I want to make the muscles pump like a heart (Resident Evil 4 Final Monster) I want the muscles of the legs pumping and have translucent properties so to show something is pumping inside. I know I can do soft body or cloth sim but I'm not sure how. I don't know how to pump it after that softness.

I want these marked areas to pump and act like flesh in my scene. I have one year of experience in Blender but still don't know many things so please suggest tips that are beginner-friendly.
The look I'm inspired from is this:
I'd probably do it using shape keys:
Blender Character Animation: Shape Keys