The Anatomy of Freediving 

Understanding the Body’s Adaptations Underwater

Freediving is an intense and beautiful sport that taps into our body’s innate ability to adapt to the underwater environment. Understanding the anatomy of freediving, from the respiratory system to the nervous system, reveals how freedivers achieve incredible feats of breath-holding, depth, and relaxation. Let’s explore how our bodies support us as we dive deep and hold our breath, and how freediving harnesses unique biological responses to thrive in challenging underwater environments.

The Respiratory System: Breathing Before the Dive

The respiratory system plays a key role in preparing the body for freediving, allowing freedivers to maximize oxygen intake and manage carbon dioxide buildup. Unlike with normal breathing, breath-hold diving requires special techniques, such as diaphragmatic breathing and “packing” to increase lung capacity and oxygen storage.

Diaphragmatic Breathing: By breathing deeply into the diaphragm before a dive, freedivers optimize oxygen intake and activate the parasympathetic nervous system, which calms the body and mind. Practicing deep, relaxed breathing prepares the body for a more extended breath-hold and greater relaxation underwater.

Lung Compression: As a diver descends, the increased pressure compresses the lungs. In deep freediving, the lungs may shrink to as little as one-fifth of their normal volume (Schagatay, 2010). Proper training helps freedivers tolerate this compression, keeping the respiratory system relaxed and allowing for greater depth.

For more on controlling breath and preparing the body, explore our guide on How to Control Your Urge to Breathe for freediving techniques that make each breath count.

The Mammalian Dive Reflex: Tapping into Evolutionary Adaptations

The mammalian dive reflex (MDR) is an evolutionary response seen in all mammals, designed to help conserve oxygen and protect vital organs during breath-hold dives. When we submerge in water, this reflex kicks in automatically, triggering three main physiological changes: bradycardia (slowed heart rate), peripheral vasoconstriction, and blood shift.

Bradycardia: The heart rate slows down, sometimes by up to 50% (Gooden, 1994), conserving oxygen by reducing the blood flow to non-essential muscles and organs, preserving it for vital organs like the brain and heart. This adaptation helps freedivers stay underwater longer with limited oxygen.

Peripheral Vasoconstriction: Blood flow to the extremities is restricted, preserving oxygen for the brain and core organs. This process is vital for deep dives, as it enables freedivers to go deeper without suffering from hypoxia.

Blood Shift: During deeper dives, blood flows into the thoracic cavity, which protects the lungs from being crushed under pressure. This blood shift is critical for dives beyond residual lung volume (Schagatay, 2010), preventing lung collapse at greater depths.

Curious about the dive reflex? Check out our post on Freediving and the Mammalian Dive Reflex to learn how this reflex enhances underwater endurance.

The Role of the Cardiovascular System in Freediving

Freediving places a unique demand on the cardiovascular system, as the heart and blood vessels must adapt to conserve oxygen and regulate pressure changes. As the mammalian dive reflex initiates bradycardia and vasoconstriction, these adaptations ensure oxygen conservation and support a freediver’s ability to dive deep.

Blood Pressure Adjustments: As pressure increases with depth, the cardiovascular system naturally raises blood pressure to compensate. This blood pressure rise is balanced by the peripheral vasoconstriction in the limbs, ensuring that oxygenated blood is directed toward essential organs.

Splenic Contraction: Freediving stimulates the spleen to release red blood cells into the bloodstream, boosting oxygen-carrying capacity (Hurford et al., 1990). This “blood doping” effect is temporary but offers freedivers a natural advantage, giving them access to additional oxygen reserves when holding their breath.

The Nervous System and Mental Focus: Staying Calm Under Pressure

The nervous system plays a significant role in freediving, as it helps maintain mental calmness and physical control. Freediving often pushes the body’s limits, and a steady nervous system response is crucial to handling these physical demands.

Parasympathetic Activation: Diaphragmatic breathing techniques before and during dives activate the parasympathetic nervous system, promoting relaxation. This relaxation response helps divers remain calm, conserve energy, and prolong breath-hold times.

Mental Focus and Visualization: Freedivers often use visualization techniques to prepare for deep dives, mentally rehearsing each part of the descent and ascent. Mental focus supports the nervous system by reducing anxiety and promoting relaxation, which can be particularly helpful when overcoming challenges like the urge to breathe or pressure at depth.

For mental techniques that can help you relax both in and out of the water, check out our post on Freediving Techniques for Better Sleep and explore how breathwork can bring calm to your practice.

The Respiratory and Digestive Systems: Adapting to CO2 and Oxygen Levels

Freediving requires adapting to changes in carbon dioxide (CO2) and oxygen (O2) levels, which is why CO2 tolerance training is central to the practice. The urge to breathe is triggered by rising CO2 levels, rather than low oxygen, and learning to manage these sensations is essential for staying calm and safe underwater.

CO2 Tolerance Training: Through CO2 tolerance training, freedivers condition their body and mind to tolerate higher CO2 levels, delaying the urge to breathe. This helps divers extend their breath-hold times without panic, enhancing the overall diving experience and safety.

Hypoxia Management: At deeper depths, oxygen levels decrease, requiring the freediver’s body to adapt to hypoxic conditions. With regular practice, freedivers improve their ability to handle low oxygen levels, making each dive more comfortable and extending the time spent underwater.

Final Thoughts on the Anatomy of Freediving

Freediving is not just about holding your breath—it’s a finely tuned synergy between the respiratory, cardiovascular, and nervous systems. Each system has its role in supporting a freediver’s endurance, focus, and safety underwater. By understanding how these systems function together, freedivers can practice more effectively and develop techniques that harness the body’s natural adaptations.

From activating the mammalian dive reflex to controlling oxygen levels through CO2 training, the anatomy of freediving is a testament to how adaptable our bodies are in the underwater environment.

Scientific References:

• Gooden, B. A. (1994). Mechanism of the human diving response. Integrative Physiological and Behavioral Science, 29(1), 6–16. DOI:10.1007/BF02691277

• Hurford, W. E., Hong, S. K., Park, Y. S., Ahn, D. W., Shiraki, K., Mohri, M., & Zapol, W. M. (1990). Splenic contraction during breath-hold diving in the Korean ama. Journal of Applied Physiology, 69(3), 932–936. DOI:10.1152/jappl.1990.69.3.932

• Schagatay, E. (2010). Predicting performance in competitive apnoea diving. Part 1: Static apnoea. Diving and Hyperbaric Medicine, 40(1), 11–22.