What is the best way to go heavy on weighted decline sit-ups?? I have tried using plates + DBs, but they just slide around making it very difficult to do reps.
Slide around? How are you holding your plate?
If I try to go heavy, I have to use at least two 45 lb plates. It doesn't work too well with this method.
Hold a plate over your head rather than on your chest, that will totally crush your abs.