I've been working my core fairly hard daily for a few months. Went from planks to weighted planks, and further from body weight core work to weighted cable crunches and other machines at the end of all of my weight training sessions. I've even found myself able to do headstands up against a wall, which is pretty neat.
Functional core strength progress is pretty fantastic, as though the muscle groups seems to be low volume, it has a fast recovery that allows it to be worked daily.
At the start, I was working it really hard, until it hurt. I remember once i sneezed and it made me jolt. Since then I started doing a more regimented rep scheme of 3 sets of 15 at most, graduating the weight as I progress. Unfortunately, I've hit an unexpected wall. I'm out of weight to add on my machines. I've maxed out the cables for kneeling cable crunches, crunches with oblique twists and standing cable crunches. I've maxed out the weight on my abdominal crunch machine, the rotary torso machine, and some other things. I don't want to do a lot of decline crunches or leg raises like I used to do because there is a lot of lower back activation, and I kind of need to baby my lower back. Frankly, I don't really like as many of the other body weight core exercises.
I don't really feel much of a burn anymore, certainly nowhere near what I used to. Volume through sets doesn't really seem to strain it so much, at least in the sets. I often do the cable crunches back to back, so 6 sets at a time and it's not really that intense.
Should I start doing sets to exhaustion so I feel actual burn and strain?
Am I doing enough right now as it is?
Does anyone have any suggestions on other weighted exercises that may hit the muscle well in a more efficient way? The planks are great, but even those are getting kind of annoying as I'm getting close to being able to do those for 3 minutes with a half plate on my back. Some people find planks meditative, I'm somewhere in-between there.