Exercises for a person with a bad back

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Okay all my MFP friends...
I'm a 31 yr old ex-athlete with back problems. I have several bad discs that cause an awful case of sciatica when they are aggravated. I'm really serious about my weight lose journey because my husband and I want kids and I need to be healthy. As of now, I workout by doing Zumba and different Kinect games. Sometimes I go out for a walk. The problem is I'm afraid to push myself to full potential because I don't want my back to go out. Please help I need workouts that won't cause me to hurt myself and will help me on my journey.