Start: Grab the barbell with a full, overhand grip that's just narrower than shoulder width. Lie on a bench holding the bar over your eyes with straight arms. Your upper arms aren't perpendicular to your torso in this position but this angle makes the exercise harder for your triceps and easier on your elbows.
Finish: Bend at your elbows as you lower the bar until it almost touches your head. Pause, then lift it back to the starting position. Keep your upper arms in the same position throughout the exercise.
Use an EZ-curl bar to do triceps extensions while lying with your head, neck, and shoulder blades in contact with a ball, your lower back off the ball, your feet shoulder-width apart, your hips parallel to the floor, and your knee bent 90 degrees.