Lie supine on a bench with a pair of dumbbells pressed up above you and the palms facing each other. Bend the elbows and allow them to move back slightly to bring the dumbbells to the top of the head. Keeping the elbows from flaring out and the upper arms slightly behind vertical to maintain tension through the entire motion, extend the elbows into full lockout, then lower again under control.
 
Purpose
The skullcrusher trains the triceps and can be loaded heavily.
 
Programming
Generally sets of 6-15 reps are appropriate.
 
Variations
Dumbbell skullcrushers can be done with the hands in any position, from supinated, neutral and pronated, or done starting in one and rotating to another (eg starting neutral and pronating during extension). They can also be done on an incline bench.