I remember hearing long ago that we only use 10% of our brains. However, this is absolutely false. Every (or nearly every) part of our brain is active for all of our daily functions (Edwards, 2011). Sometimes it may not feel like we are using 100% of our brains if we are being forgetful or having an off day. So "unlocking or awakening the other 90%" could sound quite enticing! However, everything we do from the smallest to the largest motor skill requires functioning from many parts - not just 10%.        

When it comes to muscle memory, what seems to cause confusion is that as neural pathways are formed and strengthened, the movement becomes automatic to the point one doesn’t have to consciously think about performing the skill as much or at all. It just seems to be “remembered”. However, despite "muscle memory" being a frequently used term, “muscles do not remember” (Edwards, 2011).

I don’t have to consciously think about many motor skills - such as brushing my teeth or tying my shoes. And highly trained athletes have practiced their skills to the point that they don’t seem to consciously think about routines they do for their sport either. So, while it appears to be due to "muscle memory", the brain is very active (despite the relative ease one is performing at) and proprioceptors are constantly sending messages about the body’s position and movements it is making (Edwards, 2011).  

 Reference

Edwards, W. (2011). Motor Learning and Control: From Theory to Practice. Wadsworth, Cengage Learning.