I was bedridden from 01-03 with 2 badly torn lumbar disks. I've been improving ever since, and last summer i was able to ride across the country.
www.crazyguyonabike.com/doc/2391

My back likes my road bike more than my more-upright mountain bike. I think it's because when your leaning forward, your spine opens up, and your disks get more space, with little or no compression.