I don't have a bad back, but work keeps me away from the gun safe for extended periods of time. I always get sore when I start shooting again. I shoot high power and not f-class, but I participate in the 600 x3 matches that we have. At the end of the day I am usually uncomfortable. The point is dry fire and work on your NPA at home to build up to three strings of shooting prone. ETA: If the folks where you shoot are anything like my club they will bend over backwards to accommodate you.