Quote:
Originally Posted by Jon
Peter,
My question is on just how big of an exhale you do when diving this way.
While playing around with this all winter, in shallow water, I felt the blood shift after a single dive, or two at the most, and really liked how easy the decent was- plus, I was able to dump a full 10 pounds off of my winter weight belt. 
I found my self taking a big breath, exhaling completely, and then diving. Re-reading through many of these posts it sounds like other divers are taking some type of partial inhale before they dive- which would extend both my depth and bottom time.
So, how big an inhale/exhale do you take before decent?
Thanks,
Jon |
Obviously, how much you exhale is subjective. And there are other factors like body composition (inherent buoyancy) and wetsuit thickness/ballast to take into account. There's definitely an advantage to being slim and not wearing a suit when it comes to FRC diving, but it is not essential. Consider that I've done most of my recreational diving in the last year and a bit in a 6.5mm/5mm combo without fins. And usually with a camera.
I also think that the specific lung volume is not crucial and that there is a range - this range gets fairly narrow with experience.
So sit comfortably in a chair or lie down. Breathe softly through your nose. Relax your breath so that your tidal volume becomes apparent. Your diaphragm should barely move only slight movements in your lower diaphragm. Definitely do not chest breathe here. This is close to your final lung volume.
Now take a deep breath through your nose again and simply relax your diaphragm completely (it will feel like a downward shrug of your shoulders).
This could be your final lung volume.
Here's where you experiment. After the inhale/exhale-shrug, inhale slightly - barely a sip. I would describe it as a momentary flaring of the nostrils that allows some air into the lungs.
Through a snorkel or through your mouth, this would be a very small sip. The sip can vary in quantity. Sometimes I will actually sip air and let it into my lungs and other times I will primarily fill my mouth up with as much air as can fit (ie. for a shallower dive or a deep line dive).
The key with this type of diving is that the final amount of air (within the tidal volume range) doesn't make much of a difference in the dive time/depth/02 supply. Dive response is the key. But taking too much air in will make the descent harder and retard the dive response. There may be times when that's a trade off to use.
I would say that if you are exhaling fully and going down, that it too little air in your lungs. The guiding principle for me is that FRC should feel comfortable. FRC is a misleading term. In fact, I would like to rename FRC diving as something else. I've written a new term down that I liked long ago, but now I can't remember it!
FRC should feel like a gentle stretch at first. That's why I recommend sticking to shallow depths in the beginning. Because then you can really learn to refine and tune your lung volume.
Hope that helps.
Pete
