kronk said:
By using only one arm (I guess I should have said one arm) you are better able to isolate the specific pec muscle. You will also depend much less on your deltoids and tris. This is also great if you have one pec that is lagging. This is the best excercise I have ever found for pecs. I usually do it as a finishing move, cause you cant do as much weight with one arm.
So do you hold on to both dumbells but only move one at a time?