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Freediving, also called breath-hold or apnea diving, is diving without benefit of a breathing apparatus. Freediving is a sport with several different competition categories such as diving with or without fins, weight-sleds, depth records set in the ocean and breath-holding records set in pools. There are both men and women’s competitions in professional freediving.
Freediving requires extreme physical fitness, mental discipline and training. While human brain cells do not tolerate periods of apnea longer than five minutes and can become damaged after just three minutes, an understanding of the body’s reflexes, combined with training, allows world-class professionals in freediving competitions to hold their breath up to nine minutes. This is due mainly to taking advantage of the mammalian diving reflex.
The mammalian diving reflex is a key factor in any freediving sport. When a person is submerged in water, certain processes naturally take over. Heart rate begins to slow. With practice, it can beat as little as four times per minute. Blood vessels constrict in the limbs, forcing blood into the body’s vital organs. At the same time, blood vessels in the lungs fill with plasma, reducing volume to prevent them from collapsing in on themselves.
When the heartbeat slows, the body saves energy. Air trapped in the lungs continues to oxygenate the blood. This extends the amount of time the body can safely go without breathing. However, because there is no respiration, carbon dioxide (CO2) builds in the bloodstream and muscles. The build-up of CO2 is a limiting factor in freediving. When the body becomes saturated with CO2, it trips an overwhelming reflexive response to breathe.
Inexperienced freedivers sometimes hyperventilate before freediving, believing this saturates the blood with oxygen, allowing a longer dive. In reality, it does not increase oxygen, but removes CO2 from the blood, simply delaying the reflexive need to breathe. This is extremely dangerous and even life threatening, as the body can run out of oxygen before the diver feels a need to take a breath. When this happens, the diver can black out underwater. Shallow water blackout is believed to be responsible for many drowning accidents.
Freediving is an exhilarating but potentially dangerous sport that can result in severe injury or death. Pressures on the body in deepwater freediving can reach 235 pounds per square inch (16.5 kilograms per square centimeter). Though freediving has roots that reach back over 4,000 years, when people often dived for pearls and food, today’s enthusiasts are encouraged to take professional classes to learn how to enjoy this extreme sport safely. For those that follow safety first, freediving can be a beautiful way to experience the ever-exotic underwater world.