this shake weight be power by ... you . I must have conveniently block it out of my brain while watch the infomercial . seriously think you turn it on and it shake ... and you use you muscle to hold it in place , thereby burn the fat . NOT SO . you shake this thing and geesus , I can barely make it to the 2 min mark . hit my face a couple of time . and then shake it from side to side - uh , that be IMPOSSIBLE . it be not that it take up so much energy I cant do it , but i cant even START to shake it from side to side -lrb- hold it like a steer wheel and shake leave to right -rrb- . I be 34b in chest , 5 ' 3 , 118lb and workout my arm 3-4x a week . I seroiusly can not see how a woman w \/ a bigger chest can manage this little shakeweight . I keep it for 3 day , it go back . do not waste you money ... weight be so much better ... this thing be so tiring by the time i even complete the 1st minute , im do . those woman on tv use the shake weight , must have have major practice doin it , causeit not even as close to be as ez as it look .