useless . very disappointing product . I try to like it , but find that it do absolutely nothing for someone like I who do even simple exercise on my arm five day a week . I use it several time figure I must be do something wrong , but even after get the hang of it , my muscle do not feel like they be work any differently or harder than exercise such as bicep curl or tricep kickback with light hand weight . this be a waste of money and I throw it away .