Benefit of Nitrox?

[Zeagle Eagle]

I am nearly 67 and I definitely feel less fatigued after diving Nitrox. Placebo effect? Could be, I really don't know; but, I do feel a noticeable difference. I dive about 1/2 my dives with air and the other half with Nitrox so I have a fair amount to compare it with.

 

[Storker]

if we're talking about reducing decompression stress/sub-clinical DCS/micro-bubbles,

Maybe I'm naïve, but I though that this is just what we've been discussing.

rather than any physical property of nitrox that makes us feel better.

What on Earth should that be?

nitrox does not make you feel 'better'.

Well, I'm rather prone to characterize 'less lethargic' as 'better'

 

[DevonDiver]

Maybe I'm naïve, but I though that this is just what we've been discussing

There was a comment earlier (pg 1/2?) that differentiated the 'fatigue' tested in studies from the actual post-dive experiences (reduced vitality, drowsiness, loss of energy etc) that many divers actually suffer.

What I'd be interested in was if someone had ever measured post-dive vitality in relation to bubble-score / decompression stress.

All the studies I've seen have tested nitrox vs air on identical dives.... and (I assume) ones that involved insignificant decompression stress.

The issue with reduced post-dive vitality is decompression stress (increased micro-bubble frequency). The greater off-gassing efficiency of nitrox helps reduce decompression stress versus air.

However, if no decompression stress exists, then no noticeable benefit will be appreciated.

There are other methods, besides nitrox, to reduce decompression stress. The varied methods are, however, cumulative... and using nitrox adds to the overall effect.

What on Earth should that be?

A lot really.... if we were, for instance, considering increased oxygenation of body tissues or any chemical/physiological benefit that higher ppO2 might have on the body.

That what, as I understand it, the quoted studies disproved.

They did note, however, that nitrox reduced decompression stress. It is postulated (proven?) that decompression stress can have an adverse impact on post-dive vitality.

Well, I'm rather prone to characterize 'less lethargic' as 'better'

Me also.... I work in diving. I have better things to do every night after diving than zombie out on the couch. And on a diving vacation, I like to enjoy my evenings

 

[DaleC]

The problem with looking for dive specific studies is that the dive industry has no need to do them. We are a relatively small sub set that already purchases the product.

However... there are lots of studies about using supplemental oxygen to enhance athletic performance in other sports. Just google the above bolded words to see the results. Skip past the studies that show there is no benefit for post exercise recovery and look at those that deal with benefits during performance. It gets downplayed a bit because most sports cannot be performed while using supplemental 02 ( Diving oddly enough being one of the few) but it gets talked about as a training tool. I have also read articles where it enhances driving performance as well. Studies of this sort usually focus on the effects on high caliber athletes to increase maximum intensity or duration but some of these effects might transcribe to older, weekend warrior types trying to perform at moderate intensity (high for them of course). As divers at this point in time, I think we need to look at studies from other fields and see if they would relate to our situation.

There is one situation, however, in which sports-related oxygen supplementation is very helpful – and that is during exercise. A plethora of scientific research suggests that athletes can exercise longer and more intensely when they breathe in extra oxygen during their exertions...

If you are an oxygen-supplementation sceptic, you might at this point be asking that short but often critical question: ‘So?’ As you are undoubtedly aware, even if taking in additional oxygen during exercise did boost performance, it is hard to imagine football players running around the pitch with oxygen tanks strapped to their backs or swimmers tethered with oxygen tubes... These are fair points, but the basic idea would, of course, be to use oxygen during training rather than competition...

There is one oxygen-related problem which must still be surmounted, however: although the basic ‘meet the muscles’ demands’ rationale for using oxygen during training seems unarguable, it has not stood up well to scientific scrutiny. In fact, one well-conducted investigation found that, although the breathing of hyperoxic gas mixtures did indeed increase the oxygen content of arterial blood, this process was perfectly balanced by a decrease in blood flow to the working muscles – so that the actual amount of oxygen delivered to the muscles remained exactly the same(1)...

Nonetheless, VO2max (the maximal rate of oxygen consumption) does increase by 2-5% when athletes exercise in a hyperoxic environment, and performances improve by up to 40% when athletes breathe pure 100% oxygen instead of the standard 21% oxygen air (2). How can these findings be reconciled with the fact that there is no actual difference in oxygen delivery to muscles?...

There are various possibilities... In one study, nine well-trained individuals ran to exhaustion on a treadmill on five different occasions, while breathing in one of five different gas mixtures – 20%, 40%, 60%, 80% and 100% oxygen. In all five cases, the running speed selected for the treadmill exertion was exactly 10% faster than the velocity required to elicit VO2max(4)...

In a unique follow-up study(3), ten athletes ran to exhaustion on a treadmill while breathing in one of four gas mixtures:

1. 20% oxygen and 80% nitrogen (very similar to ‘normal’ air);
2. 20% oxygen and 80% helium;
3. 80% oxygen and 20% nitrogen;
4. 80% oxygen and 20% helium.

In this investigation, performance times increased significantly under hyperoxic conditions (conditions 3&4), but they also improved appreciably whenever helium was ‘in the mix’ (2&4). How should we interpret these findings?...

As it turned out, the mass of air moved in and out of the lungs was less whenever helium – rather than nitrogen – was combined with oxygen (remember that helium is considerably lighter than nitrogen), and thus the work performed by the respiratory muscles was considerably less. In addition, the work carried out by the muscles was lower whenever oxygen levels were elevated...

A reasonable broad conclusion is that performance rises whenever the load on the respiratory muscles is reduced. There are two possible reasons for this:
1. Perceived effort – the level of difficulty an athlete consciously assigns to a specific type or intensity of exercise – depends on a variety of physiological cues, including the degree of stress experienced by the respiratory system during the conduct of the exercise. If this respiratory stress is lightened, the intensity of exercise is felt to be lower,

and an athlete will usually have confidence that he or she can perform at the given intensity for a longer period of time; 2.

A reduced respiratory workload translates into a lower whole-body demand for oxygen during exercise (don’t forget that the respiratory muscles require oxygen during exercise too). Since the oxygen cost of exercise is reduced, an athlete will be operating at a lower fraction of VO2max and thus the duration of exercise can be increased, there being a direct inverse relationship between exercise sustainability and %VO2max...

There is one other key reason why oxygen supplementation can work. Interestingly enough, some athletes who are able to sustain exercise at very high intensities experience ‘desaturation’ of their haemoglobin (ie, the amount of oxygen bound to haemoglobin declines) when they work very strenuously under normoxic conditions...

Athletes in both groups performed two incremental cycle ergometer tests at sea level to determine VO2max(5); one test was completed under normoxic conditions (at 21% oxygen) and the other in a slightly hyperoxic situation (26% oxygen). As it turned out, the percentage of oxygen bound to haemoglobin during maximal exercise was significantly higher for both groups under hyperoxic conditions...

The benefits of oxygen supplementation for workout quality became apparent in research carried out at the University of New Mexico several years ago(6)...

Note that this is exactly the kind of situation in which you would expect oxygen supplementation to be beneficial. The athletes were experienced and they were working at close-to-maximal levels during their workouts. Thus, their haemoglobin was likely to be desaturated, a situation which the supplemental oxygen could at least partially correct. Voila! The better oxygen supply to muscles allowed exercise to continue longer at the chosen red-hot intensity. Undoubtedly, the added oxygen also decreased respiratory-muscle work and made the intense efforts feel a bit easier.

 

[RJP]

but the basic idea would, of course, be to use oxygen during training rather than competition...

[Hijack]

Actually, it's the reverse is beneficial. Assuming, of course, that the purpose of training is to perform better in competition... rather than merely performing better in training.

This is why US Olympic athletes train in Colorado Springs at 6,000ft elevation instead of Palm Springs at 400ft, and why cyclists from Columbia (who train at nearly 10,000ft in places like Boyaca) are some of the best climbers around.

When you train in a slightly hypoxic state, your body acclimatizes by producing higher red blood cell volume and greater hemoglobin mass. Accordingly, when you then compete in a normoxic environment your body can more efficiently transport oxygen.

If you acclimated to training in a hyperoxic state, you body would respond by DECREASING red blood cell volume and hemoglobin mass. Accordingly, competing in a normoxic environment would essentially feel "hypoxic" to your body.

Of course when I say "your" body I don't mean "your body" because research seems to indicate that none of this is meaningful for anyone but highly conditioned athletes who are already at the edge of human performance. That's where the incremental benefit is seen. If you're not already maximizing the use of the O2 your blood is already carrying... adding more isn't going to help.

 

[AfterDark]

The last time I went on a charter was in 2011 to NC. We did 2 dives a day for 5 days and didn't get washed out one day. More than half the dives were 100FSW or more some days back to back other days the 2nd dive would be shallow but that was because of weather not dive related.

All those dive were done on 21%. By mid week I felt great! No post dive fatigue and I slept like a well fed baby at night! I commented to my wife, "I think being out on the ocean all day agrees with me, I should have a job on the water"! I actually felt good for almost all of the following week also! If I had dived nitrox I'd probably be claiming it works it works!!!

The truth of the matter was that all I needed to do was gear up, jump into the water and dive. No carrying gear over hill and dale walking back to car with shaky legs from being weightless for an hour, no driving home post dive. Just dive, drink, eat, lounge around the deck and sunbathe! No wonder I felt so good!

 

[Tigerman]

[Hijack]

Actually, it's the reverse is beneficial. Assuming, of course, that the purpose of training is to perform better in competition... rather than merely performing better in training.

This is why US Olympic athletes train in Colorado Springs at 6,000ft elevation instead of Palm Springs at 400ft, and why cyclists from Columbia (who train at nearly 10,000ft in places like Boyaca) are some of the best climbers around.

When you train in a slightly hypoxic state, your body acclimatizes by producing higher red blood cell volume and greater hemoglobin mass. Accordingly, when you then compete in a normoxic environment your body can more efficiently transport oxygen.

If you acclimated to training in a hyperoxic state, you body would respond by DECREASING red blood cell volume and hemoglobin mass. Accordingly, competing in a normoxic environment would essentially feel "hypoxic" to your body.

Of course when I say "your" body I don't mean "your body" because research seems to indicate that none of this is meaningful for anyone but highly conditioned athletes who are already at the edge of human performance. That's where the incremental benefit is seen. If you're not already maximizing the use of the O2 your blood is already carrying... adding more isn't going to help.

And this is how the debate of "altitude tents" in professional sports became a big controversy in the early 2000s, as some considered it "artifical" while others consider it nothing but saving expenditures for travel. WADA afaik does not consider it to be cheating and there is of course also a "new" product out there called "the training mask" which is for the same purpose...
Shop - Elevation Training Mask

 

[beachbummer28]

Read the studies.

The first was one tank in a chamber, exercising not diving.

The second was only two tanks, but at least it was diving. They did find a difference between air and nitrox. The problem, I see, is they were only measuring fatigue which they see as different than the side effects of offgassing of N2 which they were not measuring. What they found was on the fatigue test there was no difference but the on another test the divers felt better on Nitrox. The lesson I see is that you will get just as fatigued, but feel better.

Reduction of fatigue or less stress from offgassing, for me, I don't care which is making me feel better. Also I see no difference over one or two dives so for that I dive air, it makes a difference on multi day multi dive trips, and on those I now dive Nitrox. So far there is no study on over 2 dives a day over multi day period, although the author of the second study thinks it might be worth a study.

The studies, so far, have focused on fatigue, not the overall effect on the diver. From what I gathered from both studies is that fatigue has a very specific meaning in the scientific community that is not the same or as broad as I would use. The last study said there was no difference in fatigue, but ran across the "feeling better" effect of Nitrox, since it was not being studying they could only comment about it.

Bob

This post was pretty much ignored and it's one of the few throughout these 10 pages that actually addresses the facts, instead of opinion.

Out of the three studies linked earlier in the thread, only one has any validity. The first link from DAN is simple a regurgitation of the 2003 Harris study, which is the second link. The Harris study, as mentioned above, was a single test done in a dry chamber and the scientists themselves later admitted that the study may have been inadequate in determining any fatigue-related differences between air and Nitrox. (Quoted from the third study - "Harris et al. acknowledged that the single, dry chamber dive profile used in their study may not have induced enough decompression stress to observe a difference between air and EAN36 post-dive fatigue levels.")

The third study found that there was no difference in post-dive fatigue regardless of air vs. Nitrox, but "fatigue" here is being defined in a pretty narrow, scientific way. The Diver Health Survey (DHS) was also administered and it was found that the Nitrox divers in general "felt better" than the air divers post-dive. This is a wider definition than fatigue but the point is still the same - the divers generally felt better on Nitrox.

The only remaining question is why the divers felt better on Nitrox versus air. It certainly was not a placebo effect; it was a double-blind study and the divers had no idea if they were diving with Nitrox or air. The "why" of this is up for debate, although I'm skeptical of any stances that insist it has nothing at all to do with Nitrox. The divers used in the study were experienced male divers, ages 18 - 35, all certified as either AAUS scientific divers or dive leaders (i.e., Divemaster, Assistant Instructor, or Instructor). The study was also appropriately rigid and things like the divers' diets, water consumption, descent rates, ascent rates, underwater activities, etc. were standardized, documented, and controlled in order to try to eliminate those sort of influences. To suggest that all of the air divers that generally felt worse after the dive were all practicing incorrect diving techniques that solely contributed to their post-dive states is a stretch, especially when the hypothesis that increased nitrogen absorption may make the human body feel like crap is reasonable.

And as a reference to the bickering in the middle pages, I have zero experience diving on Nitrox ... but I (unfortunately) have lots of experience with reading through and interpreting tedious studies, so I guess I at least have that going for me in forming my own opinion. :biggrin: It's safe to say that the medical community isn't sure why Nitrox divers feel better post-dive than air divers - indeed, the scientists operating the third study readily agree that further testing is needed - but the fact remains that they do, based on the latest study. We're left to form our own theories as to why.

 

[RJP]

And this is how the debate of "altitude tents" in professional sports became a big controversy in the early 2000s, as some considered it "artifical" while others consider it nothing but saving expenditures for travel. WADA afaik does not consider it to be cheating and there is of course also a "new" product out there called "the training mask" which is for the same purpose...
Shop - Elevation Training Mask

The problem with altitude tents is that you can't stay in them 24/7 nor can you actually "train" in them... so your body doesn't actually acclimatize.

The training mask is nonsense, pure and simple. All they do is make it physically more difficult to inhale, which is not the same thing as training at lower O2 pressure. Best case, all it does is strengthen your diaphragm.

 

[NAM001]

Thats not how I read it. It was very clear....It was nit picking and saying the same thing a different way, to have the last word.

How would one fix the problem? I doubt that doing jumping jacks each morning is a solution.

I think what he's saying is that Nitrox masks the underlying problem... when the better approach would be to FIX the underlying problem.

---------- Post added September 7th, 2015 at 06:08 PM ----------

Im in hte over 60 croud

I don't know if any of you posting in this thread that post nitrox reduces fatigue are over 60 but when you get there let us know if nitrox is still working for you.

After I get done toting dive gear down the rocks, gear up, dive, and tote it all back up the rocks only a miracle would make me not fell fatigue.

You guys dive in an entirely different reality than I do. Liveaboards, charter boats, nice but it's not part of my reality.