I used to be able to do back extensions well on the chair but can't no longer. It just brings too much pain. I pushed it yesterday cause I haven't done them in awhile and ended up having severe lower back pain. It felt like my whole lower back cramped. I couldn't even run the pain was so severe. I haven't been able to get much more then 15 reps at a time and been trying this for months. Looks like I'll just have to give it up cause it's not helping. Deads and different type of core work seems to do fine.. just wondering if it's not in your routine and if you believe it's not necessary.