Stamina
I think stamina is often neglected in piano playing. It’s great to be super-accurate and to be able to play a piece with great musical story-telling, no wrong notes and perfect voicing. But if you get to the end of a big piece like Rachmaninov’s Sonata No.2 and you have expended almost all your energy in the previous two movements, then your accuracy will be compromised because you are simply too tired to maintain good form and technique.
What is the solution?
Specific training for stamina. This doesn’t necessarily mean playing a difficult stamina-intense piece loads of times through, just so you know you have the physical reserves to do so. The key is to remember that in live performance you only have to play it once, and not four or five times. I think if we try to overtrain for stamina then we risk injury as we begin to play at the limits of what our muscles can deal with. I try to think more along the lines of an athlete. A sort of piano equivalent of HIIT.
So how can you do this at the piano?
Well, how about taking short sections of the music and practising it above tempo with breaks in between each repetition? I did this with Schubert’s notorious ‘Erlkönig’ and it worked well. Playing short sections above tempo means you really push your muscles, but the break allows you to avoid building up a tonne of fatigue which can result in bad form (collapsing finger joints, inflexible wrists). Try it and see if it works for you.