I've been trying to bulk up recently, especially my legs and butt (lol). I created the 20x10 which is designed to give your arms, abs, back, butt, and legs a well rounded workout. It may be a bit too intense though (especially if your upper body isn't strong). Check it out anyway there are some good ab and butt exercises on it that you can incorporate into your workout routine. Also, planks are great (side planks, elbow planks, full planks) they workout your entire core (abs, hips, and butt). Hip-ups (aka Bridge) and the Locust Pose work great on back and butt check them out at ab-workouts-guide.com under planks and core exercises. Vups are probably the most challenging abs exercise you can do (you can also find the there). Combine the exercises above with a good cardio routine and a healthy diet and you can't go wrong. Good luck and God Bless!