I try it for a week just for fun . just like any-other sport equipment , you just have to keep up with it and have patience . I lose a inch off my arm in 7 day -lrb- i have the measure tape to prove it -rrb- . my arm be definitely tighter . it be a ok equipment , but i think i will stick to the traditional dumbbell ; maybe once in a while , i will switch to the shake-weight -lrb- since it be not refundable -rrb- . -lrb-  _  -rrb- \*