P90X - Core Synergistics question

amicklin

There is a move in the workout that involves holding yourself in the plank position with your forearms parallel to the floor while throwing your knees up towards your head.... then, not to mention the 'prison' push ups.....

I have been doing P90X and P90X+ for a while but have only done the core syn. workout one before (I don't follow the program to a 'T') any suggestions on how in the world to get the rhythm/ dynamic of those two moves?