Preventing osteoporosis: does exercising more prevent the formation of osteoporosis?

Osteoporosis: Yes, progressive exercise can slow down osteoporosis by virtue of wolff's law, which states that bone forms in relation to stress. If done without excessive loading, it will be safe and effective.

Yes: But only weight bearing exercises and things that stress the bone like jumping, lunges, walking with ankle weights or lifting weights etc will actually help to build bone. However, if you already are at risk for fractures you have to be careful doing some of these in order to avoid getting fracture.