Especially if you're sitting at a computer all day. Gotta strengthen that back to keep your shoulders from curling in too much. Then everything starts to go wrong =/
If the pushup is done properly the shoulders should be in the correct alignment. I do agree that I would add pull ups and then some band exercises to make sure the shoulders are kept in proper form.
The other thing I would add is core work, and not just strengthening, but also correcting posture (pelvic tilt).
All of the above just scratches the surface on how to correct the bad things that happen to your posture when sitting at a desk for hours each day.
Well, it's beyond just shoulder alignment during the exercise. Your shoulder and upper back posture is pretty much dependent on the interplay between your pects (chest), upper and lower trap, and lat muscles. If you start getting a severe strength imbalance between these muscle groups, you can start getting posture problems. That's in the long term. There's also short term stuff with your sore muscles avoiding stretching, resulting in some curling in.
All of this only gets worse if your typing at a keyboard because of the 'natural' position you assume.
It leads to terrible neck problems, like the pinched nerve I have. It causes significant discomfort, then intense pain and, eventually, numbness in one or both arms. Recovery is on the order of several years (and counting).
