To many, the feats achieved by freedivers – particularly those competing at the highest levels of the sport – seem physically impossible. 

In fact, until elite divers proved them wrong in the 1960s, scientists believed 63.7m was the deepest humans could dive. Since then, assumptions about freediving physiology, and what the body can and cannot do, have been consistently challenged.

At the same time, our understanding of how freediving works and the impact it has on the body has advanced greatly. This has allowed us to refine the techniques we use to further optimise performance and minimise the risk of severe complications. 

Here we explore the contemporary understanding of freediving physiology, and the impacts diving can have on the body.

What impact does freediving have on the body?

Freediving triggers the mammalian dive response, which conserves oxygen by slowing the heart rate (bradycardia) and restricting blood flow to the limbs (peripheral vasoconstriction). This process prioritises oxygen supply to vital organs like the heart and brain, allowing divers to stay underwater longer.

The Impact of Low Oxygen Levels when Freediving

During freediving, blood oxygen levels drop and carbon dioxide levels rise, causing the spleen to release more oxygenated blood. If oxygen levels fall too low, a blackout can occur. This is a protective response where the brain shuts down non-essential systems to conserve oxygen for vital functions.

This is when a freediving buddy can be truly lifesaving! 

Common freediving physiology questions

Each time you go freediving, the body’s response is largely the same. However, there are some conditions that make certain risks and responses more pronounced. Some factors are also linked to increased incidence of different health implications and medical conditions.

What happens to the body when you dive frequently?

As every experienced freediver will tell you, diving regularly can provide a range of health benefits. 

Over time, the breath-hold nature of freediving should help increase your lung capacity and improve your overall lung function. The physicality of diving often also results in muscle development, and increased endurance and flexibility.

Although there are some risks associated with freediving, such as ear, nose, and throat issues identified in studies of subsistence diving communities, these findings highlight the importance of proper techniques and professional guidance. 

Proper training is essential for recreational divers to understand freediving safety and minimise risks to brain and lung health. Practising safe diving techniques ensures a positive and enjoyable experience.

What happens to the body when you dive deeper?

While elite divers may be able to reach great depths, this is not a natural environment for the human body. As such, the deeper you go, the greater the stress on your key systems.

When diving deeper, its crucial to understand the Bohr Effect. This effect helps divers manage their breath-hold times more effectively. During a dive, as CO₂ levels rise and blood pH drops, the Bohr Effect enhances oxygen delivery to vital organs, helping to delay the onset of hypoxia.

Proper breathing techniques and breath-hold training leverage this effect, optimising performance and safety during deep and prolonged dives.

Additionally, one of the most noticeable risks when diving deeper is nitrogen narcosis, which becomes significantly more likely when diving beyond 50 meters. This is a temporary condition that can make you feel drunk and disoriented, and can even cause hallucinations.

Deeper dives also increase the risk of decompression sickness – also known as the bends – though this is rare in freedivers. This is why proper freediving training is essential, as it keeps diving healthy and fun while avoiding these unnecessary complications.

What happens to the body when you dive in cold water?

Water temperature can have a big impact on how your body reacts during a dive, with colder waters creating a few unique responses. On the plus side, diving in cold water can lead to improved blood flow, a stronger blood shift,  increased cold tolerance, and even boost your immune system.

As one of the body’s natural responses to cold is to release endorphins, cold water dives often also result in bigger post-dive highs.

However, cold water environments are also much more challenging for freedivers. Heat loss starts the second you enter the water and can lead to hypothermia and other life-threatening conditions. The body also expends much more energy in cold water, meaning you will tire quicker, and your performance will decline faster.This makes it imperative that you have the right dive gear for the conditions.