Position a loaded barbell by the head of a declined bench.
Lie supine (on your back) on the bench, making sure to hook your feet firmly under the foot pads.
Grasp the barbell using a close pronated (overhand) grip, and carefully lift it onto your chest.
Press the barbell up so that your arms are vertical.
Allow your arms to tilt backwards a little. (Note: This is not expressed in the illustration, in which the arms are kept vertical.)
Keeping your upper arms fixed, inhale as you flex your elbows and lower the barbell toward your face in a smooth semicircular motion.
Exhale as you extend your elbows until the barbell returns to the starting position.
Comments and tips
Keep your elbows tucked in.
Be careful with the decline skull crusher as it can be dangerous. Slow the movement down as the barbell nears your face.
This exercise is called a skull crusher because when performed on a flat bench, you lower the barbell to your forehead.
If you go heavy, have a spotter ready, who can also hand you the barbell when you lie down.
You can perform the decline skull crusher in a different way. Instead of keeping your upper arms fixed in a slightly backward-tilted position and lowering the barbell in a semicircular motion, you can start with your upper arms vertical and allow your upper arms to tilt forward as the barbell descends and return to vertical as the barbell ascends. This will allow the barbell to descend and ascend in a vertical motion.