Examples of this Duality:
As instances: (a) to raise your arm you are aware of the necessary muscular exertion,
but to retain it raised, it seems as if there is no effort at all, because the "small" muscles alone then remain active.
(b) To sound notes we have to use the "strong" flexor muscles of the fingers situated on the forearm, a fact we become conscious of by the sensation of tension through and at the lower side of the wrist-joint (fulcrum).
Whereas, we can and should hold the keys down quite lightly, after their sounding, by using only the activity of the "small" (or weak) muscles inside the hand. (These are known as the lumbricales[1] muscles).
(c) Much of the failure to understand how
forearm rotational actions can help or hinder playing, arises from the fact that we can so easily recognize that an exertion
is necessary to turn the hand into its playing position, for we then use the strong rotatory muscles.
Whereas, to maintain the hand in its thus turned-over position, we find that the small or weak muscles fulfill this task quite well.
We are apt to overlook this fact, and are then likely to be deceived into imagining that we are "doing nothing" muscularly.
From where arises the fault, that when we try to use a finger at the fifth-finger side of the hand after the thumb, we are likely to continue this unperceived light action of the rotatory small musdes towards the thumb (which is incorrect) and we shall thus inevitably impede the exertion of those other fingers by hindering their free rotary movement.
The 4th and 5th fingers are adequately strong if only we do not impede their action by continuing this faulty but invisible rotatory exertion towards the thumb when it should be discontinued.1
These discoveries in fact clarify and simplify the explanation of keyboard passages that seemed somewhat difficult prior to the acquisition of this knowledge.
For instance, we used to think that in making a strong effort with the fingers and then continuing it lightly that this implied reducing the same exertion to the precise minimum needed.
On the contrary, we now realize, that at we must first exert both sets of the finger flexing-musdes concerned,
but must then simply cease all activity promptly, of the powerful musdes, while holding the keys down
solely with the "weak" muscles of the hand.
[1] lumbricals:
The lumbricals are deep muscles of the hand that flex the metacarpophalangeal joints and extend the interphalangeal joints. It has four, small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone.