I started trying out the Jillian Michaels workouts. She uses low lb. weights (Yes, I know I need to incorporate higher lb. weights with less reps) with resistence exercises/cardio. You can check out a few of her videos on Netflix Instant View if you have it. http://www.netflix.com/Search?v1=jillian+michaels&search_submit.x=0&search_submit.y=0 I usually do two per night, roughly 45 - 50 mins. total. She has videos for working the front and for the back. Should I not be doing both on the same day and instead do some kind of cardio that doesn't involve weights? After two days of doing this, with a break in between because my back was having issues, I am aching a bit on one side of my back. I am concerned that I may be doing the exercises wrong, but I feel like I get a good workout with her videos. I am using five lb. weights while doing it. Anyone care to take a look and make some recommendations?