If you do the workout correctly, you should not be very taxed after. Most people don't do them correctly, sadly. Funny, when I train people with these workouts, they can barely finish, and some want to puke. When people train themselves, they're "too easy." So be sure you've read the workout instructions, not just the printout page.
Do more NEPA too. Incline walks will do the trick.
I put some friends on the vdiet this year and they also thought the workouts were too easy.....until we showed them the correct way to do them w/ proper weights/reps and the timing/rest periods. They went from 'easy' to some of the hardest workouts they've ever done. Re-read the instructions and follow them to a T - instead of wanting more, it'll probably leave you wanting less. :)