What freediving can reveal about human well being — and our limits

At 19, Tucker Francis was dwelling his dream.

A couple of decade earlier, he had sailed across the northwest Atlantic along with his household, and his ardour for the ocean and journey blossomed. He beloved snorkeling and leisure freediving, the free time period for diving deep underwater with no respiratory gear. He would head down after the colourful creatures he noticed and keep underwater so long as potential to see as a lot as potential.

Then, whereas chaperoning a 2017 snorkel journey within the U.S. Virgin Islands, Francis did one final freedive and disappeared. The boat’s captain discovered his physique 10 meters down an hour later.

Investigators later decided that Francis had suffered from a hypoxic blackout, additionally typically known as a shallow water blackout: He handed out when his mind couldn’t get sufficient oxygen — an issue that may come on with out warning even amongst skilled swimmers. As soon as unconscious, the physique sinks and the lungs can fill with water.

The grieving Francis household determined to attempt to do one thing to scale back the chance of such blackouts amongst different freedivers. In order that they turned to integrative physiologist Erika Schagatay of Mid Sweden College in Östersund. She research individuals who threat blacking out daily as they dive deeper than the Statue of Liberty is tall: aggressive freedivers, also called breath-hold divers or apneists. With assist, the most effective of those divers can maintain their breath for almost half-hour — about so long as it takes to sing “The 12 Days of Christmas” 10 occasions.

Indigenous peoples in Japan, Korea, the Philippines, Indonesia and elsewhere have been freediving to forage underwater for sea urchins, fish, seaweed and shellfish for hundreds of years. Freediving competitions didn’t get off the bottom till the Nineteen Seventies. On this more and more standard aggressive sport, athletes swim as far, dive as deep or maintain their breath so long as potential, both in swimming pools or in open water. At this time, an estimated 4 million individuals around the globe like to check how far they’ll go underwater in a single breath.

These athletes mix psychological, bodily and social methods that rival and even surpass what high-altitude climbers make use of. As such, “freediving actually does provide a singular window into human efficiency,” Schagatay says.

Analysis into freedivers from all backgrounds is offering a greater sense of the best way to deal with and maybe at some point forestall severe well being issues associated to lung and coronary heart perform within the normal inhabitants. The work can also assist the Francis household understand their objective of offering a warning system for swimmers that may forestall deaths like their son’s.

An excessive endeavor

Aggressive freedivers push the physique effectively past what was as soon as thought humanly potential. At a depth of 70 meters, water strain shrinks the lungs to concerning the dimension of a soda bottle. Blood oozes into the thorax, which caves in, leaving pores and skin flapping across the rib cage. Go deeper, and blood leaving the mind resembles black sludge as a result of it comprises so little oxygen. But freedivers often return to the floor, no hurt achieved, and as such have been “rewriting the medical textbooks,” says physiologist Damian Bailey of the College of South Wales in Pontypridd.

Freedivers “should steadiness the unpredictable, rapidly-changing, and interdependent physiological, psychological, and environmental calls for with their very own motivations for the dive,” Suraiya Luecke, an anthropologist at UCLA and the College of Southern Denmark who research Indigenous freedivers, wrote in 2022 in Phenomenology and the Cognitive Sciences.

In 1976, French diver Jacques Mayol set the aggressive freediving document with a 101-meter descent. In 2023, the deepest descent with fins was 136 meters. Some rivals additionally see how far they’ll swim in a pool whereas staying submerged. In 2025, a swimmer utilizing a fin reached 326.5 meters. One other diver surpassed a complete time of 11 minutes underwater whereas not transferring in 2009. And by respiratory pure oxygen prematurely of his try, a special stationary apneist reached 29 minutes in 2025, setting a controversial world document.

Such makes an attempt to push the physique’s limits might be perilous, as a number of high-profile deaths have proven. After reaching 72 meters in 2013, American freediver Nicholas Mevoli surfaced and shortly started bleeding from the mouth. He died later that day.

And Russian freediver Andrey Matveenko died final November of issues after blacking out throughout a coaching dive at a world championship competitors in Greece in September.

Elite athletes aren’t the one ones succumbing: Shallow water blackout is an insidious threat for a lot of different skilled swimmers, says Britt Jackson, govt director of Underwater Hypoxic Blackout Prevention, a nonprofit based mostly in Norcross, Ga., that educates the general public concerning the dangers of breath-holding. As an illustration, it additionally impacts synchronized swimmers, in addition to underwater rugby and hockey gamers.

Developing with laborious numbers is troublesome as a result of there’s often no distinction made between blackouts and different types of drowning. Nonetheless, by combing the web and investigating drowning loss of life experiences, Jackson’s group has documented 110 blackout deaths during the last twenty years. These could also be only a drop within the bucket, she factors out. Greater than 50 such deaths supposedly occurred in Hawaii alone within the final decade.

Deep Breath-Maintain Diving

The physique experiences a number of physiological adjustments throughout the descent and ascent of a deep breath-hold dive. Well being dangers (textual content in bins) will not be associated to sure depths however fairly to depth ranges throughout the descent or ascent. Skilled freedivers can survive these extremes, however for some dangers, like shallow water blackout, the indicators might be troublesome to sense till it’s too late.

“We don’t have dependable information,” Jackson concludes. However the information they do have present that males ages 15 to 45 are at biggest threat, presumably as a result of they fight too laborious to final underwater. Those that have survived a blackout say they felt as if they might maintain their breath endlessly. “It’s like a runners’ excessive,” Jackson says. 

Schagatay herself started freediving for enjoyable at age 13 off the coast of Portugal. “There have been many extra fish than in Sweden,” she remembers. Time and again, she would dive down till she was blue and shivering.

Schagatay by no means dreamed that somebody may keep submerged for a number of minutes till 1982, when she watched a Bedouin diver disappear within the Purple Sea. The dive lasted longer than what had been thought-about the utmost time people may go with out a breath and never die or undergo mind injury. “I used to be afraid the individual I noticed was going to wish my assist, however then he got here up with a moray eel in his spear,” Schagatay says. She puzzled how was that potential.

So in graduate faculty at Lund College in Sweden, Schagatay started specializing in marine mammal physiology. She ultimately turned her consideration to freedivers to see how a lot their our bodies mimic a seal’s or dolphin’s as they dive.

Even earlier than the Francis household approached Schagatay six years in the past, she had been attending freediving competitions and outfitting athletes with displays that tracked their oxygen consumption by measuring oxygen within the blood. She additionally tracked coronary heart charge, lung quantity and the rise of carbon dioxide ranges within the physique as measured in exhaled air. Her objective has been to grasp what the physique experiences and the way it copes with the stresses of diminishing oxygen and rising CO₂.

With new funding from the Francis household, Schagatay constructed a conveyable lab, which she units up in locations comparable to Dahab, Egypt. There, alongside the Purple Sea, a 100-meter-deep sinkhole known as the Blue Gap attracts freedivers of all ability ranges. In a few of her experiments, amateurs and expert freedivers repeatedly held their breath for specified time durations on land; in others they swam successively better lengths underwater in a pool. She in contrast the land-based outcomes with the underwater swims to get a way of how effectively dry-land assessments mirrored these swimmers’ and divers’ in-water talents. If we all know how lengthy we will final underwater in comparison with how lengthy we will maintain our breath on land, “this might enable us to foretell how lengthy one can safely maintain the breath,” she says.

One downside Schagatay observed with some freedivers, particularly rookies, is that they involuntarily hyperventilate — taking a number of fast breaths — proper earlier than they submerge. That will increase the chance of blacking out as a result of they expel CO₂ that may in any other case give the physique an pressing “BREATHE NOW” command.

“Carbon dioxide is our greatest buddy,” says Juan Valdivia-Valdivia, a neurosurgeon at BayCare Medical Group in Tampa, Fla., who practices freediving.

When CO₂ ranges within the physique get excessive sufficient, the diaphragm begins to spasm to pressure inhalation. Freedivers be taught to manage this impulse. However, particularly in the event that they hyperventilate, novice divers can blow out a lot CO₂ that the physique doesn’t begin to spasm they usually “prolong the dive too lengthy,” Schagatay says. Then the divers usually tend to black out.

A stationary bike and a bath of water

Again in Östersund, Schagatay’s college lab is just some kilometers away from the Swedish nationwide biathlon heart. In the identical constructing as her lab, Sweden’s high Nordic skiers are studied on a {custom} treadmill, and there’s a particular chamber the place oxygen content material and temperature might be managed to create close to Everest-like circumstances. In a room one ground above, Schagatay’s postdoc Frank Pernett has arrange a stationary bike with a basin of water strategically positioned above the handlebars.

The objective is to check a standard security observe amongst swimmers or spearfishers who repeatedly submerge to discover coral reefs or try to catch fish. When these freedivers floor to take a breath, they have a tendency to relaxation on the floor twice so long as that they had simply spent underwater to “catch their breath,” so to talk, earlier than diving once more. But it surely was unclear whether or not this relaxation size supplied ample restoration time. If that point was too brief, the physique would develop into extra vulnerable over time to blacking out.

Within the lab, volunteers pedal slowly — an alternative to swimming movement — as they place their face within the water and maintain their breath for a set period, then pull out and breathe usually for twice so long as they have been underwater. They do that 10 occasions, and on the finish of every submersion, they exhale right into a tube hooked up to a machine that measures oxygen and CO₂. They’ve an oxygen meter on a finger and an electrocardiogram monitor across the chest. After a number of submersions, the researchers gather a finger prick blood pattern to measure lactic acid accumulation, which signifies how oxygen-deprived the physique has develop into.

The researchers discovered that the double relaxation time method is ample in solely about 70 % of the research members. Which means nearly a 3rd of the divers don’t replenish their oxygen adequately and may very well be at better threat of blacking out, Schagatay and Pernett reported final 12 months in Helsinki on the annual assembly of the European Underwater and Baromedical Society. They plan to publish these outcomes later this 12 months.

The workforce had assumed that the quantity of oxygen within the physique can be key to lasting the total time underwater throughout every try. Certainly, good freedivers are likely to have massive lungs. However how lengthy the oxygen saved in lungs, blood and tissue lasts varies relying on metabolic charge and to some extent, coronary heart charge. Skilled divers additionally are likely to have low coronary heart charges. However as soon as the physique runs low on oxygen, it begins to build up lactic acid, which implies the physique will want a for much longer time to recuperate. So, Pernett says, newbie divers or these dealing with tough circumstances must tempo out their dives much more, respiratory on the floor 3 times so long as the time submerged.

A superpower of the spleen

Extra components can affect the blood’s oxygen provide, research present. As an illustration, there’s the spleen, which is a reservoir of crimson blood cells, which carry oxygen. Underneath stress, this organ contracts and floods the blood with these cells, offering an oxygen increase to the physique. This contraction is a part of what’s generally known as the human dive reflex, says evolutionary genomicist Melissa Ilardo of the College of Utah Faculty of Medication in Salt Lake Metropolis. When the mammalian physique submerges in water, this reflex kicks in to keep up the mind’s oxygen provide. The guts charge slows, blood strain within the arteries will increase and capillaries within the limbs constrict, shifting blood movement to the physique’s core, significantly the mind.

The spleen-provided increase throughout the dive reflex is so crucial that the Bajau, an Indigenous freediving group in Indonesia, Malaysia, and the Philippines, have developed larger spleens, which helps them forage for fish and different seafood. They carry a genetic mutation that impacts the spleen’s progress, Ilardo and colleagues reported in 2018 in Cell. 

Coaching nonetheless makes an enormous distinction. Schagatay’s workforce had beforehand proven that observe results in a stronger dive response within the Bajau. Then, final 12 months in Cell Stories, Ilardo and her workforce reported that the Haenyeo, a bunch of Korean ladies who freedive to depths of about 10 meters to reap seafood, even have larger spleens than their land-based friends. However that appears to be as a result of diving is a lifestyle; they begin as children and proceed by way of pregnancies and effectively into their ninth decade. To date, scientists have discovered no genetic element to their spleen dimension distinction.

Apply can equally assist aggressive freedivers improve different elements of the dive reflex to allow them to higher address the pressure of low oxygen and excessive CO₂.

A freediver’s well being additionally impacts their success, particularly these attempting to succeed in document depths. Any energetic or latest respiratory an infection appears to predispose the lungs’ air sacs to clog with fluid as a diver swims again to the floor. That may impede regular respiratory even after surfacing.

Different research had concluded that divers with coronary heart points or issues compensating for altering strain of their ears usually tend to black out, in response to a evaluate revealed in 2009 within the Journal of Utilized Physiology by environmental physiologists Peter Lindholm and Claes Lundgren of the Karolinska Institute in Stockholm. Fasting and an excessive amount of train previous to diving might be detrimental too, as each can have an effect on the quantity of CO₂ within the physique. In not less than one case documented by Schagatay and colleagues, an erratically beating coronary heart appeared to result in the blackout.

Freediving teaches about illness

Information about freedivers have already offered clues concerning the well being of nondivers.

“Freediving is the right mannequin to grasp what occurs with low ranges of oxygen within the blood,” Pernett says. This deficit is an issue in lots of circumstances — lung infections, persistent obstructive pulmonary illness, lung scarring or thickening and sleep apnea. He and others assume making use of the teachings discovered from freediving analysis can enhance the standard of lifetime of sufferers with these circumstances.

For instance, freediver coaching workout routines that assist increase the lungs and absorb extra air for holding the breath longer may assist asthmatics breathe higher, Pernett suggests. Likewise, individuals with sleep apnea may profit if they’ve a powerful dive reflex.

Research of freedivers may also inform clinicians about how the guts works. The low oxygen and excessive CO₂ and lactic acid ranges related to deep dives appear to predispose athletes to irregular heartbeats. If that’s the case, comparable adjustments could improve the chance of irregular heartbeats in nondivers.

Bradycardia, a gradual coronary heart charge, is one other situation higher understood by way of the lens of freedivers. Throughout a dive, the guts slows down as a part of the dive reflex and thereby conserves oxygen. “Within the ambulance, they shouldn’t attempt to treatment this downside,” Schagatay suggests. “The [low] coronary heart charge is the physique attempting to manage.”

Freediving analysis can also be serving to to enhance our understanding of the blood-brain barrier. This mobile and molecular “wall” retains toxins out of the mind. Bailey, the College of South Wales physiologist, finds freedivers helpful for understanding how the barrier works — and why it fails. His topics are typically very wholesome. So, the mind “will not be contaminated by any type of illness, and we will decode” what occurs when the barrier will get confused. 

Throughout very lengthy breath-holds, blood strain and blood movement rise sharply to get valuable oxygen into the mind, “which has one heck of an urge for food for this fuel,” Bailey says. In his work with freedivers, Bailey found that low oxygen actually stresses the mind, inflicting a short lived disruption of the blood mind barrier. “When it breaks down, dangerous proteins can slip into mind tissue,” Bailey says. Over time, the repeated stress of deep dives can result in results that resemble neurodegeneration, each his and Schagatay’s groups have proven.

“Freediving could act as a sort of accelerated mannequin of mind getting old,” Bailey says. “It’s like stress-testing a machine to see the place it cracks. That teaches us about vulnerability, and in the end resilience.”

The mind could have methods to deal with low oxygen to some extent, says physiologist Anthony Bain of the College of Windsor in Canada. He has achieved research exhibiting that prime ranges of CO₂ may assist a confused mind gradual its vitality use, briefly decreasing its wants for oxygen. 

There’s additionally an necessary psychological element to breath-holding that may very well be useful for individuals with anxiousness, panic problems, PTSD or, for that matter, anybody feeling confused. “These athletes have an exceptional potential to deal with stress,” Bailey says. Whereas there’s solely scant anecdotal proof, the breath management that comes out of freediver coaching could assist these individuals, he provides.

Oleg G. Melikhov agrees. “The power to manage oneself, focus and chill out are expertise which can be very useful in on a regular basis life,” says the medical and science officer for the Worldwide Affiliation for the Improvement of Apnea, a global group that oversees freediving competitions.

Breath-holding, like meditation, appears to activate calming nerve circuits, a sense that makes freediving interesting. “The deeper you go, the extra relaxed you get in the event you actually know the best way to do it,” says Valdivia-Valdivia, who each competes and research freedivers. He thinks his freediving has made him a greater surgeon not simply due to the self-discipline required to go deep but in addition due to what occurs to his thoughts when he does. 

At better depths, self-awareness and a way of detachment from the remainder of the world soar. “It’s addicting to really feel disconnected from regular ideas,” he says. “Virtually each time, I really feel pleasure.”

On the way in which to a warning system

Though the implications of freediving analysis might be broad reaching, the objective of the Francis household is kind of slender. They wish to develop a watch or equally sized system that may warn when blackout may very well be imminent. However they’re additionally life like. Schagatay “is doing terrific work,” says Peter Francis, Tucker’s dad. “However whether or not it can result in a tool, I don’t know.”

Schagatay’s experiments and different work have offered a lot of the information wanted to compute when an individual’s blood oxygen is approaching critically low ranges, however turning these insights right into a sensible system continues to be a frightening job. “There are some 30 components that have an effect on this stuff,” Schagatay says.  

Divers in whom oxygen drops early within the dive are at better threat of blacking out, Schagatay says, and that may occur even in reasonably deep dives that freedivers don’t really feel are dangerous. Individuals don’t attain the floor in time.

Pernett has additionally been engaged on creating units that detect if somebody about to dive underwater is hyperventilating, although extra testing is required. In the meantime, “there’s so much [that can be done] with training,” Pernett says. “I don’t assume there’s an opportunity {that a} system might be the one resolution.”

Tucker’s dad and mom agree. “We wouldn’t recommend that folks not freedive, however there’s sure issues it’s important to do to do it safely, not least of which is to make darn positive that you’ve any individual watching you who can pull you out,” Peter Francis says.

Valdivia-Valdivia is aware of all too effectively the worth of not diving alone. He’s blacked out however was okay as a result of security divers close by instantly pinched his nostrils shut and coated his mouth to shut the airways and rapidly introduced him to the floor. “I didn’t comprehend it was taking place till I used to be rescued.”

“I want extra individuals would bear in mind [of blackouts],” Valdivia-Valdivia says. “Freediving can provide you a really healthful life, or it may well take your life.”