For many, it’s the ulti­mate night­mare: sink­ing ever deep­er into the abyss, ’til you’re so far below the sur­face that no pen­e­trat­ing day­light can illu­mi­nate the way. It’s just you, unpro­tect­ed, in a watery, alien world. For oth­ers, it’s the ulti­mate test of phys­i­cal sta­mi­na, an oppor­tu­ni­ty to con­quer a realm nor­mal­ly reserved for finned creatures.

Free­d­iv­ing is many things to many peo­ple. What­ev­er its ulti­mate goal, the sport has the pow­er to trans­form its par­tic­i­pants and con­nect them with some of the human body’s most aston­ish­ing capabilities.

Acti­vat­ing the Mas­ter Switch of Life
Free­d­ivers slip into the water unen­cum­bered by oxy­gen tanks or oth­er gear and kick until they begin to sink with appar­ent ease, an eerie sight doc­u­ment­ed in the video below of div­er Guil­laume Nery in the Bahamas.

How do they do it? Human beings don’t seem built for hold­ing their breath upwards of 10 min­utes. But with train­ing, divers have indeed accom­plished this feat. Our phys­i­ol­o­gy takes care of us in the water if only we learn how to mar­shal it.

When the human body is sub­merged in water, a process called periph­er­al vaso­con­stric­tion trig­gers blood to begin flow­ing from the limbs to the vital organs, giv­ing the brain and heart an oxy­gen boost that makes pos­si­ble the wild stunt of sub­merg­ing your­self to the depths.

Swedish-born researcher Per Scholan­der termed the phe­nom­e­non the “Mas­ter Switch of Life”. Free­d­ivers flip that switch and become one with the water.

Com­pet­i­tive Freediving
There are three main events in the sport of freediving:

• Con­stant weight (CWT): the div­er uses a monofin and their own phys­i­cal pow­er to reach a cer­tain depth and back to surface
• Con­stant Weight No Fins (CNF): the div­er uses only arms and legs, unas­sist­ed by fins
• Free Immer­sion (FIM): the div­er pulls her­self down on a weight­ed line then back up to the surface

Many divers con­sid­er CNF the purest vari­ety. The cur­rent record for CNF—over 331 feet— is held by William Trubridge of New Zealand.

While the sport gives ath­letes an unmatched oppor­tu­ni­ty to become one with the ocean, it’s also dan­ger­ous. Pass­ing out cold or sur­fac­ing with blood bub­bling from your mouth and a glazed, unre­spon­sive expres­sion are very real pos­si­bil­i­ties in this sport.

Free­d­iv­ing for the Sake of Science
Free­d­iv­ing gives sci­en­tists and con­ser­va­tion­ists a unique oppor­tu­ni­ty to inter­act with the marine world. Sci­en­tists decked out in div­ing gear, masks and tanks can dis­rupt the nat­ur­al behav­iors of the ani­mals they study. A human wear­ing noth­ing more inva­sive than a fin can get a lot clos­er and more per­son­al in pur­suit of research.

For­mer com­pet­i­tive div­er Han­li Prinsloo holds sev­er­al free­d­iv­ing records in South Africa. But Prinsloo chose to focus on teach­ing div­ing as a way to immerse him­self in and appre­ci­ate the ocean environment.

Mean­while, divers with Project DAREWIN are using their skills to study marine mam­mal communication.

Plac­ing Our­selves in Our Environment
Whether for pride of com­pe­ti­tion or for the oppor­tu­ni­ty to par­tic­i­pate in the life and rhythm of the ocean, free­d­iv­ing is an expe­ri­ence unlike any oth­er. Turn­ing your body over to the force of the ocean might be the ulti­mate act of trust, but it’s also the ulti­mate act of con­nec­tion: con­nec­tion to the world around us and con­nec­tion to the capa­bil­i­ties of our own mirac­u­lous physiology.

Note: For an awe­some primer on Free­d­iv­ing, check out Deep: Free­d­iv­ing, Rene­gade Sci­ence, and What the Ocean Tells Us About Our­selves, by James Nestor.