OK, I'm revisiting this topic after initially obsessing about it, then abandoning it for a while after I found it too hard to do effectively.
Just to bring everyone up to date, I'm a very dense sinker, and because my legs are particularly dense. By pushing my head and chest down to level, I can only float horizontally below the surface for a short while with gliding with some forward velocity before my legs start to drop, drastically reducing the velocity further.
While swimming, I tried to keep some air in my lungs for buoyancy, but it only seemed to keep my trunk up, and didn't help the legs to stay up. Then I ran into some subjective shortness of breath that after thinking about it, likely came from retained carbon dioxide, as a result of shutting my throat and not letting any breath at all out (see "How Important is Exhaling Underwater?" thread). That's when I abandoned any idea of finessing my exhalation -- too difficult to do while micromanaging so many other details.
But now, I'm coming back to the topic because for the last month I have been trying specifically to increase my stroke length/decrease my SPL, using short one length sets with this single focus. One aspect of this quest has been to self observe what's happening on my initial push-off, and I notice the glide is getting better and better as I learn how to align my overlapping hands, squeeze my elbows to my head etc. but this all deteriorates when my legs start to drop (at the end of the glide), and I can't seem to prevent this.
That's when today I thought about trying again for a large inhalation to start with before the push off. Only this time, I thought I would try it with particular attention to getting a good diaphragmatic breath in, which I find difficult while breathing that quick gasp of air during that narrow time window while the mouth is half out of the water. My theory was that if I was really successful in displacing my diaphragm inferiorly and holding it there during my glide, my centre of buoyancy would move closer to my centre of gravity, thus reducing the rotational lever that was pushing my (hips and) legs down.
It seemed to work, and not only did I sink overall much less during my push-off glide, but the ending phase was much less decelerated by sinking legs. As I mentioned today in the "Favourite Practices and Sets -- Gearing Practice (no TT)" thread, I hit an SPL of 20 for the first time today, although I am not sure if this had anything to do with the diaphragmatic focus of my first hyper-inhalation on push-off. But it's certainly a possibility, maybe even likely.
But I'll keep on practicing this one huge inhalation at a time, (i.e. at the beginning of each length) and as I get used to it, and get used to holding the breath with a sustained lowered diaphragm, maybe I can do the same for subsequent inhalations during whole stroke swimming, and maybe with good enough control that I can dribble it out slowly through my nose in between top-up inhalations, but retaining enough for lower body buoyancy.
Last edited by sclim : 04-02-2015 at 08:06 AM.