What is freediving?

August 23, 2021

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Freediving is quite probably the world’s most spectacular sport. This amazing activity where human beings descend to incredible depths while holding their breaths dates back to ancient times. That’s why Freediving is also called the Original Extreme Sport, because as a manifestation of the human spirit, it was born way before there were bicycles, skates, surf boards, parachutes, or skis. As such, Freediving enjoys the prestige and awe inspiring mystique that amazes thrill seekers and scientists alike. Indeed, those divers who can descend to such depths rely on unique adaptations of their bodies which enable them to survive the crushing pressures found at depth, in exactly the same way that dolphins and whales do it. It could be said that top class Freedivers are not only extremely gifted athletes, but also some sort of evolutionary mutants, a different specie on their own. The race for the World Records started officially in 1949 and, since then, only a handful of men and women have been able to put their names in the select book of records. That first record saw a man reach depth of 30 meters/100 feet then, and fifty-two years later the current records stand at 150 meters/492 feet!

Freediving Physiology

Mammalian Diving Reflex

This is an adaptation found on all diving mammals, which comprises a set of changes that allow them to perform extended depth/duration dives under phenomenal pressures. This amazing phenomenon was first observed and documented on animals such as whales, dolphins, penguins, seals, etc., but up until as recently as the 1950’s it was thought that the human being did not posses any of these faculties. The era of deep breath hold dives that started at that time proved science (or scientists rather) wrong, and studies the human diving potential began. So far, all of the different manifestations that form the mammalian diving reflex have been observed in human beings, proving that this fantastic capacity lays dormant in all of us.

Bradycardia

Bradycardia is the most common of all the manifestations of the mammalian diving reflex. As soon as the brain detects the signs that come with immersion in water, such as decreased temperatures and an increase in ambient pressure, it slows down the heart, thus the name brady (low) cardia (heart beat). The heart is the muscle in the body, which is always working, thus its energy and oxygen consumption is high, so by decreasing the frequency of its beats, a reduction in the use of oxygen is achieved. As the immersion becomes longer and/or deeper, the heartbeat becomes slower and slower, allowing the body to survive under such extreme conditions.

Peripheral Vasoconstriction

As the mammal, or in this case the human being, continues to be immersed other adaptations come into play. At higher pressures, which means deeper depths, the blood from all the periphery starts being taken away. All blood vessels and capillaries and toes, fingers, hands, feet, and ultimately arms and legs, constrict themselves reducing circulation in these areas to a minimum. This blood will be used to irrigate more important organs which require a steady supply of oxygen such as the brain.

Blood Shift

The most amazing, and profound in meaning of all the adaptations associated with the Mammalian Diving Reflex, the blood shift is truly what saves a mammals life during deep dives. In simple words, the blood shift means that all the blood pulled from the extremities will be forced into the organs of the thoracic cavity, to prevent them from collapsing under pressure. This applies also to the lungs, where every alveoli is engulfed with blood plasma from the surrounding tissue. So that in fact the lung volume never goes below residual capacity as the diver dives deeper, this adaptation will become more acute, and will consequently revert itself upon ascent.

Blackout

The word “blackout” means, literally, absence of light, or obscurity. This defines very well an unconscious state, which can result during freediving. Why and how does unconsciousness happen underwater? Most commonly, it will be the result of a brain reaction to the balance of the 2 most important gases in our body: oxygen (O2) and carbon dioxide (Co2). Oxygen is the body’s fuel, needed for all tissues and cells to function, like the gasoline to run an engine, and Co2 is the waste product of this engine, the “exhaust fumes” that remain. A proper balance will have adequate levels of both, with O2 not dropping too low and C02 not climbing too high. Whenever this equilibrium is broken, and one or both of these gases goes off its normal values drastically, the brain can shut down all main activity (resulting in unconsciousness) and remain in an “energy conservation” mode until balance is restored. All sensory activity is decreased to a minimum, and only the essential functions are kept. If the brain receives an adequate supply of oxygen within an acceptable time limit, then all nervous activity will be “restarted” and consciousness will be restored, but this must happen quickly, the quicker the better. The longer it takes for the brain to receive oxygen, the more damage it will sustain and the more permanent this damage will be.

The most common cause for a blackout is lack of oxygen, which can be compounded by high levels of Co2, as happens during a freedive, when the body is working without a constant supply of O2, and creating more and more Co2 as the diver works underwater. This scenario affects the O2/Co2 balance both ways, decreasing the former and increasing the latter one. Typically, and most commonly, the blackout happens as the diver is ascending, close to the surface and near the end of the dive. When the diver descends, the pressure exerted by the surrounding water on his lungs and blood will effectively increase the partial pressure of oxygen in the blood (not the amount of O2, just its pressure) so this will be enough to maintain functionality at depth. However, as he ascends, the surrounding pressure decreases and so does the O2 pressure, while the Co2 amount rises as a result of the effort of ascending, which can potentially lead to a blackout. However, the generalization that this will only happen upon ascend must not be accepted as the norm. A blackout can happen anywhere, to anybody and at any time during any dive.

Freediving Categories

Freediving is divided into several categories. Basically, any activity that is performed underwater while breathholding can be considered freediving. However, depending on whether the diver wants to reach a depth, a distance or a time, and what equipment and techniques the diver is using to achieve these goals, then the categories will be different. The most respected and important categories are the Vertical Immersion categories, although the Horizontal Immersion categories are very popular due to the availability of practice means.

Vertical Immersion

In these categories the objective of the diver is to reach a certain depth and they are divided in two main groups: Constant Ballast and Variable Ballast.

Constant Ballast

In this group, the diver must complete the dive and return to the surface carrying with him/her exactly the same equipment that he/she took underwater at the beginning of the dive. This includes any weight, and thus the category’s a name. The allowable equipment is only equipment that remains attached to the diver and which must be activated by the diver’s own physical energy. This may include fins, masks, suits, snorkels, or nothing at all. Based on this, there are three different categories in this group:

Equipment Assisted Constant Ballast

Diver may use any diving gear, but must complete the dive without any other assistance, including the descent line or rope used for reference. This is usually achieved with the use of fins so the diver basically kicks down and up. This is considered as the most popular category since it has long had the push of diving gear manufacturers to show off their products.

Line Assisted Constant Ballast

The diver is not allowed to use any diving gear that may provide propulsion, like fins. The only accepted means of propulsion is by arm-pulling on a line/rope that goes from the surface to the goal depth. Any equipment used for purposes other than propulsion, such as wetsuits, masks, etc, is accepted. This category is very respected, since it requires great physical strength and flawless technique.

Unassisted Constant Ballast

This is the purest form of freediving, only accepted as an official category very recently. The diver may not use any equipment for propulsion nor the line for pulling, thus having to swim on his/her own all the way down and up (hence the nickname “frog style”). Both men and women records in this category are still open, as no official dive has been performed in the presence of Judges yet.

Variable Ballast

The diver may use a weighted device (known as “sled”) to speed up his/her descent, which can be abandoned once the intended depth is reached.The ascent, however, must be performed under the diver’s own power, although he/she may use any gear of preference and/or pull on the line. This category is a cross between Constant Ballast and Variable Ballast and this is well like by all freedivers.

Limited Variable Ballast

Unlimited Variable Ballast:

The diver may use the sled for the descent and, in addition, an auxiliary device such as a balloon or lift-bag may be used to speed up the ascent as well. This is the deepest and most extreme of all freediving categories, and thus the most spectacular.It is on this type of freediving that the popular film “The Big Blue” is based on. The logistical and financial requirements associated with this category make it almost prohibitive, so new records here are always eagerly anticipated by the legion of fans around the world.

Horizontal Immersion

In these categories the objective of the diver is to reach a certain depth and they are divided in two main groups: Constant Ballast and Variable Ballast.

Constant Ballast

The goal of this type of freediving is to reach a distance underwater rather than a depth. The depth is not important here, as long as the diver remains submerged while swimming horizontally. This is usually done in a swimming pool, although horizontal immersion is also practiced in the sea or lakes in shallow depths.

Equipment Assisted Horizontal Immersion

In this category the diver can use fins or any other swimming gear of preference. The diver must complete the dive with same equipment from beginning to end.

Unassisted Horizontal Immersion

In this category the diver is not allowed to use fins.

Yasemin Dalkilic