Forearm plank, knee to elbow, climb the wall.
Keep your hips from rising as the knee comes up, stay long and tight.
This takes the forearm plank, already an anti-sag core hold, and adds a knee driving out and up to the elbow, so the obliques have to produce movement on one side while the rest of the core locks the trunk down. The lower forearm position keeps the hips closer to the floor than a high plank, making the crunch path shorter and tighter. It is a smart pick when a static plank has stopped being hard and you want the hold to earn its time again.
Same knee-to-elbow drive, but from a forearm plank instead of a high plank. Being on your forearms keeps you lower and makes the anti-sag challenge stronger, so it feels harder even at the same rep count.
No, that is the main cheat to watch. Keep your body long and low as the knee travels, if the hips pike up you are stealing the work from your obliques.
Quality beats quantity here. Sets of eight to twelve per side with a controlled tempo and dead-still hips do more than twenty rushed reps with a rocking torso.
