Exhale Diving for the "average" diver

[Mullins]

when you dive full lung or pack,versas 1/2 lung, there is much more nitrogen available in the lung to diffuse into the bloodstream. More nitrogen into the bloodstream = more narcosis. At least that is the theory as I understand it. Maybe also, lower lung volume means less surface area for gas to diffuse across.

Mmm, I'd be interested to hear an account of why that might be the case. Given ppN2 is the same regardless of lung volume, and only a small fraction of the available volume is ever dissolved, the only remaining variable is surface area, as you say. I'm not too sure about that being a limiting factor either but might have a trawl through Trux's site to see if anything's said about it....

I reckon the reduced narcosis you get with FRC might simply be due to the lower CO2 production. I get very narked on inhale dives but I think that might be because of the extra energy expenditure I need to overcome the buoyancy change that comes with high lung volume. Unfortunately I haven't done any deep FRC dives so can't compare.

 

[Mullins]

Exhale (FRC) theory says static till the first urge to breath then you should be able to swim an equivalent amount of time.

I've always wondered about this. I don't suppose you can take it literally because the locomotors are never on an entirely 'closed-circuit', and do steal a bit of O2 from the core. If they were genuinely isolated then you would always want to swim as fast as possible upon reaching PBP, limited only by muscle failure. So there might be, say, the assumption of a <1.2m/s swimming speed hidden in there.

 

[azapa]

Connor, sorry if this sounds like an interrogation, even though it is, but how long are you breathing up in between these "swims"?

 

[efattah]

1. Narcosis
My guess is that the no-narcosis of FRC dives is due to less CO2. I agree with Mullins' calculations that the available N2 is still large, so dissolved N2 would appear similar. However,
A) as you are doing way less work on the descent, your heart beats less, and less blood flows over your lungs, absorbing less N2 maybe?
and
B) More plasma or alveoli collapse could mean compromised gas exchange in the deep phase, possibly limiting N2 absorption
and
C) Seb Murat quoted a study on rats that showed that minor changes in available N2 could change DCS risk a lot, and N2 absorption is a factor for both DCS and narcosis

2. Static/Dynamic
When training horizontal swims in the ocean with a 6.5mm suit and mask (i.e. lower dive response), at the moment I can do a 100% sprint for about 0'50" - 0'55" (75-82 monofin strokes). If I instead start with a 1'40" static on the bottom at 8m (taking one stroke to get down), then I can follow the static with a full out sprint of 0'44" (60 strokes). So I do lose out some O2 from the static but I lose less than you might think. Interestingly, a flat out sprint off the bat gives me dead legs at 55 strokes (i.e. last 25 strokes are with terribly weak legs). However doing the static first and my legs die at 30 strokes (much earlier).

 

[laminar]

For clarification on Eric's post, "dead legs" is a good thing.

 

[Mullins]

Eric, how much does your swimming speed affect the time to BO after PBP?

Just re-reading your post. So if you go dynamic after 1:40, you should normally be able to maintain a slowish pace for another 1:40 as per standard 'FRC wisdom'? And when sprinting that dynamic phase is reduced to 0:44? And does the sprint end with legs failing or BO?

 

[efattah]

I experimented with 'slow' swimming speeds, but really slow swimming speeds are useless in a vertical dive as the tiny propulsion force doesn't even cause any vertical movement. I found that the force I exert when ascending from a dive under negative buoyancy is more of a sprint style action.

The effect of slow vs. fast swimming depends on the style of dive:

Straight dynamic
FRC Sprint 0'50"-0'55" (75-82 strokes)
FRC Slow swim 2'06" to 2'08" (38-40 strokes), kick & glide

Static/Dynamic
1'40" FRC static + 0'44" sprint (60 strokes) (=legs die at 30 strokes, then I crawl along with slower strokes until the edge of samba)
1'40" FRC static + 1'10" slow swim (28 strokes)(=legs never get tired, end near samba)

Keep in mind that the above is with a 6.5mm suit and a mask. If I do the same with fluid goggles and wet sinuses, the times increase. Also with no wetsuit the times increase still further.

I know Seb Murat was doing 1'40" FRC static + 1'50" DNF for 100m distance and 3'30", though he said the deepest vertical FRC CNF he did was 81m.

I have been training pretty hard lately and the sprint phase at the end of the static/dynamic has been increasing by 1-2 seconds per week quite consistently. However I will need to do 1'40" static + 1'25" sprint to have any chance of doing a 120m dive.

 

[Mullins]

You'd need to be pretty heavy to average 1.2m on the descent (unless there is a dyn phase at the start of the dive) which would make 120m ascent in 85s (1.4m/s average) pretty tough going. Didn't Murat simulate negative buoyancy in the pool by using a drogue?

I was asking about the difference between sprinting and moderate pace because I was interested to hear just how isolated the leg muscles were from the core when FRC diving i.e. complete isolation would mean no difference and a 1:40 dyn phase regardless of swimming speed.

 

[cdavis]

Degree of isolation of the legs from the core during frc dives?

No question, in my case the isolation is not total. However, the more I train, the more isolation there appears to be. I don't know where the end point will be, but I expect that training for a stronger dive reflex will continue to increase the degree of isolation.

Eric, thanks for the insight on the relation between swimming slow horizontal, sprint and ascent. Also for your numbers on static/dynamic swims. I had been wondering about the first and it helps to compare on the second.

Connor

 

[fflupo]

isn't there a change that the blood-shift (torso)is too slow with these FRC / speeds ?

 

[ezequiel]

I dont understand what are the benefits of "Exhale diving, aka, half lung, FRC" against diving with a full inhalation, I understand you will diving with less oxigen, may be more relaxed, but you get the same results as a full inhalation ?

bytheway, this is my first post, hi everyone!!

Ezequiel
miami

 

[azapa]

Hi Ezequiel, welcome to DB, another fortunately located freediver. Read through this thread and search and read about FRC on DB and you will see what the differences are. It's quite a different dimension

 

[ezequiel]

Hi Ezequiel, welcome to DB, another fortunately located freediver. Read through this thread and search and read about FRC on DB and you will see what the differences are. It's quite a different dimension

thanks, I been reading, looks interesting, but as a newbie, I will stick with a full inhale with out packing for a while , for what I read looks like you cannot go both ways, .

 

[blueface]

I read this thread yesterday and tried a few dives on 50% breath and even less. I was only diving to 20 meters to see how it felt and it was amazing! I used only my mask/snorkel and fins without weight and it was so easy to get down. No fighting with bouyancy. I was neutral at about 18-20 meters on 40% lung capacity (estimated). My dive reflex came earlier it seemed. I was laying on the bottom as if I was wearing a weight belt! I also cut my times short because I wasn't sure about the whole thing. Is there a greater chance of BO because of the lower amount of air in the lungs? Or, because of not working as hard to get down, does the chance of BO stay the same?

I see an advantage especially with spearfishing. Sometimes I need to dive shallow (10 or 15ft.) and I don't have a caddie following me around with different weight belts. I normally weight myself to be positive from about 25 ft.. By taking a 30% breath I can hover at shallow depths.

 

[laminar]

I see an advantage especially with spearfishing. Sometimes I need to dive shallow (10 or 15ft.) and I don't have a caddie following me around with different weight belts. I normally weight myself to be positive from about 25 ft.. By taking a 30% breath I can hover at shallow depths.

I would caution you on using it for spearfishing. Spend many months getting used to FRC and how it feels when you are running out of air. It is a lot different. On an inhale you may getting C02 contractions if you've exerted yourself on the way down and these may be part of your early warning system. If you are treating the descent like a static breath hold, no such warning. You can get hypoxic without noticing it, especially at first when you try FRC dives with an inhale style. (I'm assuming that you do expend energy on the descent).

Also, I would imagine that FRC is not very well suited to fighting a fish or untangling yourself from a reel or any other unexpected events that require additional gas in the tank. One could argue that the extra dive response could help there, but I would rather have a full inhale for that kind of diving.

Anyone use FRC for spearfishing?

 

[dave]

Anyone use FRC for spearfishing?

I started using FRC for spearfishing this year. It has taken a lot of getting used to after 20+ years of inhale diving, but I am an almost total convert.
I still use inhale if i am having to work hard between dives (eg keeping position in a current) or if I know I will have to work hard early in the dive (eg freeing an anchor or getting a fish out of a hole) This may change as I adapt more to FRC
Most of my diving is agachon (aspetto) style, so FRC fits in really well; glide to the bottom, and lie motionless apart from very small head movements until it is time to ascend, or you shoot a fish. I think FRC actually makes agachon more effective as you are forced to be smooth and non threatening in your movements, particularly in the early part of the dive
Most of my diving is <20m and about 1minute to 1.30 , with the occasional 2minute dive. I am a great believer in shortish dives so as to have a shorter recovery time. All of my diving is spearfishing
The fighting a fish thing is not a problem, (that is what float lines are for) but I suspect FRC may make a problem at the end of a dive more survivable, certainly I feel better after an extended FRC dive than a similiar inhale dive

cheers
dave
Spearguns by Spearo uk ltd finest supplier of speargun, monofins, speargun and freediving equipment

 

[blueface]

I would caution you on using it for spearfishing. Spend many months getting used to FRC and how it feels when you are running out of air. It is a lot different. On an inhale you may getting C02 contractions if you've exerted yourself on the way down and these may be part of your early warning system. If you are treating the descent like a static breath hold, no such warning. You can get hypoxic without noticing it, especially at first when you try FRC dives with an inhale style. (I'm assuming that you do expend energy on the descent).
Also, I would imagine that FRC is not very well suited to fighting a fish or untangling yourself from a reel or any other unexpected events that require additional gas in the tank. One could argue that the extra dive response could help there, but I would rather have a full inhale for that kind of diving.

Laminar, Thank you for the input. In a typical shallow dive situation (While Spearfishing) I would take a 1/3 breath and descend to about 15 ft. for no more than 1 min. I expend very little energy to get to 15. I would knowingly keep these kinds of dives short because of the smaller amount of air. The only danger I can see is if I repeated this so many times without recovering properly I could become hypoxic. Is this correct? On deep dives I will always take a full inhale.

Would it be advisable to recover longer when taking partial breaths?

 

[laminar]

dave, thanks for sharing your FRC spearo experience! My comments were based on what I assume to be potentially different ways of diving rec vs. spearo. Sounds you've figured it out.

Blueface, the biggest re-calibration issue is that because you expend (ideally) much less energy on the way down, you don't necessarily have a breathing reflex on short dives. I can do an FRC to 2 minutes without a real breathing reflex, for example, on a good day. However, a fast feeling of recovery doesn't mean that you've actually replenished the oxygen. So FRC can give you a false idea of a fast recovery.

So best to keep it shallow and relatively supervised as you experiment.

Mind you, if a lot of spearos dive heavy to wait on the bottom, then FRC is a bit less disparate from inhale dives.

 

[cdavis]

Hi Blueface,

Pretty neat, isn't it? That said, Laminar is right, it feels different and needs practice to get you to the point where you can read your body correctly.

One thing that makes it tricky to spearfish FRC is the necessity of the static phase of the dive. Since you are taking down less 02, you must use what you have more efficiently. That pretty much requires a static phase to allow time for the dive reflex to kick in hard. Once kicked in, you should be able to fight a fish just fine(IMHO), but if you start too early, its more like a full lung dive with less air and less safety factor.

To address your specific questions: The risk of BO is reduced with FRC diving, but that requires that you do it right, which takes practice. Do it wrong and you are worse off. You work much less hard getting down(that is the static phase), but what really makes frc work is the stronger earlier dive reflex.

Connor

 

[cdavis]

Laminar,

Could you expound a little on recovery time? FRC recovery times for me(when I don't push the dive) appear to be so short as to be down right unbelievable. I've always been skeptical of what it feels like. The typical full lung 3:1 up to down time ratio seems too long for frc, but 1.5:1, which feels fine, seems awfully short. What's a good ratio for recovery time (1) for easy dives and (2) for dives where you push and come up with a strong urge to breath?

Connor