If you want huge pecs you'll need to challenge all of your chest muscles. Before we let you in on the secret of how to build your chest, let's first go over some of the reasons why your chest might not be growing. For instance, if you're not using correct form or warming-up properly, you may struggle to pack on size. Growth struggles may also be caused by your technique. Pumping out fast reps is unlikely to be giving your chest the muscle-building stimulus it needs. ~ Berceste