Humans have been diving into the deep blue for millennia. The Bajau of Indonesia dive for food and spend so much time in the water that the soles of their feet are soft and their spleens are notably larger than their land-based companions.
Free-diving, both breath hold and depth, have become competitive sports; but why this obsession when breathing is life?
One amateur freediver describes the sensation as being taken by an angel and carried up to the sky. For others, it provides the freedom to experience the aquatic environment without the encumbrance of scuba equipment.
Humans also possess the mammalian dive reflex when submerging one's face — the heart rate slows, blood is redirected to the vital organs and the spleen releases stored, oxygen-rich red blood cells.
South African freediver and filmmaker Beth Neale took her daughter underwater at three months. “She held her breath, exhaled a little, but it was obvious that her mammalian dive reflex had kicked in. She’s so comfortable in the water that the other day when I went into the ocean, as the water went above my knees and touched her feet she put her face in the crook of my neck and fell asleep.”
Based on her research into the dive reflex in children and observing her toddler, Neale says the dive reflex eases beyond the age of six or seven months. Babies experience a laryngospasm — the instinctive locking of the throat.
“With Neve it was still natural until about seven months. Now at eight months she comes up and coughs a little, so from now on I’ll teach her,” says Neale.
Chemoreceptors around the eyes trigger a more rapid dive reflex, prompting Neale to forgo a mask when attempting two free-dive records so that more of her face was exposed to the water. Her attempts raised funds for ocean conservation and young freedivers. Neale’s two African and two South African records have since been broken, which Neale says is a good thing because it keeps the discipline competitive.
Chris McKnight, a marine mammal biologist and physiologist from the University of St Andrews in Scotland, has been tracking seals and human freedivers to learn more about what happens to the body when submerged.
McKnight and his team developed tools to track diving mammals, measuring their heart rate, blood oxygenation, changes in blood volume and in brain oxygenation. “Doing research on humans is a great stepping stone for us because we can ask questions to deeper understand what happens to the body during a dive,” says McKnight.
He explains that one of the crucial differences between humans and marine mammals is that we have sinuses and they don’t; without air-filled sinuses a diving marine mammal isn’t affected by the changing water pressure as humans do. We need to equalise to match the pressure in the middle ear to that of the depth.
Another fundamental difference is that mammals don’t get involuntary breathing movements, or contractions, and we do. Those who have held their breath to the point of these contractions know that they are uncomfortable. The involuntary breathing reflex causes the muscles around the rib cage to contract and it only stops once the carbon dioxide that has built up in the lungs is exhaled.
“What freedivers who go to depths of 60m to 100m have conditioned themselves to tolerate is phenomenal. They present an incredibly unique model for research,” says McKnight.
The research hopes to uncover how freedivers condition themselves to endure bouts of exceptionally low oxygen, which could help doctors treat cardiac patients.
A key finding was the reduction in the heart rate. “The freediver’s heart rate declined through the descent, just like a dolphin’s, until it was 11 beats a minute at the bottom of the dive. In some of the deep dives that went past 90m the heart rate got lower than what we’d expect to see in marine mammals, which was a surprise. Physiologically, deep diving is a stressful situation and I didn’t expect the heart rate to get as low as that,” McKnight says.
“Other interesting changes occurred in oxygen levels. We measured the oxygenation of blood being delivered to vital organs like the brain. At the onset of exercise during descent, these levels, which are normally at 98%, dropped enormously to as low as 25%, which is well below the point at which we expect people to lose consciousness, which is at 50%. One particular diver was tolerating levels of brain deoxygenation that far exceed those of marine mammals.
“Brain metabolic rate also drops, so it shuts down. A lot of the body is shut down so that it can better utilise oxygen for the major organs. It goes back to normal in 45 seconds once the diver surfaces and concomitant with that is brain oxygenation.
“We also saw a big increase in blood pressure and high intracranial pressure, deep diving is a complete physiological assault,” says McKnight.
So why do they do it? According to the late Natalia Molchanova, an icon of the sport who went freediving with a group of friends and never resurfaced: “freediving is not only a sport, it’s a way to understand who we are”, is revealing about the way these athletes challenge themselves.
In July 2021, her son Alexey Molchanov, who holds multiple world records, reached a depth of 131m in a vertical dive — the equivalent of a 40-storey building. “I’ve been in the water all my life, my mom taught me how to swim properly and at a young age I was competing regularly. I started freediving in open water when I was five in the Black Sea. There was some archaeological research and we joined the team to participate but I was, of course, just playing around and helping a little bit. Every year we went to the sea and I think this determined my path to becoming a freediver,” he says.
Molchanov trains at dive sites to get used to the environment and conditions his body to tolerate high carbon dioxide levels. If he “packs” by sipping more air into already fully inflated lungs, he can hold his breath for 11 minutes.
Focus is key in breath hold and Molchanov is no stranger to fine-tuning this skill. “I practice a lot of attention-control techniques and I also teach it. As you progress as a freediver, you learn to move your attention around your visual field, around your body. I work with this meditative state of mind.”
Molchanov doesn’t adhere to a special diet. Outside competition periods he focuses on healthy eating and a variety of food as that is what his mother taught him. “In general, I avoid unhealthy products like sugar and bread, but I’m not strict about it. When I’m training a lot, I have a high metabolism and I need to recover fast, so I’m not too fanatical about diet,” says Molchanov.
His diet does change before a competition and it adjusts a lot more for freedivers who practise static breath hold. “Those who specialise in static breath hold really try to eat less. In this case you lose muscle, which is beneficial for this discipline.
“For depth I need strong muscles and more power. I’m not reducing calories intake because for deep diving you’ve got to have enough power and speed of recovery, and that’s why it’s different to static breath hold.”
The evening before diving he avoids food high in fat and protein as it is hard to digest. The morning of the dive he shifts to carbohydrate-heavy porridge or oats. “The idea is to get to the dive without feeling hungry but not feeling heavy. For me this works, but it’s not one rule for everyone,” Molchanov says.
On March 5 , South African ice diver Amber Fillary broke the Guinness World Records overall title for the longest under-ice swim with breath held and without fins or a wetsuit. She had already claimed the women’s record but she was determined to push herself further.
Fillary’s ability to hold her breath while swimming under a blanket of thick ice in a bikini is nature-defying. While she promotes the benefits of cold water swimming, she knows that her record-breaking feats are not for everyone. Holding one’s breath in sub-zero temperatures requires more energy and focus.
Paradoxically, the cold water calms her. “I know what I do is extreme. It’s difficult getting into cold water and being totally relaxed. It’s kind of a challenge,” she says.
Fillary is an anomaly in the world of freediving. She doesn’t fill her lungs to capacity before plunging, she smokes and doesn’t experience contractions. Her mammalian reflex kicks in quickly and she hasn’t experienced the side-effects of ice water diving.
Others may complain about sore ears or suffer hypothermia but not Fillary. She attributes this to a training regime she begins months before her record attempts, and acclimatising to the cold by swimming in lakes in Germany.
For freediving instructor Zandile Ndhlovu, breath hold reminds her of the currency of life, especially when she gets contractions. “The urge to breathe is a beautiful way to hold the life force. I love holding my breath, I enjoy the whole process,” she says.
What McKnight observed but didn’t document while researching elite freedivers was their desire to push the limits; how much pressure they could withstand and how much longer they could descend into the depths using only the oxygen they took into their lungs at the surface.
Free-diving is considered one of the most dangerous sports and yet people are seduced by it. While the long-term effects on the mind and body haven’t been clearly established, some athletes feel a change in their mood. “Some of the divers told me that after a number of days of doing deep dives they had to take a day off because they felt cranky, emotionally vulnerable and got easily upset,” says McKnight.
As freedivers immerse themselves deeper into the blue and as research on them continues, who knows what else they will uncover?
