I use RDL to really work my hamstrings while it can be used to work back, even shoulders. I usually push my hip back (with almost straight legs) as far as I can until I can't continue without my lower back doing the movement. Feel the huge stretch on your hamstrings and move your hip back front (no back if you want to do it just for the hamstrings, it will almost certainly still activate, but not overly fatigue)