your body will adjust to everything you do. So if you are a cardio whore and do it balls out year round then your body will adapt to it. That means when you go to cut down your body wont respond to the cardio because guess what? you have been doing it intensely all year so it doesnt shock the body. So you should cycle your cardio just like you cycle your diet and your training and your usage of gear. But I highly recommend doing cardio whether bulking or cutting. When bulking, doing cardio once a day, 5 days a week, for 45 minutes each session keeps your heart healthy and keeps the bodyfat from accumulating. When cutting down really step up the intensity and do 2 cardio sessions daily, 6 days a week, at a heartrate of around 135-170 (varying the intensity throughout the session). I always burn a minimum of 500 calories each cardio session. I can knock out 700 calories in 45 minutes. I have an exercise bike in my living room and although I piss my wife off every morning by getting up at 430am I find nothing more satisfying than a morning cardio session while watching UFC fights on my DVR recorder. Yeah doggy! (dont believe the myth that doing cardio will eat all of your muscle. Especially if you are eating right and using gear fuuuuughet about it. Your muscle will stay on your bones just fine) now if you are eating a ridiculously low amount of cals and doing shit loads of cardio and not "on cycle" then you can kiss your hard earned muscle goodbye. I like to say that Juicers can break a lot of rules because research involving muscle gain and muscle loss is 99.9999% completed using test subjects who arent on steroids.