Purpose of Exercise: To isolate and work the rear head of the deltoids. By bending over while executing a Lateral, You force the posterior head of the deltoid to work more directly. Doing them seated allows you to do a stricter movement than when standing.
Sit on the end of a bench, knees together, and take a dumbbell in each hand. Bend forward from the waist and bring the dumbbells together behind your calves. Turn your hands so that your palms face one another. Keeping your body steady, lift the weighs out to either side, turning your wrists so that the thumbs are lower than the little fingers. Be careful not to lift up your body as you lift up the weight. With your arms just slightly bent, lift the dumbbells to a point just higher than your head, then, keeping your knees together, lower them again slowly behind your calves, resisting all the way down. Try not to cheat dong this exercise. Also be sure you are lifting straight out to either side; the tendency doing this exercise is to let the weights drift back behind your shoulders.