Passagework and the loaded hand

Hello hello, I'm trying to develop my fast passagework, and revisited Alan's DVD (plus got a lesson from the amazing pianist Taylor Eigsti). my understanding is to try and work the finger as much as possible, healthily, using the same sort of motion as the one-hand-clapping technique. I have noticed this causes a sort of mini-recoil, raising the back of my hand - it all seems part of the motion and keeps my hand loose. what I would like is some exercises/advice on how to transition from a super staccato pluck as described above, to a more sustained sound, while being able to remain fast, mobile, powerful. Alan talks in one of his books about putting the fingers in a drawn back position to load them - harnessing their pent up energy. I have noticed in YouTube videos this kind of clawed hand in fast playing (I often see the pinky practically fully curled - why? is it part of this loading process?). but the clawed hand is in my mind associated with tendonitis. are there any experts out there who could shed some light on the issue? thank you, Tom