Is cardio, e.g threadmill a good butt work out? Does it stress the glutes enough to *tone* them? Also, I've seen this guy doing cardio holding low weight dumbells, what would the benefit of that be?
losing bodyfat by doing the treadmill will tone them,but to target them you want to do squats,rev hypers,legpressesetc,...your leg exercises will involve your glutes.......