My first venture onto the forums! I have a lot of lower back pain, right down in the sacrum, which I think is originating from my SI joints. It started about six months ago, before I started regular exercise, but after a few weeks of using a recumbent exercise bike (pretty high resistance) it went away completely. Now that I've added in regular Pilates classes (3 a week) it's come back, as bad as ever. What should I do? I have no Pilates instructor in my area, so I can't consult anyone in real life. I am very loathe to cut back on the Pilates, it's my favourite form of exercise. I do have an office job, so I sit most of the time. I also have a very tight back and hamstrings. And I'm bottom heavy, so have to be very careful lowering my legs too far in exercises like the Hundred. Is it that? Or too much back extension work? Help!