The illustration of key lever lengths and how they relate to touch-weight at various positions on the key has shed some light on an issue that has been troubling me.
I'm still a relative beginner, approaching my third-year anniversary of lessons. At home, I practice on a Yamaha YDP-223 digital (which has the GH action.) My teacher's piano is a 9' Steinway D. Those are the only two instruments I have any amount of experience on.
This past year, as my lesson pieces have become more "advanced", I've begun to have problems with tension in my playing, which leads to fatigue and soreness, especially in my right arm. What I found intriguing was I seemed to have a much easier time on the 9' grand than on the DP, my assumption being that the DP action should have been the lighter of the two. (Certainly in the bass, the Steinway does have more inertia in the key travel, but the treble feels much lighter than the Yamaha DP.)
I decided to measure the touchweight of my DP, and came across this article
, which characterizes a typical piano as having ~50g down-weight, and ~20g up-weight. My DP has "graded hammers", but I measured only the lightest (treble) section, and found it had a ~70g down-weight, and ~50g up-weight. With 50g of up-weight, that's already more than double the force of a "normal" piano, required to hold a chord.
Taking into account hpeterh's observations about how the short keys in a DP multiply the required force: Playing high on a key (nearer to the fulcrum), I approach ~400% on the already-heavy DP, compared to only ~200% on the grand.
Knowing what I know now about the tough-weight of the DP action, it's no wonder that I'm having such a difficult time eliminating tension. (It's not for lack of trying either. I've been paying very close attention lately to posture and technique.) Maybe my next step will be to adjust my hand positions so that I'm playing as far down the keys as possible, closer to the "100%" zone.