Freediving myth #1
The dive response does not exist, aqautic ape theory is a romantic myth
Yes the aquatic ape theory sounds good with its´ talk about our adaptations to breath hold, a survival instinct - problem is - it is not true. The arguments consists of a little mish mash of everything that supports the theory, but taking in the full picture then another story emerges. We are land animals - we like breathing.
Our instincts implanted in the autonomy sympathetic nerve system (fight and fligth system) knows this. When we stop breathing, alarm bells start to go off and soon an emergency system starts to operate. Some like to call these reactions "The dive response". Well, I got news for you - there is no such thing. The correct term is "general adaptation syndrome", and its not pretty. It is a general response to stress that all organism display when living conditions deteriorate (such no access to oxygen).
The "general adaptation syndrome" consists of:
The liver releases glucose.
Stress hormone release (that among others) promote fat/protein conversion to sugar.
Heart rate and blood pressure rises.
The muscles tense.
If you would check the cortisol levels of the blood (or urine) in association to a maximum dive they would probably be sky high. Cortisol is a stress marker.
In a competition, having announced above your PB, Just by thinking of that long horrible dive in front of you will probably start these responses.
And also in any situation of stress the following happens:
Digestion slows down (Saliva dry up).
Endorphins are secreted (feels like euphoria).
Surface blood vessels constrict.
And the romantic freediver might think that this last phenomena is to cause bloodshift to make you able to dive deeper.
Nope, the reason of vasoconstriction is to stop possible bleeding in case of injury.
So why do we get a bloodshift? To help you swim below RV? No.
Take any system made up of hoses and a pump and immerse it into water and the pressure will affect it. Pumping will be harder/slower and not have the strength to reach the periphery. Simple mechanics, nothing biological.
Ever wondered why we have those staring eyes when we come up. Dilated pupils is part of the general adaptation syndrome. Stress, pure and simple. Happens on land in a stress situation as well.
None of all these responses has anything to do with your belief that your ancestor had the habit of diving below RV to look for food. Why would you chase after fish at depths below 30 when crabs, muscles, seaweed can be found at depths were you hardly have to equalize. And in those days there were plenty of it. Why even submerge, wait for the tide to pull back and there it is.
And anyhow, why chill yourself down and enter a medium where you can´t see or breath. There was no masks in those days. Why even go to the beach when the jungle was full of fruit easily to pick and eat.
But... but the dive response, isn´t it designed to save oxygen, shaped by our ancestor "the snorkeling apes" on the east coast of the African peninsula, you may ask?
Of course we consume less oxygen during breath hold, because there is less available.
You actually consume more during the initial stages of Apnea. Scientist had to drive subjects to the verge of BO to see "an oxygen consumption effect". And by the way, the O2 saving was only proven on land, on a bicycle. At depth, under the very unnatural stress of pressure, we probably consume more.
But, look some might say, the overall spending is less. Of course it is, if you give a child one cookie he can never eat more than one cookie. Stop breathing and your O2 supply is less. So off course you spend less.
Less O2 spending also comes from anaerobic metabolism, but that was evolved when were on land, hunting after game, most presumably.
If you still think the Aquatic ape theory is true because we have no body hair. What about diving Otters full of hair? Land living rhinos with no hair? And some humans that actually are full of body hair?
If you still think the Aquatic ape theory is true because heart rate drops on face immersion in cold water. Dream on - Heart rate slows down because of the temperature change, not the water.
Bottom line is:
It is extremely stressful and unhealthy to hold your breath for long periods under water.
And there is no such thing as the dive response.