Sergio had such full bicep he could not contract them in a double bicep pose, forearms hit the biceps before full contraction. Probably the most genetically gifted person to this date.
Don't forget the fact that the Antagonist (Triceps) also inhibited a full biceps contraction. I mean, look at the size of his Tri's proportionately to his Bi's.
Trust me when I say, most of your Antagonist groups can inhibit the full contraction of the Agonist. This is why I usually throw one quick set in for the opposite side before I hit my muscles of focus.
Back before Chest, Tris before Bis, vice versa... Hams before Quads... you get the picture.