I used to have back pain.can i use the stepper machine to lose weight?. or is it harmful for my back?

Yes: A stepper machine should be fine, especially if progressively increased in difficulty. For my patients with back/joint pain, i generally recommend avoiding impact activities such as running. Unfortunately, any activity has the potential for causing pain, but in most cases the pain does not mean that any damage is being done. See your physician if you are unable to exercise without severe pain.