My recommendation is that even if you can't do all the exercises, watch the tape. It's all about developing routine. Take the time to do as much as you can do while watching the tapes. When they do exercises, do as many as you can, but instead of focusing on matching their reps, do 15 compared to their 25 reps (at first), and force yourself to participate in each exercise, even if you're only doing it 60% of the time. I think it's all about developing routine.