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Spearfishing an Extreme Sport

Posted by Silverback on 06 November 2007 at 01:28 PM

What makes freedive spearfishing an extreme sport

The sport demands a high level of fitness and an unusual mindset. Spearo’s are prepared to become part of the food-chain in an obviously unfamiliar environment and then hold their breath to achieve their targets.

The single most important killer of breathhold freediving spearfishers is SHALLOW WATER BLACKOUT. To understand SWB you need to have a reasonable idea of how your body responds to a breathhold. I am a medical professional and am often criticised for making my explanations too complicated but I am going to try to keep this as simple as possible.

The oxygen O2 concentration in the atmosphere is higher than a normal lung needs to maximally oxygenate all the available haemoglobin in your blood. That means that under normal circumstances, O2 cannot be used to regulate your breathing reflex. Low O2 levels will affect your conscious state. When you become tired, you begin yawning to elevate your O2 uptake to keep you conscious.

The normal breathing reflex is therefore controlled by carbon dioxide CO2 levels. When low, you do not feel the urge to breathe but as the level increases, the urge becomes stronger. This is where voluntary control of breathing comes in. Freedivers condition their bodies to allow extended breathholds because they are able to tolerate the CO2 build up.

Simply put under normal conditions, you can feel the effect of elevated CO2 levels but are ignorant of decreasing O2 levels.

Let’s consider what occurs during a freedive. Initially the O2 levels are high and CO2 levels low. As the dive progresses, the lungs become fluid filled & compressed at depth while O2 is used up and the body produces CO2. The increase in CO2 stimulates the need to breathe. This is controllable and can be suppressed with suitable training. Eventually the desire to breathe as a result of the elevated CO2 level encourages the diver to the surface. All the while, O2 levels have been gradually decreasing without the conscious knowledge of the diver. On approaching the surface, the lungs expand drawing the dissolved gases from the blood into the lung space. Any increase in activity consumes more O2 and produces more CO2.

This dramatic change in anatomy and gas dynamics causes O2 levels to drop below the threshold for remaining conscious. This occurs with extended breathholds and high levels of activity. Typically the diver losing consciousness close to the surface. The reflex to breathe results in drowning!

Never hyperventilate or dive alone!

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