freediver physiology
Physiology and the bluewater hunter
This chapter, written in two sections, covers physiologic principles important to your success and well-being as a bluewater hunter. The first half deals with the specter of freediver blackout, its causes and prevention. In the second half, I discuss selected topics aimed at enhancing your performance in the bluewater environment.
FREEDIVER BLACKOUT
Freediver blackout is also known as shallowwater blackout. You might think that shark attacks, line tangles and boat accidents are the freediver’ s worst fears; in reality those risks pale in comparison to the death and destruction wrought by freediver blackout.
BLACKOUT TYPES: Blackout is the sudden loss of consciousness caused by oxygen starvation. Divers can experience two types of blackout. Shallow-water blackout occurs when divers ascending vertically in the water column undergo pressure changes that influence the
body’ s physiology and trigger a blackout. Staticapnea refers to blackout that doesn’ t involve a deep dive. It is generally related to breath-hold attempts in a shallow pool.
Shallow-water blackout strikes most commonly within 15 feet( five meters) of the surface, where expanding, oxygen-hungry lungs literally suck oxygen from the diver’ s blood. The blackout occurs quickly, insidiously and without warning. Due to their lack of adaptation, beginning breath-hold divers are not generally subject to this condition. It is the intermediate diver who is most at risk. He is in an accelerated phase of training, and his physical and mental adaptations allow him to dive deeper and longer with each new diving day— sometimes too deep or too long. Advanced divers are not immune.
Skip Hellen’ s story is typical of many shallowwater blackout incidents. Skip and I were diving at Ship’ s Rock, one-half mile off of Catalina Island, California. We were competing in the
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