Start: Grab the barbell with a full, overhand grip that's just narrower than shoulder width. Stand, or sit on the end of a bench. Hold the bar over your head with your arms straight but your elbows unlocked. Your upper arms should be just outside your ears.
Finish: Bend your elbows and slowly lower the bar toward the back of your neck. Stop when your forearms are just past parallel to the floor. Pause, then press back up to the starting position throughout the exercise.