I don't know... Occam's Razor: 3 bikes... few of us buy 3 bikes all at once. How long has this back pain been an issue? Shouldn't be that hard to figure out which bike is the problem... IF a bike is the problem at all. I'm not a doctor, but it wouldn't be my suspicion that the problem needs surgery unless there has been some kind of trauma. Has there? I mean there is no mention of such. That is likely why the doctor prescribed exercises. Which ones? Is the o.p. doing them correctly? Did the doctor suggest Planks? Start planking right now. Work up to a minute. Do a couple every day. My wife took my advice and thanks me every now and then . She makes me do them with her, and being a more is better kind of gal we do 2min planks about every morning. Some people do them in sets. 1min plank, 1min rest, 1min plank, 1min rest, etc. - 3 to 5 sets. Again, I'm not a doctor but I guarantee results. Doctors don't know everything. I consider the "see a doctor" advice to be laziness. It isn't much better than no advice at all. Instead I would advise the o.p. to find out as much as they can about the causes of back pain and the treatments, as is possible. Google is great for this. I mean... unsaid so far is the o.p.'s health history. It is entirely possible that with scant insight into key health indicators, that their present back pain could have been predicted. Water under the bridge. Plank o.p. and thank me later.