The human body is capable of accomplishing incredible feats. Freediving is one of the greatest; in apnea, the diver relies only on his or her ability to dive and ascend on a single breath of air. While diving, the body responds to the demands of the physical environment and breath holding in a variety of ways. Understanding how the body works in the freediving environment may help you to become a more efficient freediver.
Body Pressure and the Lungs
For many years, doctors believed that if a freediver were to descend beyond a certain depth, the lungs would be crushed by the pressure of the underwater environment and death would be the ultimate result. After all, if you push a closed container filled with air slowly into water, it eventually crushes in on itself. When you freedive, no additional air enters your lungs to equalize the pressure that occurs, so how is it possible that the lungs are not crushed in the same way as the container?
After researching freedivers’ physiology, it was discovered that humans possess a blood shifting mechanism that occurs when the body is submerged and no additional air enters the lungs as greater depth is attained. How does it work? As we dive deeper, blood begins to shift from other body parts, flooding our lungs and automatically equalizing the water pressure from outside. At the same time, the heart rate slows down, and our blood pressure increases.
Ear Pressure
Ear pressure affects freedivers just as it affects scuba divers. As you make your descent into deeper water, the pressure affecting the outside of the eardrum begins to increase. As a consequence, the eardrum begins to press inward, often causing a great deal of pain. Using ear pressure equalization techniques such as the valslava maneuver, you can easily overcome the effects of pressure, forcing air into the middle ear and thus equalizing the pressure on each side of the eardrum.
Bradycardia and the Mammalian Diving Reflex
All diving mammals, including seals, dolphins, porpoises, and whales, have a physical adaptation called the mammalian diving reflex. This reflex allows them to dive for an extended period of time while subjected to intense water pressure. Like these diving mammals, humans possess the mammalian diving reflex, which is accompanied by changes in heart rate called Bradycardia.
Bradycardia literally translates to “low heartbeat.” It happens as soon as the brain detects that the body is immersed in water, slowing the heart rate. At the same time, the heart, which is arguably the most important muscle in the body, begins to consume less oxygen. In a nutshell, this means that the body as a whole requires less oxygen.
Peripheral Vasoconstriction
When you remain in the water, your body continues to adapt to the environment. As you move into deeper water at higher pressure, blood starts to leave the body’s peripheral regions and supply oxygen to your core. The fingers, toes, hands, and feet start to constrict, reducing the circulation requirements and increasing blood supply to the vital organs.
Familiarize yourself with the sensations associated with freediving and practice often. The more often you do, the more successful you’ll be as a freediver.