Quite often, I start a beginner Freediving course by asking my students whether they think freediving is a dangerous activity or not. Some say yes, some say no, it is absolutely safe.
The truth is somewhere in the middle.
If you follow safety rules, Freediving is safe and enjoyable water-based activity. But if you break these rules, then Freediving becomes a Russian roulette without guaranteeing of a happy end.
And one of such rules is – don’t do hyperventilation before a breath hold!
But first of all, what is hyperventilation?
Hyperventilation is over-breathing – when you breathe more than you need to. Usually, the rate and depth of your breathing depend on a current metabolic activity (mainly on how much CO2 you produce). So, more CO2 you make – deeper or faster you breathe.
For example, when you are sleeping, you are not producing that much CO2, and your breath is shallow and quiet. But in contrast, if you are running, you create much more CO2, which dramatically affects your breathing rate and depth.
Back to Freediving. Remember, how breath-hold looks like? Relaxations breathing, breath-hold itself, and recovery breathing after.
Relaxation breathing can vary among freedivers, and we like to experiment with it. And some freedivers intentionally or unintentionally can do hyperventilation instead of relaxation breathing.
Why would someone do it intentionally? Is it an attempt to bring more O2? Unlikely, since the vast majority of O2 in your body is already connected with hemoglobin, this will not be affected by manipulation with breathing.
The answer is that someone does hyperventilation to decrease CO2 in the blood and delay the urge to breathe.
And what about unintentional hyperventilation? It can happen with a freediver who thinks that only fast breathing is hyperventilation. For example, you can hear such advice as “exhale as twice longer as inhale.” This is indeed a mild version of hyperventilation
But why is hyperventilation is not a good idea for Freedivers?
1. HR will go up. If you do deep and fast breathing, your heart rate will inevitably increase. And the heart is the muscle that requires O2. The more it works, the more O2 it consumes.
2. Lower CO2. Think about your urge to breathe as an alarm clock. When you have it, consider it a signal that you might come close to your hypoxic limit. If you remove too much CO2 by hyperventilation, you can come too close to your hypoxic limit and have a Black Out.
3. Also, removing too much CO2 will increase the blood pH level, making it alkaline. It will lead to cerebral vasoconstriction (constriction of the blood vessels in your brain), and as a result – less blood, less O2 will be delivered to the brain.
4. Hyperventilation suppresses the Bohr Effect. The presence of CO2 makes an easier O2 release from hemoglobin. If CO2 goes down, this mechanism is not working that well anymore.
Bottom line – hyperventilation should be avoided by beginner and intermediate freedivers by all means! It doesn’t give you any benefits but puts you at unnecessary risk.
More about Hyperventilation here