I am 16 months post S1-L4 fusion. Like you I had isthmic spondylolisthesis due to an old football injury 18 years ago. I wrestled with back pain starting at 22 that progressivily got worse every year until at age 39 I couldn't move because I was in so much pain. I elected to have the surgery and even though the first 3 to 6 months were difficult I would do it again and would have done it at a younger age. I started playing golf at 7 months and have not stop since. Lateral movement doesn't seem to be effected too much but bending up and down is somewhat effected. I spent many extra hours rehabbing to gain back as much flexibility as possible. I can touch the tops of my shoes when I bend over and don't try much more after that. Went bowling last night and noticed that I couldn't bend quite like I could before, but I was playing without pain. As a matter of fact I can say that I am virtually painfree. My Dr. removed all physical restrictions on me during my 1 year checkup. I'm not flexible like I was when I was 18 but I'd say I'm at about 88%. My understanding from my Dr. is that for every disk that is fused you lose 6 degrees of flexibility. I had two disks fused and it has not effected my activities since about 9 months post op. Hope this helps.