Technique is Mental

During piano playing, the mental state is primary, the technical stage is secondary.

Question: What should be the limb conditions of the fingers, hand and forearm during keyboard practice?
During keyboard practice, it is essential to maintain proper limb conditions for the fingers, hand, and forearm to ensure effective playing and avoid injuries.
Here are some guidelines:

1. The finger should descend as one component descending from the first phalanx and metacarpal bone while the fingertips makes contact with the keys. Avoid excessive tension or stiffness, as this can lead to strain and limit dexterity.
2. Hand: Maintain a relaxed, natural hand position, with the knuckles slightly raised. Your hand should be shaped like a rounded dome, with each finger ready to press a key. The thumb should be flexible and relaxed, neither too far under the hand nor stretched too far out.
3. Wrist: Keep the wrist flexible and at a neutral level, slightly above the keyboard. Avoid bending the wrist excessively upwards, downwards, or to the sides, as this can cause strain and limit the range of motion.
4. Forearm: The forearm should be parallel to the floor or slightly sloping towards the keyboard. Ensure that your elbow is slightly away from the body to allow for freedom of movement. Avoid locking the elbow or tensing the forearm muscles, as this can hinder fluidity and lead to strain.
5. Upper arm and shoulder: Keep your upper arm and shoulder relaxed, with the shoulder blades gently resting against your back. Avoid hunching or raising the shoulders, as this can lead to tension and discomfort.

During practice, it is essential to remain aware of your body and any signs of tension or discomfort. Regularly check your posture and limb conditions, making adjustments as needed. Taking breaks and incorporating stretching exercises can also help to prevent strain and maintain good playing habits.

As already noted, you cannot teach your limbs or your muscles to act. All you can do is teach your mind to direct the required limb-conditions of activity and inactivity.
Note: There is no such thing as "muscular habit". It is always mental habit located either in the brain itself or in its subsidiary automatic centers. The first important thing to learn physically (i.e. mentally) is to supply solely the required exertions, without interference from any undesirable ones.

1. Gross physical structure:
   1. There is one axon that branches.
   2. There is a dendritic tree that collects input from other neurons.
2. Axons typically contact dendritic trees at synapses.
   A spike of activity in the axon causes s charge to be injected into the post-synaptic neuron.
3. Spike generation: There is an axon hillock that generates outgoing spikes whenever enough charge has flowed in at synapses to depolarize the cell membrane

If we allow the opposite exertions to be provoked into action along with ths required ones, then we experience "stiffness" which can be described as a tug-of-war within the limb, or portion of it.
Note: If the two antagonistic exertions are precisely equal, then nothing happens visibly, but you can feel the tension if you are observant, and your audience will certainly hear it if they are musical. If the two exertions, however, are not quite of equal intensity, then some action or movement may result, but it will be constrained. Any such "stiffness" will preclude our attaining any accuracy in tone, or ease in performance. Therefore, it must be carefully guarded against.

Now remember, as already pointed out you cannot directly will, prompt or think any muscle into action. You can only induce the exertion of a muscle by willing the required exertion of a limb or portion of it.
If you try directly to actuate a muscle, you will only petrify yourself and lose all control, for you are taking your mind away from the only road open to you, and that is to concentrate upon the limb-action itself in strict association with the musical effect needed from that particular piano-key at that particular moment.
Paramount concept for mastering technique: You must be able to recall the sensation accompanying the correct exertion or movement of the limb and to acquire such sensations of correct execution. One must experiment, guided by information such as here given on this website.