What’s stillness got to do with it? Move all you want in meditation. You only sit still in meditation to better follow the movement of life. It is a natural repose, not something forced.
When you are deeply absorbed in something—conversing, reading a book, listening to a piece of music—you will sometimes be very still. You become poised in order to better follow the flow of the conversation, the arc of the plot in the story, or the movement of the music. That is the way to be in meditation as well. So stillness of posture happens spontaneously; it is not something you focus on or make a rule out of.
Life is movement, an infinite dance on every level—atoms move and vibrate, cells undulate, blood pulses, breath flows, electrochemical impulses charge through your nerve pathways. If you are sitting while reading this book, your postural muscles are making lots of tiny little corrections to keep you upright, and the muscles in the diaphragm and ribs are moving with the gentle rhythm of respiration. Each of these little movements is part of the meditation experience.
The dance of life changes its pace according to whether we are walking, sitting very still, or lying down, but there is always a dance, always the hum and undulation of life.
Excerpt from Meditation Made Easy book by Dr. Lorin Roche.