Shaking up the way you work out, the Shake Weight is a revolution in strength training. Boasting a legion of devotees who enthusiastically confirm the Shake Weight's claim that it shapes and tones the upper body, this product is hard to ignore. The way it works is this: a special pulsating dumbbell with the dynamic inertia technology increases upper body muscle activity by 300 percent compared to traditional weights as you shake the 5-lb. weight several different ways. This repetitive shaking stimulates muscle toning and adds shape to your upper arms, chest and shoulders.