Static apnea is floating face down in a swimming pool whilst holding your breath is quite possibly the most boring sport in the world to watch (it makes cricket look exciting) but physiologically quite interesting. For example divers now use glossopharyngeal insuffation - this is a method of pumping additional air into the lungs widely used by reptiles and amphibians (picture a frogs bulging neck) but not by humans. Until a few decades ago when free divers discovered that by using the tongue as a piston an additional liter or so of air can be forced into the lungs. Don't try this at home though, rupturing the lung is a real possibility unless you work up to it.
How long can you hold your breath? A minute? A minute and a half?
What do you think the world record is. Four minutes? Five minutes? Ten minutes? Think again. The static apnea record is ELEVEN AND A HALF MINUTES!
Curiously the techniques involved don't involve keeping the brain alive
without oxygen, that's simply not possible, but getting oxygen to the
brain even though you aren't breathing.
If you breath oxygen beforehand though the record is much longer - two people have now exceeded TWENTY MINUTES.
(Here's a challenge - using knowledge of physiology and physics could you predict that the record would be almost twice as long using pure oxygen compared to the ~20% oxygen in air?)
Free diving is much more challenging because you must perform physical exercise without breathing (and face the changing pressure at depth.) There are all sorts of
categories including 'no limits' where divers use a weighted sled to
pull them down and then air bags to ascend. You still have to hold your
breath of course... The world record for this is an amazing 214m (over
700 feet). But the purest form of the sport is where the diver swims
down and back under his own power without even the benefit of fins.
Watch this amazing dive by William Trubridge, who has set further
records since this video - currently his record is an amazing 101m. I love how calm and collected he is. Every
movement seems perfectly choreographed and he is clearly maximizing
efficiency and not speed.