What Is The Mammalian Diving Reflex?


Breathing is an important part of diving and swimming and even when using a snorkel gear package. Before you can perfect your swimming one of the skills that you will need to master is your breathing technique particularly how to hold your breath underwater.

Several physiological processes occur when your face hits cold water which makes you hold your breath. It is called the mammalian diving reflex.

The mammalian diving reflex causes a slowing down of the heart rate, vasoconstriction of the blood vessels and blood plasma flows through the body organs helping to protect them from the high pressure of deep dives.

Note that the mammalian dive reflex is not affected by wearing a swim cap as it is activated when the face hits the water.


This is where the heart rate slows down. It can be anywhere from 10% to 30%. Sometimes in trained individuals, it can be up to 50%.

The rate at which the heart beats drop when the face comes into contact with cold water is incredibly fast. Nerves on your face particularly the trigeminal facial nerves send information to the brain. As a response, the various nerve innervates which results in both peripheral vasoconstriction and bradycardia.

The temperature has a lot to do with how fast the body reacts and colder water causes a faster reaction. However, it’s important to note that warm water temperatures above 210C do not result in a reaction.

Since there is a low heart rate, the amount of oxygen pumped in the body is minimized which allows the mammalian body to conserve oxygen. You may find wearing swimming goggles makes your experience easier as water is kept out of your eyes.

Peripheral vasoconstriction

This is where the blood vessel at the extremities such as the hands and limbs constrict reducing oxygen supply to the muscles in these areas. It allows the more essential body parts such as the heart, lungs, and other internals to receive priority in oxygen supply.

The reaction is meant to be protective or preventative in nature since it takes place before there is a critical drop in the oxygen levels.

If you plan on swimming on open water then triathlon goggles for open water swimming will help you maintain your vision by keeping water out of your eyes.

Blood shift

This is all part of the mammalian dive reflex. It often happens during deep high-pressure dives. Such pressure could cause damage to the internal organs. The blood shift allows blood plasma as well as water to pass through the circulatory walls and the organs themselves.

You may need to wear earplugs for swimming to keep water out and perhaps to slightly lower the pressure on the ears.

The lungs in particular will fill with blood plasma. When the pressure drops, the blood is then reabsorbed into the body. Besides, the blood plasma that accumulates in the lungs and other internal organs protect them since the fluid cannot compress. It is this blood that prevents the high pressure from compressing the lungs.

When vasoconstriction occurs, the majority of the blood is held in the lungs, the brain, the heart, and the circulatory system. These organs are the most sensitive to oxygen in the body and thus the body’s natural reaction is to ensure that they receive adequate amounts of the gas.

More body responses


Another type of body response that can be seen in infants of less than 6 months is when they are dropped in water. The windpipe will automatically shut near the vocal cords which prevents water from getting into the lungs. However, when the child grows beyond 6 months, the reflex is no longer there.

Study shows that the spleen has a significant role in allowing the diver to hold the breath for longer and to recover faster when they finally resurface.

The spleen contracts when the body is underwater at a slower pace than the other diving reflexes. Since it contains the red blood cells, they are released into the bloodstream. This allows the body to carry more oxygen enabling the diver to stay under for a longer duration. Also, more red blood cells mean that you can absorb more oxygen when breathing allowing the body to recover faster.

Diving marine mammals

Whales, seals, and dolphins all have a mammalian diving reflex that is far superior to ours. It allows them to stay under the surface for extended durations as they hunt for their food. In fact, seals and sperm whales can hold their breath for more than an hour.

The agility and depth that these animals can achieve are certainly unachievable for us even with using the best swim fins. The monofin design of marine mammals fins makes them highly adept in their watery world.

For starters, they have a high amount of blood containing high amounts of red blood cells. An iron-rich molecule called myoglobin is present in whale and seal tissue. This allows oxygen to bind to the molecule and enables the animal to remain without breathing for a long time.

If you were to hold whale meat in hour hands, you would notice that it is very red and this is because of the high iron content.

Another interesting ability of diving mammals is that they can cool down their brains. This allows them to dive deeper for longer.  By bringing down their body and brain temperatures sometimes by up to 3 degrees Celsius, their metabolism reduces which also brings down their body’s consumption of oxygen.

While humans are not able to shoot down their blood supply completely, seals and other marine mammals can do this by concentrating the blood on the vital organs.

How to make use of the diving response

Activating the mammalian dive reflex can be one of the most effective ways to boost your performance during a swimming competition. And you don’t have to stick your head in freezing water either, simply take a towel, dip it in cold water, rinse it and place it on your forehead or above your nose.

This will cause your heart rate to drop, helping you relax and lowering your body’s consumption of oxygen. You will be able to use your swimming snorkels or stay underwater for longer than you would if you didn’t activate the dive response.

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This goes to show how much similar anatomy there is between humans and diving marine mammals. That said, mammals have had millions of years of evolution which allows them to make the most of the diving response. Humans can also boost their ability in the water by making use of the diving response.

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My name is David Hamburg. I am an avid water sports fan who enjoys paddle boarding, surfing, scuba diving, and kite surfing. Anything with a board or chance I can get in the water I love! I am such a big fan I decided to start this website to review all my favorite products and some others. Hope you enjoy!