The excercises themselves are easy, anyone can do them. However, because of the short burst of intensity they are able to help tone your body. As Jillian herself says "even 400lb people can do jumping jacks!"
I can't believe how quicly the workout is, it seems much shorter than 20 minutes. After the first day I was a bit sore, mainly my thighs. I'm not the fittest person in the world either and overweight, but I would definately recommend this one. Happy Shreding!