This is used to develop the traps and will isolate the traps.
Begin by standing with a dumbbell in each hand at your side. Next, lift the dumbbells by raising your shoulders into a shrug position. You should try to touch your ears with the top of your shoulder. Hold the contraction at the top for a second and then lower the weight.
Many people use weightlifting straps, because your forearms will usually drop the weight before your traps are tired. You can use heavy loads for this movement, and should be careful not to strain your neck or back. Some people rotate the shoulders back as they shrug the weight, but this puts a lot of stress on the rotator cuffs since you are lifting heavy loads.
This same exercise can be performed with a barbell or also on a cable machine. Also, you can use a neutral grip (palms facing each other) or a double overhand grip (palms facing your body).