OK, here is a link to professional research article on the very topic with which we're engaged.
I have exerpted a bit of it below which is in lay language (mostly) which I was able to understand.
The entire paper is "heavy sledding" -- at least for me -- backed up by all sorts of scientific findings, graphs, statistics, etc.
If this doesn't do it for you then, I guess we'll simply have to drop it.
The gist of the paper is how novice pianists accomplish movements at the piano versus trained professionals.
The remainder of my post is the excerpted material.
Here's the link if you're interested in wading through the paper.
https://music.unt.edu/pianoresearch/reference/Furuya2.pdfOrganization of the upper limb movement for piano
key-depression differs between expert pianists
and novice playersThe effective use of shoulder flexion when the experts
depress the keysOne interesting finding of the present study concerning the
kinematics of the arm during key depression was the distinct
expert-novice difference in the use of upper arm
rotation. From the onset to the end of key depression, the
experts used marked shoulder flexion. Because the shoulder
flexion in the experts was proceeded by a greater burst
of the AD and Biceps muscular activity, this shoulder joint
motion appeared to be caused predominately by volitional
active muscle contraction rather than by passive movement
action. We also found that this shoulder flexion in the
experts was coupled with a forward rotation of the finger at
the MP and wrist joints as the fingertip depressed the key,
thus indicating that the shoulder flexion was aimed to
facilitate depression of the key by the finger. For the
novices, on the other hand, small amount of shoulder
extension predominated to generate a downward movement
of the hand till the end of key depression. The novices
mainly relied on shoulder and elbow extension for the
downward movement of the forearm and hand. Interestingly,
the characteristics of upper limb’s joint kinematics
for key-depression by the present novice players were quite
similar to those observed during striking a computer key by
ordinary people (Dennerlein et al. 2007). These findings
suggest that the novices have used a fundamental keystroke
synergy that is developed through everyday experience of
key hitting and pressing tasks. The experts, on the other
hand, have used a key-depression synergy that should be
specifically acquired with a long-term training as a most
efficient way to produce a target sound on the piano. These
synergies could include the formation of attack angle as
well as the posture of the limb at the end of key depression
movement.