I often talk about muscle memory with my students during their lessons. We talk about how in the heat of the moment, your body must react. If you have to think about what you should do and then do it, usually you are already sailing through the air.
I had to laugh at myself last night. I was laying in bed thinking about horses. I was planning on showing my assistant something with my stallion and was thinking through the highlights of our lesson. I started getting sleepy and I was to that point where your thoughts start wandering and it feels like you are no longer in control of your thoughts. It was that point where you may fall and then your whole body jerks. Well in my thoughts (dream if you want to call it that though I wasn't completely sleeping) Achilles took a step forward and I immediately corrected him. Laying in bed, my arm jerked across my body as if I were stopping his forward movement! Talk about muscle memory! Ha!