Recently I re-homed my sheet music collection into a proper filing cabinet and rediscovered a book on scales by Leo Brouwer and Paolo Paolini. The book itself has some often repeated advice and some scale patterns, but one thing did stand out.
Tension and realization are two concepts that must always be combined, like day and night: their alternation is present in all motor activities.
Later, in a section on speed bursts, Brouwer and Paolini call out that the longer pauses between bursts are an opportunity to relax.
Tension is a part of playing, even for those superhuman performers for whom everything seems easy. We all get tense.
So we must all find space to relax. Music is often not constant bouts of motion. It ebbs and flows — a fast passage may get some resolution or a hot lick may be the only really hard part of the piece. So during those times when things relax, one should make an effort to relax and release any pent up tension in the hands as well.
This, like everything, can (and should) be practiced. Hard section? Don’t just hammer on it over and over again, practice it but also feel the release of tension as that section resolves. This is another reason, beyond musical continuity, that one should practice harder passages to their resolutions rather than in isolation.
Also: consider that certain movements are easier for certain players. Even in pieces of music where the motion seems constant, some parts — right or left hand — will feel easier basic on individual anatomy. Use those times to release tension.
Find space to relax.