I am already a pretty advanced player but I've not been able to practice seriously for a few months. What's the most efficient way to rebuild strength? Are Hanon or Czerny good for this? Would scales/chords/arpeggios suffice? I'm not looking for the pedagogical pros/cons of each, I just want my strength back. Thanks!
How did you build your strength in the first place? I would say do that. Also, do something that you like to do because you'll do more of it and get stronger more quickly. The exercises you mentioned are tried and true, all of them.
Watch any baby bang on a toy piano. All motion comes from the arm and shoulder. What do babies know that we don't? They know that the fingers are weak and designed for gripping, not playing the piano.
First, technique is all in the brain. Do you need to practice riding a bike or walking or build strength and endurance each day to keep up your walking and balance skills? Once the brain figures out how to use the proper muscles to balance, it is there forever - until wear and tear or entropy affects our nervous system. Strength and endurance are only needed if you use the wrong, weak and improper muscles to play. When you use the proper muscles, the body will give you what you need with zero effort. If you use the improper muscles, the body will do its best to acclimate and make the hand submissive but, miss a few days of practice and what you built, that which you don't need, will atrophy. When you have a proper, ergonomic technique which obeys the laws of physics (a HS course which apparently has nothing to do with real life) you should be able to go several days without practicing and when you sit at the piano, it all comes flooding back. Like walking.
Without pressing into the key bed, allow gravity to relax the fulcrum of the elbow to softly drop the arm/hand/fingers onto a chord. Do you see how effortless that was and how you used minimal flexation of the flexor muscles in the forearm? Where on earth does strength and endurance fit into all of this?
The foundation of all technical ability is learning to use the arm with its weight and its fulcrums and direction to place the fingers where they need to be. If you try to play from the fingers (which have no muscles) you risk using the wrong muscles resulting in strains, muscles pulling the hand in two or more directions at the same time (force vectors), imbalance, weakness, fatigue, strain, cramps - and if you are lucky, you will only have poor technique and not injury. Other than beating the hand into submission, strength and endurance won't fix any of that. If it does, it won't last long, you will have to maintain it and it will lead to injury eventually.
Daniel-san, without pressing, wash a window, write on a chalkboard, wax your car . . . That is the foundation of piano playing. The fingers, hand and wrist obey the physics of the arm. The fingers don't drag the arm behind it. The fingers don't work independent of the arm. Once you free the fingers of doing all the work, you can fine tune their grouping and directions giving you speed and the appearance of strength and endurance.
Some people already have all this and their problems with playing come from other incorrect movements creeping in and hindering "strength and endurance." These include twisting, pressing or abducting but also not having enough up/down, in/out, lateral arm movement to place the fingers, not using the pronator and supinator muscles to play the thumb and pinky, not aligning the elbow for crosses and direction changes . . . The arm is a machine with pulleys and levers, thus, must obey the laws of physics for optimal performance and avoidance of wear and tear. Force it to cheat those laws and muscular anarchy will reign resulting in poor technique or injury. Technique is knowledge, not rote.
Go fly fishing. You don't just use brute strength to cast your fly. It will land three feet in front of you. Instead, you cast from the shoulder and elbow, you use equal and opposite muscles to find the weight of the fly, the weight of the pole, the flexation of the pole and when you find all that after four or five swings, you let it go and the fly catapults fifty feet. All because you innately used physics, not Hanon or hours in the gym.
Why do some golfers throw their backs out while others play for a lifetime with no injury? Physics. Were you taught to lift with the knees? Physics. Ask any architect how he designs a building. Physics. Wax on, wax off? Physics. Want to control the playground see-saw? Sit further out than your opponent. Physics. Want to make the keys feel lighter? Play on their outer edge. Physics.
I always had poor technique and struggled with many passages. Then I found a new teacher that I addressed a problem passage with and she said "Adjust your elbow here, forward shift your thumb there" and like magic, the passage was there. No submission, no exercise, no strength, no endurance, no hours of practice - just knowledge and physics. After doing it three times the correct way, it was mine forever.
Any teacher who prescribes practicing more or building strength and endurance should be avoided. In time, they will cripple you. Any time there is a passage, scale or arpeggio we can't play, we don't need strength or hours of Hanon. We need to find what law of physics is missing or which erroneous movement is getting in the way. Like the precise movement of a Swiss watch, our bodies yearn to move in ergonomic perfection. Why do we get in its way?
Hanon and Czerny are the fake news of the music world. If there is a scale in a song that you can't play, don't practice Hanon and Czerny, just learn to play the scale.
When I was about 13, whenever it snowed my dad would take me to the school parking lot and he'd let me do donuts and skids. What I thought was fun was him teaching me about gravity, weight, force, direction, torque . . . how to work with physics, not challenge it.
An example of an improper muscle to use is the thumb's abductor. We know abductors are weak muscles yet most pianists use them all the time. Most of us are taught to use the thumb's abductor to play down. Makes sense. However, if you use a forward shift from the shoulder, the fulcrum of the elbow and weight of the arm, and a slight rotation from the pronator, the thumb plays effortlessly and possesses tremendous power. The same is true for the ring and pinky fingers. We think they are weak but what is really wrong is that we are not using their strong muscles and are trying to use the wrong ones. Often a subtle adjustment of the elbow will give the pinky just as much coordination and power as all the other fingers.
My car mechanic would make a better teacher than most piano teachers. Do you know why? He knows about physics. Every motion has an equal and opposite motion. In order to walk up stairs, we must press down. Walk forward, press backward. Swing a bat, back swing. Swat a fly, back swing. Kick a ball, back swing. Slap a face, back swing. Play down on a piano? Play up. Let gravity do the rest. Playing down is more about controlling gravity and resting up rather than pressing. Get this into your arms and your fingers require no strength nor endurance.