I have been crossfitting for a few years but seem to have not fixed a weakness in my lower back. My coach is not sure what to do to fix this issue. My upper back stays strong and extended all the way through the lift, but my lower back has increasing arch as weight and reps increase. I stay tight in OLY and power lifting because of the lower weights, but the issue seems to resent itself as I get heavy and increase the reps. The effort posted is 3 reps at 315#. I have pulled 5 reps at 335, but this issue is always there. My 1RM is 375, but I wasn't being coachd at the time I pulled it. I do not ever have any alarming pain, but this problem bothers my coach and I want to fix it to avoid getting hurt or stunting progress. Any advice or help would be great. I have wondered if wearing a belt, doing RDLs or good mornings, or anything else might help. Thanks in advance.