The world record for the longest time a human has held their breath underwater is 19 minutes and 21 seconds which was set by Swiss free diver Peter Colat in 2010.

A Swiss freediver held his breath underwater for 19 minutes and 21 seconds, according to news reports this week. The gasp-inducing feat beat the previous world record by 19 seconds, and blew away the record of 17 minutes and four seconds that magician David Blaine set on Oprah Winfrey's talk show in 2008.

For most ordinary humans, all that breath-holding can be hard to fathom. The feat might also bring up some basic questions about biology. For example: Is it really possible to survive without inhaling for that long? And is it healthy?

"It is, as a matter of fact, possible -- with certain tricks," explained Claes Lundgren, a physiologist at the University of Buffalo School of Medicine in New York.

It is probably not, however, good for you, and consequences can be deadly.

"Sooner or later, kids will read this and do something silly," said Lundgren. "It's not recommendable at all. Anything written about this should be accompanied by a strong admonition not to try this without someone knowledgeable present."

Breathing is obviously an important way to stay alive, and our bodies have a built-in system of sensors and signals to make sure we keep doing it. When you hold your breath, carbon dioxide builds up as your body uses up oxygen. After a minute or two for most people, the result is an overwhelming urge to breathe.

"All sorts of alarms go off," said Ralph Potkin a pulmonologist and hyperbaric physician at the University of California, Los Angles School of Medicine. "The brain tells the body to breathe. The diaphragm gets electrical signals to stimulate breathing."

To fight those powerful instincts, a competitive breath-holder starts by hyperventilating for as much as 10 minutes while breathing from a tank of 100 percent oxygen. Breathing hard and fast expels carbon dioxide from the body, buying time before CO2 levels get too high. Likewise, boosting oxygen stores with pure oxygen buys time before O2 levels fall too low. After hyperventilating, if a person isn't unconscious, he'll probably feel dizzy and have extreme cramping in the arms and legs.