So why does the weight of a bass matter and why does heavier basses contribute to back pain? With perfect posture alignment gravity presses down on your body, the weight goes through the spine, hips, legs and feet to the ground with little damaging load placed on any of these joints, the spine being the most vulnerable. Now add 8-10lbs, 10 -14 " from your spine. The back muscles contract to offset the weight in the front, so now that 10lb bass creates about 70, 80, 100 +- lbs of compressive load on the lumbar spinal discs L5/S1 being the most common site of disc problems. Play for a few hours and those back muscles fatigue generating chemicals that irritate your nerves along with all that compression on the spinal discs drives the fluid from them leaving them compressed and vulnerable to tearing, rupture, herniation. Now do this everyday, several times a day. Add to this working at a computer all day slumped while you sit, slumping while watching TV and driving. This is the basic back injury scenario. Then if we add an over weight, very large bellied person with poor posture and weak back muscles, abs and hips you've got thousands of pounds of compressive load placed on a spine with poor alignment. Then to complicate matters you have a bass guitar where the neck is a long lever arm with heavy tuners (Fender basses) placed 24-32 inches from your spine. The load of the bass plus the weight of cantilevered neck is borne on one shoulder, the left one if you are a right handed player, as well as the opposite side low back - the right side if you are a right handed player. The muscles on the side of the back contract to keep you from falling sideways or you have to contract them to hold up a heavy neck w/neck dive. So now we compression on the lumbar spine in 2 angles/planes as well as pressure on the shoulder. What holds your shoulder up are muscles that originate on your cervical spine - just like the support wires on a suspension bridge. The whole fatigue, compression scenario that happens in the low back will also happen in the neck/cervical spine. The neck problems will overlap with shoulder problems such as rotator cuff issues, carpal tunnel, tennis elbow, tendonitis etc. In the arm/shoulder we have not only compressive type injury but repetitive strain injury from long hours holding a heavy bass with poor posture. I could keep going