Like peeling an onion
Musician's focal dystonia can also develop after a muscular or joint problem occurs. You change your position or your movement to compensate for an injury or hide a problem. It can also happen if you play an instrument not adapted to your body size.
The problem comes when you develop a new movement for the same note. You end up with one bad movement or two fighting each other. Parallel movements, behave like multiple circuits trying to operate same light!
When you try to learn a new movement instead of "peeling the onion" you end up of with an extra parasitic movement.
When trying to move a finger in a conscious manner, you contract a muscle but you often don't release the opposite muscles, which work together. So the finger locks up as both contract at the same time, or don't react in sync... and so on...
With "peeling the onion" you first learn how to relax the hand, and find its original position without intervention. Then as you start to move the finger, you can feel all the little parasitic movements which have been layered on top of the primary one. Slowly, those extra movements fade away, like peeling the layers of an onion, and you end finding the original finger movement.
The proper movement has the joints in line, moving on their proper axis, without parasitic side to side, or distortion along the way.
You can later, as you rebuild the movement from the source, improve your technic and clean up your fingers motions.
Also, as the movement cleans up, the proper muscles strength and range will be limited. It will take time to built or rebuilt the correct muscles mass. Same as removing a cast, all the muscles are atrophied and need to be rebuilt or if the technic was poor from the beginning the proper new learning of a clean movement.
How long should you practice?
As you learn to use muscles which have never been used or not been used in a long time, you get tired quickly, like a beginner. If you play too long, then you'll start playing with the old dystonic position. Stop playing before it goes bad, as to reinforce the brain memory with a good experience instead of a bad and frustrating one. Each time you play in a dystonic manner, you reinforce the bad movement through neuroplasticity.
The greatest issue, is to try to consciously fix the issue by trying to control a movement. In controlling, you end up creating an unnatural movement. Only through removing the extra layers, can the pure original movement be found. There comes the important work of relaxation and where the mind is focusing. A multitude of other technics can also help achieve it.
The whole emotional state, will also tend to trigger the unnatural contraction.
We can't fix, only release.
The perfect movement becomes a state of bliss, of complete calm.
Peel off the layers