Chest
Two heads, one continuous muscle, and why 'upper chest' and 'lower chest' need different equipment to train properly.
2 min read
Function
Pectoralis major has two heads with genuinely different origins: the clavicular head ("upper chest") originates at the collarbone, the sternal head ("lower/mid chest") originates at the sternum. Both converge on the same insertion at the humerus, and both adduct the arm (bring it across the body) and internally rotate the shoulder. The clavicular head additionally assists shoulder flexion — raising the arm forward and up — which the sternal head does not do.
Pectoralis minor sits underneath, originates at the 3rd–5th ribs, and inserts at the coracoid process. It is a minor stabiliser of the scapula, not a meaningful hypertrophy target.
Why the two heads need different angles
Because the clavicular head assists shoulder flexion and the sternal head does not, the incline angle of a press directly changes which head is doing more of the work. An incline press (30–45°) recruits the clavicular fibres more heavily, because the movement path more closely matches that head's own line of pull. A flat or slightly-declined press biases the sternal head.
This is not folklore — it follows directly from the two heads having different lines of action relative to the shoulder joint, which is standard biomechanics.
The stretch problem with barbells specifically
A barbell's fixed bar path caps how deep the bottom position can go — the bar stops at the chest. Dumbbells, cables and machines with a genuine arc can descend further, loading the chest at a longer, more stretched position at the bottom, which is where mechanical tension on the fibres is highest.
This is why a deep dumbbell press or a low-to-high cable fly earns a place in the programs on this site rather than being treated as a lesser substitute for the barbell version — for the stretch specifically, it is the better tool.
Exercise selection
| Exercise | Head bias | Range advantage |
|---|---|---|
| Incline press (30–45°) | Clavicular ("upper") | Depends on implement |
| Flat/decline press | Sternal ("lower/mid") | Depends on implement |
| Dumbbell press (either angle) | As above | Deeper stretch than barbell |
| Cable fly, low-to-high | Clavicular | Constant tension, genuine stretch throughout |
| Cable fly, high-to-low | Sternal | Constant tension, genuine stretch throughout |
| Dip | Sternal, lower fibres | Real stretch if depth allows; loads triceps and anterior delt too |
Source tier: the two-head anatomy and their distinct actions are standard anatomical fact. The angle-to-head-bias link follows directly from moment-arm geometry — well-supported biomechanics, not speculative.
Up next
Back — lats
The muscle that is longest overhead, trained by most programs in its shortest position.
2 min