I buy the man 's Shake Weight , read the instruction and watch the enclosed dvd . I have also watch the ad online . the product in the ad and the one you buy be totally different . absolutely do not buy it . you can get the same benefit and perhaps better by shake any dumbell you exercise with . the spring on each end only react once with every shake you make yourself . the one in the ad vibrate many time for each shake you make and even sound like it have a small dynamo in it and probably do . it be a exercise scam , do not be fool !