Animating Arm Swings

I was trying to search the Internet to look for a simple diagram on the concept of the figure of eight “8” motion for an arm swing in a walk cycle. Surprisingly, I was not able to find any!
So I drew a few images to explain the concept of figure of eight “8” in an arm swing and the pros and cons between using IK or FK to animate an arm swing in 3D. Hope it’s useful to some! :)