I be very skeptical before buy this . I have be work out use standard dumbell but never be able to get a clear definition on my arm . I buy this and after 2 week , I can see my triceps come out of under the layesr of fat . I always have a challenge with biceps show up . . but if I keep work relegiously , I be sure I will see some bicep muscle in a couple month . this be much better than dumb bell and all the curl I have be do . effective product .