Freediving to depth is generally a comfortable and enjoyable experience. This can also be explained from a scientific standpoint. When we freedive to depth, our lung volume decreases due to increasing ambient pressure. This results in a significant increase in our blood concentration, despite the large amount of oxygen consumed during the first stage of our freedive. According to Boyle’s Law, at 10 meters (33 feet) depth, our lung volume is already two times smaller than at the surface. Our blood oxygen concentration is therefore two times greater (just imagine what is happening at even greater depths).

While oxygen is transported through our body bonded with hemoglobin, there is always a small amount of oxygen dissolved in our blood plasma which enables the transfer of oxygen both into and out of our bloodstream. This small amount of oxygen dissolved in our blood plasma continues to increase as we freedive deeper. The dissolved oxygen is used for metabolic processes within body tissues together with oxygen transported by hemoglobin, and so at depth our blood is saturated with oxygen faster and oxygen is more easily transported to our body tissues. As a result, we feel in better condition at depth than at the surface. This is known as hyperoxia and is caused by an excess supply of oxygen to our body tissues, that is, a higher than normal partial pressure of oxygen.

There are also a number of effects of hyperoxia on our body’s central nervous system. It can inhibit and suppress brain activity and consequently during a freedive, our internal dialogue halts and we withdraw. This is one of the reasons that freediving to depth gives feelings of joy, harmony, peace and a sense of reuniting with nature. However, for this reason it is important to be prudent at depth to ensure our freedive is performed safely and conservatively.

U/W camera: George Oikonomidis

Vassilis is a passionate and knowledgable freediving and spearfishing trainer.

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