10 metres. Monofin, bi-fins or no fins are all permitted. Sled may be used for descent. | ||||
| No-limits apnea (NLT) | depth | – | Any means of breath-hold diving to depth and return to the surface is permitted provided that a guideline is used to measure the distance. Most divers use a weighted sled to descend and an inflatable bag to ascend. | ||||
| Skandalopetra | depth & min. time | – | The only true team event in freediving. Diver 1 descends, usually assisted by a stone or marble slab attached to a rope, while Diver 2 waits on the surface. Diver 1 reaches the target depth and is hauled to the surface by Diver 2 using only muscle power. No diving mask, suit or fins are permitted, only nose clip. | ||||
| Static apnea (STA) | max. time | Timed breathhold endurance while floating on the surface or standing on the bottom. Usually in a pool. | |||||
| Static apnea with pure oxygen (STA O2) | max. time | Timed breathhold endurance, pre-breathing 100% oxygen for up to 30 minutes prior to the breathhold is permitted. Usually in a pool. Although no longer recognised by either AIDA or CMAS there were three instances of records being approved by AIDA. | |||||
| Speed-endurance apnea (S&E apnea) | min. time | – | Shortest time over a fixed, underwater distance. An endurance sub-discipline is swum in fractions of a pool length alternating apnoea swimming with passive recovery at the intervals. Disciplines are SPE – 100m speed apnoea, END 16x50 – 800m and END 8x50 – 400m endurance apnoea. | ||||
| Variable weight apnea without fins (VNF) | depth | – | Descent is assisted by a weighted sled sliding down a line, the ascent may be by pulling up along the line or swimming without fins. | ||||
| Variable weight apnea (VWT) | depth | – | – | Descent is assisted by a weighted sled sliding down a line, the ascent may be either by: 1.) pulling up along the line or swimming with or without fins under AIDA rules 2.) swimming with fins under CMAS rules. | |||
| Discipline | Aids permitted | Weight change permitted? | ||
|---|---|---|---|---|
| Descent | Ascent | |||
| CNF | None or weight | None | No | |
| CWT | BF / MF and/or weight | BF / MF | No | |
| CWT BF | BF and/or weight | BF | No | |
| DNF | – | – | – | |
| DYN | – | – | – | |
| DYN BF | – | – | – | |
| FIM | Rope or none | Rope or none | No | |
| JB | Sled and/or BF / MF or none | BF / MF or none | Sled only | |
| NLT (No Limit) (Only AIDA) | Any | Any | Yes | |
| Skandalopetra | Stone | Hauled up | Yes | |
| STA | – | – | – | |
| STA O2 | – | – | – | |
| S&E Apnoea | – | – | – | |
| VNF (only CMAS) | Sled | Rope or none | Yes | |
| VWT | Sled | BF / MF or rope | Yes | |
Following the deaths of two freedivers in competitions, AIDA has a system set up for monitoring and if necessary, recovering competitors who lose consciousness underwater.As of 2022 the incidence of adverse events in depth competitions varies between 3 and 4%. This rate is considered relatively low and is expected during competitions where divers push their breath-hold limits. Almost all of these divers are successfully assisted and recover completely. There is a much lower incidence of more serious injuries.[2]
The safety team is usually made up of volunteers, but in major events they may be paid staff, and is supervised by the . Each competitor is monitored by a team of breath-hold safety divers who will descend in time to meet the competitor during their ascent, and monitor them for the rest of the ascent. They will intervene if necessary, typically by securing the competitor's airway and swimming them up to the surface. The first safety diver will meet the competitor at somewhere around 1/3 to 1/4 of the target depth, usually with a maximum of 30m. The second will meet them about 10m shallower, and a third will be on standby in case of an emergency. The work can be challenging as many dives are done in a day, so the team of safety divers is usually rotated to ensure that they are not overtasked.[2]
In case of a deeper incident, the competitor is clipped to the downline for the duration of the dive, which can be rapidly raised by the surface support team, which includes a medical support group.[2]
The best official result in static apnea is the Guinness WR of 11:54 by Branko Petrović in 2014, a freediver who has results over 10 minutes under both AIDA and CMAS.The best no limits result is 253.2m by Herbert Nitsch in 2012; his intention of having the dive sanctioned by AIDA fell through due to a sponsoring conflict.After 2001, AIDA International no longer separated the records achieved in fresh water from those in the sea.
, the CMAS recognized world records are:
| Static apnea | STA< | -- time --> | Men | – | – | 10:45.000 | 2017-11-11 | Subotica, Serbia | |
|---|---|---|---|---|---|---|---|---|---|
| Women | – | – | 08:53.150 | 2017-06-15 | Cagliari, Italy | ||||
| Dynamic apnea with fin | DYN < | -- distance --> | Men | – | 321.43 | – | 2022-06-15 | Belgrade, Serbia | |
| Women | – | 275.36 | – | 2022-06-15 | Belgrade, Serbia | ||||
| under ice< | -- distance --> | Men | – | 175 | – | Lake Sonnanen, Finland | |||
| Women | – | 140 | – | Lake Anterselva, Italy | |||||
| open water < | -- distance --> | Men | – | 200 | – | ||||
| Women | – | – | |||||||
| Dynamic apnea with bifins | DBF | Men | – | 274.70 | – | 2022-06-13 | Belgrade, Serbia | ||
| Women | – | 250.00 | – | 2022-06-13 | Belgrade, Serbia | ||||
| Dynamic apnea without fins | DNF-50< | -- distance --> | Men | – | 236 | – | 2019-06-19 | Istanbul, Turkey | |
| Women | – | 210 | – | 2022-06-12 | Belgrade, Serbia | ||||
| DNF-25 < | -- distance --> | Men | – | 220.70 | – | 2021-03-28 | Sisak, Croatia | ||
| Women | – | 206.20 | – | 2021-03-28 | Sisak, Croatia | ||||
| Speed 100 m. | SPE | Men | – | – | 00:30.350 | 2018-06-15 | Lignano, Italy | ||
| Women | – | – | 00:35.860 | 2017-06-15 | Cagliari, Italy | ||||
| Endurance | END16x50 | Men | – | – | 09:10.030 | 2019-06-19 | Istanbul, Turkey | ||
| Women | – | – | 10:41.120 | 2021-06-23 | Belgrade, Serbia | ||||
| END8x50 | Men | – | – | 03:25.720 | 2019-06-22 | Istanbul, Turkey | |||
| Women | – | – | 04:10.190 | Kuwait | |||||
| END4x50 | Men | – | – | ||||||
| Women | – | – | 01:33.860 | Kuwait | |||||
| Jump blue apnea with fins | at sea < | -- distance --> | Men | – | 201.61 | – | 2015-10-09 | Ischia, Italy | |
| Women | – | 190.48 | – | 2015-10-09 | Ischia, Italy | ||||
| < | -- distance --> | Men | – | 170 | – | ||||
| Women | – | 132.92 | – | ||||||
| Constant weight with fins | at sea < | -- depth --> | Men | 136 | – | – | 2023-08-23 | Roatan, Honduras | |
| Women | 122 | – | – | 2021-07-21 | Long Island, Bahamas | ||||
| fresh water < | -- depth --> | Men | 80 | – | – | ||||
| Women | 57 | – | – | 1998-12-28 | Ocala, Fl, USA | ||||
| Constant weight with bifins (CWT BF) | at sea < | -- depth --> | Men | 124 | – | – | 2023-08-25 | Roatan, Honduras | |
| Women | 106 | – | – | 2021-09-30 | Kaş, Turkey | ||||
| fresh water < | -- depth --> | Men | 75 | – | – | ||||
| Women | – | – | |||||||
| Constant weight without fins | at sea < | -- depth --> | Men | 100 | – | – | 2023-08-23 | Roatan, Honduras | |
| Women | 78 | – | – | 2023-08-24 | Roatan, Honduras | ||||
| fresh water | Men | 65 | – | – | 2016-07-10 | Weyregg, Austria | |||
| Women | – | – | – | – | – | – | |||
| Free immersion apnea | at sea < | -- depth --> | Men | 132 | – | – | 2022-10-04 | Kaş, Turkey | |
| Women | 72 | – | – | 2021-07-17 | Long Island, Bahamas | ||||
| Variable weight apnea monofin | at sea < | -- distance --> | Men | 131 | – | – | 2012-09-11 | Soverato, Italy | |
| Women | 116 | – | – | 2022-06-25 | Sharm el Sheik, Egypt | ||||
| Variable weight apnea bifins | at sea < | -- distance --> | Men | 130 | – | – | 2021-10-21 | Sharm el Sheik, Egypt | |
| Women | - | – | – | ||||||
| Variable weight apnea without fins (VNF) | at sea < | -- depth --> | Men | 140 | – | – | 2023-12-11 | Sharm el_sheijk, Egypt | |
| Women | 106 | – | – | 2023-10-17 | Hatay, Turkey | ||||
| Skandalopetra | at sea < | -- depth --> | Men | 112 | – | – | 2014-06-26 | Red Sea, Egypt | |
| Women | 68.9 | – | – | 2012 | Bonaire, Caribbean |
The AIDA recognized world records are:[3]
| Discipline | Gender | Depth [m] | Distance [m] | Time | Name | Date | Place | |
|---|---|---|---|---|---|---|---|---|
| Static apnea (STA) < | -- time --> | Men | – | – | 11 min 35 sec | Hyères, Var, France | ||
| Women | – | – | 9 min 02 sec | Belgrade, Serbia | ||||
| Dynamic apnea with fins (DYN)< | -- distance --> | Men | – | 316.53 | – | Turku, Finland | ||
| Women | – | 257 | – | Vienna, Austria | ||||
| Dynamic apnea with bifins (DYNB)< | -- distance --> | Men | – | 250 | – | Vienna, Austria | ||
| Women | – | 208 | – | Moscow, Russia | ||||
| Dynamic apnea without fins (DNF)< | -- distance --> | Men | – | 244 | – | Turku, Finland | ||
| Women | – | 191 | – | Opole, Poland | ||||
| Constant weight apnea (CWT)< | -- depth --> | Men | 133 | – | – | Dean's Blue Hole, Long Island Bahamas | ||
| Women | 123 | – | – | Camotes Island, Philippines | ||||
| Constant weight apnea with bifins (CWTB)< | -- depth --> | Men | 122 | – | – | Dean's Blue Hole, Long Island Bahamas | ||
| Women | 111 | – | – | Dean's Blue Hole, Long Island Bahamas | ||||
| Constant weight apnea without fins (CNF)< | -- depth --> | Men | 102 | – | – | Dean's Blue Hole, Long Island Bahamas | ||
| Women | 73 | – | – | Dean's Blue Hole, Long Island Bahamas | ||||
| Free immersion apnea (FIM)< | -- depth --> | Men | 133 | – | – | Dean's Blue Hole, Long Island Bahamas | ||
| Women | 102 | – | – | Dean's Blue Hole, Long Island Bahamas | ||||
| Variable weight apnea (VWT)< | -- depth --> | Men | 150 | – | – | Sharm el-Sheikh, Egypt | ||
| Women | 130 | – | – | Sharm el-Sheikh, Egypt | ||||
| No Limit apnea (NLT)< | -- depth --> | Men | 214 | – | – | Santorini, Greece | ||
| Women | 160 | – | – | Turks and Caicos |
| Discipline | Gender | Points | Team / Individual | Date | Place |
|---|---|---|---|---|---|
| AIDA team | Men | 840.6 | Goran Čolak, Božidar Petani, Veljano Zanki | 2012-09-16 | Nice, France |
| Women | |||||
| Men | 313.3 | 2010-07-06 | Okinawa, Japan | ||
| Women | |||||
The following table only includes those disciplines that are modifications of existing AIDA or CMAS disciplines and Guinness-exclusive (as it recognizes and inherits some AIDA/CMAS records) or Guinness-conceived (CMAS and AIDA do/did sanction at some time) disciplines.
| Discipline | Gender | Depth [m] | Distance [m] | Time | Name | Date | Place |
|---|---|---|---|---|---|---|---|
| STA O2 | Men | – | – | 24:11 | 24 February 2018 | Zagreb | |
| Women | – | – | 18:32 | 10 July 2009 | Florianopolis | ||
| DYN under ice | Men | – | 175 | – | details under CMAS world records | ||
| Women | – | 125 | – | ||||
| DNF under ice | Men | – | 84 | – | Feb 2013 | Weissensee | |
| Women | – | – | |||||
| DNF under ice (no diving suit) | Men | – | 81 | – | Feb 2021 | Lahošť lake | |
| Women | – | 50 | – | Mar 2015 | Päijänne | ||
| NLT under ice | Men | 65 | – | – | Feb 2013 | Weissensee | |
| Women | – | – | |||||
Freediving as a recreational activity is widely practiced and differs significantly from scuba diving. Although there are potential risks to all freediving, it can be safely practiced using a wide range of skill levels from the average snorkeler to the professional freediver. Compared to scuba diving, freediving offers:
Freshwater springs, often with excellent visibility, provide good freediving opportunities but with greater risks. Diving into spring caverns with restricted access to the surface is very different from diving in open water. The time available to a freediver to solve problems underwater before hypoxia sets in is severely restricted in comparison with scuba. Freediving into confined cave systems such as Eagle's Nest Cave, Florida and Blue Springs State Park, Florida has resulted in several deaths. Cave freediving is commonly discouraged in basic freediver safety training.
See also: Human physiology of underwater diving. The human body has several oxygen-conserving adaptations that manifest under diving conditions as part of the mammalian diving reflex. The adaptations include:
Significant drop in heart rate.
Blood flow and volume is redistributed towards vital organs by means of a reflex vasoconstriction. Blood vessels distend and become engorged, which in the case of the pulmonary capillaries assists with pressure compensation that comes with increasing diving depth, and without which a largely air-filled chest cavity would simply collapse for lack of compliance.
Releasing red blood cells carrying oxygen.
See also: Skandalopetra diving. Breath-holding ability, and hence dive performance, is a function of on-board oxygen stores, scope for metabolic rate reduction, efficient oxygen utilization, and hypoxia tolerance. Athletes attempt to accomplish this in various ways. Some divers use "packing", which increases lung volume beyond normal total lung capacity. In addition, training is allocated to enhance blood and muscle oxygen stores, to a limited extent.Most divers rely on increasing fitness by increasing tolerance and lung capacity. Simple breath-holding practice is highly effective for the build-up of tolerance to CO2 and to some degree increased lung capacity. In an interview on the radio talk show Fresh Air, journalist James Nestor, author of the book , stated: "Some divers have a lung capacity of 14 liters, which is about double the size for a typical adult male. They weren't born this way. ... They trained themselves to breathe in ways to profoundly affect their physical bodies."
See also: Skandalopetra diving.
There is no requirement by law that free-divers are required to do freediving courses or get certified. Although, due to the risks, it is recommended to take lessons and get certified. The free-divers course contains three levels: theory studies, a confined water sessions generally completed in a swimming pool, and open water sessions in the ocean or Reservoir. [4] [5]
Training for freediving can take many forms, some of which can be performed on land. The University of Miami presents a scientific freediving class that was developed by Claire Paris, a professor and freediver,[6] the class is the first of its kind at the university.[7] [8]
One example is the apnea walk. This consists of a preparation "breathe-up", followed by a short (typically 1 minute) breath hold taken at rest. Without breaking the hold, participants then begin walking as far as possible until it becomes necessary to breathe again. Athletes can do close to 400 meters in training this way.
This form of training is good for accustoming muscles to work under anaerobic conditions, and for tolerance to CO2 build-up in the circulation. It is also easy to gauge progress, as increasing distance can be measured.
Before competition attempts, freedivers perform a preparation sequence, which usually consists of physical stretching, mental exercise and breath exercise. It may include a succession of variable length static apnea and special purging deep breaths. Results of the preparation sequence are slower metabolism, lower heart rate and breath rate, and lower levels of carbon dioxide in the bloodstream and overall mental equilibrium.
The most obvious hazard is lack of access to air for breathing – a necessity for human life. This can result in asphyxia from drowning if the diver does not reach the surface while still capable of holding their breath and resuming breathing. The risk depends on several factors, including the depth, duration and shape of the dive profile.
Latent hypoxia is a specific hazard of deeper freedives. This effect can cause hypoxic blackout during surfacing.
There is also a wide range of environmental hazards possible specific to the site and water and weather conditions at the time of diving, and there may be other hazards specific to the freediving activity.
See also: Freediving blackout. Failing to respond to physiological warning signals, or crossing the mental barrier by strong will, may lead to blackout underwater or on reaching the surface. Trained freedivers are well aware of this and competitions must be held under strict supervision and with competent first-aiders on standby. However, this does not eliminate the risk of blackout. Freedivers are encouraged by certification and sporting organisations to dive only with a 'buddy' who accompanies them, observing from in the water at the surface, and ready to dive to the rescue if the diver loses consciousness during the ascent. This is only reasonably practicable if the water clarity allows observation, and the buddy is capable of safely reaching the diver. Due to the nature of the sport, the risks of freediving can be reduced by strict adherence to safety measures as an integral part of the activity, but cannot be eliminated. Competition rules may require all participants to be adept in rescue and resuscitation.
Nicholas Mevoli, a diver from New York died on 17 November 2013 after losing consciousness on surfacing from a 3-minute 38 second dive to a depth of during an official record attempt in the "constant weight without fins" event. He had previously reached greater depths and longer times in other disciplines.