Most of us have an unhealthy, abusive relationship with the bench press. You love it and you dote on it, placing it first in your workouts and visiting it every week. It's your most favorite exercise and, if given the choice, you'd forsake all other exercises for just one more night with it.
But the ungrateful bastard doesn't like you at all. For all your devotion, your max still sucks and your shoulders hurt. But, like any fool in love, you can't help yourself, and you can't live without it and the way it makes you feel.
While the bench press is widely regarded as probably the most dangerous free-weight exercise, I haven't completely forsaken it, and I'm sure you haven't either, so fools like us will have to make the best of it. To that end, I'll offer some tips to keep your shoulders healthy and strong so that you can bench for many happy years to come.
Treat the subscap
The subscapularis muscle is part of your rotator cuff. It rotates your upper arm bone forward and helps in pulling it closer to your body (the same motions that take place during a bench press). Lots of benching without an equal amount of pulling motions to balance this action leads to the subscap getting overworked. According to Dr. Ken Kinakin, author of Optimal Muscle Training (published by Human Kinetics), the subscap prevents your upper arm bone (humerus) from moving forward when the bar is at your chest, and this causes the pain you feel in the front of your shoulder after a heavy set. This undue stress creates scar tissue in the subscap over time, and weakens it.
Fix it by doing cable internal rotations. Make sure the cable is parallel to the floor and in line with your forearm when it's bent 90 degrees. Pin your upper arm to your side and rotate your arm in as far as it goes or until it touches your torso. Do 2-3 sets of 15 on each side. See a video of it here.
Treat the teres minor
Another rotator cuff muscle, this guy rotates the humerus away from and behind the body. In other words, it has pretty much the opposite function of the subscap. If too much benching has left your shoulders rounded and your arms unable to reach behind your back to the opposite shoulder blade, teres minor weakness is part of the problem. Set up as you did for the internal rotation for the subscap but have the cable start in front of your body and rotate your arm away from your side. Again, 2-3 sets of 15.
Think of these moves as a sort of couples' counseling session. They won't solve all your problems, but they'll make the bench press easier to live with.