I think it's because the muscles feel the resistance and so don't cramp as severely. I have a mooncup, but as my symptoms are so severe, it doesn't make a big difference, but it was noticeable the first time I wore it PRIOR to coming on.
I have endometriosis & unfortunately it makes my life very very miserable.
I suffer from period pains everyday of my life even when I am not bleeding, its pretty grim.
