what exactly is the difference between RDL and good mornings? It looks like it is the same kind of movement, only the position of the bar is different.
Well yes the bar placement and the leverages on you really are different try a relative light load with each and you should feel the difference for me seems a LOT morer lower and upper back strenght for the static hold of a GM. The load Is WAY!! out on you where as a RDL stays closer to the centerr of gravity.
Both are great moves though
I find I tend to feel RDL’s in my hamstrings more where as goodmornings are glute killers. Mike Robertson has an article Erector Set that goes over both lifts which might help you.