I was thinking along these lines in your other thread. Almost posted, but it seemed you wanted a quicker fix, and increasing your strength could take some time.

I' d recommend some basic push ups, taking your time and going slow, to really isolate and work the muscles. I' d also do some weighted rows to build your upper back musculature. Do you have any or access to free weights or machines? If not, take a strong broom handle or piece of pipe. Put it between two stable items, such as a chair or saw horses, something that will be off the floor about 3 feet or so. Lie on your back, and grasp the bar with your palms facing your head and with your hands shoulder width apart. Pull yourself up, concentrating on using your upper back muscles.

These two moves should give you additional upper body strength. Try to do 2-3 sets of 10 or as many as you can do, going slow and controlled, and allow yourself a day of rest in between and the weekends off.

Good Luck.