Recently I heard, 'Your waist isn't a hinge. But pelvis is.'. So I looked at myself while playing with bokken and jo. (and some basic kamae too..) So, I found out that my waist area is too much pulled back along the back foot while my belly is pushed front along the extended arms or weapons. Read the following article.
http://www.fightingarts.com/content01/mechanics.shtml