When we begin to learn how to play guitar, our bodies change the way they work and our brains get connected to our bodies through the new skills we are learning. After a few months of practice plus some guidance from a teacher, we become familiar with the process of learning a new song, scale or chord. We become acquainted with ourselves so the pleasure we take in playing music helps us to learn how to progress further. There are certain times of day when our feelings are more willing to stand by and watch our bodies spend fifteen minutes doing boring guitar practice.
The more we come to know how our bodies, minds and feelings work together, the better we get at learning new skills. But there are some areas of learning that we need help with. One of these areas is muscle memory. The idea that the body learns movements by means of repetition is commonly used in many areas of life, notably sport and music. But the fact that the more relaxed our muscles are and the more attentive we are when we practice routine movements does not readily jump out at us. We need to read and learn about muscle memory and we need to practice it.
The basic principle behind muscle memory is this: you learn a posture or series of movements, for instance a chord fingering; you then put your fingers in the chord position and take them away and put them back again, returning to the chord position lots of times until your fingers just take their places whenever you need them to. Of course, the way we practice chord shapes is to learn a few chord shapes at first and practice moving from one to the other.
The thing about muscle memory that we do not realize at first is that our muscles record things that our minds don't notice. If we are tense in the jaw when we play a barre chord, then that tension will appear as part of taking the chord. If we hold our breath when we play a scale, or grunt every time we make a mistake, those things gradually become habits and it usually takes someone else to draw our attention to it. So a part of learning the movements necessary to play the guitar is attention to how precise and relaxed we are when we learn new chord shapes and scales.