Funkyjazzfunky, I used to have no problems with heavy basses. I used to weight train 4 times a week, benching around 250lb, 10 reps at 220 at weight of around 11 and a half stone (those were the days!). Strict curls with 58 lb dumbells etc. Then my back/neck problems started. Now wearing a heavy bass for any period of time causes spasm and pain throughout my pelvis, legs, back, neck and arms. A bass over 10lb causes my legs to go cold/numb (I assume the disc is compressing a nerve). I've actually had my right arm go into such spasm I could barely play at some gigs. I'm extremely grateful that I learned to play using a pick because if it was down to fingers I'd be in trouble. I have nerve root irritation in both lumbar and cervical spine, and any bass over 8 lbs causes me some problems. 10 is the absolute limit. My problems with my Alembic are well documented, and although I'm getting by at the moment, to be honest I play it as little as possible standing up. I now go to the gym again, and do lots of stretching and some Pilates and yoga exercises but to be honest the problems, while varying from day to day, are not going away. Be grateful that your back is still good and make sure you try & keep it that way!