Discovering the Benefits of the Mammalian Dive Reflex
As us humans are, for the most part, land-dwelling mammals, plunging to the deep, dark depths of the ocean on just a lungful of air might strike some as a mix of unnatural and downright terrifying. However our bodies, just like those of seals, dolphins and whales, have an incredible natural physiological adaptation, known as the Mammalian Dive Reflex (or MDR), which means that not only is it safe for us to dive to depths on a single breath, our bodies are actually built to do it.
The Mammalian Dive Reflex is one of the many fascinating things you learn about when taking a freediving course, and it’s this adaptation that inspired our ‘Born to Dive’ mantra. In this post, we’ll dive into the wonders of the MDR and how you can utilise it to enhance your freediving performance.
Just like seals, humans are able to elicit the Mammalian Dive Reflex to enhance their dives.
What triggers the Mammalian Dive Reflex?
The MDR is a set of physiological adaptations that occur in humans (and aquatic mammals) when submerged in water, enabling us to dive deep safely, on a single breath. So, what triggers the Mammalian Dive Reflex? Three simple factors that we experience with every dive:
Breath-holding
Being exposed to pressure
Cold water facial immersion - where receptors on our lips and under our eyes are exposed to water cooler than 24 degrees
What are the effects of the Mammalian Dive Reflex?
1. Bradycardia - Slowing of the heart rate
When a freediver engages in facial immersion or descends underwater, their body activates bradycardia as a way to conserve oxygen. This enables the heart rate to rapidly decrease by up to 50%, enabling the freediver to better conserve their oxygen stores and therefore dive deeper and more comfortably.
2. Peripheral Vasoconstriction - Constricting blood vessels in extremities
Peripheral vasoconstriction is the body’s way of protecting the vital organs. During longer, deeper dives, blood vessels in the arms and legs will constrict, directing more blood to vital organs such as the heart, lungs, and brain. Minimising non-vital oxygen use allows for extended breath-holds and deeper dives.
3. Blood Shift - Protecting the lungs from pressure related injury
The blood shift is an effect that kicks in during deep dives where divers’ lungs have compressed significantly. Here, blood is shunted to the chest, acting like a protective, fluid cushion for the lungs’ delicate tissues, helping to maintain their shape and prevent compression related injury.
4. Spleen Contractions - Releasing red blood cells to improve oxygen circulation
Another impressive effect of the Mammalian Dive Reflex is the contraction of the spleen. The spleen acts as a reservoir for red blood cells, and during breath-holding, it releases additional red blood cells into circulation. This increased oxygen-carrying capacity prolongs breath-holds and improves the body’s efficiency when consuming oxygen.
How can we leverage the benefits of MDR in our training?
Sydney freedivers - this is where you can rejoice at the fact that our local dive sites are not quite as tropical as we might wish they were. With the water temperature being below 24 degrees for the most part of the year, we are able to include cold water facial immersion into our pre-dive warm up to elicit a strong MDR response. Anyone that has dived with me will know this is my favourite way to begin any depth session, and I never skip it.
Adding cold water facial immersion into your dive routine in simple - before your first dive, take your mask off and breathe through your snorkel while floating face down on the surface of the water. Complete at least 2 minutes of ratio breathing in this position. By doing this, your whole face, including the receptors on your lips and under your eyes (which are usually covered by the mask), will be exposed to the cool water. This will trigger bradycardia - dramatically lowering your heart rate, making you better able to conserve oxygen when you dive.
Cold water facial immersion not only an effective way to elicit the MDR, is also a great way to enhance mindfulness by removing distractions and forcing you to be present by focusing on your breath, helping set you up for a positive dive. If you want to take facial immersion to the next level, you can even try no-mask or nose clip diving. This is an even more efficient way to harness the benefits of the Mammalian Dive Reflex during your dives.
If you’re intrigued by the Mammalian Dive Reflex and want to learn more about the ways our bodies are build to accommodate diving on a single breath, join one of our upcoming courses.
Another world awaits…
See you underwater soon!