top of page
  • Writer's pictureHarry Chamas

A comparison of STA and depth diving with regards to CO2 build up/Urge to breathe

Updated: Mar 17, 2020

A comparison of STA and depth diving with regards to CO2 build up/urge to breathe Deep diving is my passion. The vast majority of my time and energy is spent training to get better or training other people to become better at the depth disciplines. It has been a thoroughly enjoyable journey. Since historically there was very little information with regards to deep diving, I have embarked in a lot of experimentation, some worked well, some taught me hard lessons. The process of trying new things, discarding what doesn’t work and fine tuning what does is a big part of what keeps me doing this. One thing which I have found myself to be wrong about, is the relationship between full lung STA and deep diving. For a very long time, I didn’t do any full lung STA. It was my belief that since in depth we spend the majority of our dive below our residual volume, that we should solely train STA with empty lungs.

There is also the old adage within freediving that your STA time should represent half of your potential dive time (on a deep dive). This too, in my experience is way out of touch with reality.


What I have found during my latest training period, was quite shocking to me. Although my findings are purely empirical, I can read a lot into them – Why? Because I have spent years developing comfort at depth, building awareness of what is happening within my body and what feeling is attributed to each specific causation. So, when I do make a targeted change to my training and I then see a correlative change in performance… I can attest to the proficiency of the training. The thing that will stop most people from understanding what I am about to talk about is the overwhelming nature of deep diving. As you can see from the title, the main topic is related to CO2 and the urge to breathe. The problem is that most people in deep diving put any uncomfortable feeling at depth under the umbrella of urge to breathe. When in reality early contractions, discomfort on the descent and feelings of anxiety usually have nothing to do with CO2. There may be an urge to breathe, but it is brought on by you being overwhelmed by the situation you have put yourself into.

So what have I noticed? With regards to depth diving, the most efficient form of CO2 training is full lung STA. Not a table, just a few statics - each one started with no hyperventilation and a normal CO2 level (so not the classic CO2 table). Why? Somehow the true CO2 urge to breath in a deep dive comes on very late. For most recreational divers, it shouldn’t even be experienced. So, becoming used to holding the breath for longer periods, with no urge to breath, and becoming comfortable/familiar with the slow rise in CO2 preceding the urge to breath is a vital skill to be trained. In other forms of CO2 training such as dynamic, CO2 tables or apnea walking – the comfortable period and build up period is too short to really be trained, so all we end up training is how to suffer. In full lung STA, the CO2 build up is comparative to a deep dive, we get to gradually make peace with these slowly rising CO2 levels and extend how long we feel comfortable on our deep dives. The added bonus is that we can repeat more STA than deep dives and therefore have a stronger training effect. The second point that I have noticed is just how similar my CO2 build up is between my STA time and my dive time. In my experience equivalencies are as follows (depths are in FIM):- CO2 build up in Depth compared to STA

40m FIM feels like a 1:40 STA 60m FIM feels like a 2:30 STA 80m FIM feels like a 3:30 STA 90m FIM feels like a 4:00 STA I find this fascinating and liberating. In the past I imagined that to build the CO2 tolerance to get beyond 100m would require a huge STA, something which seemed so far away and unattainable that I was put off even trying. But my experience over this training period has showed me the power of regular mild CO2 training. That STA holds don’t have to be massive if you are truly relaxed and using efficient technique on your dives. And that our current equivalencies 2:00 mins = 20m, 2:45 = 30m, 4:00 = 40m are way off given a certain level of relaxation, understanding and technique.

My experience over this training period consisted of 3 90-92m FIM dives in around 3:16, I had performed mostly 3 minute dry breath holds for 3 months prior and about a week of 4 minute breath holds leading up to my last dive. I felt absolutely prepared for the CO2 build up I experienced, and during my last and most relaxed dive only had contractions on the last 30m of the ascent. So what to take from this? If you have not trained CO2 or breath holds recently, don’t feel like you have to do something massive to have a good training effect. CO2 training should be mostly about extending how long you feel comfortable. Training to understand what is going on within your body on a deep dive is vital to maintain relaxation. Proper technique and efficiency of movement can do incredible things to reduce your CO2 production. I would love to hear about your own experiences with how CO2 relates between STA and Depth. Feel free to comment or share on social media if you found this interesting.

Recent Posts

See All

From Fear to Flow

The interesting thing about this video is the contrast in reactions between the professional and the brave new comer. What can this tell us about fear? They are both in the same situation, with the

Breath Control does NOT = Hyperventilation

Hello all, this blog is written in anger. I have just read another post claiming that any breath manipulation is hyperventilation. The conspiracy goes all the way to the top - even most education sys


bottom of page