i've done all sort of experiments with this one...and personally i think its all about body composition...if u have excess fat, with decent muscle mass...u wont b as defined...if u have hardly any fat but hardly any mass...same principle... the way i see it u need the mass first ( Heavy weights, low reps) to get your muscles larger, then switch your routine up after you've gained enough mass( light weights, higher reps + crazy cardio(HIIT) to burn off extra fat