The Science of Swim: Mammalian Dive Reflex

                                         (Photograph by Brian J. Skerry, National Geographic)

This past weekend at the Wave One Open Water Clinic, I was chatting with one of the instructors and he brought up the mammalian dive reflex.  While I'd heard about this phenomena before, I couldn't remember the particulars.

So I looked up on Wikipedia of course and it said:

The mammalian diving reflex is a reflex in mammals which optimizes respiration to allow staying underwater for extended periods of time. It is exhibited strongly in aquatic mammals (seals, otters, dolphins, etc.), but exists in a weaker version in other mammals, including humans.  Every animal's diving reflex is triggered  by cold water contacting the face – water that is warmer than 21 °C (70 °F) does not cause the reflex, and neither does submersion of body parts other than the face. Also, the reflex is always exhibited more dramatically, and thus can grant longer survival, in young individuals.

So basically, when your face touches cold water, your heart rate drops (making you more relaxed), and focuses blood flow to your vital organs, which enables you to hold your breath longer. 

Truly amazing!  Want to see it for yourself?

• The website Evolvify has a a great page on the mammalian dive reflex which features a short clip of Bear Grylls of Man vs. Wild demonstrating it in a frozen lake in Canada.  Nuts!
• The BBC has an article called What Freediving Does to the Body which features a two minute clip of a Bajau man from Southeast Asia spearfishing at the bottom of the ocean.