In baseball, especially when training pitchers or hitters, the term "muscle memory" is heard all the time. In order to understand how muscle memory is created, read the Wikipedia on Muscle memory:
"When an active person repeatedly trains movement, often of the same activity, in an effort to stimulate the mind’s adaptation process, the outcome is to induce physiological changes which attain increased levels of accuracy through repetition. Even though the process is really brain-muscle memory or motor memory, the colloquial expression "muscle memory" is commonly used.
Individuals rely upon the mind’s ability to assimilate a given activity and adapt to the training. As the brain and muscle adapts to training, the subsequent changes are a form or representation of its muscle memory.
There are two types of motor skills involved in muscle memory: fine and gross. Fine motor skills are very minute and small skills we perform with our hands such as brushing teeth, combing hair, using a pencil or pen to write, touch typing, playing some musical instruments, or even playing video games. Gross motor skills are those actions that require large body parts and large body movements as in the throwing sports such as bowling, American football, and baseball, sports such as rowing, basketball, golf, martial arts, and tennis, and activities such as driving a car (especially one with a manual transmission), piloting aircraft, playing some musical instruments, and marksmanship.
Muscle memory is fashioned over time through repetition of a given suite of motor skills and the ability through brain activity to inculcate and instill it such that they become automatic. To the beginner, activities such as brushing the teeth, combing the hair, or even driving a vehicle are not as easy as they look. As one reinforces those movements through repetition, the neural system learns those fine and gross motor skills to the degree that one no longer needs to think about them, but merely to react and perform appropriately. In this sense the muscle memory process is an example of automating an OODA Loop insofar as one learns to Observe, Orient, Decide, and Act.
When one picks up a hair brush, one automatically has a certain motion, style, number of strokes, and amount of pressure as the hair is brushed without requiring conscious thought about each movement. Other forms of rather elaborate motions that have become automatic include speech. As one speaks, one usually does not consciously think about the complex tongue movements, synchronisation with vocal cords and various lip movements that are required to produce phonemes, because of muscle memory. In speaking a language that is not one's native language, one typically speaks with an accent, because one's muscle memory is tuned to forming the phonemes of one's native language, rather than those of the language one is speaking. An accent can be eliminated only by carefully retraining the muscle memory."