Cycling can be bad for your back but it depends upon your position on the bike. I had problems with my lower back but I cycle regularly on a road bike and I haven't had any issues for a long time. One thing is that the lower handlebars on a road bike takes weight off the lower back and onto the shoulders and arms. It also makes you build up your core which is one of the main causes of back pain. Too low or too stretched out is not good. But if your position is right theres no problem.