I just flew into lovely (term used loosely) Baltimore. The approach was so bumpy I thought I was Kilimanjaro Safaris. That got me thinking. I have a bad back. I had back surgery when I was 17 and since then it hasn't taken much to put my back out.
As you know many rides in Disney World warn that people with back problems should not ride the ride. I've been on everything and have found that some are rough on the back while others are fine. What rides would you really warn someone with a bad back about?
These are the ones that made my short list.
Kilimanjaro Safaris is bad. Really bad, and there is no good reason for it. They thought making the road really bumpy would mimic a real safari. What it did was make it hard take pictures and make it brutal for anyone with a bad back.
Space Mountain is rough but any coaster built that long ago is rough. Space Mountain was built just before computers became common place in roller coaster design.
Dinosaur might be the worst of any ride in Disney World. It's in the dark so you have no idea where you are going or what direction you are going in. This ride will whip you.
Parts of Test Track will rough you up. For the most part on the rough road section is bad. The rest isn't too bad.
Star Tours - enough said.
Stitch's Great Escape is so bad it hurts. Doesn't really hurt you back, just your head.
I did not put Big Thunder Mountain, Rocking Roller Coaster, or Everest on my list because they tend to be some smooth that they don't bother me at all. They are the product of the computer age. Big Thunder was one of the first and it shows.
Everyone is different. I've put my back out bending over but have had no problem picking up my 80 pound dog. So that leads to another issue. G force rides. For some people these are a killer for others it's no problem.
Mission Space - This doesn't bother my but it will compress your spine. If that tends to bother you avoid this ride.
Everest - Some parts late in the ride pull some positive G forces which could bother people.
Tower of Terror - In this case it's the G forces at the bottom of the drops. They will compress your spine.