All the motions of the body or any of its parts are produced by muscles in action. There is never a time when all of them are quiet. The body as a whole might seem to be at rest, yet breathing goes on, the heart beats regularly, and muscles in other internal organs are at work. The heart itself is a hollow mass of muscle.
There are two kinds of muscles. One kind works whether we wish it to or not. The work of the other kind is to a great degree under our control. It's an interesting fact that life depends on muscular behavior that cannot be controlled, while conscious work is governed by muscles that move by choice. This suggests that humans receive the gifts of life together with the freedom to choose what to do with them.
I'm reminded of the Aries-Capricorn relationship.
Maybe the wise and patient bones guide the eager and impetuous muscles, much like the system guides the individual ideally. The structure provides restraint, control, and stability following the initial muscular impulse. And I suppose the action loving muscles keep the bones from becoming too locked and rigid, besides adding curvaceous beauty to the form.
Aries-Capricorn. A fine combination, keeping the body in motion.
Muscle information from The Modern Medical Counselor, published in 1943.