Freediving is a discipline where individuals descend underwater solely on a single breath of air, contrasting with scuba diving that uses compressed gas tanks. The medical condition commonly known as “the bends” is Decompression Sickness (DCS), which occurs when absorbed gases form bubbles within the body upon a decrease in ambient pressure. Traditional DCS is highly unlikely for a typical recreational freediver, but it is not entirely impossible, especially for those who push the limits of human depth and repetition. The physiological mechanisms governing gas absorption explain why this risk is minimal for most breath-hold dives.
Understanding Decompression Sickness
Decompression Sickness is fundamentally a result of the body’s interaction with inert gases, primarily nitrogen, under increased pressure. This is described by Henry’s Law, which states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas. As a diver descends, the ambient pressure increases, causing nitrogen to exert a higher partial pressure, forcing more of it to dissolve into the body’s blood and tissues.
For significant nitrogen saturation to occur, the body must be exposed to this elevated pressure for a sustained period. During a dive using compressed air, such as scuba diving, the diver continuously breathes high-pressure air, allowing nitrogen gas to load into various tissue compartments. DCS manifests when the diver ascends too rapidly, causing the surrounding pressure to drop quickly. This rapid depressurization means the dissolved nitrogen cannot be offloaded safely through the lungs and comes out of solution as bubbles, leading to the symptoms of “the bends.”
Why Traditional DCS is Rare in Freediving
The singular factor that dramatically reduces the risk of traditional DCS in freediving is the limited time spent underwater. A breath-hold dive is too short to allow the body’s tissues to absorb a significant amount of nitrogen, even at extreme depths. Nitrogen loading is a time-dependent process, and the few minutes a freediver spends at depth are insufficient for the gas to saturate the slower tissue compartments. Therefore, the brief exposure prevents the necessary saturation required for subsequent bubble formation upon ascent.
The risk is elevated for elite athletes or spearfishers who perform highly repetitive deep dives with very short surface intervals, a pattern sometimes referred to as Taravana. The repeated, rapid cycle of descent and ascent, combined with inadequate surface time for off-gassing, can lead to a cumulative build-up of nitrogen in the body. While still rare, this specific scenario can lead to documented cases of Decompression Sickness. Expert divers must implement extended surface intervals, often three times the duration of the preceding dive, to allow the nitrogen absorbed during the descent to safely leave the tissues before the next dive.
The Primary Physiological Hazards of Freediving
While traditional DCS is an uncommon event in freediving, the sport carries other serious and more frequent physiological hazards related to oxygen depletion and pressure changes.
Shallow Water Blackout
The most common and dangerous risk is Shallow Water Blackout, which is a loss of consciousness near the surface, typically within the last ten meters of ascent. This phenomenon results from critically low oxygen levels (hypoxia) in the brain, not nitrogen bubbles. It is often triggered by hyperventilation before the dive or pushing the limits of a breath-hold.
Barotrauma
Another significant risk is barotrauma, a pressure-related injury that occurs when the pressure difference between a gas-filled space in the body and the surrounding water pressure becomes too great. This injury follows Boyle’s Law, which states that the volume of a gas is inversely proportional to the pressure exerted on it. As the freediver descends, the air in their lungs and other body cavities compresses.
In freediving, this can lead to a Lung Squeeze, or pulmonary barotrauma, where the lung volume is compressed past its residual volume, causing fluid and blood to leak from the capillaries into the airways. Middle ear and sinus barotrauma, often called “ear squeeze” or “sinus squeeze,” are also common occurrences in breath-hold diving. These injuries result from the inability to equalize the pressure in these air-filled spaces to match the external water pressure during descent. Symptoms can range from mild pain and discomfort to ruptured eardrums or sinus tissue damage. These pressure-related injuries underscore that the immediate concerns for freedivers are fundamentally different from the gas-saturation problems that define Decompression Sickness.