Anyone who has been doing bench press in some variation will have had or still suffer from shoulder pain. Usually around the anterior deltoid (front shoulder) or impingement in the rotator cuff area. Though you would think otherwise the flat bench press tends to irritate the shoulder more than the overhead press. This is because the flat bench utilises the anterior deltoid heavily, especially with a medium to narrow grip, developing mainly the front part of the shoulder. Whereas the overhead press (performed correctly) develops the shoulder as a whole.
Most bodybuilders believe that the chest should be worked at all angles and that decline is for the lower chest only. In fact during EMG studies it has been shown that the decline bench press (at a minimal angle i.e 15-20 degrees) actually activates more total chest muscle than other angles. Not only that, but there is a lot less pressure on the anterior deltoid seriously reducing chance of injury and less irritation for already damaged shoulders. Many of the biggest names (and bodies!) in bodybuilding – Yates, Coleman & Cutler to name a few, swear by the decline bench and use it as a main stay of their training, this should make it definitely worth considering if mass is your goal.
One of the things I particularly like about the decline bench is that it feels so much better, the angle feels more natural (it resembles the movement the pectoral muscles are mainly responsible for) and certainly for me, I am more aware of my chest in the movement and so find it easier to focus on the lift rather than the pain in my shoulders!! You can also move more weight in a decline position, increasing your strength and confidence under the bar, which can then help you past sticking points when you return to flat benching.
If you haven’t tried it before (or even if you have), replace your flat bench with it for a while. When you reach a plateau swap it back out again and see how it has helped your strength come along, as well as your physique! Just be sure to have a spotter to hand as any bench, and worse case, dare I say it? use a smith machine for safety.