The shake weight is a modified dumbbell that oscillates, supposedly increasing the effects of exercise. It was initially supposed to be for women only but now has both a male and female versioin. As per press release "Based on groundbreaking workout technology called Dynamic Inertia, which engages the muscles and arms, shoulders and chest in an entirely new fashipn, the Shake Weight increases upper body muscle activity by more than 300% compared to traditional free weights."

It gained popularity because its use involves pumping a phallic object.