You exercise to build health, and when you're healthy you don't hurt and you aren't exhausted. The last thing you need is an exercise program that makes you feel awful. This program won't do that. You may ache a little after starting rung 1, but that should stop in a few days. After that, only move up to the next rung when you're comfortable at the current level however long that takes. If you advance to the next rung and find it's making you sore, or exhausted, or you have trouble completing the exercises in 15 minutes, no problem! Just drop back down to the previous rung, where you know you're already comfortable, and try the next level in another week or so. In all likelihood by then it won't present any problem. If it does, be patient; your body continues to gain strength and capacity even as you remain on a given rung.