In his magisterial book The Hand Frank R. Wilson wrote, “From the perspective of biomechanical anatomy, the hand is an integral part of the entire arm, in effect a specialized termination of a cranelike structure suspended from the neck and the upper chest.” A prominent hand doctor and professor of medicine, Wilson was a ranking authority on the subject of how we get our hands to do the things they do in a muscular sense. That includes all of their activities, including playing the piano.
This is to say, Wilson’s expertise is applicable to playing the piano even if he is not a piano expert.
To help pianists start to wrap their brains around Wilson’s statement, my book Pianist’s Guide to the Upper Body offers this chart (p. 20):
It can be argued that all these muscles (twenty one in all according to boundaries established by anatomists) evolved as they did, along with our upright posture, so as to position the hands. (For the sake of argument I leave out the muscles that move the trunk, which also helps position the hands.) Through acts of teamwork they help create all the subtle changes of location in the wrist. They are also on the ready to play roles of various kinds when you rotate your forearms. They get your fingers to the extreme ends of the keyboard and everywhere in between. When you need your fingers to play the notes of chords together with razor sharp precision, they officiate. The problem is not whether they do these things but how, and how efficiently.
Pianists tend to receive some pushback from the shoulder area in the form of tightness and pain when some combination of those muscles is overused. Tight muscles of the upper body also act as brakes, making it hard for the fingers to get to their destinations on time. Carping about fingers is unlikely to change the muscular habits that create this trouble in the back and shoulders. Ditto with forearm rotation.
Unfortunately, no amount of intellectual knowledge of these muscles is going to change unhelpful habits. How do you create the changes that filter down so that your fingers do what you want? That involves a reflective, meditative process of monitoring the upper body, coaxing it into a new and vital role. But understanding that this part of your body invariably does something when you play can help you get the ball rolling.
Sometimes in order to undertake a difficult task we have to be convinced that there is no way around it. The good news, where training the upper body is concerned, is that the potential payoff is huge.