I often think that one can tell a lot about the technique of a pianist (who also happens to be a composer) by the music they've written for the instrument.
On second thought, though, this isn't actually true. A good example is Ravel, who wrote some of the most atrociously difficult piano music in the repetoire, yet by all accounts wasn't an outstanding pianist himself, although he must have been a decent one to be able to play pieces like Gaspard de la nuit and Jeux d'eau.
However, if there is one pianist whose piano music is an indicator of their own piano technique, it would have to be Rachmaninov. It's easier to judge how Rachmaninov's technique relates to his piano writing than it is for many other composer-pianists, since he fortunately left behind what is a fairly extensive collection of recordings for someone who was alive when recording was only a recent invention.
There are a couple of things one immediately notices about Rach's pianism.
Firstly, he appears to have had an extraordinary technique. He was voted 'greatest pianist of all time' in Limelight and I think this is entirely justified, judging from the recordings I've heard. His playing had an incredible clarity and precision, combined with a gorgeous tone. Technical difficulties which would cause many other pianists to sacrifice tone, balance or clarity for accuracy didn't bother Rachmaninov at all. On top of that, his interpretation was very tasteful and simple, and he never over-used the pedal (as many pianists - even brilliant ones - seem to do these days.) This cleanness and understatement was quite unusual for his time, and I suppose his technique could be considered the forerunner of 'modern' piano technique (as exemplified by pianists like Pollini and Brendel.)
Secondly, Rach famously had very big hands (apparently he could span a 13th), and his piano music often
incorporates impossibly large stretches which would have been quite easy
for him and for anyone else with big hands, but can pose serious
problems for other pianists! As I've discovered, however, the effect of Rach's technique on his writing for piano goes far beyond huge stretches.
For the past few days I've been working on a section of the 2nd concerto (specifically, the first movement, pages 19-20 in the Schirmer edition.) Rachmaninov never skimps on virtuosity in the left hand as well as the right, and beautifully written though it is, I've been struggling particularly with the second half of page 19 (for some reason, I don't have any trouble with page 20.)
I've found that in order to make the very dense and complex textures of this writing actually sound good, it's necessary to have a virtuosic command of the pedal, a very refined spacial awareness of where every key on the piano lies, and a lot of strength and dexterity. These qualities seem like something Rachmaninov would have had in great quantity.
After working on pages 19 and 20 of the concerto this evening, as usual I finished my practice by playing Chopin's Etude op. 25 no. 12.
Since this etude is the perfect way to instantly put a piano OUT of tune, I've actually stopped playing it at the end of practice sessions since getting my piano tuned a few weeks ago. Playing this etude is the way I build and maintain the muscle in my arms, and I notice very quickly if I don't play it for a while, so the last time I attempted it (a few days ago), it was a bit of a disaster.
When I tried again today, however, something had changed. I found myself hitting a lot more of the right notes than before, and had a much stronger sense of spacial awareness and coordination.
I feel quite certain that the intensive practice I did earlier on Rach 2 has improved aspects of my technique I wasn't even aware were lacking. Maybe the reason is that through his piano works, Rachmaninov has passed on his own technique to anyone prepared to spend the time and effort required to develop that technique?