I didn't find that I was too sore after doing this for the first time. The workouts are relatively short and are based on a balance of abs, strength and cardio, so you're not overworking any one area over another.
There are also two girls who work out with Jillian - one does the complete workout, and the other demonstrates easier versions of some of the moves. For example, one will do real push-ups while the other does them on her knees (which I do!). So if you can't perform a certain exercise, you can do the modified version to make it slightly easier.
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