Decline Barbell Bench Press

Trains the Abdominal Head.

How to do it

Set a decline bench so your head sits below your hips, and hook your legs under the pads at the top.
Lie back and take the bar with an overhand grip a little wider than your shoulders.
Set your shoulder blades back and down against the bench before you unrack.
Unrack the bar and hold it over your lower chest with straight arms.
Lower it to the base of your chest, keeping your elbows at roughly forty-five degrees from your body.
Press back up in a slight arc toward your shoulders, stopping short of locking the elbows hard.

Getting into position without help on a heavy set. The decline puts your head below your heart and the bar above your throat, and there is no way to sit up out of a failed repetition. A spotter is part of the setup here in a way it is not on a flat bench.
Lowering to the same point as a flat press. The decline changes where the bar meets the body — it comes down to the base of the chest, not the middle, and forcing it higher puts the shoulder in a position the angle was chosen to avoid.
Assuming it builds a separate lower chest. The fibres running from the ribs to the arm are best placed to do this angle, and they are part of the same pectoralis major as everything else. The angle shifts emphasis; it does not add a muscle.
Letting the head hang. Keeping the head against the pad stops the neck from bracing against the descent, which is where the strain lands when the position is uncomfortable.