A whole discussion in the link.
"Voluntary muscles are like the ones in your back or legs; they can be strengthened with use or become weak from lack of use. The pelvic muscles help other special muscles, called sphincters, with bladder and bowel control."
"The voluntary muscles are like the hinges on the robot that allow it to move. Smooth muscles are like the parts that allow the robot arm to keep working."
"Involuntary muscle is like your heart, muscles that you can't control and move on their own."
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.