first I want to address the guy that give low rating . if you can not shake this little 5lb weight , then you be very weak , and need it more then any one . if you be weak , it do make it awkward to use at first . that because you not use to it yet ... duh ? do you expect to be a pro the first time you use it ? do you expect to look like the guy on tv after 1 day ? another guy be surprise to find out you have to shake it ? ok that all I will say on that ... I think it speak for it self . now for review : I have be work out since I be in weight training class in high school , I be 37 now . this weight do perform exactly as advertise . I be pleasantly surprise to find this little 5lb weight can make I break a sweat and feel the burn after only a few min of use . you will use and build fast twitch white muscle from the short burst of movement , and you will also build slow twitch red muscle from the hundred of muscle contraction do in just a couple minute . fast twitch muscle be tight and compact , slow twitch be large bulk of the muscle for size and endurance . I can see how this will bennifit both . I do not know if you will build raw power with this , but you will most certainly burn calorie , lean muscle , get rip , and even some bulk after long term use . -lrb- natural look bulk , not wrestler look bulk . one thing people must realize . the only way to look like the guy on tv be many many year of very hard work , and a strict diet . -lrb- 5-10 year -rrb- it be a shake weight , not a magic wand . I recommend this for any one