jay its technique sort of, when i use the pull down bar behin my head it gets so far down then my shoulder and back move,i can carry on but its my shoulers/arms im more using due to the angle of my back,, its a little like arching your back on a bench

but its like that with any weight,,, i go lighter and it dont happen but theres no resistance,, its as if i cant control my body

and cause of this my shoulders are getting bigger but my back sucks

lifting weights aint a issue, im one of the few people who can bench 2 plates each side all day, every day