Cardio: You need to do at least 15 minutes for a proper response to aerobic activity. During the anticipatory phase your heart rate will increase and blood vessels will dialate, then the steady phase kicks in allowing your heart rate to stabilize and muscles to become more efficient in O2 exchange, and last the final phase where blood is shunted to the muscles for increased endurance...this is when you sweat and your muscles become even more efficient. For bulking cycles or any other cycle... cardio needs to be incorporated!