Technique is movement made conscious. This is true of all practiced actions, from cooking to playing tennis to race car driving. For musicians, our technique is the way we move to make sound. Our most reliable technical approaches are the ones that allow to us be reasonably consistent as well as congruent with the structure of the body and the design of our instruments.
Because the body is a wonder of inter-related systems, it will respond to the goals we set for it in the most coordinated fashion - UNLESS we ask it do something that interferes with its natural design. Good technique depends not only on instructions for doing but also on avoiding instructions that plain old get in the way.
Let's look at some ideas that can cause conflict with our natural coordination:
1. Sliding on the keys. The piano, unlike the clavichord, does not respond to sliding motion on the keys. It does not have a mechanism that changes the sound based on sliding. What will happen is that the speed of descent will be impacted by the slow approach to setting the action in motion. However, this is not the easiest kind of work for the hand when playing a succession of keys. Note that the four basic finger movements we examined were flexion, extension, A-B-duction, and adduction. Sliding can also cause the player to be unsure of the relationship between key descent and the release of the hammer. Sliding after the hammer has been released is a waste of energy as it makes no difference to the sound whatsoever. Sliding may occur as unconscious movement as the hand travels, which is different from using it as a technical approach.
2. Over-flexing or curling fingers. Because the hand is well-designed to grip objects, it has the ability to change to accommodate objects of different sizes and shape. The piano does not require gripping of any object, however. One of the unfortunate words we sometimes use is "grab", as in "grabbing chords". If our literal brains attempt this, there will be constriction in the muscles of the hand, making free finger movement very difficult.
3. Retracting or over-retracting fingers. There is an old European exercise called "extensions". This exercise requires the pianist to bring the finger up and back as far as possible while curving it, then releasing it to play the key. The pianist may also be directed to do this after playing the key. This is a challenge brought on by attempting to flex and extend at the same time. Presumably it was designed to strengthen finger "muscles". Instead, it results in over-working and unnecessary tension. A piano action in good regulation allows the key to return to its level starting position when the pressure of the finger is released. There is no reason to retract high in the air for this to happen. As William S. Newman wrote in his comprehensive classic, The Pianist's Problems, what goes down, must come up. (p.50) The finger will likewise return to a comfortable neutral without effort.
4. Pulling down on the keys. The average depth of key travel before a sound is made is 3/8 inch. Any movement made after the action has been activated will not change the sound. Pulling the wrist and forearm down is sometimes associated with sending weight into the keys, which doesn't happen, as we know. Pulling as a finger technique creates unnecessary tension in the hand and forearm with no advantage in sound production. Pulling may also encourage collapsing at the finger joints closest to the nails. This causes the extensors to be unable to allow the fingers to move up from the keys. Madeline Bruser, author of The Art of Practicing and renown pianist and teacher, discourages this collapse by advising her students to "stand" on their fingers. (p.119) Be aware that she does so in conjunction with excellent advise on how to play with freedom so the "standing" does not include tension.
5. Over-stabilizing finger joints. A joint is a meeting of two or more bones in order to provide movement. While there are certain inherent challenges with fingers that collapse, there are also limitations that result from locking them. Fingers change shape while playing, just as the whole hand does. It is more beneficial to map finger joints accurately than it is to predetermine a shape for those joints. Free joints allow for greater control over the speed of key descent.
6. Collapsing at the MCP joints. As we have discovered, the MCP joints are critical in terms of the action of sending down keys. The arch they create with the phalanges allows for the small amount of pressure required to play the piano (the piano technician's static touchweight of 50 grams) to be controlled with ease. Even a player who seems to play with "flat" fingers - Horowitz comes to mind - is still employing an arch in the hand, albeit of a wider angle than someone who plays with curved fingers most of the time. The tried-and-true advice to allow the arm to drop to the side so the hand finds its natural arch still works. Just be aware that the arch is likely to change in the process of playing.
CAVEAT: Pianists with hyperextension in their connective tissues, popularly known as being "double-jointed", may be quite challenged to find the right amount of support for finger joints. This is a genetic trait. Encouraging awareness of the arch may be the best you can do to help them. For some students, softness in the joints is a temporary condition which rectifies as they develop, but true hyperextension lasts a lifetime.
7. "Stretching". I put this word in quotes because it is important to distinguish healthy, elongating movements from attempts to reach beyond the ability of the hand to open. As noted in Part Four, the innate quality of the muscles between the bones of the hand varies from person to person. Attempting to change this quality by stretching may be futile and potentially harmful. I have also seen young students strain to reach an octave long before that is a comfortable distance for them to cover, and I wonder if this early impression of the octave is what causes us to find octaves intimidating well into adulthood. My preferred phrase is "opening the palm" in order to cover bigger intervals.
It is much easier to find the natural span of the hand when the direction to open is aimed at the muscles of the hand, not the fingertips. Attempting to open from the fingertips results in gripping.
8. Over-focusing on fingers. As mentioned before in this series, there are many ways that fingers can produce sounds on the piano. Playing on the pads is a popular way to slow the descent of the key subtly due to the added friction with the key, while playing on the tips has the opposite effect. Various musical styles may encourage these different approaches. Be aware that the freedom in the hand and fingers to make these changes is related to the freedom in the whole arm and whole body. A body that is out of balance will cause bracing in the arms and bracing in the hands. If you are spending a lot of time looking at fingers without checking overall balance, you may need to widen your field of awareness.
TOP TIP: As my old Red Cross Safety Badge said - knowledge replaces fear. If you know how the body works and the piano works, you can make informed decisions about healthy sound production.