The internet of freediving is full of discussions on hyperventilation. For some time, the biggest question out there was: Should you or should you not hyperventilate before dives? By now, freedivers and agencies agree in stating that hyperventilation before freediving is counter-productive and dangerous, so at least there is a consensus of the majority.

But Wait.. There's a Flaw!

What renders this consensus less meaningful, is that there is far less agreement on what hyperventilation actually is.

The _right_ vs. a _useful_ Definition

We can avoid a lot of messy forum posts by not looking for a right definition, but for a useful one. We can define hyperventilation whichever way we want, but can we come up with a definition that allows us to work with it in a meaningful way and helps us in our training? -- Or maybe one that is useful for our teaching? Let's find out.

Let's keep it simple for now and just understand the word. _Hyperventilation_, from Greek, (and adopted into latin): "too much breathing" Simple enough.

Hyperventilation is too much breathing. Now we can start to think about "Too much of what?". What does "too much" refer to? - As in the question on hyperventilation itself, we are not looking for a right answer, but for a useful one.

When we ask people in our courses why they breathe, the first answer is pretty much always "Because I need Oxygen" or derivatives thereof. So let's see if we can create a useful definition based on that answer.

Testing the definition: Hyperventilation is breathing too much oxygen

This is a relatively easy one to test. In everyday life, we breathe in 21% of O₂. An average exhale contains around 17-19% O₂. - Now, we know from our first aid training that the oxygen in a normal exhale is enough to sustain the life of another person, even if that person is in a bad state. After all, that's why rescue breaths work.

What does this tell us? This tells us that we exhale the majority of the oxygen we breathe in, even though it would still be useful for us! Now, if - according to the definition we are testing - hyperventilation is breathing more oxygen than we need, then reality tells us that we are hyperventilating almost always!

As you are reading this, you are probably not been breathing not a lot, likely about 15-20 times per minute and each of your breaths expels most of the last breath's O₂. Would you intuitively say you are hyperventilating? Probably not, right? So, from what we can tell, breathing more O₂ than we need is perfectly normal (_normal -> adequate -> not too much_) and we commonly breathe far more than would be necessary to supply us with oxygen.

So, while this definition of hyperventilation is possible, it does not seem to make a lot of sense, as it defines breathing normally as breathing too much. That just doesn't seem very helpful, so, let's throw this one out of the window. Thinking of oxygen when defining hyperventilation isn't helping.

What other definitions could we test? We know that all the nitrogen we breathe is effectively too much anyway as we are not making use of it. So it is an easy one to discard. A useful (for a freediver) definition of hyperventilation probably has nothing to do with N₂. ...and that leaves us with - you guessed it: CO₂ - good old carbon dioxide.

The act of breathing - exhaling to be exact - down-regulates the body's CO₂ level, so breathing more would remove more CO₂ from the body. A candidate definition for hyperventilation would thus be:

Testing the definition: Hyperventilation is breathing that reduces CO₂ below a useful or safe level

If we can agree that breathing is a CO₂ down-regulating mechanism, then adequate breathing would be breathing that maintains (or works towards) a useful CO₂ level in the body and over-breathing (hyperventilation) would thus be breathing that reduces CO₂ below that level.

What do we do with this? Let's dig deeper. What is a useful - or safe - level of CO₂? _Useful_ depends on what you want to use it for, right? So in a CO₂ tolerance training table, for example, you would want to keep as much CO₂ as possible (or as much as you designed the table to provide - more on that in another article to come). If, on the other hand, you are freediving and you want to use your CO₂ level as a gauge for your dive and as a trigger for your dive response, then you want to make sure that you begin each dive at _the same_ CO₂ level every time and that that level is not so low that it triggers an increased heart rate, stress response, and too strong a bond between O₂ and haemoglobin (see also: Bohr effect).

So far so good. We have something that has the potential to be useful in our freediving. I'll use this definition for now.

Hyperventilation is breathing that reduces the CO₂ level below a useful or safe level

So now we just need to know how to avoid it. Easy, you say? Let's see.. In order to avoid hyperventilation, we first need to be able to recognise it.

What does Hyperventilation look like?

Down regulation of CO₂ depends of course on the production of CO₂. This means we cannot recognise hyperventilation without knowing our (or our buddy's) current level of physical activity, which plays a major role in our CO₂ production.

The more active we are, the more CO₂ we produce. When we are at rest, we don't breathe much, which is perfectly adequate. Why? Because at rest, we don't produce a lot of CO₂, so we don't need to breathe (out) a lot (of CO₂).

When we are exercising - say, we are running - we will be breathing more, increasing breathing amplitude and/or frequency. This is also adequate in this situation, as we are producing more CO₂ and need to breathe (out) more (CO₂) to maintain our normal CO₂ level.

Very fast or deep breathing is not necessarily hyperventilation

Here comes the interesting point: By our definition neither slow, easy breathing, nor fast, deep breathing are hyperventilation in the described circumstances. Yet, fast, deep breathing would be hyperventilation if you were to breathe like that while at rest.

Applying this Definition to Freediving

Now, we have looked at a high-contrast scenario to gain an overview, and we will find that this understanding of adequate- and hyper-ventilation also helps us understand our own breathing when freediving.

If you are at rest before a dive, how much do you need to breathe? - Well, not much, because you are not producing a lot of CO₂, right? So, adequate breathing before a freedive would be quite slow and shallow.

What about breathing (almost) full lungs before a dive, like the infamous 2-, 3- or 4-section breathing, purge-breaths™ and whatnot? Is that adequate or more than adequate? ...or _less_ than adequate? (Yes, I am deliberately keeping this question vague.)

Facit

Using the above definitions and understanding, we can make sense of pretty much any type of "breathe-up" and find out for ourselves if/when it would be adequate or too much breathing.

Questions

How d o you define hyperventilation?

How do you prepare for your dives?

How do these last two answers match?

Tell us in the comments below!