>>565
https://www.t-nation.com/training/inside-the-muscles-best-shoulders-and-trap-exercises
には、
However, my research indicates that muscle fibers within a muscle can function differently from one another even if they don't have separate heads.
For example, during my research I noted that the upper rectus abdominis and lower rectus abdominis function differently.
とあってちょっと驚いた