DON'T WORRY, it's not me being injured again, lol.
My fiance has the most horrible posture, like a sack of potatoes. He's unable to keep his shoulders back and back straight while leaning forward. He says he can't breathe if he tries to stay straight. This worries me of course, since I don't want to do anything that will cause him to get injured. We did stifflegged deadlifts yesterday and he said he felt it only in his lower back and calves, not the back of his legs. The same goes for rear lateral raises, tricep kickbacks, more or less anything where you lean forward. He starts shrugging his shoulders and arching his upper back.
What should I do? What exercises should we do to strengthen his lower back, which I think is the root of the problem. Or might it be his pecs are too tight? He has a very physical job so he's got a strong upper body, but his lower back is weak.