Back And Hand

I read a lot about proper sitting position to avoid back pain,I talked to both doctors and read Thomas Mark's book-two different attitudes about sitting:many doctors say that it is critical to work on stronger back muscles (and sitting in a proper position), in order not to have back pain,yet,in Marks's book ,he just talks about proper bone alignment. What do you recommend? is it necessary to work on stronger back muscles and for how long is it possible to sit pain-free without getting up? -I once had a teacher who talked about changing hand position (lower/higher) in a repetitive motion (like the tremolo in Beethoven's Pathetic sonata) ,to avoid pain in the hand,in addition also he talked about "saving" the hand's power in a long and techniquely difficult piece and knowing when not to give all of the hand's power in playing loudly. is there such a thing? Thank you in advanced

Proper bone alignment in the back allows the muscles to power the back elastically instead of with tension. It is not clear what the doctors mean. They may mean, develop the back's capacity for elastic, well-organized movement. They may mean just strengthening muscles. Strengthening muscles could inadvertently lead to a good result but could also lead to more strain, tension and an even worse situation. Aligning the bones will work if you don't hold them in the new alignment. If they are held, they can't move, so you're no further ahead. We need a much more accurate language to describe these things - which is why I am busy writing books about it. AFF