Prone Bridges With Manual Perturbation

[Brisks]

Is it possible to recreate this by balancing on an exercises ball and medicine ball?

Also how long should it be held for?

[tyciol]

That's cool, reactive stability. For directly opposing the muscles that planks mainly target, where's the best place to apply the high weight?

[StaleyTraining]

In this drill, you're training the core to prevent unwanted movement of the trunk/spine. So honestly, you want a lot of variety— push and pull in every direction you can think of, and if you watch carefully, you'll see sometime's I'll apply two forces (sometimes opposing) simultaneously)