@alexv thanks for the feedback. i figured out the iso hold from the top + slow descent thing but i haven't tried those intermediate holds. sounds like a good plan. i'd like to think that my lower abs are reasonably strong and that the problem is more with my hip flexors restricting full extension throughout the movement. regardless, i can obviously improve in both areas.
It is great to think that but.... In my experience it is not properly engaging the core (IE to weak). You can plank/crunch/etc.. all day but you need to be able to hold the pelvis in neutral under high forces. The GHR is a dynamic plank on steroids! Your COG is so far from the fulcrum. Doing the holds will help a ton. Once you get there you will see tremendous carryover in the exercise. Problem is it is easier for people (not you but athletes I have seen, consulted, trained) to keep progressing with crappy form than it is to focus on getting the core straight.
Ugh... I have turned into the core guy
I always hated that guy. Although once you get it, like really get it and not become NASM certified or fall in love with boyle or vestergen, you will be a core guy too. Good news is once you can do proper GHR's your core will probably be strong enough for the rest of your life.
Just keep doing GHR's and you never have to train the abs again.
I really do like banging iron and lifting heavy.
It is worth the effort. EVERY athlete I have personally trained has been able to do a proper GHR after a few months (usually 1) The holds are the key! Hell most of them could do Schroeder EDI's on the GHR with perfect form