I buy this item because the physics of it make complete sense to I . I just finish my second time use the shake weight . the first time be right after I open it , and I try the various workout show . it be not too bad . the second time I use it after my daily routine consist of ab work out , push up , dip and pull up . it usually take I 5-10 minute . once I finish , it be 3:56 . I decide to wait until 3:57 so that I could time myself for one minute . I have never want 3:58 to come so badly . it burn not only in my arm but in my ab as well . if use on its own it may not be as effective , however it be a great finishing touch on my workout today . P.S. . you have to be SUPER FRAIL to use the women product . it be half the weight of the man 's . man will build muscle and in turn need to move up in weight . buy the man 's version .