The Shake Weight, a plastic dumbbell, weighs 2.5 pounds. It uses vibration technology, with spring-loaded weights on each end. The vibration is supposed to tone muscles in the arms, shoulders and chest in workouts lasting just six minutes.

Doesn't Produce Muscles

The Shake Weight does not produce muscle definition, according to the American Council on Exercise. It’s designed to provide high repetitions using a low weight, but the way to gain muscle definition is to use heavy weights with fewer repetitions.

May Offer Some Toning

Exercise professor Daniel Cipriani told the "Los Angeles Times" that people new to exercise would probably see some toning results. But people who strength train regularly probably won't. A better way to get muscle definition would be to work out with regular weights for 30 minutes.