Muscle Fiber Orientation and Why It Matters

I was just thinking about how the infraspinatus can help shoulder flexion. The fiber orientation is a clue. It's an external rotator, so how does it get involved in shoulder flexion? How does the Pectoralis Major flex the shoulder? Look at the fiber orientation.   How does Gluteus Minimus (abducts and internally rotates the hip) which doesn't flex the hip, cause an anterior pelvic tilt? Fiber orientation.  https://richardhazel.podia.com