I did lots of "core" at the gym ..loads of crunches, reverse crunches, twisting sit ups with medicine ball , reverse sit ups, planks etc etc and lots with an ab roller but found it did not transfer well to climbing.
So now I am: 1. using a hold at the top of a steep board to "fish" and use poor footholds ( 20) 2. Hang two big holds near middle of the board and lever my feet to the furthest corners and press out on footholds. 3. At the gym I've been using slings as in "gimme kraft". 4. I've adapted one of the gk exercises ... hands in slings feet on gym ball ... walk the ball around 360 degrees... this is brutal.... ( started this using hands on a bench.)
Early doors but this seems to be producing results especially in getting force through my feet at full extension and controlling any sag or twist when I try problems on my board.
I think the unstable nature of the slings work is probably what makes the difference.
Might be something useful in there.