Here's a dumb question inspired from the opening post. Does one usually do 4-5 trills in the first place? How often does that happen, and does one try to avoid and change fingering?It's not a matter of "strength" of fingers, but how to use the hand and the whole complex.
I am all right with trills because I have always practised double ones in all fifteen striking combinations, still do. Don't ask me why as the sound of trills lacks interest for me and doesn't feature much in my improvisation, which activity is almost all I play these days.
Can you expand on your double trills exercise a bit?
I described it in this thread. https://www.pianostreet.com/smf/index.php?topic=66546.0