Be sure to use the rest between the crunches and hollow rocks because those 30secs get really hard.
I tried to challenge myself by adding weight and doing it on the boxes but for beginners this can be performed on the ground.
Maintain 10/12 AB Mat Sit-Ups on every 2nd set of Tabata, while trying to continue to accumulate 50reps of Around the world ? on the opposite round of Tabata.