When I do L-sits from a bar hanging, I can get my legs perpendicular to the ground but when I hold it I get pretty bad pains in the lower back. I tighten my abs as hard as possible and that doesnt help. Why do these affect my lower back so much, and how can I reduce the pain involved. Do I need to just keep working on them with bent legs to help strengthen my abs and back before I go back to the full version? Thanks