Try something right now: hold your breath for 5 seconds. Probably easy, right? Now, take a deep breath and double it: hold your breath for 10 seconds. Then 20.
You may have felt the urge to breathe at around 15 seconds, or even 10; that's when most people start feeling uncomfortable. Actually, you're still nowhere close to running out of oxygen. You are building up carbon dioxide in your body, and that signals to your brain that you need to breathe. The bad news is, if you continue to hold your breath, you'll eventually pass out. The good news is, as soon as you pass out, your brain will kickstart your breathing -- and you'll wake up and be fine.
If you practice holding your breath a bit longer each session, your ability will gradually improve. It's the basis for what freedivers do -- dive to incredible depths on a single breath of air. Competitive freedivers have attained record depths of 429 feet, seemingly defying human abilities.
In fact, humans have been freediving for thousands of years, mainly to gather food and resources from the ocean floor. For example, Japanese diving women, called "ama" (which translates to "sea women") still dive down to 150 feet, holding their breath for 3 minutes at a time to collect seafood. People in many parts of the world have done the same.
It seems human brains and bodies are equipped to adapt to deep-water diving. Here's everything you need to know about the science of freediving -- and how to get started yourself.
Normally, when the body reaches very low oxygen levels of 65 percent, it seriously impairs the brain. Yet, expert divers have reached blood-oxygen saturation levels as low as 50 percent, writes science journalist James Nestor in his book, DEEP: Freediving, Renegade Science, and What The Ocean Tells Us about Ourselves. Scientists used to think humans would die by the time they descended 100 feet, at which point their lungs would collapse, and blood would dribble from their mouths -- only to discover that the rules are different underwater. Divers can not only reach those depths, but surpass them, and return to the surface with no harm -- all on a single breath.
Dr. Peter Lindholm, a professor of diving medicine at the University of California, San Diego, and an expert in the physiology of breath-hold diving, is also a freediver. Once, he reached the bottom of a 130-foot quarry on a single breath. Lindholm explains to Popular Mechanics what people experience on a freedive.
First, know that it takes at least months of training to learn how to push your body to these extremes, Lindholm says. Divers who rely on their own breath must condition their bodies to withstand rising rates of carbon dioxide (CO), and to resist the internal alarm bells urging them to breathe. They start with breath-hold practice on land, then in a swimming pool, and finally in a natural body of water. Having control over their mental state eventually leads to a sense of calm underwater for several minutes at a time, allowing recreational freedivers to explore the ocean environment.
If you push through the discomfort of your brain shouting at you to breathe, "a normal healthy person can hold their breath for about one or two minutes, while still having 100 percent oxygen in their blood," Lindholm says. "If you do that three or four times, the brain realizes that it didn't die, so you can sort of get used to that feeling, and it kind of goes away."
Beside breath-holding practice, part of a freediver's conditioning is strength training. They also do exercises that stretch the chest muscles, to allow their lungs to expand farther and hold a greater volume of oxygen on the pre-dive breath, Lindholm says.
Before a dive starts, some divers purposely hyperventilate, while making each exhale last longer than each inhale. "So they breathe too much before they swim; they lower the carbon dioxide in their blood, which means they can hold their breath longer," Lindholm explains. In fact, kids who like to swim underwater at the pool sometimes teach themselves to do this, too, but are then at risk of drowning, he adds.
👀 Freedivers get closer to undersea life than scuba divers do with their chunky, noisy gear. Underwater photographer and freediver Fred Buyle captures rare sounds and images of whales, sharks, and other animals. Scientists use his unprecedented observations to study these animals' behaviors in their natural environment.
Advanced divers also use a technique called "lung packing," Lindholm says. This method does what the name suggests, forcing more air into your lungs than they would normally be able to hold. "You can actually learn to swallow the air into your lungs," says Lindholm, but you need a teacher to show you how. Scientifically called "glossopharyngeal inhalation," this method helps patients with conditions like muscular dystrophy, so that they can survive if their breathing machines fail.
Imagine you are a freediver. You relax your mind in preparation. Then, you take one last deep inhalation, plus extra sips of air, and slip underwater.
At first, you work harder to swim lower, as the water's density exerts a pressure that keeps you buoyant. However, somewhere past about 45 feet deep, the water pressure is so great, you become "negatively buoyant" and sink toward the ocean floor. Freedivers describe this free-falling sensation as flying. The deeper you go, the more your lungs compress under the water pressure; at 130 feet, your lungs have squeezed to â…• of their volume at sea level.
All the while, your mammalian dive response causes your body to do the opposite of what happens on land when you hold your breath for a long time: your heart rate slows, even as the oxygen level in your blood drops. To make up for the oxygen loss to vital organs, blood rushes from your limbs to your torso and brain. Studies have shown that exposure to cold water -- even just your face in cold water -- triggers this "Master Switch," getting your body ready for diving conditions, Nestor explains in his book. Oddly, even some birds appear to have this oxygen-conserving response underwater, though scientists don't yet understand why.
In mammals, the response could be an evolutionary adaptation to a sudden drop in oxygen, one that could help a fetus survive a difficult labor, for example, according to Lindholm. "So it's a saving response -- you're temporarily letting your muscles suffer, because the brain [and heart] can't be without oxygen for too long."
Meanwhile, the nitrogen buildup in your blood as you go deep underwater can have weird effects, triggering sensations of peace, and even euphoria, writes artist Martina Amati, who describes her own freediving experiences in The Conversation. And your body does something else astounding when your oxygen supplies dwindle -- your spleen releases up to 15 percent more oxygen into your bloodstream. Among other bodily signals freedivers learn to recognize, they sense this rush of oxygen, Nestor writes in his book, and it supports a feeling of calm.
✅ The world record for a breath hold is 24 minutes, 37 seconds, by freediver Budimir Šobat.
Getting to the deep is not easy, however. Nestor describes the feeling of convulsions as he practiced holding his breath for nearly two minutes -- his body was reacting to the buildup of carbon dioxide. (Nestor overcame it and learned to freedive, himself.)
Deep divers also have to overcome the problem of rapidly changing pressure as they descend. For every 32 feet you go below the surface, the pressure increases by one atmosphere, which is the average air pressure we experience at sea level at 59 degrees Fahrenheit. "When you dive to 10 feet, your eardrums are going to be squashed in because the gas on the inside of the eardrums is compressed," Lindholm says. "You equalize, which most people do with pinching the nose and they push a little air up behind those eardrums. But if you go deeper and deeper, you need to add more air on the inside of the ears continuously." Freedivers also learn special techniques to do that.
Competitive freediving tests the limits of human ability. While the death rate is low -- 1 death in every 50,000 dives, according to Apnealogy, a publication covering freediving and spearfishing -- divers risk death when their zeal to beat a record overtakes their caution. Some close calls happen because divers don't get back to the top until it's too late -- at which point they blackout, or become unconscious. That's why you should never freedive without a buddy, and why freediving competitions have multiple people on hand to assist if needed. Recreational divers actually die at higher rates -- 1 death in every 500 dives -- because help may not be nearby in an emergency.
🎥 To get a taste of the world of competitive freediving in just under two hours, we highly recommend binge-watching The Deepest Breath, a 2023 Netflix documentary in which "a record-setting champion and a heroic safety diver try to make history with a remarkable feat." It's an educational -- and heart-wrenching -- story of taking an extreme sport to, well, the extreme.
Divers could also experience pulmonary edema, where fluid collects in the lungs' air sacs, or decompression sickness, when the oversaturated gasses in the body form bubbles in the blood on a diver's ascent, says Lindholm, who studies these problems. Divers could also blackout when they reach the surface, because they waited too long to ascend.
The deepest divers may have to contend with hallucinations, due to the buildup of nitrogen in the blood, writes Nestor in an article for Spirituality & Health magazine. "The effects of nitrogen narcosis at 300 feet down are so strong that you forget where you are, what you're doing, and why you're in this dark place, fumbling around. Hallucinations are common. You lose motor control. Everything around you appears to slow down."
If you were one of these deep divers, holding your breath for perhaps 5 minutes, you'd have to rely on a dive watch whose beep would tell you when to head back up, and a rope to guide your descent and ascent. Divers usually pull themselves back up until they reach positive buoyancy again. You might exhale during the last few seconds of your ascent, so that you waste no precious seconds getting your next fresh breath of oxygen.
💡 Definitely don't try it alone or at home. Freediving Instructors International, a U.S.-based recreational freediving educational agency, is a great resource for finding lessons. Also check out Apnealogy, a freediver-founded website all about the sport, including safety tips and educational articles.