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 cherished snorkeling and leisure freediving, the free time period for diving deep underwater with no respiration 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 usually 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 danger blacking out day by day as they dive deeper than the Statue of Liberty is tall: aggressive freedivers, also called breath-hold divers or apneists. With assist, the perfect of those divers can maintain their breath for practically 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 Seventies. On this more and more well-liked 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 will 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 novel window into human efficiency,” Schagatay says.

Analysis into freedivers from all backgrounds is offering a greater sense of how you can deal with and maybe someday stop severe well being issues associated to lung and coronary heart perform within the common inhabitants. The work can also assist the Francis household notice their objective of offering a warning gadget for swimmers that can stop deaths like their son’s.

An excessive endeavor

Aggressive freedivers push the physique nicely past what was as soon as thought humanly potential. At a depth of 70 meters, water stress shrinks the lungs to in regards to 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 incorporates so little oxygen. But freedivers often return to the floor, no hurt performed, 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 competitive freediving record with a 101-meter descent. In 2023, the deepest descent with fins was 136 meters. Some rivals additionally see how far they will 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 shifting in 2009. And by respiration pure oxygen prematurely of his try, a special stationary apneist reached 29 minutes in 2025, setting a controversial world report.

Such makes an attempt to push the physique’s limits might be perilous, as a couple 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 danger for a lot of different skilled swimmers, says Britt Jackson, govt director of Underwater Hypoxic Blackout Prevention, a nonprofit primarily based in Norcross, Ga., that educates the general public in regards to the dangers of breath-holding. As an illustration, it additionally impacts synchronized swimmers, in addition to underwater rugby and hockey gamers.

Developing with exhausting numbers is tough 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 dying stories, 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.

“We don’t have dependable knowledge,” Jackson concludes. However the knowledge they do have present that males ages 15 to 45 are at best danger, presumably as a result of they struggle too exhausting to final underwater. Those that have survived a blackout say they felt as if they may maintain their breath ceaselessly. “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 recollects. Again 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 Pink Sea. The dive lasted longer than what had been thought of the utmost time people may go with out a breath and never die or undergo mind harm. “I used to be afraid the particular person 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 college 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 screens that tracked their oxygen consumption by measuring oxygen within the blood. She additionally tracked coronary heart fee, lung quantity and the rise of carbon dioxide ranges within the physique as measured in exhaled air. Her objective has been to know 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 transportable lab, which she units up in locations equivalent to Dahab, Egypt. There, alongside the Pink 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 higher lengths underwater in a pool. She in contrast the land-based outcomes with the underwater swims to get a way of how nicely dry-land assessments mirrored these swimmers’ and divers’ in-water skills. If we all know how lengthy we are able to final underwater in comparison with how lengthy we are able to maintain our breath on land, “this might enable us to foretell how lengthy one can safely maintain the breath,” she says.

One drawback Schagatay seen with some freedivers, particularly novices, is that they involuntarily hyperventilate — taking a couple 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 pal,” 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 drive inhalation. Freedivers be taught to regulate 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 “lengthen 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 middle. In the identical constructing as her lab, Sweden’s prime 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 situations. 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 typical security apply amongst swimmers or spearfishers who repeatedly submerge to discover coral reefs or try and catch fish. When these freedivers floor to take a breath, they have an inclination to relaxation on the floor twice so long as they’d simply spent underwater to “catch their breath,” so to talk, earlier than diving once more. However it was unclear whether or not this relaxation size provided ample restoration time. If that point was too quick, the physique would turn into extra prone over time to blacking out.

Within the lab, volunteers pedal slowly — an alternative choice 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 connected 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 couple of submersions, the researchers gather a finger prick blood pattern to measure lactic acid accumulation, which signifies how oxygen-deprived the physique has turn into.

The researchers discovered that the double relaxation time method is enough in solely about 70 % of the research members. Meaning virtually a 3rd of the divers don’t replenish their oxygen adequately and may very well be at higher danger 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 crew had assumed that the quantity of oxygen within the physique could be key to lasting the complete time underwater throughout every try. Certainly, good freedivers are inclined to have massive lungs. However how lengthy the oxygen saved in lungs, blood and tissue lasts varies relying on metabolic fee and to some extent, coronary heart fee. Skilled divers additionally are inclined 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 get well. So, Pernett says, newbie divers or these dealing with tough situations have to tempo out their dives much more, respiration 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 purple 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 often called 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 take care of the mind’s oxygen provide. The guts fee slows, blood stress within the arteries will increase and capillaries within the limbs constrict, shifting blood circulate to the physique’s core, notably the mind.

The spleen-provided increase through the dive reflex is so essential that the Bajau, an Indigenous freediving group in Indonesia, Malaysia, and the Philippines, have advanced 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. 

“Freediving actually does provide a novel window into human efficiency.”

Erika Schagatay
integrative physiologist & freediver

Coaching nonetheless makes an enormous distinction. Schagatay’s crew had beforehand proven that apply results in a stronger dive response within the Bajau. Then, last year in Cell Reports, Ilardo and her crew 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 kids and proceed by way of pregnancies and nicely into their ninth decade. To date, scientists have discovered no genetic element to their spleen dimension distinction.

Follow can equally assist aggressive freedivers improve different facets of the dive reflex to allow them to higher deal with the pressure of low oxygen and excessive CO₂.

A freediver’s well being additionally impacts their success, particularly these attempting to achieve report 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 respiration even after surfacing.

Different research had concluded that divers with coronary heart points or issues compensating for altering stress of their ears usually tend to black out, in response to a overview printed in 2009 within the Journal of Applied 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 no less than one case documented by Schagatay and colleagues, an erratically beating coronary heart appeared to result in the blackout.

Freediving teaches about illness

Knowledge about freedivers have already offered clues in regards to the well being of nondivers.

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

For instance, freediver coaching workouts that assist broaden the lungs and soak up 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 robust dive reflex.

Research of freedivers may also inform clinicians about how the heart 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 enhance the chance of irregular heartbeats in nondivers.

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

“It’s addicting to really feel disconnected from regular ideas.”

Juan Valdivia-Valdivia
neurosurgeon & freediver

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 usually very wholesome. So, the mind “just isn’t contaminated by any type of illness, and we are able to decode” what occurs when the barrier will get confused. 

Throughout very lengthy breath-holds, blood stress and blood circulate rise sharply to get treasured oxygen into the mind, “which has one heck of an urge for food for this gasoline,” Bailey says. In his work with freedivers, Bailey found that low oxygen actually stresses the mind, inflicting a brief 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 effects that resemble neurodegeneration, each his and Schagatay’s groups have proven.

“Freediving could act as a sort of accelerated mannequin of mind growing old,” Bailey says. “It’s like stress-testing a machine to see the place it cracks. That teaches us about vulnerability, and finally 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 performed research exhibiting that top ranges of CO₂ may help a stressed brain slow its energy use, quickly reducing 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 skill to deal with stress,” Bailey says. Whereas there may be solely scant anecdotal proof, the breath management that comes out of freediver coaching could assist these individuals, he provides.

Oleg G. Melikhov agrees. “The flexibility to regulate oneself, focus and loosen up are abilities which are 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 should you actually know how you can 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 higher 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 best way to a warning gadget

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 gadget that can warn when blackout may very well be imminent. However they’re additionally lifelike. Schagatay “is doing terrific work,” says Peter Francis, Tucker’s dad. “However whether or not it’ll result in a tool, I don’t know.”

Schagatay’s experiments and different work have offered a lot of the info wanted to compute when an individual’s blood oxygen is approaching critically low ranges, however turning these insights right into a sensible gadget continues to be a frightening activity. “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 higher danger of blacking out, Schagatay says, and that may occur even in reasonably deep dives that freedivers don’t really feel are dangerous. Folks 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 quite a bit [that can be done] with training,” Pernett says. “I don’t suppose there’s an opportunity {that a} gadget might be the one resolution.”

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

Valdivia-Valdivia is aware of all too nicely 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 lined his mouth to shut the airways and shortly introduced him to the floor. “I didn’t understand it was taking place till I used to be rescued.”

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