This is much more challenging than it looks, but you must be an active participant. In all planking variations, the participant MUST engage the intended musculature, not by just holding a position, but by activating the correct areas of the body.
In this particular case, the entire anterior side can be activated by actively “pulling” your hands towards your toes. If you look closely, you can see Coach Brandon do this, and it immediately changes the stimulus of the exercise.
Give this exercise a shot!