If you want to develop deep definition between your pecs, go beyond the bench. Although bench presses are a great way to build size and strength in your chest, they don't activate the inner pectoral muscle fibers nearest the breastbone, which is what you need to do to really get that deep center line. For that, you need to add in exercises in which your arms cross the midline of your body, or at least meet in the center, including cable crossovers and cross-body cable presses.
Do these exercises after your bigger exercises like bench presses to really target and fatigue the inner pecs.
Cable Crossover High to Low
Cable crossovers are similar to dumbbell flyes, but they allow you to the flexibility to work your lower, middle and upper pecs in one exercise without having to change the incline of your bench. On the Built Lean website, strength and conditioning coach Marc Perry recommends using lighter weights and higher reps -- a minimum of 10 to 15 -- to really burn out the muscle. Each time through the exercise counts as three reps.
Position the cables of a cable machine at about shoulder level. Grasp a cable handle in either hand with your arms extended out to either side. Step forward far enough that you feel a stretch in your pecs when your arms are fully extended.
Bend your elbows slightly, and pull your shoulders back. With a slow and controlled motion, bring your hands together as you raise your arms up. Your biceps should be right in front of your face at the end of the movement. Return to your starting position with control.
Bring your hands together right in the center of your chest. Return to the starting position.
Bring your arms together in front of your thighs, then return to the starting position.
Cross-Body Cable Presses
This exercise is similar to cable crossovers, but involves pressing out and bringing the arm across the center line of the body. As a single joint, single-sided movement, you won't be able to use as much weight as you would in, say, a bench press. Use lighter weight and higher reps to burn out the muscles. ''
Stand perpendicular to the cable weight stack holding a cable handle in one hand with an underhand grip.
Position your arm out to your side at about a 45-degree angle with your torso and your elbow bent to almost 90 degrees. In this starting position, your hand will be around hip level.
With a slow and controlled motion, press your arm out away from you and slightly across the midline of your body, rotating your torso a few degrees and straightening your arm. At the end point of the exercise, your hand will be a little higher than face level. Slowly return to your starting position.