I had a lot of issues around the type of pain you described (pain walking extended distances and it getting better if I lean forward). My MRIs often showed some lumbar stenosis but my rheumatologist said that some degeneration in the spine is normal in all of us as we get older and mine wasn't that significant. I dealt with by getting my weight down to a healthier weight. That being said, it helped the stenosis pain but the AS flares aren't helped by losing weight.

Male, early 50s, Dx AS+ 1991, HLA B27+, Tylenol 3 PRN for flares. Off NSAIDs due to stomach issues. Considering a biologic. SI and thoracic involvement and costochondritis. Many bouts of uveitis. Small bowel issues, anemia.