Residual Volume

Understanding residual volume and the mouthfill technique, and subsequently breaking through the depth at which you really need to understand these subjects, is sort of a dry and technical matter.  Unsure how to tackle the subject, I decided to rely on a fundamental technique utilized in educational institutions across America: plagiarism.  Joking aside, it's not actually plagiarism, I give full credit to whoever wrote this article:
The mouthfill- how to equalize deep in freediving
Also check out:
The Frenzel Technique, Step by Step

To practice these techniques, I'm using FRC dives and variable weight (as can be seen in Deeper Perspectives- Episode 6).  It really only makes sense to perfect equalization this way, rather than trying to head straight for the abyss.  Can you imagine trying to learn to drive, grinding gears, and riding your brakes  on the Autobahn?  Of course you wouldn't do that; you'd find an empty parking lot, a back road, or some other controlled environment.
Variable weight obviously allows you to concentrate on your equalization technique without the bother of all that kicking and oxygen consuming activity.  FRC allows for short and shallow dives that can be repeated many times in a session and easily monitored by a spotter.  I still don't precisely know what volume of air I'm working with on an FRC dive.  I think it's something like 40% (2/5) of my total lung volume.  By going to only 20 meters, I'm able to reduce that volume to 1/3 (http://www.ehow.com/how_7436_understand-underwater-pressure.html).  1/3 x 2/5 = 2/15.  This would be the same lung volume experienced at 7.5 atmospheres, or 65 meters.  In other words, you can experience the same pressure and equalization demands of a 200+ foot dive in less than 70 feet.  Of course, this also means you are susceptible to injuries normally reserved for deep depths, most notably lung squeeze.  So bear that in mind; this isn't professional instruction, I'm just some chump with a blogger account.

Lung Volume, Part 2

In Part I we described methods for measuring lung capacities.  But why would we ever do such a thing?  For one thing, it's just interesting to know.  As a freediver, I see it is a measurement as integral as my height or weight.  But more importantly, I want to see how my training affects my lung capacity and better understand what volumes of air I'm using during the various types of dives I intend to do.
A quick look at an online forum will let you know divers are always looking for ways to increase their lung volumes.  Frequently they ask about gadgets like the Expand-A-Lung.  These are unlikely to work, but the good news is you can probably increase your lung capacity without buying anything at all.  It is generally accepted that aerobic exercise will give you small gains in lung volume.  Stretching your upper body has also been reported to result in an increase in volume.  Lung tissue is somewhat elastic, so volume can be limited by an inflexible chest.  Packing relates directly to chest flexibility, but is a subject beyond the scope of this blog.  I intend to use it during my training, but packing-related injuries are numerous and well documented, so take that for what it's worth.  It is also highly advisable to learn proper breathing technique in order to maximize the volume you have.  I personally hope that through cardiovascular exercise, stretching, and breathing exercises to increase flexibility and perhaps lung capacity.
Although you don't need large lungs to dive deep, knowing the volume of your lungs will help you better understand your training.  Many freedivers hit a barrier at around 130 feet where they can no longer equalize.  The reason for this is lung volume, specifically residual volume.  Water pressure at this depth has reduced your lungs to 20% of their volume on the surface (roughly residual volume).  Remember, residual volume cannot normally be exhaled, and so advanced equalization techniques must be learned to go much beyond that depth.  If gains can be made to vital capacity without increasing residual volume (such as by packing or perhaps through cardiovascular exercise) you could push this depth deeper.  FRC dives will also be an integral part of my training, and it will be valuable to understand exactly how much air I'm retaining on a dive of this method (perhaps the subject of a future article).  Lastly, I don't currently pack on my dives.  However, I was surprised to find I add 50% to my vital capacity through packing.  Of course, the last few packs I do make me want to pass out, so through experimentation I hope to find an optimal compromise between added volume and comfort.
So measuring your lung volume can be a fun and informative training tool.  That said, it is far from crucial.  Whether you find out you have small lungs, or you never test your lung volume at all, you can still reach abyssal depths.

Don't forget to check out Deeper Perspectives- Episode 5

Measuring Lung Volume

I think you could still dive well without arms, sight, or even missing a leg.  But everyone agrees, you definitely want your lungs working optimally.  You'll frequently see questions on forums regarding increasing lung capacity.  To what extent you can do this, and whether it's necessary are both debatable (and we will debate them in future articles).  But in order to know if you've increased lung volume, you must first know what your lung volume is.
Let's lead off by learning the language of the lungs.  A few terms need to be understood.  First is "vital capacity."  Take a big breath.  Now exhale all the air you possibly can.  The volume of air you just exhaled is your "vital capacity."  Try as might, you didn't actually empty your lungs.  A small amount of air called your "residual volume" was still left over.  Combine these two measures (vital capacity and residual volume) and you have your "total lung capacity."  The average adult has a total lung capacity (TLC) of somewhere around 5.5L, made up of about 80% vital capacity and 20% residual volume. But what's yours?

The best way to measure your lung volume would be a spirometer, which is a medical device that none of us have.  What you probably do have, or can get for a couple bucks, are a clear plastic container larger than your lungs, a larger container filled with water, and a plastic tube to make a water displacement apparatus.  Calibrate the clear plastic container by dumping water in a liter at a time and making a mark.  Then, put this plastic box up-side-down in a larger container and fill with water (making sure no air is trapped in your up-side-down box).  Slip one opening of the tube into the up-side-down container, take a big breath, and exhale fully into the other end of the tube.  The contents of your lungs are now trapped in the box you have marked volumes on.  Make sure it's floating level and take a reading- that's your vital capacity.
An even easier method of measuring your vital capacity is to measure the circumference of a balloon you have exhaled into.  Unfortunately, this method is fraught with even more inaccuracies than the previous one.  Generally balloons are not exactly round, and therefore a volume cannot be extrapolated from their circumference.  I have taken the average of multiple circumferences of a single balloon to calculate a volume, and it seemed to compare similarly to volumes measured with the water displacement apparatus.  I also think it's a little harder to blow into a balloon than a plastic tube with little resistance.  Air can also be lost when tying the knot.  Nonetheless, I guess it's still a valid method for it's simplicity.
Residual volumes are a little more difficult to measure.  The simplest way is probably to use figures published in medical journals.  Divide your vital capacity by 4, and that's a good estimation of your residual volume.  I would like to try exhaling all my air at 10m below the surface, leaving me with only my residual volume.  Upon ascending, this volume will double, leaving me with a volume of air available for exhalation (a de facto vital capacity of sorts) equal to my residual volume.  I could then measure it with the displacement apparatus or a balloon.  In fact, I will do that soon.  Then we'll be able to see how it compares with the simple division method, which is all I've attempted so far.
So how does this all pertain to freediving?  Once again take a deep breath.  Now gently exhale, relax, and wait until next week for part 2 of this article.

Don't forget to check out Deeper Perspectives- Episode 5