The weight I think is pushing down the keys, not the finger! The finger only acts to take the weight from the previous finger, so we guide the finger horizontally to the key we want to sound. This to me is like walking, that we don't stomp our foot down to take a step, we only have the foot over the spot we want to walk to, then allow gravity to work. So we probably just disagree on this point.
I am not sure if there is a disagreement. I think we are still not clear what we are talking about. I try again:
Finger method: Hand hovers over the keys. The fingers are lowered to push the keys down, while hand and arm are stationary. All the work must come from muscles: holding arm and hand in place (back and upper arm muscles), moving the fingers up and down at the knuckle joint (muscles in the forearm, very little hand muscles involved). This is similar to having your back against the wall and pushing a weight with your legs. Muscles do all the work, gravity is not involved.
Weight method: Arm and hand are lifted up a bit then the hand is dropped towards the keys. Fingers are only there to direct the weight to the desired spot. Muscles are used to keep the hand/fingers rigid so that the weight/force can be transferred. The weight/force itself is provided by gravity. Muscle action is required to lift the hand/arm to move the fingers to another key. This is similar to walking.
I agree the fingers act as levers with the 'finger' method, but there are I am sure many muscles in the hand that partake in this as well as in the forearm.
The muscles in the hand only flex and extend the finger joints. They are used to make a nice curve, but they don't provide any real force. Practically all of the force is provided by muscles in the forearm (thumb and pinky excluded to some extent).
The way I see it, the muscles that lift the arm/hand would be the shoulder muscles, back, etc. To simplify this, if you put your hand on a table, then allow the weight of your arm/hand on 1 finger, say the 3rd, you can feel the work going on to hold it there. Take the other hand and put a finger under the supported hand and feel the tendon bulging. I suspect that one could hold it in this position only so long, as the working muscles would tire. You could try it for say, 5 minutes and see if you can sustain it. Lots of muscles in the hand are working say I.
As I said above, in the weight method, muscles are required to keep hand and fingers rigid so that the force provided by the weight of hand and arm can be transferred onto the fingertips. Of course, this is tiring if you do it for a while without relieve. And so is keeping keys depressed by finger action alone. The goal, I think, is to use as many different muscles as possible, so that no single muscles ever tires or gets cramped.
Not sure you are right in this one. When one is at total rest standing with the arms at their side, observe the position of the hand! Would you say the hand in not in 'equilibrium'? I think it is. And I suspect the reason the finger extends as the speed increases is a lack of 'relaxed' strength. It is possible that enough training in the correct condition had not been acheived. For example, years ago if I tried to play at the speed I can now with perfect accuracy, my fingers would have extended with a much slower speed as a result of the weakness. I think this makes sense to most people. So if that is true, it seems logical that one could continually climb the speed ladder if the conditions are correct. I may be wrong, but as I said before, time with keen observation will tell.
There are two issues here. When you let the arm hang and observe the "natural" curve in the fingers, they are indeed at rest (in equilibrium), but you cannot transfer force through them without making them rigid. When you make them rigid and attempt to move this rigid structure up and down at the knuckle joint with high speed, what rigid structure will allow you the highest speed with least effort? For me, it is when the finger is extended. In fact, only then can I truly hover my hand above the table and tap my finger rapidly on the table without my hand bobbing up and down. When I curve my finger and fix it and then tap rapidly, I cannot keep my hand still. In this position, I am involuntarily using a combination of finger and weight method! Ha, I just realized: I am unable to use the 'finger' method as my hand is always assisting. Well, in the end, we all use a combination of weight and finger method. It's just that the proportions differ from person to person and from technique to technique.
It is certainly true that one can over time increase the speed with which one can move the fingers up and down, but make sure that you retain a natural curve as well as a natural wrist orientation in order to minimize chances to get tendonitis and carpal tunnel syndrome.
So you are using the weight method mostly I gather?
It's a combination of both, but I am I am trying to use as much weight as possible and as little muscle action as possible. Absence of antagonistic muscle action means no tendons moving back and forth and potentially contracting or stretching (yikes!), therefore no problems with the tendons. That's what I am trying to minimize.