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The one minute CO2 tolerance test

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Well-Known Member
Jan 21, 2004
On a previous thread there was mention of the "one minute test" used for underwater hockey training and as it looked like an interesting way to get a reference point for CO2 tolerance I gave it a go. Here are the somewhat uninspiring results.

5min deep slow breathing, 3 purge breaths, inhale and hold for 55secs, exhale and inhale again (one breath 5secs) and hold again for 55secs…….repeated this one minute cycle until I failed on the 13th one. I didn’t have any contractions until hold 5 and from hold 9 I was having contractions for the entire 55 secs(boy the exhale and inhale were a relief if only for 5secs) I failed on the 13th hold when I lost the ability to hold the air in.

I remember Eric saying he did 2min cycles on a single breath recovery and did this for 30+ mins which by comparison I can probably deduce that we are at the two opposite ends of the capability spectrum when it comes to CO2 tolerance. :)

…..for those still reading thanks and here are my questions.

1. From this, is it fair to deduce that my CO2 tolerance is rather poor……therefore a great area for me to work on and see improvement.
2. Is there a similar test (maybe empty lung cycles) that gives an indication/reference point for hypoxia tolerance as well?
3. Is it possible to work out which of these two are my weakest area and while needing to improve both I could add some emphasis to the weaker of the two?


This test is not a good indicator of CO2 tolerance. Your results depend on primarily on your metabolic rate. If your metabolic rate is such that you need less than one breath every 55 seconds, then you could continue the test forever, without the slightest tingle in your lungs. You would then erroneously conclude that you have a fabulous CO2 tolerance, when in fact you may have none.

The only reliable way to test your CO2 tolerance is by using a capnograph, which measures the CO2 tolerance in your expired breath. The test I usually use is to take two breaths, inhale, pack, and then exhale into the CO2 monitor at the moment of the first contraction, or, alternatively, when I can no longer hold my breath.

Using this method you can also judge how much your CO2 tolerance increases after doing CO2 tables. For example, off a cold start I can usually only withstand 8.0% CO2, but after a long CO2 table I have gone over 10% (which is off the scale of the monitor and it gets pegged at 9.9%).

Eric Fattah
BC, Canada
well if i can only take one breath a minute for 25 minutes, it cant be to hard :D and its only a bit harder each time but could go for a half hour if i had to maybe i will try. but it cant meen to much

Thanks for responding as I'm aware that typing for you at the moment must be about as comfortable as strong contractions....probably worse

Apart from buying a capnograph what would you suggest is the best of the unreliable methods for measuring CO2 tolerance and tracking it over time. Are any of the tables better indicators than others, even if they remain relatively poor indicators compared with a capnograph?

On your advice from a previous post I made a choice on which pulse oximeter to buy, but like a poor exam student I didn't read the post accurately and bought probably one of the worst rather than one of the better units....the exact one you clearly suggested I should not buy - Ohmeda 3700! ! How stupid do I feel!

How best can I use the pulse oximeter to monitor Hypoxic tolerance? Would tracking the point at which the O2% begins to drop rapidly and the final 02% reached be initial relevant points to track? The 3700 will struggle a bit with the last reading 35% vs 50% I think you found yourself against other units.

Thanks for the help


Just a point of accuracy pal, its not one breath a minute, its one exhale and inhale in 5s and only one of those per minute. If I take one breathe a minute as slowly and comfortably as I like it would take 30secs and the whole thing gets a whole lot easier and goes for a whole lot longer. It seems from Erics post I'm not getting what I was hoping for out of the exercise anyway so it's all a bit academic I guess:)

I can suggest quite accurate ways of measuring your CO2 and O2 tolerance with your oximeter, but it isn't simple -- I will write more tomorrow.

Eric Fattah
BC, Canada
" I can suggest quite accurate ways of measuring your CO2 and O2 tolerance with your oximeter"

Now you really have my attention! ! If I can measure both via the oximeter (granted it could be rather complicated), it would be huge step forward for tracking progress.......boy am I going to be logging in to DB a lot over the weekend in anticipation.

Thanks Eric, I tried to send you some more karma but apparently I'm not allowed to as I have to share it around. That bothers me a little as it suggests your help to me this time somehow isn't as important as last time which is obviously wrong!......but you seem to have an ample supply anyway:p


The CO2 test (with only an oximeter)
[this gives only relative progress]

Similar to the 3'30" test as described in a previous thread:
- First thing in the morning, at the same time of day each time
- Warm your hands in a bowl of very hot water for at least several minutes, until they are choked with blood
- sit comfortably in your standard position in front of the oximeter (or lay down, whatever is normal for you). Rest for a given number of minutes. Preferably take your oral temperature, keeping in mind that drinking any water or liquid before hand will corrupt the measurement.
- Once you are completely rested (pulse returned to baseline), exhale, inhale to the max, hold for a fixed number of seconds (decide upon a number and stick to it), then exhale
- Again, inhale to the max, hold for fixed number of seconds
- exhale, inhale -- at this point you could pack if you want, but if so you must pack the same amount every time -- if you pack to the max you introduce variance based on lung flexibility

So, now you have taken two deep breaths and are holding your breath. Record your SaO2 every 30 seconds. Or, for more accurate results, record the transition times from one saturation to the next, i.e.
98-97% @ 1'32
97-96% @ 2'01
96-95% @ 2'33

Record the time of the first contraction. For best results, hold for perhaps 30 or 60 seconds of contractions.

The total time of the breath-hold should be the same each morning, for example 4'00". Record the saturation at the moment you end the breath-hold, and then record the minimum saturation which should occur a while later.

Your recording may look like this:
CO2 test: 4'00" (1st contract: 2'55", 12 contractions total, oral T=98.1F)
99% @ 1'00"
98% @ 1'30"
88% @ 4'00"
86% minimum
(or, it could should transitions such as 99->98% @ 1'39" etc.)

Each day you do the same. Keep in mind that the difference between the end-SaO2 and the minimum SaO2 depends on the blood flow to your hands -- poor circulation means there will be a bigger difference in saturations and a longer lag to reach the minimum. If you notice an unusually long or short lag to the min SaO2, it means your circulation is higher or lower than usual, which means the saturations at each given time (that you recorded) are not accurate. Remember that the saturations are delayed by X seconds, where X depends on your circulation. So, when you record 98% @ 1'30", actually it means 98% occurred at 1'30"-X, so if X is different than usual, then the numbers have less meaning. (By the way, if the minimum saturation appears on the oximeter 12 seconds after your resumed breathing, then X=12; if you want to complicate things, you could actually then measure X and re-adjust the readings to compensate for X).

Eventually, as the days go by, you will end up with a breath-hold that has identical transitions & saturations, that looks identical in every way, including body temperature. However, the single difference which may show up is that the contractions came sooner (or later) than before.

As your CO2 tolerance increases, you should find that a breath-hold with identical saturations (and temperature), becomes easier in terms of later contractions.

This test only works if the ratio of carbohydrates to fats in your diet remains constant. I diet higher in carbs causes higher O2 efficiency but greater CO2 production, and thus earlier contractions.

I'll describe the O2 test next.

Eric Fattah
BC, Canada

That’s terrific, it hadn’t occurred to me that I could use the pulse oximeter as a tool to create a standardised environment by which I could then monitor relative performance for CO2 tolerance. I can’t wait to the machine arrives this week so that I can try this out. I think my poor wife is about to get roped in to tracking and recording results I’ll let you know how it goes although I think the hands in warm water before starting will have me running to the bathroom…..I guess this is OK if I’m consistent each time.

Thanks for taking the time to share this detailed approach. There is no way I would have thought of it myself and it is therefore of great help to me. If you do find the time to post the low O2 tolerance test it would be much appreciated and definitely used.

Thanks again

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