Unveiling the Extraordinary Physiology of Free Divers
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The Fascinating World of Free Diving
Free divers are pushing the boundaries of human capabilities, showcasing remarkable physiological adaptations that allow them to thrive underwater.
Photo: Jacques De Vos
By Adam Piore
In 2011, Hanli Prinsloo aimed to break the women’s world record in free diving, a feat requiring a dive to 213 feet beneath the Mediterranean Sea while holding her breath for nearly four minutes. Up until the 1960s, many scientists believed that such depths were beyond human capability, arguing that the immense water pressure would crush the lungs.
Prinsloo, a 33-year-old South African with a background in acting, knew that achieving this goal demanded intense training and dedication. Growing up on a large horse farm near Pretoria, she felt at ease in water, having spent her childhood playing in dams, streams, and pools while dreaming of becoming a mermaid. In spring 2011, she traveled to an ashram in the Indian Himalayas for a month of meditation and Vinyasa Yoga.
After her training, she journeyed to Dahab, Egypt, a secluded Bedouin village bordered by the Red Sea and the Sinai Mountains. On dive days, she and fellow diver Yaniv Keinan would traverse a rugged desert track in a 4x4 until reaching the water. They would then wade through shallow waters to the edge of a deep sinkhole known as the “Blue Hole.”
As Prinsloo floated on her back, preparing for the dive, she created a serene atmosphere reminiscent of her time at the ashram. Focusing on her breathing and heartbeat, she aimed to clear her mind. Moving in slow motion, she prepared for the descent.
At around 200 feet deep, the water appeared to glow. “It was like a blue luminescence,” she described, noting the ethereal quality of light underwater.
Her technique involved slow, deliberate breaths to maximize oxygen absorption and maintain lung flexibility, crucial for a successful dive. After five minutes, she achieved a meditative state where the ideal dive was characterized by a tranquil mind devoid of distractions.
Prinsloo descended with her eyes closed, concentrating on equalizing pressure in her ears by pinching her nose and blowing. As she went deeper, her body underwent remarkable changes. Her heart rate slowed, and peripheral arteries constricted, directing oxygen-rich blood to vital organs. The volume of her lungs decreased, while blood filled them to counteract the external pressure.
At approximately 60 feet, she experienced “negative buoyancy,” allowing gravity to take over. It felt as if she had finally realized her childhood dream, transforming into a serene underwater version of herself.
The capabilities of free divers are astonishing, yet Peter Lindholm, a leading researcher in human physiology in extreme environments, emphasizes that there is nothing mystical about their feats; they can be understood through the lens of physiological science.
Recent achievements in free diving have prompted scientists to explore not only the depths humans can reach but also our control over metabolic functions. The remarkable feats of divers, including those experienced by Prinsloo, are documented in James Nestor's book, Deep, which chronicles the sport's evolution and the motivations behind it. Researchers suggest that free divers might be tapping into evolutionary traits shaped in a simpler time, perhaps even before modern medicine, when slowing down was crucial for survival.
The Connection to Marine Mammals
Prinsloo met me on the shores of Crystal River in Florida, a lush sanctuary along the Gulf of Mexico. Now leading a nonprofit conservation organization called I Am Water, she was filming manatees, which gather in the area's warm springs during winter. She invited me to join her, promising to teach me breath-holding techniques akin to those of a free diver.
As we kayaked down the river and entered the water, I dove beneath the surface, following Prinsloo towards a curious 10-foot manatee. It floated effortlessly, observing us with its gentle eyes while we drifted in silence, swaying with the morning tide. When I surfaced, gasping for air, Prinsloo remained submerged, exuding calmness—a clear indication of the skills I had yet to learn.
After paddling back, we settled on a grassy knoll. Prinsloo guided me through a series of breath-holding exercises, encouraging me to breathe deeply and slowly, reminding me to tell myself a positive story.
The first breath-hold was designed to be relaxing, and she instructed me to stay calm until I felt a “trigger” indicating it was time to breathe. In the second hold, I pushed past this trigger point, and in the third, I learned to embrace the contractions that signaled my body's need for air.
“Let the contractions come and go,” she advised. “They are merely sensations that require your acceptance.”
Placing my hand on my stomach, I continued to hold my breath. Surprisingly, I entered a state of stillness where time felt suspended, and I became acutely aware of my surroundings. However, I eventually had to exhale, and when I did, I was astonished by my results. My first breath-hold lasted 1 minute 45 seconds, the second 2 minutes 50 seconds, and the third nearly 3 minutes 45 seconds—over doubling my initial capacity thanks to Prinsloo's guidance.
Understanding the Physiology of Free Diving
For decades, scientists believed that free diving was not only perilous but potentially fatal. This perception stemmed from the work of Robert Boyle, a 17th-century naturalist who formulated a law predicting that at depths around 100 feet, lung rupture would occur due to immense pressure.
Boyle's law suggested that as water pressure increases with depth, lung volume and the air within must decrease proportionally, leading to potential rupture.
The myth began to unravel in 1949 when two Italian divers challenged each other to a depth contest. Raimondo Bucher, a fighter pilot, claimed he could dive to 100 feet on a single breath. Ennio Falco, equipped with scuba gear, awaited him at the bottom. Bucher surfaced victorious, launching the modern free diving sport.
Subsequent records shattered previous beliefs, including Jacques Mayol's historic 330-foot dive in 1976, which astonished the scientific community. At such depths, water pressure is approximately 11 times normal.
Researchers like Claes Lundgren explored why divers could survive on minimal air for extended periods, leading to the discovery of remarkable underwater survival mechanisms.
In 1962, Swedish physiologist Per Scholander documented a phenomenon known as the “dive reflex,” observed in both humans and aquatic animals. This reflex initiates a state similar to hibernation, preserving oxygen by slowing heart rates and directing blood flow to vital organs.
Lundgren's research demonstrated that this reflex also applies to humans, who can withstand increased pressure by channeling blood into the lungs to counteract external forces.
The sport of free diving has surged in popularity, attracting enthusiasts who appreciate its focus on mindfulness and slowing down—a remedy for the stresses of daily life.
Boyle's law wasn't entirely incorrect; scientists simply overlooked the body’s ability to adapt to underwater conditions. Lundgren noted that a significant volume of blood can be redirected to the lungs, allowing divers to withstand high pressures without succumbing to injury.
The Role of the Spleen and Evolutionary Adaptations
The spleen plays a critical role in free diving. In addition to its functions in blood cell management, it serves as a reservoir of oxygen-rich blood. Research by physiologist Erika Schagatay revealed that this reserve can enhance breath-hold times by up to 30 seconds.
Lundgren emphasized that human infants exhibit the dive reflex, suggesting an innate survival mechanism. “It is a natural adaptation,” he remarked, linking it to challenges faced during birth when blood flow is restricted.
Free diving is about harnessing these inherent physiological traits and extending them. Schagatay explained that breath-hold durations depend on oxygen reserves; however, factors like metabolic rate and movement also influence limits.
In the early 2000s, Canadian divers sought to expand their lung capacity beyond normal limits. They approached pulmonologist Ralph Potkin, who discovered that they could increase lung size significantly through techniques like glossopharyngeal insufflation, which pushes extra air into the lungs.
This method, along with targeted exercises, has proven to expand lung capacity by over 30%. While the average adult lung capacity is 6 liters, elite divers can achieve much larger volumes.
The Risks of Pushing Limits
However, there are risks associated with these techniques. Some divers experience pulmonary edema or hemorrhagic incidents. The tragic death of diver Nicholas Mevoli in 2013, following a deep dive, highlighted the dangers of fluid entering the lungs.
Prinsloo encountered her own challenges during her training for the 2011 championships. After experiencing discomfort during a dive, she surfaced to find blood in her mouth. This incident forced her to reconsider her approach, ultimately shifting her focus from competition to the more meditative aspects of free diving.
Today, the sport's rise in popularity stems not from a reckless pursuit of accolades but from the appeal of mindfulness and tranquility it offers. “In a hectic world, this practice teaches us to control our stress responses,” Schagatay noted.
Ultimately, both scientists and divers agree on the extraordinary potential of the human body, but they stress the importance of respecting nature’s boundaries. Finding balance between embracing our capabilities and acknowledging risks is key.
“You can’t force your way into these subtle states,” Prinsloo wisely stated. “It’s about stillness and letting go.”
The Science of Freediving | The Deepest Breath | Netflix - YouTube
This video delves into the science behind freediving, exploring the physiological adaptations that enable humans to dive to extreme depths.
Hyperbaric Medicine: The Physiology of Freediving - YouTube
This video provides insights into the physiological processes that occur during freediving, highlighting the body's incredible ability to adapt to underwater environments.