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Understanding Breath Holding Physiology in Freediving

Have you ever tried holding your breath? If you’re like me, you probably did this as a kid, maybe in a swimming pool contest or a dare. I loved to sink to the bottom of the pool and take a few steps before going back up for air. Did you know that breath holding is actually a fascinating physiological phenomenon? Today, we’ll take a closer look at the science behind breath holding and explore its surprising effects on our bodies and the anatomy of breathing.

Why Do We Breathe?

First things first, let’s talk about why we breathe in the first place. Simply put, we breathe to supply our bodies with oxygen. Oxygen is a key component in cellular respiration, the process by which our cells convert food into energy. When we inhale, we take in oxygen-rich air, which travels through our lungs and into our bloodstream. From there, the oxygen is delivered to our cells, where it’s used to produce energy.

But what happens when we hold our breath? Well, at first, nothing much seems to happen. You might feel an urge to breathe, maybe a little lightheaded or tingly, but that’s about it. However, as time goes on, things start to get interesting.

One of the first things that happens when we hold our breath is that our heart rate slows down. This is because our bodies are trying to conserve oxygen, and one way to do that is to slow down the rate at which our cells use it. As our heart rate slows, our blood pressure drops, which can cause us to feel dizzy or even faint.

At the same time, our bodies start to produce more carbon dioxide. Carbon dioxide is a waste product of cellular respiration, and normally we exhale it when we breathe out. But when we hold our breath, carbon dioxide starts to build up in our bloodstream. This triggers a reflex called the carbon dioxide drive, or the urge to breathe– which makes us feel like we need to breathe. This feeling is more powerful than the oxygen drive, which is the feeling we get when our bodies need more oxygen. We can train our bodies to tolerate carbon dioxide better, and be able to hold our breaths for longer periods of time more comfortably.

What Happens When We Hold Our Breath?

So, what happens if we keep holding our breath? Eventually, our bodies will override the carbon dioxide drive and force us to take a breath. This is called the breaking point, and it varies from person to person. Some people can hold their breath for several minutes, while others can only hold it for just a few seconds. It is something that you can train. In only 3 weeks of training, I took my own breath hold from 2 to 5 minutes, and believe me, I’m no super-human.

But here’s where things get really interesting. When we finally take a breath after holding it for a while, our bodies go into overdrive. Our heart rate speeds up, our blood pressure rises, and our breathing becomes faster and deeper. This is known as the diving reflex, and it’s the same response that allows marine mammals like dolphins and whales to stay underwater for long periods of time.

Here are some exercises to help you hold your breath for longer.

Physiology of Breath Holding

First things first, what is the mammalian dive reflex? Simply put, it’s a series of physiological responses that occur when mammals (like us humans) are submerged in water. These responses help us to conserve oxygen and stay underwater for longer periods of time. And yes, you read that right: we humans have a mammalian dive reflex, just like dolphins and whales! Our bodies are amazing, and they already do half of the job without us even noticing.

So, what happens when we dive into water? First of all, our heart rate slows down. This is because our bodies are trying to conserve oxygen and reduce the amount of blood that flows to non-essential organs. When our heart rate slows down, our blood vessels constrict, which helps to direct blood flow to our vital organs, like the brain and heart.

Next, our lungs actually start to shrink. This might sound scary, but it’s a good thing. When our lungs shrink, it helps to reduce the amount of air that we consume and conserve oxygen. At the same time, our spleen starts producing more red blood cells, which helps to transport oxygen more efficiently.

But wait, there’s more! When we’re underwater, our bodies also release a hormone called vasopressin, which helps to conserve water and reduce the amount of urine that we produce. This is why you might feel like you need to pee less when you’re swimming.

When we hold our breath, the body’s metabolism slows down, and the heart rate and blood pressure decrease, which can cause a redistribution of blood flow away from the kidneys.

As a result, the kidneys receive less blood and produce less urine, which can lead to an accumulation of fluid in the body. However, when we come up to the surface and begin breathing again, the body’s normal functions are resumed, and the kidneys receive more blood, causing an increase in pee production to eliminate the excess fluid. 

But, why do we have a mammalian dive reflex in the first place? Well, it’s believed to be an evolutionary adaptation that allowed our mammalian ancestors to hunt for food and escape from predators underwater. And even though we don’t use it for those purposes anymore, it’s still an incredibly cool and useful function of our bodies.

The Mammalian Dive Reflex: Breath Holding and Water

The mammalian dive reflex is a characteristic that has developed through evolution to enable marine creatures to endure underwater for extended periods of time. Especially in response to cold temperatures or higher water pressure, the body undergoes a state of preservation that reduces oxygen intake and amplifies oxygen storage capacity even more than on the surface and when we are surrounded by air. 

This allows aquatic creatures to stay submerged for far longer than humans can without facing any harmful consequences.

As soon as an animal enters the water, the dive reflex takes effect immediately. The heart rate drops considerably, the lungs contract slightly to restrict air loss, blood vessels constrict to prevent heat loss, and the metabolism shifts to burning fat rather than carbohydrates as fuel, which necessitates less oxygen. These transformations are aimed at optimizing energy efficiency and reducing the necessity for oxygen while underwater.

Humans And Mammalian Dive Reflex

Interestingly, the mammalian dive reflex isn’t limited to aquatic animals; humans also possess this adaptation. In reality, many divers take advantage of this reflex to extend their dives when they reach depths where they would typically be impacted by nitrogen narcosis (a condition caused by breathing excessive levels of nitrogen). By stimulating the dive reflex before going too deep, divers may safely explore deeper waters without worrying about the dangers associated with nitrogen narcosis.

In freediving, nitrogen narcosis is unlikely to occur because divers typically do not go as deep as scuba divers, and they do not breathe in compressed gas. However, it is still possible to experience nitrogen narcosis if a freediver holds their breath for an extended period of time or dives to extreme depths repeatedly with little recovery time between dives. This can lead to a buildup of nitrogen in the bloodstream. Therefore, it is important for freedivers to be aware of the risks of nitrogen narcosis and to always dive within their limits and training.

The mammalian dive reflex is an exceptional evolutionary adaptation that has allowed aquatic creatures, and even humans, to explore and experience new depths. By enabling us to stay submerged longer without depleting our oxygen supplies or causing any negative effects, this remarkable reflex presents limitless possibilities for both recreational activities and scientific research. Our bodies are indeed capable of amazing things!

Now, I know what you’re thinking: “But wait, won’t my brain explode if I stay underwater for too long?” While it’s true that staying underwater for an extended period of time can be dangerous (please don’t try this at home), the mammalian dive reflex actually helps us to stay safe by reducing our need for oxygen. So, as long as you’re not trying to break any world records and away from sharp objects or bodies of water, you should be just fine.

You Don’t Need to Be a Pro to Benefit From The Mammalian Dive Reflex

But here’s the thing: the mammalian dive reflex isn’t just for expert swimmers or scuba divers. In fact, anyone can experience it, even if you’re just taking a quick dip in the pool. The next time you’re underwater, take a moment to appreciate the amazing way that your body is responding to the environment. And who knows? You might just discover a new appreciation for aquatic life. Or, at the very least, you’ll have a great excuse to stay in the pool a little bit longer.

Advantages of The MDR and Breath Holding

The diving reflex has a number of benefits. For one thing, it helps to conserve oxygen by slowing down our heart rate and directing blood flow to our vital organs. It also helps to protect our lungs from damage by constricting our blood vessels and reducing the amount of air that enters our lungs. And perhaps most surprisingly, it can even increase our tolerance to pain by releasing endorphins, the body’s natural painkillers.

Whether you’re trying to win a swimming pool contest or just curious about how your body works, breath holding is a fascinating topic that’s well worth exploring. Just be sure to do it safely and never hold your breath for too long. After all, breathing is pretty important, wouldn’t you say?

Breath Holding Benefits

Are you a runner? Okay, picture this: you’re going for a jog with a pro athlete, and you’re expecting them to be breathing easy like they’re taking a leisurely stroll in the park. But nope, they’re not even breaking a sweat! 

Now, you might think it’s because they’re just in amazing shape, but hold on to your running shoes, because I’ve got a surprise for you: their easy breathing has more to do with carbon dioxide than their fitness level. And get this, you can have the same effortless breathing during exercise, just by holding your breath. Crazy, right? Who knew the secret to being an athletic superstar was in our breaths all along!

So here’s the deal with breathing: you inhale to grab some oxygen, which your body needs to keep moving. Then you exhale to get rid of all that nasty carbon dioxide and make room for fresh oxygen in your lungs. And get this – your brain senses the levels of carbon dioxide in your body and tells you to breathe more if they’re too high. So, if you’re someone who’s super sensitive to carbon dioxide, you’ll have to huff and puff more than others to get enough oxygen. But, good news, you can hack your body’s response to carbon dioxide by practicing some breath-holding exercises! Sounds counterintuitive, I know, but this hypoxia and hypercapnia actually help your body adapt to improve your athletic performance and make breathing easier. The next time you’re struggling to catch your breath after a jog, try holding your breath for a few seconds – it might just give you the advantage you need!

What is Hypoxia?

Hypoxia is a fancy term for not enough oxygen getting to your tissues. And let me tell you, there are tons of things that can cause it – like being stranded on a mountain without an oxygen tank or just holding your breath for way too long. But listen up, because this lack of oxygen is no joke. It can seriously mess with your brain, heart, and lungs and cause things like seizures, comas, and even death. So, make sure you’re getting enough oxygen in your life. Don’t hold your breath for too long, and maybe invest in a good oxygen tank if you’re planning on scaling a very high mountain anytime soon.

What is Hypocapnia?

Time for a lesson on hypercapnia. Basically, it’s what happens when there’s too much carbon dioxide (CO2) in your blood. This can be caused by all sorts of things like sleep apnea, asthma attacks, and even poor liver function. And let me tell you, it’s not a good time. When your body senses all that extra CO2, it tries to compensate by making you breathe faster and increasing your heart rate. But if you don’t get treatment, it can lead to some serious problems. But, the good news is that we can use Hypocapnia as a tool to train and get better health and boost our sports performance.

How does Hypoxia and Hypocapnia Affect Your Sports Performance?

You know when you’re exercising and suddenly you feel like you’re running out of gas? That might be hypoxia, which is when your body doesn’t have enough oxygen to keep up with your activity level. This can cause high fatigue, and nobody wants to be tired in the middle of a workout.

On the flip side, hypercapnia is when you have too much carbon dioxide in your body, and it can seriously mess with your breathing. Your body might try to compensate by breathing faster, or breathing through your mouth instead of your nose. But that can lead to even more problems. It’s like trying to get rid of a bad smell in a room by spraying a whole can of air freshener – it might make things worse instead of better.

How Can I Train in Hypoxia and Hypocapnia In A Safe Way to Step Up My Game?

If you’re an athlete or an athlete in the making, or just a human trying to get fitter, I suggest looking to step up your game by training in hypoxia and hypercapnia. There are a few things you need to keep in mind so you don’t end up face down in the dirt. Here are some tips for you:

  • Make sure you have the green light from your doctor before trying any of this stuff. You don’t want to be like “hey doc, I wanted to train like Rocky in the Russian mountains, but now I’m gasping for air and seeing stars!”
  • When you start, take it easy, don’t go all-in right away, and gradually build up your endurance. Otherwise, you’ll be breathing like a pug chasing a frisbee after five minutes.
  • Stay hydrated! Drink fluids and avoid stuff like booze and caffeine. I know, I know, but think about it, do you really want to end up more dehydrated than a cactus in the desert?
  • Take breaks, listen to your body, and don’t overdo it. You’re not Superman (unless you’re actually Superman, in which case, hi there!).
  • Don’t push yourself too hard every time. You want to associate good sensations when breath holding, or your body is going to start associating it with something that sucks, and eventually, you’ll stop doing it altogether.
  • If you feel like something’s not right, get help! Don’t be a hero, it’s not worth it.

Can I Train Breath Holding Safely?

If you’re thinking about trying those cool breath holding exercises, make sure you’re healthy enough to do so! And if you’re not sure, talk to your doctor before giving it a go.

And please don’t even think about practicing those exercises near water or if you’re pregnant.

Also, it’s important to note that you should avoid breath holding if you have any of the following: 

  • high blood pressure
  • epilepsy 
  • diabetes
  • schizophrenia
  • uncontrolled hyperthyroidism 
  • chest pains or heart problems
  • sickle cell anemia
  • cancer
  • arterial aneurysm 
  • kidney disease 
  • panic disorder
  • severe anxiety*

*If you suffer from a moderate anxiety disorder, breathwork would actually be great for your health. You can read more on this here.

Can I Overdo Breath Holding?

If you’re gonna try those easy breath hold exercises, just remember not to hold your breath for more than half your BOLT score, or else your breathing could get all outta whack. And when you do finally take that sweet, sweet breath of air, try to inhale through your nose, not through your mouth like some kinda fish outta water. If you start getting cottonmouth or your hands turn into icicles, or you feel like you’re about to suffocate, that’s a clear sign to cool it for a moment and take a breather.

If you push yourself too hard, you might even end up peeing yourself! When your brain is all like “dude, I need some oxygen right now,” your diaphragm will contract and you might just let it all out. Don’t hold your breath longer than you can handle – or maybe do if you are sitting in an empty bathtub.

Now, some breathing techniques will tell you to hyperventilate before a breath hold. This is supposed to make you hold your breath longer by getting rid of carbon dioxide in your body. But beware, people have fainted or had other not-so-fun side effects from these types of breath holds. Try it out and sass out if it’s something you enjoy and feels good.  And if you’re anywhere near water, just forget about breath holding altogether. It’s better to find a comfortable place away from sharp objects and edges, the best place to breath-hold is lying on your bed or sitting on your couch. People have even drowned because they passed out while holding their breath in shallow water. Not worth it.

If you’re healthy and feeling good, you can totally hold your breath after exhaling normally. 

Are you totally hooked and want to learn more? Here are our favorite books on breathing and breathwork to take your health to its best place!

Will Breath Holding Make Me Lose Weight?

When you lose weight, your body breaks down fat into some molecules, including carbon dioxide and water. That’s right, you breathe out a good chunk of that fat! So, it makes sense that exercising makes us lose weight because we breathe more when we move our bodies. But, did you know that practicing breathing exercises can make exercise easier and more enjoyable? When your breathing is efficient, you’ll feel better during your workout, and you’ll be able to do more before getting tired. Plus, the better you can breathe, the more energy your body can get from the food you eat, which means you’ll burn more calories overall. And who wouldn’t want that? 


Scoggin et al. stated that endurance athletes have a decreased ventilatory response to hypoxia and hypercapnia compared to non-athletes. (Scoggin CH, Doekel RD, Kryger MH, Zwillich CW, Weil JV. Journal Applied Physiology 1978;(Mar;44(3)):464-8)

Martin BJ, Sparks KE, Zwillich CW, Weil JV found that endurance athletes have low exercise ventilation. (Med Sci Sports.1979;(Summer;11(2):):181-5)

Miyamura M, Yamashina T, Honda Y studied ventilatory responses to CO2 rebreathing at rest and during exercise in untrained subjects and athletes. (The Japanese Journal of Physiology 1976)

Woorons1, P. Mollard1, A. Pichon1, C. Lamberto1,2, A. Duvallet1,2, J.-P. Richalet discovered that moderate exercise in hypoxia induces a greater arterial desaturation in trained than untrained men. (Scand J Med Sci Sports 2007)

Jakovljevic DG, McConnell AK showed that different breathing frequencies influence the severity of inspiratory muscle fatigue induced by high-intensity front crawl swimming. (J Strength Cond Res, 2009)

Ferreira, Inês Raquel Antunes studied the effect of intermittent hypobaric hypoxia on induced muscle injury repair in laboratory rats. (Master’s thesis, 2012)

Jash, Sukanta, and Samit Adhya explored the effects of transient hypoxia versus prolonged hypoxia on satellite cell proliferation and differentiation in vivo. (Stem cells international 2015)

Arce-Álvarez, Alexis, et al. investigated hypoxic respiratory chemoreflex control in young trained swimmers. (Frontiers in physiology 12 (2021))