madhatter131 saidCardio is important, so ideally you should do it. And, results depend on your fitness goals. If you want to build muscle, from all I've been able to study, keep a close eye on your heart rate. Once it gets up too high (like the HIIT), then you are burning less fat and more muscle. So, a brisk walk/slow jog for 15-20 min. is all you'd need for a solid cardio workout if you're trying to gain muscle mass.
I read the exact opposite, that HIIT was activating hormones that only burned fact and, even, that "sprinting in particular is known to raise hormone levels that encourage muscle growth – perfect for body builders and one of the principal reasons they use HIIT" (from http://www.thefatburner.net/articles/hiit.html
I also read this in the same article :
Cliff Baker saidIf you really want to burn very large amounts of calories, nothing beats an hour of any cardio exercise at medium intensity. Not relaxing, mind you – but sweating hard throughout. You can burn anywhere from 500 to 900 calories – depending on your weight – and this can be repeated 5 times per week giving you a total of 2,500 to 3,500 calories burned per week.
Contrast that to HIIT programs where even 2 sessions of 15 minutes per week at high intensity will only burn from 300 to 600 calories. Add this to the secondary effects and you still will not even get near the 2,500 mark. Increasing the number of HIIT sessions will help, but you still you’d probably need to do it every day which would increase your risk of injury and is not recommended.
So if your principal goal is to burn off large amounts of body fat, go with steady state cardio like brisk walking, using the elliptical machine and stationary bike or any other moderate intensity, long term aerobic activity.
However, if you want to increase muscle mass and don’t have problems keeping the fat off, HIIT may make sense - if you are a body builder, even more so.
Though, another article states that...
Jared ConleyThe factual part of this belief is that the longer you perform an aerobic activity, the more calories you will burn. Actually, your body will gain roughly 50 percent of its energy for this workout from your fat stores. Not considered, however, is that these long sessions also force the body into a catabolic state, where it will begin to eat its own muscle tissue for energy. So the end result is weight loss consisting of both fat and muscle. Good, but not ideal.
HIIT sessions, on the other hand, only consume 40 percent of their energy from fat stores, while participating in the workout. What this ignores is the fact that interval training raises your resting metabolic rate for up to 24 hours after finishing a HIIT session. Whereas aerobic activities burn fat for the duration of the workout, HIIT sessions burn fat for an entire day!
The bottom line is that HIIT sessions have been shown to be 200 percent to 900 percent more effective at burning fat than traditional cardio, depending on whose numbers you believe. But again, HIIT sessions also spare your muscle mass. They even help build muscle up. So not only are you burning more fat, but you're also building more muscle, which helps your body burn even more fat in the future. (http://ezinearticles.com/?Build-Muscle-Up-Fast-and-Burn-Fat-With-HIIT-Sessions&id=1591316)
Both make sense... So considering I wanna build muscle mass, but also lose the extra fat (I'm around 23% of adiposity right now, referring to my Weight Watchers balance (lol)), what should I do?