Almost every complex contains both single-complex muscles and multi-complex muscles.
Single-complex muscles are responsible for moving only one complex, mostly in either a clockwise or counterclockwise direction. However, they can sometimes move it in both directions. Despite moving just one complex, they often engage multiple joints (see chapter 4.2).
Single-complex muscles are considered direct or prime movers.
In contrast, multi-complex muscles are responsible for moving two or more complexes simultaneously, either in a clockwise or counterclockwise direction.
Multi-complex muscles play a crucial role in motion, coordination, and stability across multiple complexes, often affecting many joints at the same time.
It is important to realize that a muscle generates motion in one or more anatomical planes and that it moves one or more complexes. In other words, whether a muscle is classified as a single-complex or multi-complex, it can move in one, two, or all three anatomical planes.
