I've looked through the book again, and either I'm missing it entirely or I'm just misunderstanding.

Do we do/can we do the same exercises for any given muscle group for "x" amount of time, or do we switch it up EACH time?

For instance: If I want to do leg raises for lower abs (5 sets) and one set of crunches, and the and the next ab workout day do the opposite? Same with legs, and upper body??

Thanks in advance, all!