I used to do a full body(excluding legs) workout alternating with a leg workout every day. My stepbrother has recently started coming with me to the gym but he tells me its better to isolate body parts per day ie. chest/tri's, bi's/upper back, sholders, legs. But my concern is, dosent it seem like too long an interval (3 days) before working out the same body part again, it seems not as productive, building muscle wise, as working out the whole upperbody every other day. So....am I wrong?