When performing standing cable crunches I experience some lower back pain. It begins as soon as my lower back starts to round the slightest bit. I read Thib's description on the excercise and try to focus on keeping a straight lower back.
However, I do not achieve nearly the range of motion he seems to in his pictures. I am guessing that it is due to a need for more flexibility in my hamstrings. Could it also be due to a lack in lower back strength? I do posterior chain excercises with no problem though.
Also, I tried the excercise with very little weight (still experienced the same problems) in order to eliminate the possibility that I was using too much.