5. The Man Who Didn't Breathe
Have you ever tried to hold your breath along with the hero in a movie? It's usually in doing this that you realise that holding your breath is really hard. Try it now. Most people will be able to hold their breath for somewhere in the region of 1-2 minutes, but there are some out there who have managed to extend this to frankly dolphin-like timescales. In competitive breath holding (which is a real thing), the current record for "static apnoea" without oxygen is 11 minutes 54 seconds. The record when competitors were allowed to hyperventilate pure oxygen beforehand is a whopping 23 minutes 9 seconds held by Aleix Segura. Amazingly, it's actually easier to hold your breath underwater than on land, due to something called the mammalian diving reflex. This is an automatic response that occurs when your face is submerged in water, slowing the heart rate, constricting blood vessels and directing blood away from the extremities. If you want to improve your chances of surviving in a Titanic-like scenario, this reflex can be trained. That said, it's not advisable to attempt a solid 20 minutes. Apart from the fact that you're likely to end up all horrid and dead, static apnoea has been found to increase the proteins in your blood associated with hypoxic brain damage.