I be unsure about purchase this product because of review and other comment . I go ahead and take a leap of faith . glad I do , this really work if you use it correctly . there be a lot of confusion out there that this item run on battery power ... this be not true !! you have to use you energy and muscle to make this work . it take awhile to work up to the full 6 minute , dont give up . I start out in 30 second interval until I could work myself up to minute . I could tell a difference in my arm within a couple week ... still have a while to go but between this item and the resistance band I feel like I be get a really nice workout on my arm .