The Most Amazing Thing About Nature - The Human Diving Reflex
I had trouble coming up with something I wanted to write about for this post. There are so many incredible things about nature; I mean simply the fact that it exists in the complex way that it does is a feat in itself. I’ve finally landed on something that might not typically be related exactly to nature, but I do believe speaks to the impressive and extensive relationship humans have with nature.
Over the summer, I read a book by James Nestor, titled Deep: Freediving Renegade Science, and what the Ocean Tells Us about Ourselves. In this book, he dives deep (pun intended) into the world of freediving, the competitive and human aspect of it, as well as how it can be used within science to aid in discoveries (Nestor, 2014). Of particular interest to me was in a section where he discussed what he called “the master switch of life” (Nestor, 2014). This has been better described in scientific papers as the mammalian diving reflex, or diving response, whereby mammals undergo certain physiological changes when submerged underwater (Godek & Freeman, 2019). This response has been found in all of the mammals studied in experiments relating to this reflex (Godek & Freeman, 2019).
While it is not known for sure why this occurs, it is thought to occur in mammals as a way of conserving oxygen (Godek & Freeman, 2019). When submerged underwater, the human heart slows, blood vessels constrict, our spleens constrict, blood pressure increases, and we see a reduction in blood flow (Foster & Sheel, 2005; Andersson et al., 2002; Gooden, 1994). All of these responses are thought to redistribute blood to our vital organs and conserve oxygen (Godek & Freeman, 2019). By redistributing this blood to our organs, we are able to keep our brains and hearts oxygenated for longer, thereby increasing the amount of time we can stay underwater (Nestor, 2014). Similarly, with less blood pumping throughout our bodies, we are better able to conserve oxygen, making us able to stay underwater for longer (Nestor, 2014). Submersion in water is the only thing able to trigger this response in humans; even just splashing cold water on your face can prompt this physiological response! This is something I find incredibly profound.
As Nestor notes, Swedish scientist Per Scholander made great progress in understanding this phenomenon with his experiments (Nestor, 2014). He found that human heart rates immediately decreased when underwater, with some divers noting a drop to around 20-30 beats per minute, but, in his experiment, he instructed participants to dive underwater, strap themselves into workout gear, and perform short, vigorous workouts (Nestor, 2014; Foster & Sheel, 2005). Even after performing these workouts, the participants' heart rates still dropped (Nestor, 2014)! These results have been verified by other researchers, with one study finding that participants performing simple exercises with only their faces immersed in water even still saw decreases in heart rate and increases in blood pressure (Andersson et al., 2002).
After learning about this response over the summer, I decided it was time to test it out for myself. My backyard has a pool, so I suited up and got ready. I had my mom and sister supervising just in case, and I took my three deep breaths, then submerged myself under water. After about the first 30 seconds, I felt my lungs burning and it just about took everything in me not to come up for air. Somehow I fought off my initial bodily responses and toughed it out, and after that, the burning feeling went away and I felt, what I can only describe as, peaceful. I could physically hear my heartbeat slowing in my eardrums - the rhythmic thump-thump sounds becoming further and further apart. It was almost like I could feel my whole body tighten underneath the physiological processes happening. I felt calm, and if I was trying to count how long I’d been underwater in my head before, I had completely lost track as my mind went blank. It was almost like I was in a meditative state.
When I came up, my sister told me that according to her timer, I had only been underwater for just over a minute and a half, but to me, it felt like I had been under there an eternity. I tried and tried again, just wanting to push myself and see how long I could stay under, and I finally was able to stay submerged for nearly three whole minutes! Never in my life had I ever been able to come close to holding my breath for that long, but in one afternoon, I was able to experience and teach myself first hand the wonders of how the human body reacts underwater, and it amazed me. For me, and many others, this was not only a physical response, but a mental one. The mind and body shifts when underwater.
To be clear, I don’t exactly recommend doing this! I wanted to experience this reflex, but I was also trying to see how long that reflex would allow me to hold my breath. I had my sister squeeze my hand every 30 seconds so that she could check if I was responding and squeezing back. Additionally, since I had begun reading the book and learning about this stuff, I had been practicing holding my breath out of water before actually trying it in water. Holding your breath for long periods of time underwater can be extremely dangerous and can lead to blackouts consequential drowning, especially if you’re doing it unsupervised! Just a side note, but back to the post…
We can essentially bypass our body’s terrestrial form to undergo a transformation that allows us to better survive underwater. You might say that this is simply a survival response, and you would probably be right, but I think this can provide insight into something much deeper than that. I think that our bodily reactions to being submerged in water can largely speak to the fact that we are connected to all parts of nature - land and sea - more than we even know. As Nestor mentions extensively in his book, the feeling of triggering this diving response is indescribable to most people who are attuned to what it is and how it has the innate ability to calm us.
I have always found that many people have some sort of aversion to water. For some reason or another, people just don’t like water, unless of course they’re swimming in a heated pool or relaxing in a hot tub. I’ve heard most people claim that they don’t like the unknownness that comes with water, usually lakes or oceans. I used to be one of these people. The ocean was terrifying, and even when swimming in lakes, I was on edge, always half expecting something to grab me by the leg. But, if our bodies are programmed to undergo such a profound physical and mental response to being in water, why would we ever consider water as something that is inherently not for humans to explore? After understanding how this human response to being underwater triggers something so amazing within us, it is hard to argue that we are not all connected to water in some sort of special way. Once we understand this reflex, we can understand the undeniable human connection to water and nature.
Humans and nature are inherently connected in so many ways. While many of us have a fear of water, it uniquely helps us to achieve certain responses that we cannot elicit in any other way, and in this way, we are explicitly connected to it, be that in an evolutionary, survival, or spiritual way.
So, overall, the most amazing thing I know about nature, is that we, as humans, are connected to it in ways we might not even know.
I would encourage everyone to look into James Nestor's book that this post was largely inspired by! It was an incredibly interesting read, especially if you have an interest in diving, or specifically free diving!
Andersson, J., Linér, M., Rünow, E., & Schagatay, E. (2002). Diving response and arterial oxygen saturation during apnea and exercise in breath-hold divers. Journal of Applied Physiology, 93: 882-886.
Foster, G. & Sheel, A. (2005). The human diving response, its function, and its control. Scand. J. Med. Sci. Sports., 15: 3-13.
Godek, D. & Freeman, AM. (2019). Physiology, diving reflex. StatPearls Publishing.
Gooden, B. (1994). Mechanisms of the human diving response. Integrative Physiological and Behavioral Science, 29(1): 6-16.
Nestor, J. (2014). Deep: Freediving Renegade Science, and what the Ocean Tells Us about Ourselves. Houghton Mifflin Harcourt.