Your chest muscles, called the pectorals, pull your arms and shoulders across the front of your body. 1. Flat barbell or dumbbell bench presses tone and strengthen your whole chest. 2. Dumbbell flys and cable crossovers help define your chest muscles. 3. Use a weight that allows you to complete two to three sets of each exercise for eight to 12 repetitions. These exercises also work your shoulders and arms and should be completed before other exercises.