I thought you post was on topic. I was going to ask about Zercher carries. Also my “secret” core exercise is kneeling Zerchers. I’ve used 100-140 pound sandbags but also slip a squat pad and a long piece of 4” pvc tube over a bar to put more torque on the core.
It’s great for boosting my squat and dead, but I was looking for some direct flexion options to go with a “bracing” exercise.