at first i be very skeptical . be in gym i say no way a little dumbbell can do all they claim . it do but the rip part that be good genetics . i have be work out over ten year i be no slouch but the shakweight be hard i have trouble do twenty seconds . some review say it be hard to get it shake that be the point if it be easy you muscle would get no challenge . i personally work out a hour and a half a day that be not for everyone but i do recommend additional exercise it be not a magic weight . but very good addition . try it i do and i be happy even with all the negativity .