I was wondering about this too because my spine is -4.1, so my doctor send me to the UBC Sports Medicine Clinic to see a specialist about exercise. I currently do light weights, resistance training (mostly planks and push-ups), and lots of walking. I was hoping to get back to jogging. He said no jogging until I'm at least -2.5 and keep up with what I'm doing. He also said the best thing I could do right now it hopping off a step, 15 times on each side, then 15 times landing on both feet. He said it will benefit my entire body. He also recommended doing the Mayo Clinic osteoporosis exercises.