I have had a fusion in my lower back (2 lower vertebrae) and biking has been very good for me except for when I built a ss. That thing killed my back and I only rode it a couple times. If I ride my geared bikes it feels fine. In fact in the past if my back bothers me I jump on the bike and *poof* the pain is gone. It must stretch the muscles in your back or something. All I know is if I stay in good bike shape my back is good. Except for that blasted ss.