Muscle Group: Forearms
Grab a pair of dumbbells, and lie face down on a high bench. If you do not have a high bench, simply incline it ever so slightly, but keep it as flat as possible.
Now allow the dumbbells to hang in front of you, with your palms facing downward. Moving nothing but your wrists, curl the dumbbells simultaneously upward until you get a peak contraction in your forearm extensors. Pause for a peak contraction and then lower slowly under control.