As you can probably imagine, to become a musician, you develop very specific muscle memory, which in fact has very little to do with memory being stored within muscles themselves. Instead, it's a feedback loop between the brain, the many neurons of the body (mechanoreceptors, proprioceptors, and more!), and muscles, in a class of memory called Procedural Memory (or motor learning). P.M. is the sort of memory that allows us to perform actions without thinking about them consciously.
ex. You had to think a lot about tying your shoe twenty years ago, but you probably never think about it now. You revamped your bow hold/setup/embouchure in college, and thought a lot about maintaining those changes as you play. Now, it's second nature.
To get to Procedural Memory, one works on Procedural learning, which is repeating an activity until the brain and body automatically creates the action. Hopefully, this is what you do every day when you practice! Ideally, we are isolating difficult actions and skills and training our body to make them second nature. Think of how many string players practice the first page of Don Juan- the goal is to make execution automatic, often. I think it was Malcolm Gladwell that came up with the idea that one has to log 10,000 hours to become an expert at something, although I imagine that number is dependent on quality over quantity. It also explains why true beginners need lots of hours of repetition to master a basic task, like holding a violin bow, or understanding quarter note rhythmic durations.
Now whatever you repeat in your procedural learning becomes ingrained in your body, so if you choose to repeat poor habits, those will become second nature too. You can see this with your students, who often speed through scales and technique, and don't realize that there is direct crossover with the rest of our repertoire and performance. We want to integrate mindfulness with instrumental practice in order to reinforce good habits and awareness of what we're trying to learn and perfect.
ex. Many of us practiced scales and etudes in front of the TV when we were younger. If you're an auditory learner, maybe the extra stimulus helped you focus, but for most of us, it was just an excuse to log practice time and let our body execute scales automatically, without us thinking about quality.
Lastly, this feedback loop between the Central Nervous System and muscle proprioceptors (which tell you where your body is in space) is what allows you to take time off from practicing, and then get back to it without starting at the very beginning of your learning.
ex. You take two weeks off from practicing, and then when you return, it's challenging to start, but you get back in shape in about a week, instead of starting as an absolute beginner.
Part of this ties into the idea of the practice/mastery matrix, which has a few different variants. One is this idea of moving from unconscious incompetence (I don't know what I don't know) to conscious incompetence (I know I don't know this) to various levels of conscious and unconscious competence. With any piece of music, we are going through these levels, whether it's in a quick period of time of listening to a recording, understanding the challenges, and then targeting them, or whether part of a larger process.
What I find especially neat as a musician is that multiple aspects of your brain are being engaged simultaneously- you know what something should sound like, what it feels like in your hands (or with your breathing or tonguing), you hear how it sounds and respond accordingly, and maybe you see yourself in the mirror and adjust accordingly. There's so much going on to make music! (More on this later-)
I've been thinking about all of this a lot lately, as a I embarked on a beginning Crossfit trial a while ago, which involved a lot of motions and actions which I'm not used to performing as a yoga teacher/musician. Many of the actions are performed for time, which I could care less about. I'm so much more interested in lifting a weight with good form then finishing a certain number of reps, because my body will remember my poor form in the future more than I realize. Conversely, I've been doing pilates teacher training in the last year and have focused most of my efforts on good quality movement and ingraining good habits. The movement method isn't the problem-it's how you learn (I need to do things slowly and practice by myself!) and how to learn, coordinate, and ingrain things over time. In the end, all of our movements are not just training muscles to be stronger or weaker, but instead are training our brain, which is pretty amazing stuff.
*Thanks to Jonathan FitzGordon's initial blog post on muscle memory and being a beginner for inspiring this!