Originally Posted by
Steamer
Apples and oranges. Your back is fully supported on a recumbent.
I don't think I have ever heard of someone's pelvis or spine being permanently deformed by a seat (of any type) they sit on.
Core work, stretching, etc. is a virtue, regardless of what kind of bike your ride, and what shape the seats are you sit on. Riding a bike is riding a bike. It's not exercise for your back. Exercise your back using back exercises.
I'm not concerned that the act of resting my back on the seat would hurt it, I'm concerned that while pushing hard on the pedals it would put a lot of stress on the lower back in that position. You wouln't round your pelvis/lower back while doing reps on a leg press machine, so I don't see what would make the recumbent different from that.