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.
Keeping your upper arms vertical, inhale as you flex your elbows and lower the barbell toward your face in a smooth semicircular motion.
Exhale as you extend your elbows so that your forearms return to the vertical 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 (see video), 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 vertical so that the barbell descends and ascends in a semicircular motion, you can allow your upper arms to tilt forward as you flex your elbows and then return to the vertical position as you extend your elbows. This will allow the barbell to descend and ascend in a vertical motion.
Using an EZ-curl bar can reduce the pressure on your wrists.