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After reading a thread recently about being knackered/dehydrated from holiday diving it got me thinking.

What makes us tired when we dive? It must have something to do with the dissolved gas in the bloodstream/tissues. I'm guessing it is caused by inert gases as people feel less tired with nitrox.

So whats the cause? Does it make it harder to circulate the blood due to sub-clinical bubbles? Does it make it harder for muscles to contract with higher inert gas dissolved? Or do we just not really know?
 

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Winding up the precious since 2009
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Short Answer: No one really knows, no one is even that sure that Nitrox does help or if it is simply a placebo.

Medium Answer: Tiredness after a dive is often referred to as a sub clinical bend, i.e. bubbles floating around general messing stuff up which you body/immune system is running around fixing, it may also be dehydration which has it's own set of symptoms AND can make sub-clinincals worse and/or lead to a full blown bend (stay well hydrated kids!) It's possibly nitrox has a couple of effects 1) reduced N2 loading, increased O2 that helps to counteract the tird feeling.

Long Answer: A good place to start is here: Deco for Divers by Mark Powell, brilliant book, all divers should read it from fresh out of OW to full well 'ard techy.
 

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Muppet
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Another reason might be the cold. Your body needs to generate a lot of heat to keep you warm during a dive. Even if it is in warmer water.
 

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Naturally blonde - please type slowly
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What about physical and mental exertion too. I know that I spend a large proportion of the day luggin heavy kit around, in and out the car, to get fills etc etc. More so than I would usually lift in a day anyway.

There's still quite a bit mental stress for me as well...have I remembered everything (note to self a WING is useful ;))...have I got a good plan, will I be on time etc etc.

Not to mention the quite likely early start and late finish for the day with probably long drives to and from the site.

And then there's the diving physiology... ;)
 

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What about physical and mental exertion too. I know that I spend a large proportion of the day luggin heavy kit around, in and out the car, to get fills etc etc. More so than I would usually lift in a day anyway.
You're still Garf's kit bitch? ;)
 

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Jesus don't want me for a sunbeam
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Another reason might be the cold. Your body needs to generate a lot of heat to keep you warm during a dive. Even if it is in warmer water.
I think heat loss is by far the biggest cause of fatigue rather than some half-hearted theories on air vs nitrox. It's easy to misunderstand what is happening, because you don't feel cold doesn't mean you aren't losing energy to the water. In the best suit on the planet you're still losing energy to the water. I really noticed spending winters in the mountains in Canada, I was eating about 50% more calories than I was at home and I'd still lose at least 2 stone over the winter: you can lose a lot of thermal energy without any discomfort but it still takes it's toll, especially when you get into the warm and start eating, then you're blood sugars end up all over the place... guaranteed massive fatigue. Same on the RIB in winter, all I've done is sit there at the helm all day but I'll be absolutely wiped out at night. That's not a bend.

Simply breathing from a regulator is a massive energy drain with evaporation from the lungs, all that energy is lost on each exhale. When I went to CCR I really noticed both feeling a lot warmer and less tired post dive. I think the air vs nitrox argument is bollocks. I'm tired after most dives, I'd guess that if that was being bent then after 19yrs of diving I'd be starting to show signs of long term effects.

I had massive fatigue when I was bent however I'd also spent close on 6hrs in the water over the course of seven dives, I don't think you can always necessarily conclude fatigue = bend. The two other times I was bent I had no fatigue whatsoever. That's the difficulty of taking symptoms in isolation.
 

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I really noticed spending winters in the mountains in Canada, I was eating about 50% more calories than I was at home and I'd still lose at least 2 stone over the winter: you can lose a lot of thermal energy without any discomfort but it still takes it's toll, especially when you get into the warm and start eating, then you're blood sugars end up all over the place...
I know a bear that you all know, Yogi, Yogi :D
 

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I think some people are just unfit. We have a technical term for this at work : "fat knacker".

It's a term of endearment when someone is out of shape.

Stress is tiring, and I find being cold tires me. But holiday diving is generally easy and relaxing - and sometimes people feel "tired" when they are very relaxed and de-stressed.
 

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Nigel Hewitt
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I personally blame seasickness remedies.
I wake up, dive, fettle the kit for the next dive and nod off again unless somebody wants to feed me.
 

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I definitely feel much less tired diving CCR than OC.

Doesn't seem to make a difference whether I am diving air dil no stop dives, or diving trimix decompression dives, I am definitely much less in need of a nap on the boat ride home than I used to be diving OC.
 

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Winding up the precious since 2009
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Don't underestimate the effort needed to shift you and your kit around in the water either, just because you are, hopefully, neutral doesn't mean it has no mass, it still takes effort to move it.
And drag!
 

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Winding up the precious since 2009
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depends how average your trim is :D
Even with god like trim some of us still have a fair cross section to push through the water.*


*because of the twinset obviously!
 
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