If you want to have thicker, fuller looking pecs then you need to take your lower chest training more seriously. Let me show you how. So, the two primary functions of the lower chest are to bring your arms down to the sides and across the front of the body. Best exercises that include both of these actions are dips which also give you a deep stretch at the bottom and high to low cable flies that allow maximal contraction of the lower pecs. However, lower chest also performs shoulder extension. So for a fully rounded workout you want to throw in a classic pullover exercise as well.