Playing an instrument requires the use of both your muscular and nervous systems. Musicians are athletes. Unlike runners or swimmers, we use mostly the smaller muscles which we all tend to take for granted in everyday tasks such as using a knife and fork or tying our shoe laces. The difference of course lies in the degree of organisation and rapidity required to choreograph the hands to a musical image created in the brain.
Some people mysteriously possess this degree of coordination as a gift. They are called prodigies. The rest of us have to work hard to acquire this facility through patient and methodical study. However even prodigies can lose their amazing facility through misuse of their bodies if they are unlucky. The legendary virtuoso Leon Fleisher is probably the most famous example of this, although there are numerous other examples.
Posture is extremely important, whether we are talking about how we sit at the piano or how the hands are positioned on the keys. How high should the wrist be in relation to the fingers? How passive should the arm be prior to and after a note or chord is played? How can we balance the need to relax with the need to be primed for precise movement? These basic questions dominate the field of piano pedagogy and the variety of approaching piano technique is truly perplexing. Piano teachers need to be flexible in their approach. A method that works for one person may not work for another. The first principle has to be to be aware of how the body is required to move and to listen to your own body so as to avoid injury. This is something that should be emphasized in every piano lesson.
Because our joints and muscles function best when they are well within their extreme range of motion, it makes sense to establish as great a freedom as possible in the joints whilst maintaining an economy of movement in the muscles. The fact that muscles tire very easily is not something that is changed by doing hours of exercises to build them up. It is important to acknowledge this, especially given that the muscles for the fingers reside in the forearm. So any exercise we do at the piano that frees the joints and involves the immediate release of tension in the muscles being used is likely to improve performance.