jhov is correct, however, you can still find exercises that give you a tighter contraction over all. Think of it like this... You do concentration curls for biceps and get a strong contraction but a weak stretch.. (if you do it right), then you do incline dumbell curls, where you get a GREAT stretch, but average contraction...
Likewise with chest. I find that medium grip flat bench presses cause a greater contraction in the inner chest area. And doing cable crossovers utilizing only the last 1/3 of the movement (no need to stretch back) keeps the fibers fresh as you expand all possible energy on that contraction area.