What is the Mammalian Diving Reflex? All You Need to Know

What is the mammalian diving reflex? This question is indeed common among new or amateur divers. It’s because this is a concept that any diver in general should be familiar about. Today in this blog post, we’ll talk about all things about this reflex. Moreover, we’ll tackle what it has to do with freediving. Make sure to stick around until the end.

The mammalian diving reflex is also simply known as the diving reflex or diving response. It’s a set of physiological responses to immersion in a body of water. Basically, it refers to the involuntary reactions of mammals when put into any aquatic environment. Moreover, this can be very much seen with infants who have no previous experience with water. With them, you can definitely observe that humans are predisposed to act in certain ways when put in water.

Furthermore, this is often used interchangeably with “swimming reflex.” Bear in mind that these two are different and that swimming reflex is actually a part of the entire diving reflex. Swimming reflex is as simple as the tendency to swim when suddenly put in water. Once again, this can be seen with newborns when placed in water. They will quickly move in ways depicting swimming. Additionally and obviously, that’s without being taught that it’s the right thing to do.

Physiological Responses When Diving

Here are the physiological responses that mammals such as humans inhibit when diving:

Heart Rate Reduction

This condition is also called bradycardia or slow heart rate. Of course, bradycardia is a problematic condition if it happens on its own. On the other hand, it’s a normal occurrence in mammals or humans when diving.

During diving, one of the human’s reflex is to reduce its heart rate by about 10-25%. That is actually right at the very contact with water. Moreover, this can also already happen by just splashing water into your face. Furthermore, what comes out of it is that the oxygen that enters the bloodstream is reduced. When that occurs, oxygen is certainly conserved within the body. The said conservation is very much needed by mammals when immersed in water for the use of their vital organs.

Peripheral Vasoconstriction

This condition is the involuntary narrowing of one’s blood vessels when diving. This happens by the muscular contraction of the blood vessels. In addition to this, this results to the reduction of one’s blood flow.

At the moment of diving, one’s capillaries or tiny blood vessels in the extremities constrict. The said extremities are the arms, hands, fingers, legs, feet, and toes. Through this process, blood flows into the much more important organs in the body. Once again, this occurs so that survival when underwater is definitely possible.

Blood Shift

This condition is simply the blood filling in the empty spaces in the different organs of the body. Moreover, these spaces have been emptied out because air has been compressed. Obviously, it’s a no-brainer that when you’re diving, the air in your lungs will be compressed. It’s because as you go further down the water, the atmospheric pressure certainly increases. At the same time, take note the nature of the blood wherein it can’t be compressed. It’s because of its liquid or fluid nature. So clearly, it will be filling the body when the latter is experiencing underwater pressures.

Furthermore, bear in mind that because of this blood shift, your organs won’t collapse when underwater.

Splenic Contraction

First of all, the spleen is the largest organ of the body’s lymphatic system. Additionally, it’s the organ responsible for keeping bodily fluids balanced. Moreover, the spleen is located under the ribcage and above the stomach.

Now, splenic contraction is the condition where the spleen contracts resulting to releasing of blood. The spleen stores large volumes of bloods. For this reason, when it contracts because of the atmospheric pressures underwater, it gives out blood. Furthermore, this additional amount of blood circulating within the body is vital. It’s because the important organs need all the support when the body is underwater.

The Mammalian Diving Reflex and its Connection to Freediving?

Freediving is breath-hold diving or skin diving. Basically, this is diving only with the air of your lungs and no other apparatus like scuba gear. Moreover, this diving is as far as you can go underwater.

Nowadays, this activity is a recreational pastime of many divers around the world. At the same time, it’s also a sport now. Take note also that how long and how deep a freediver can go depends on the type of freediving. He/she can definitely decide the dive’s time or duration, depth, as well as distance. Without a doubt, limitation of breath-hold and exposure to high ambient pressure are the challenges of freediving.

Furthermore, the most important takeaway here is the connection between the diving reflex and freediving. You see, the mammalian diving reflex plus apnea or the natural instinct to hold breath when underwater is what makes freediving possible. Moreover, freediving is also about the power of the diver’s body and the will of their minds. It’s a no-doubt indeed that this activity or sport deserves all the awe from its spectators.

Types of Freediving

Here are the different types of freediving:

Constant Weight Freediving

This one is an open water depth diving that is deemed as the purest form of freediving. Why? It’s because the divers take everything from their own bodily power. Also, the weight (or not) that they wear will remain all throughout the entire dive. Moreover, it can be done with or without fins. Furthermore, the said fins can either be monofins or bi-fins.

Before, it’s only a depth discipline. On the other hand, as time passed by, this has become a competition discipline too. Take note that competitions where divers don’t use fins are much harder. Additionally, this kind of competition has really amazed spectators too because it proves that farther depths are definitely possible. And these depths are actually depths that weren’t even considered before in No-Limits freediving!

Free Immersion Freediving

This one is a warm up for constant weight freediving. Obviously, this is the diving activity that amateur divers undertake first. Here, the diver pulls down a rope and then back again. The purpose of this dive is to warm up the legs as well as the body for the pressure by depth. At the same time, checking the ears’ equalization is also done here.

In this dive, new divers typically go in with feet first. Then they will pull down the rope with effort. Moreover, fins are for aid and safety to be able to easily go back up again.

Variable Weight Freediving

In this kind of freediving, divers use a heavy sled to pull them down faster. Moreover, this sled is attached to vertical ropes. The purpose of this dive is for the diver to easily get to farther depths without using up too much oxygen in swimming downwards. At the same time, all they have to do is pull on the rope as well as swimming too for them to ascend.

Furthermore, take note that only professional, experienced, or advanced divers are the only ones who participate in this. It’s because it’s naturally dangerous. The diver can indeed go swiftly to really far depths. The issue of equalization is also a subject matter here. For these reasons, this kind of freediving isn’t an official freediving competition.

No-Limits Freediving

Last but definitely not the least of the freediving types is this one. This is the most extreme and risky of all because it’s all about the unlimited possibility of depth. Just like with variable weight freediving, the diver uses a sled to descend fast. At the same time, they use inflatable lift bag to ascend quickly. Furthermore, this is also not an official freediving competition since it’s way too dangerous.


The mammalian diving reflex is an innate response of mammals when immersed in water. This blog post has covered all the physiological changes that take place when this reflex is triggered. Additionally, the reflex is definitely a means of survival. Moreover, the connection between the reflex and the sport of freediving is also covered. Freediving has always been a thing ever since the world began. Humans have been doing this for necessity such as hunting for food. However, this has gained tremendous popularity nowadays for its recreational nature. Pictures of freedivers under far depths induce reverence. The said photos are naturally aesthetic for the wonders deep down there and the diver’s amazing form when underwater.