Lungs at Depth

Lung Measurements

lung capacity image

Tidal Volume (TV)
The tidal volume is the amount of air inhaled and exhaled during relaxed breathing. For a relaxed person, one tidal breath is about half a liter (500ml) in volume and is repeated about 10-20 times per minute. Ideally, the inhalation is done by activating the diaphragm while the exhalation is passive: The air is not getting forced out of the lungs, but rather expelled by simply “letting go”....

Inspiratory Reserve Volume (IRV) & Expiratory Reserve Volume (ERV)
The inspiratory reserve volume (IRV) is additional amount of air that can be inhaled after a relaxed tidal inhalation. The expiratory reserve volume (ERV) is the maximum amount of air, which can be exhaled after a passive exhalation

Vital Capacity (VC)
The vital capacity (VC) is the maximum amount of air that can be inhaled into your lungs after a full exhalation. In other words, the vital capacity it is the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume:


The vital capacity is thus the maximum volume of air we can access in one breath. Healthy adults have a vital capacity of 3-5 litres, depending greatly on sex and bodyheight. Training can increase the vital capacity, mainly by reducing the residual volume (RV, see next).

Functional Residual Capacity (FRC)
The functional residual capacity (FRC) is the volume of air remaining in our lungs after a relaxed exhalation. It can also be described as the sum of expiratory reserve volume and residual volume (see next):


A “passive exhale” is reached when your airways are open and no air flows in or out. You can easily do this by producing a sigh: Relax completely, especially your abdomen, and say “haaa…” until no air comes out of your mouth anymore. Then closeyour airways. The amount of air still remaining in your lungs represents FRC. In your future training with AIDA you will learn about a training form called “FRCdiving”. It is sometimes falsely labelled with “empty lungs”-diving. By no means the lungs are empty in FRC. In fact, in an FRC the lungs still hold about 50% of the “total lung capacity” (TLC, see below). Diving on “empty lungs” is dangerous and should be avoided if you are not a very well trained athlete knowing exactly what your are doing. In AIDA Education, there are no so-called dives on “empty lung”

Residual Volume (RV)
The residual volume (RV) is the amount of air remaining in your lungs after a maximum exhalation. In average it is 25% of the total lung capacity (TLC, see below). While other lung measurements are easy to acquire with a spirometer (a device to measure volumes of air inhaled or exhaled), the residual volume can only be determined indirectly, as it is not possible to “completely empty” the lungs. In freediving, the residual volume is very important as it determines how deep you will still be able to equalise normally

Total Lung Capacity (TLC)
In simple words, the total lung capacity (TLC) is the total amount of air the lungs can hold:


Healthy adults have a vital capacity of 3.5-6 litres, depending on their sex and body-height.

Lung Barotrauma

As with every barotrauma, the term “squeeze” is often used to describe the same injury. Lung barotrauma is a potentially fatal injury...

Pressure related Injury:

A lung barotrauma is a pressure-related injury of the lungs.
A lung barotrauma in freediving is most often caused by diving below residual lung volume (RV) and keeping on descending further without being ready for it. In other words, you go too deep, too early. The body needs time to adapt to depth and this does not mean days and weeks, but months and years. Even an experienced freediver can suffer from a lung injury due to other reasons than mere adaption to depth. For example, lung barotrauma can be caused by a lack of relaxation due to stress or cold temperatures. Both keep the muscles around the lungs from relaxing or stretching sufficiently to adapt to the rising environmental pressure. In any of these situations, the freediver should have aborted the dive before the injury, before the negative pressure in the lungs builds up on descent and causes the delicate lung tissue to rupture. In Scuba diving lung barotrauma is often caused by breath-holding on ascent. The compressed gas in the lungs expands beyond the total lung capacity (TLC) and causes a rupture in the lung tissue. This is not very likely to happen in freediving, but in absolutely rare cases lung barotrauma at depth leads to fluid in the lungs and thus reduces the available volume on ascent. As the air expands close to the surface, the reduced volume of air leads to lung overexpansion similar to diving with compressed air.

Fluid enters lungs

Through the injury of lung tissue, fluid is forced into the airspace of the lungs in order to equalize the negative pressure. Any liquid in the airspace of the lungs makes the gas exchange difficult or impossible.

Signs and symptoms

Several symptoms indicate a lung injury upon surfacing after a dive. You might feel tightness in the chest that does not disappear. The airways might be obstructed to a certain degree, which creates a wheezing sound while breathing. Even after a few breaths back on the surface, you have a persisting feeling of difficulty catching your breath. You might have the urge to cough to clear your airways, and if you do so, you are coughing up a pink, foamy liquid. Eventually, you might feel a fatigue that does not disappear. If you have one or several of these symptoms, you have very likely injured your airways or lungs.

* Lung barotrauma (squeeze) is a serious injury in any case. A lung squeeze can happen, but it should not. If you suffer from a lung squeeze and take it too easy, you are acting irresponsibly. Every single incident of lung barotrauma needs to be properly treated with the support of a specialized medical doctor. Stop diving for at least one week, seek medical help

How to avoiding Lung Squeeze?

It is self-evident that a lung barotrauma, popularly also called a lung squeeze, has to be absolutely avoided. All too often lung injuries have been downplayed by freedivers as a minor mishap on their heroic journey to greater depths. There are freedivers on record comparing a lung barotrauma in freediving to a torn hamstring in soccer. Nothing could be further from the truth. Repeated squeezes do result in chronic conditions. Freediving before a complete recovery from a lung barotrauma can be fatal...

Self awareness is key

Freediving on every level is about self-awareness and never about numbers. Some of the greatest freedivers of all times with multiple world records and world championship titles to their name have never experienced a squeeze (and some never even blacked out!). This was only possible due to their respect for and awareness of their physical and psychological limits as well as their persistent and gradual training over extended periods of time. Personal limits can change from day to day, and you have to become aware of these slight shifts. One day you are up, one day you are down. This is life and so is freediving

Dive relaxed or do not dive

The only safe way to approach freediving is through relaxation. From your first day with freedivig course you learned how to consciously calm your body and mind by applying relaxation techniques. At times relaxation is easy to achieve, and on some days it seems to take an eternity to “switch into freedive mode”. Always allow for the time you need to find that switch.

Stop diving if stressed or cold (shivering)

Stress is the opposite of relaxation. Stress creates tension in your mind and your body. Your breathing and heart rate are elevated. In a pool dive, this will simply shorten your dive time (or distance) because you will burn your energy reserves faster. But a dive to depth is different. Your body and your mind need to adapt to the feeling of getting compressed by the rising environmental pressure. If you try to resist that feeling – consciously or unconsciously – you are likely to hurt yourself. If you feel stressed you are likely to build up dangerous resistance. Stress takes your attention away from self-awareness. The solution is simple: Be honest to yourself and do not dive if you feel stressed in any way. If you do not feel confident to do a certain dive, then do not do it. Indicate to your buddy that you skip your dive, go back to your relaxation exercise and allow yourself the time you need. If you get cold, your body will start shivering to create heat. Now you have only two options. Either you start moving to warm up, or ignoring the shivering. Both options are not good enough for freediving as both will tense you up more, loosing your relaxation. Hence, if you start shivering, stop freediving and exit the water to warm yourself up.

Stretching of intercostal muscles

The muscles around our thorax and specially the ones we use for breathing can be trained just as any other muscle in our body. Training means strengthening as much as lengthening, you should not do the one without the other. Strengthening your breathing muscles allows you to freedive for an extended time without tiring, but it is mainly the lengthening that allows you to dive deeper

Stretching of diaphragm: Uddiyana bandha

You can train the flexibility of your breathing muscles at the end of the exhalation and thus reduce the residual volume (RV) of the lungs by exercising uddiyana bandha. You can learn this technique from a freediving Instructor or a yoga teacher in more detail.

Apply correct turn at depth

Correctly stop your descent and start your ascent by performing a forward tumble turn. This is of even greater importance when you dive around or beyond your residual volume. Execute your turn at depth slowly and gracefully, always moving in a forward roll. Avoid aggressive or jerky actions in general, and do not perform “opening” movements like the infamous “parachute turn”.

Slow adaption and inducing blood shift

You can gradually increase your depth by going beyond your previous limits in small steps. Do repeated dives to an achievable depth to allow your body and mind to adapt before setting a new goal, which should be challenging, but not too far away from what you have already accomplished. Give yourself time, enjoy the progress and stay safe.

* : Do not use a technique called “packing” for full-lung stretches! In the past, freedivers used “full lung stretches” in an attempt to augment their vital capacity (VC). As we know now, these techniques seem to be associated with long-term damage of lung tissue, especially when combined with “packing”.

Hypoxia and Blackout

Blackouts are the greatest reason freediving sometimes has a bad name in public opinion. However, as a well-educated freediver that you become by training, you should never even come close to a hypoxic state causing a blackout... Suffering from symptoms of low Oxygen as in a “samba” or even a blackout is considered a lack of skill and knowledge and has no place in recreational freediving.


This is the common medical definition: “Hypoxia is an inadequate supply of Oxygen in the body due to a low partial pressure of Oxygen in arterial blood”.In freediving, we more commonly refer to the saturation of blood with Oxygen, or in short the “oxygenation”. The saturation in a healthy person while breathing normally is at 96-98%. If the saturation drops below 86%, it is considered severe hypoxia. However, the reading has to drop to 45-50% until the person shows extreme symptoms of hypoxia such as unconsciousness.


Ischemia is a shortage of blood supply to an organ, caused by constriction or blockage The oxygenation of the blood can be perfectly fine, but the blood flow itself is locally constricted which leads to an undersupply of blood in certain body parts. This body part or organ then suffers from the consequences of ischemia.

Shallow Water Blackout:

In short, a shallow water blackout is a pressure-related hypoxia on ascent. There is a bit of confusion about the term shallow water blackout. Some organizations and individuals use it to describe any blackout in shallow water, such as in a swimming pool or a bathtub. In freediving, we use the term shallow water blackout in a different and exactly defined way, Loss of consciousness caused by hypoxia towards the end of a freedive. The hypoxia is caused or heightened by the changing water pressure when freediving down and up in water.

Bradycardia in freediving

Bradycardia generally means a slow resting heart rate of below 60 beats per minute (bpm) in adults... Medically speaking, it is a type of cardiac arrhythmia or irregular heart rhythm, but it is not considered a problem until the heart rate drops below 50 bpm under normal conditions. Freediving, in many aspects, cannot be regarded as a frame of “normal conditions”, and heart rates considerably below that may occur. There are no known negative consequences of heart rates considerably lower than what is medically marked as “abnormal”. The heart is a muscle and its reduced activity is a welcome effect under special circumstances such as breath holding to extend the conservation of energy.

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