What is Diving Reflex? Explore How Our Bodies Adapt Underwater

Last Updated: February 10, 2023

Have you ever wondered how some people can hold their breath underwater longer than you can? The longest human dive without oxygen was a staggering 11 minutes and 35 seconds, and just the thought of that has me gasping for air.

However, this is no magic; it is science.

You may haven’t heard of it before, but there is a unique physiological mechanism called the diving reflex, that enables our bodies to function with a lower level of oxygen.

Stick around to take a closer look at it and learn more about how our bodies can adapt to the underwater environment.

What Does the Diving Reflex Do?

mammalian dive reflex

The diving reflex (commonly referred to as the mammalian dive reflex, diving bradycardia, or the diving response) is an excellent feature that our bodies have inherited from our ancestors who lived in the water. When our face comes in contact with cold water, special receptors in our nose, sinuses, and the face send a message to the brain through the vagal nerve, which tells our body to make some changes to help us survive underwater.

Our airway closes automatically, and our body makes some changes to save oxygen. It’s pretty amazing how our bodies can adapt to different environments.

Here is what a diving reflex does to your body.

1. Lowers Heart Rate (Bradycardia)

Your heart rate will typically fall by 10-25% as soon as the cold water touches your face. This will slow the rate of oxygen entering your bloodstream, conserving it for other organs.

2. Constricts Blood Vessels

Your blood vessels will narrow to reduce blood flow. This allows the body to direct blood to vital organs that require more oxygen than other body parts.

3. Blood Shift

You may experience a blood shift when diving. As you go deeper, the increase in pressure causes nitrogen in the blood to come out of its solution and form bubbles. The body counteracts this by diverting blood to the lungs and heart.

4. Spleen Contracts

This may sound strange, but this helps your body maximize its use of oxygen. As you’re diving, your spleen contracts and releases more red blood cells into your blood. This allows your body to have higher hemoglobin in your blood.

How to Trigger the Mammalian Diving Reflex?

One of the many miracles of your body is that it can adapt to its surroundings without you having to do anything physically. Similarly, the diving reflex is a physiological effect that your body does without you even noticing.

To trigger your mammalian diving reflex, you must stimulate your trigeminal nerve. The simplest way is to apply cold water to your face or by holding your breath and bearing it down.

Before you try this repeatedly, be warned of the risks associated with triggering the reflex. Always attempt these activities with an experienced professional and use proper training.

Diving Reflex Benefits

The diving reflex has various benefits that help your body adapt to underwater surroundings.

  • Slows down the heart rate and breathing rate. This helps conserve oxygen and extend the time a person can stay underwater without breathing.
  • Causes blood vessels in the lungs and other vital organs to constrict. Moreover, this helps to protect these organs from the increased pressure of the surrounding water.
  • Releases a hormone that increases the amount of oxygen in the blood. This is what protects your body from harmful conditions like hypoxia.
  • Causes blood vessels in the arms and legs to constrict, and it helps to keep these areas warm and protect the body from hypothermia.
  • Slows down metabolism. This helps the body save energy and stay underwater longer.

Can Someone Train to Increase a Dive Response?

Just like we train our muscles to get stronger, we can also teach our bodies to have a more robust dive response. Here are a few ways to do it:

  1. Cold water exposure: Slowly expose your face and body to cold water over time. This will help your body get used to the cold and activate the dive response more quickly.
  2. Breath-hold: Practice holding your breath for extended periods. This will help your body learn to conserve oxygen and activate the dive response.
  3. Free diving: Freediving is where people dive without scuba gear. It can help your body learn how to conserve oxygen and activate the dive response.

It’s important to remember that while training the dive response can be beneficial, it should not be done at the expense of safety. Always dive with a professional and be mindful of your limits.


When our face comes in contact with cold water, our body triggers a dive reflex. This is a unique response that helps our body adapt to being underwater. When this happens, our heart rate slows down, which helps us save oxygen and stay underwater longer.

Our blood vessels in our arms and legs constrict, which helps keep our vital organs warm. Also, blood vessels in our lungs constrict, which makes it easier for us to hold our breath. Our breathing rate slows down and becomes shallower, again to save oxygen.

Our body also releases a hormone that increases the amount of oxygen in our blood. Additionally, our metabolism slows down, which helps us save energy and stay underwater longer.

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