For me a partial discectomy in 1995 alleviated the chronic debilitating pain; I'm left with some limitations and occasional mild pain. The difficult part was finding the limitations. I could never get a road bike fit that worked for anything over 15 miles.

I switched to a recumbent in about 2005 and never looked back. The last three years I've done long-distance riding culminating in Paris-Brest-Paris (1200 km).

Something you must keep in mind, particularly when you hear about people who ran a marathon a few weeks after back surgery, is that every spinal injury is unique. For some people, walking is therapeutic while for others it's excruciating. The same for cycling, sitting, lying down, etc.