There is a HUGE debate on LISS vs HIIT. I myself do both for optimal results! This is what I have to offer on the subject. I've been hearing a lot of arguing about which one is better - High Intensity Interval Training (HIIT) or Low Intensity Steady State (LISS). I have been researching this for some time now. I'd also like to state that I don't know whether my sources are valid, but the actual websites that I gathered the information seem very plausible. From my experiences this is also true.

Lets look at LISS and HIIT:
1. The difference in Calorie Expenditure and EPOC
2. Fat Oxidation
3. Appetite Suppression
4. Fuel Sources

Calorie Expenditure and EPOC:
It is safe to say that 30 minutes of HIIT would burn the same amount of calories as 30 minutes of Moderate Intensity Steady State cardio. The reason of course is that the interval workout is alternating between very high caloric expenditures and very low expenditures such that the average expenditure still ends up coming out about the same. That is, say I do 1 minute intervals with 1 minute rest, alternating between 15 cal/min during the hard bit and 5 cal/min during the recovery. That’s an average of 10 cal/min. I can achieve that same 10 cal/min consistently with moderate intensity cardio. The second workout will be far easier to complete. Although in 30 minute trials, both
HIIT and SS burn the same amount of calories, we are only talking about the actual energy expenditure during that 30 minute window. We haven't factored in the EPOC for each.

What is EPOC:
EPOC stands for Excess Post-exercise Oxygen Consumption. It is the recovery from a bout of exercise associated with an elevation in metabolism. Or simply stated, it is the extra calories burned after training. It is also referred to as the "Afterburn Effect" or post cardio window. SS has an EPOC of 7% and HIIT has an EPOC of 14%. Now, I won't go into detail with all the numbers and calculations on how they got these percentages.If you would like to, you can read this article which explains it all: http://www.bodyrecomposition.com/res...nsumption.html

EPOC and how it works:
Say I do 30 minutes of intervals and burn 300 calories. I get a 14% EPOC which is 42 whole calories. Total calorie burn = 342 calories.
Let’s say I do 30 minutes of steady state cardio and burn the same 300 calories. 7% EPOC which is 21 calories = 321 calories.
While 21 calories is still more calories burned, it isn't a huge increase. Now do the math one more time, but let's add in more time. Let's say I burn 600 calories in 60 minutes doing steady state. Add in the EPOC (7%) and the total is 642. Compare this to 600 calories in 60 minutes doing high interval. Add in the EPOC (14%) and the total is 684.

In a 60 minute duration, the calorie difference is only a mere 42 calories, but with interval training being the much harder exercise! The intervals only come out a TINY bit ahead if you compare workouts of identical length and even there the difference is absolutely insignificant. Although there isn't much of a difference in actual Calorie Expenditure when comparing the two, there are still Pros and Cons for each. The take away from this is simply, EPOC provides a great “fat burning window” AFTER your cardio session is knocked out as LISS primarly burns the calories (more from fat stores) at that very moment.

Increased Fat Oxidation (BIG DIFFERENCE)
A study by Angelo Tremblay on the differences between HIIT and SS showed that the interval group saw a significant increase in the enzymes responsible for fat oxidation in a fairly short amount of time. With a combination of depleted glycogen stores, full body weight training and carbohydrate restriction,cincrease in fat oxidation can happen in about three days.
Steady State increases fat oxidation enzymes as well, but it typically takes weeks (obviously you’re not going to get shredded in days) HIIT eclicts extra energy burn for up to 24 hours. This is huge when you are trying to get fat to melt away!

2. Suppressed Appetite
   While low intensity training typically only releases noradrenalin (from the nerve terminals) with only small amounts of adrenaline (from the adrenal medulla), high-intensity exercise releases both adrenaline/noradrenalin in large amounts. This hormonal response results in blunting hunger. With a suppressed appetite, less calories are consumed resulting in greater fat loss.

Aerobic VS Anaerobic Training Zones
*During Low Intensity Steady State (LISS) training, your heart rate is at a range between 50 to 80 percent of your maximum heart rate, which is in the Aerobic Training Zone. Your body primarily uses your fat stores for energy during aerobic activities. You usually do it for 30 or more minutes. Some people go over 60 minutes which to me is insane, unless you are running test (help keep those muscles intact) You actually burn more calories than you would in a HIIT session. Also you burn more fat calories doing LISS over HIIT

*During High Intensity Interval Training (HIIT), your heart rate is at a range between 80 to 90 percent of your maximum heart rate, which is in the Anaerobic Training Zone. Your body primarily uses glycogen or carbohydrates to power muscle during this brief and intense activity. Although it does sound better to do LISS for the fact that it uses fat stores directly as the main source of energy, your body only burns those fat calories at that precise moment. You have to understand this is where EPOC comes into play!

TAKE AWAY NOTES:
With HIIT your burning calories at the moment but you actually change the muscles metabolism and it boosts your metabolism because you increase the mitochondria density of your muscle, so you increase the muscles oxidative capacity and you really do burn more calories.

HIIT is quicker, proves to be more effective for fat loss, creates metabolic changes, and helps with muscle retention but not everybody can do HIIT. LISS is safer, but takes twice as long to accomplish similar things and it still has its place for fat loss in moderate amounts, from a pure calorie burning standpoint (meaning only to burn calories & not make changes to your metabolism).

I would never perform HIIT more than 3-4 times a week as it is very taxing on the CNS as well as your muscles. It would limit recovery ability if done every day, and it would downright defeat the purpose of using HIIT. HIIT should make you want to pass out or vomit if done correctly at the end of the session haha.

*HIIT PROS: Its quick, intense, the EPOC is greater, muscle preservation.

*HIIT CONS: recovery ability is limited if done to often, taxing on CNS.

*LISS PROS: Greater calorie burn from fat stores, it’s not taxing on the CNS.

*LISS CONS: *BORING, Must do atleast 30-60 min. (if not more, depending on BF) If done
in a “fasted” (no anabolics or BCAA’s) muscle preservation is jeopardized.

Overall I honestly believe that BOTH are needed to really get you into the shape you want to be in. Im not saying one is better than the other by any means. I hope you guys enjoyed reading this. I have listed my references below. My homeboy dossier will be posting a similar thread on LISS, keep an eye out for his thread!

REFERENCES:

http://www.bodyrecomposition.com/res...nsumption.html

http://www.bodyrecomposition.com/fat...plication.html

http://www.bodyrecomposition.com/fat...nect-pt-1.html

http://www.bodyrecomposition.com/fat...nect-pt-2.html