The sternal head runs from your sternum, goes across your chest and inserts at your humerus, so it’s a quite larger than the clavicular head and represents the lower portion of the pectoralis major muscle. While the clavicular head assists in shoulder flexion, the sternal head assist in shoulder extension.
Since extension of the arm by the sternal head can only occur if the arm is flexed, the sternal head cannot hyperextend the arm. Its second function is to flex and adduct the upper arm when the upper arm is slightly parallel to the ground. To target the sternal head, you need to perform decline versions of chest exercises.
Here are two great moves:
Decline Bench Press
During a decline bench press, your body lies on a slope and your legs are higher than your head so you need to be very cautious if you go heavy on this one – it’s best to use a spotter to prevent the weight from dropping on you. Take an overhand grip on the bar with your hands a little bit wider than shoulder width apart. The decline bench press also works your triceps and anterior deltoid muscles.
High Pulley Cable Crossovers
As long as you use proper form, full range of motion and weight you can handle, cable crossovers will give you a great pec workout. The constant tension provided by the cables creates a completely different stimulus than the tension produced by free weights, and you should take advantage of this in your routine.
Using high pulley machines will allow you to train your lower chest more effectively, while the clavicular head and the pectoralis minor will assist the movement. To activate your sternal head even better, make sure to turn your palms upward (supination) at the end of the movement.
This is the most overlooked part of the pectoralis major and most chest training articles don’t even mention it. It originates at the external fascia of the external oblique muscle, called the rectus sheath, runs up and across the bottom portion of the chest and inserts at the humerus.
Although from a technical standpoint it’s the abdominal head that makes up the lower portion of the pectoralis major, from an outside view it looks like both the sternal and abdominal heads cover the lower chest region, which the much larger sternal head extending up to the middle region of the chest. This head can be ridiculously hard to optimally contract and elongate, even though most exercises for the sternal head will work it to some degree.
Still, there is one exercise that will help you effectively target the abdominal head:
Years ago, dumbbell pullovers were known as the most important exercise for developing a deep chest. Today they’re largely forgotten, thanks to slightly paranoid exercise scientists who declared them as the ultimate shoulder killers, but their ability to help you build a full, majestic chest remains intact. Dumbbell pullovers primarily train your abdominal head, serratus anterior and latissimus dorsi.
To begin, lie crossways on a flat bench with only your shoulders sitting on the bench while your hips are below it. Your legs should be bent with feet firmly placed on the floor. Grasp a relatively light dumbbell with both of your hands and hold it straight over your chest at arm length with arms fully extended, while both of your palms should be pressing against the underside of one of the sides of the dumbbell. In the correct stance, one side of the dumbbell will be pointing towards your chest and the other end directly away from your chest.
Keeping your arms straight, slowly lower the weight in an arc behind your head, focusing on the muscles you feel stretching throughout the upper body. Go as far as comfortable while maintaining almost-locked arms, then bring the dumbbell back to the starting position above your chest.
2. PECTORALIS MINOR
This is a small, triangular muscle that lies deep underneath the pectoralis major. It originates from the anterior surface of the 3-5 ribs and inserts on the coracoid process of the scapula; its main functions are depression and downward rotation of the scapula. Luckily, you don’t need to perform any specific exercises to develop the pectoralis minor – most regular chest exercises will adequately stimulate it.
3. SERRATUS ANTERIOR
The serratus anterior is a group of muscles that originates on the upper eight or nine ribs and inserts on the anterior part of the medial border of the scapula and some of its many functions include abduction and elevation of the scapula. Although it’s a very underrated muscle (some don’t even consider it a part of the chest area) and you’ll rarely hear someone say “I’m looking to isolate my serratus anterior”, adding a couple of exercises that emphasize this muscle group to your routine will work wonders for your aesthetics and shoulder health.
You can best target it with push-up variants and pullovers.
Regular push-ups engage the serratus anterior, pectoralis major, anterior deltoids and triceps brachii, so there’s a lot to be gained from performing them regularly. But to achieve greater overload on the chest muscles and thus stimulate more growth, you need to go for the weighted variant (assuming you’ve already mastered the regular push-up). Begin with a weight plate, sandbag or weighted vest that equals 10% of your body weight, then as you progress you can continue adding weight in increments of 5 to 10%.
Optimal Rep Range
According to scientific studies, muscle fiber composition of the chest is 60% fast-twitch and 40% slow-twitch fibers. Fast-twitch muscle fibers are used in explosive bursts of power, for example when working with heavy loads or during sprinting, while slow-twitch fibers enable long endurance feats such as high-rep sets with light loads or distance running.
Therefore, in order to achieve maximum gains, you need to utilize different rep ranges that will activate both types of muscle fibers: use heavy-load, low-rep training as your primary style but also throw in a couple of sets with lighter loads for more reps.
Finally, don’t forget to train smart, then train hard. Good luck!