FRC/below FRC diving and exhaustion

[sxc]

Howdy,

Is FRC diving generally much more exhausting than full inhale diving?

I've been training (alternating pool and ocean) for about a month with some rest in between; the last couple of days we haven't had any depth (only about 30M) so my coach suggested doing some FRC dives instead of targets. I've never done any FRC diving before, so decided to do a pull down(FRC) to 30ish, where the pressure was quite high, but not unbearably so, my ears equalized themselves as usual, I didn't do a mouthfill (I can equalize hands-free most of the time), my mask was extremely tight, nothing surprising. I was quite exhausted after the dive, though.

The next day we decided to do a constant to 32, FRC again. Same deal, no mouthfill, managed to equalize, but last mask equalization was at 12-14ish (or shallower, but not deeper), so mask was practically stuck on my face at 32 (luckily, low volume with plastic lenses meant I didn't get a mask squeeze), the ascent was harder than a regular dive to 40+, and I wasn't able to recover to do another one (I wanted to try it with a mouthfill) even after a full 10 minute breath up.

Today, the weather was quite nice, so we decided to do a 45, but my warm-up to 25 (pulldown) felt like it was to 50, I've never felt this bad, even after targets.
We got back and talked about it, and decided I was actually doing the dives below FRC (my diaphragm was pulled in a bit after the exhale, so it wasn't really passive, and when I did an actual passive on land I felt way fuller than I felt on the dive), he ran some numbers and came up with a "simulated dive depth" of around 90M, assuming 40% TLC, which makes sense:
90m = 10 ATA = 10% original volume.
Assuming 40% of original volume:
32m = 4.2 ATA = below 10% of actual volume = 90M+

So, my questions are:
1) If you're diving at about 40% TLC (below FRC, but not anywhere near empty lung), what dive depth are simulating with a 32m dive? He came up with the 90m figure by noting that I could do a mouthfill at 38M, i.e, not below RV at that depth with a full inhale (no packing).
2) Is this exhaustion to be expected? It's not anything specific, I've just got a feeling of being quite tired. I haven't felt this bad at any point during training (including 3km of drills a day etc). I'm extremely surprised that a below FRC dive to 32m can cause this kind of long term (over 24 hours) fatigue. I slept 12+ hours on both the days after the dives, so its not lack of rest.

Thanks!

 

[rafacuatic]

Is FRC diving generally much more exhausting than full inhale diving?
I think so,over the same depth full inhale is less hard than FRC or empty lungs.
But for sure,90m is more exhausting than 30m FRC,you have to fin more.
I think than the tireless is related to the blood shift,less O2 and muscle work.
In my case,repetitive exale dives to 25m,will tire me for long time.

 

[Simos]

Any symptoms that might indicate squeeze?

 

[growingupninja]

Not ruling anything else out but if you are used to training full lung, when you switch to FRC or below you may be more hypoxic than you are used to by the end of your dive without realizing it, so your body is working more anaerobically than usual. Until you get more conditioned to this it will feel very exhausting.

 

[sxc]

Any symptoms that might indicate squeeze?

Well, general exhaustion could be a symptom of a squeeze, but I don't have any other symptoms, so I don't think it is a squeeze.

 

[sxc]

Not ruling anything else out but if you are used to training full lung, when you switch to FRC or below you may be more hypoxic than you are used to by the end of your dive without realizing it, so your body is working more anaerobically than usual. Until you get more conditioned to this it will feel very exhausting.

That makes sense, except I've been doing quite a bit of exhale training in the pool during pool training, so I don't think my body is new to doing work with hypoxia/high co2. It was obviously much harder to do exhale drills than full inhale ones, but I still recovered fine with a good night's sleep, something I haven't been able to do with these dives, so I don't think its just being more hypoxic.

 

[Simos]

How did you equalise at 32m without mouthfill? You must have been fairly empty, did you have to reverse pack?

 

[sxc]

How did you equalise at 32m without mouthfill? You must have been fairly empty, did you have to reverse pack?

Did I reverse pack: Not consciously. Equalizing hands free gives me a pretty big advantage, my ears seem to "take care of themselves" most of the time. I was very empty at 32, hell, I was empty way earlier. The last equalization I did with hands was at 12ish (same as the mask), after which I couldn't do one even if I wanted to, then I felt the ears equalize small amounts all the way down, I assume I was sub-consciously pulling up small amounts of air to equalize by reverse packing, but I wasn't paying attention to it. I felt pressure on my ears all the way down, so these weren't "full" equalizations, just enough to get the job done.

When I do a negative with a lot of reverse packing at the surface, and then one mouthfill (at the surface) so when I start the dive I'm pretty much empty, I've gone down to 15ish (hands free all the way) and still had plenty of air in my mouth(no pressure on the ears either), my chest on the other hand, felt like it was going to collapse..

My coach says equalizing hands free uses a lot less air than with hands (which makes sense), which might explain how I was able to do it.

 

[Antoine]

My ears tend to also equalise without me having to do anything. Every couple of metres my ears 'auto-equalise' without doing anything whatsoever(conciously at least). However, just like sxc, i still feel a constant but no unbearable pressure, in both ears so they are actually not fully equalising, only enough so that the ear drums aren't under too much tension. If they don't equalise, i just move my jaw slightly to the right and thery're fine.
I though something was weird about how easily i equalise but is seems to be the same for sxc. can't complain anyway!

 

[sxc]

I should add, I just did the jerry-can test in the pool to see if I had extra-large lungs or anything, turns out I actually have smallish lungs: 4.5L VC without packing, and 6.2ish with packing, so assuming that's accurate, it actually surprised me a bit.