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Which Type of Cardio is Best for Fat Loss?

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You’ve decided that you want to go on a shred. You want to get the maximum results and know at some point you’re going to have to throw some cardio in to get where you need to be.

All you need to know now is which type of cardio will help you get the best results.

Is ‘slow and steady’ really the best way to win the race? Or is a more ‘head down and work hard’ approach the key to shredded abs?

In this article we break down the science of cardio for fat loss.

What are LISS and HIIT?

When you talk about cardio you’ll often come across the terms low intensity steady state (LISS) and high intensity interval training (HIIT).

LISS refers to sustained exercise at a moderate intensity. Walking, jogging, light cycling and that sort of thing.

The focus is on duration as opposed to intensity.

HIIT though is more repeated, short bouts of hard work followed by periods of recovery. Short sprints are a good example.

The cardio continuum

Think of cardio on a continuum. At one end you’ve got the sort of exercise that allows you to plod along at a comfortable pace. It’s the sort of leisurely pace that allows you to hold a conversation but at the same time exercise just hard enough to bring your heart rate and breathing rate up.

Low intensity steady state is usually performed at an intensity no higher than 70% of your maximum heart rate (MHR).

HIIT is right at the other end of the continuum though. It involves short periods of exercise that are pretty much head down, all-out maximum intensity. It’s so hard that it has to be short in duration or you’d just never recover in time to go again.

High intensity interval training is typically performed at around 90-100% of your MHR.

Key Point: In case you’re not sure how to work out your MHR, all you need to do is subtract your age from 220. For example, if you are 27 then your MHR would be 193.

Fat Burning and Energy Systems

The science behind energy systems can be a little complex. But bear with us here as the knowledge will really improve your ability to burn fat.

In the context of human physiology you store energy as a compound called adenosine triphosphate (ATP).

You only store enough of it in your body for around 3-4 seconds of all-out intensity. And once it’s used up your body has to make some more. And this is where energy systems come in.

What are energy systems?

The purpose our our three energy systems is to primarily restore your body’s ATP so that you can keep using energy.

They take it in turns to make ATP so that you can exercise, move and even stay alive. But dependant on how hard you are exercising is to which system kicks in.

Aerobic and anaerobic energy systems

We burn energy two different ways. Either with oxygen – what’s called aerobic, or without oxygen – anaerobic.

Phosphocreatine (ATP-PC) 

  • This system works during maximal activities and can regenerate enough ATP for around 10 or so seconds of all-out work.
  • It is a primary system is sports like sprinting, shot-putt or Olympic weightlifting.
  • The ATP-PC system uses stored creatine to make ATP without the presence of oxygen and when you run out of it, it takes around 5 or so minutes to recover.

Anaerobic glycolysis

  • Once your ATP-PC system tires the next system to kick in is glycolysis
  • It lasts for up to 2 minutes before you have to drop the intensity.
  • This system uses only carbs to make ATP and it does so without oxygen.
  • It is used for high to moderate intensity exercise such as running at a quick pace or working at 8-12 reps in the gym.

Aerobic energy system

  • This is the only system that uses uses carbs and fat to make ATP. And it does so in the presence of oxygen.
  • It can only make ATP at low intensities.
  • As soon as you begin to work above 70% of your MHR this energy system can’t make ATP quick enough so you move back to one of the anaerobic systems.

Key Point: The intensity of exercise controls which energy system you use, and ultimately whether you burn fat or carb calories.

Heart Rate and Fat Burning

Now that you understand a little more about energy systems you might have picked up on one particular bit of information that was mentioned. That the only system that uses fat for energy is the aerobic energy system.

So does that mean that LISS is the best way to burn fat as you work below 70% of your MHR? 

Well not really. It’s not that simple.

Fat Burning Science

Our body uses carbs, fat and to a lesser degree protein for energy. And it does this based on how quick it needs to make ATP.

You work at a high intensity and your body uses carbs. You work at a low intensity and it uses less carbs and more fat.

Back in the 1970’s a researcher named Romijn [1] found that working below 70% of MHR burned the most amount of fat, and that as intensity increased your body started to shift towards carbs as it’s main source of energy.

And this led to many people training in the ‘fat burning zone’ throughout the 70’s and 80’s in order to maximize fat loss.

Everyone pretty much trained at a crawl-like intensity without getting a sweat on, in order to get thinner.

But science moves on. And since then, research has shown that working as high as 80% of your MHR still burns a hell of a lot of fat [2].

And the benefit of this?

You’ll get fitter and burn more calories.

So Is LISS or HIIT Better?

So far it’s looking like LISS is the winner as it’s the only training approach that uses fat as energy. But bear with us.

Calories matter

In order to maximize fat loss you need to be in a calorie deficit. So it’s not just about how many calories you burn from fat – it’s about how many calories you burn overall as well.

Now LISS burns a high proportion of calories from fat, granted. But it doesn’t burn a lot of calories in total. Why? Because it’s at a low intensity.

When you train at a high intensity you might burn more carbs and a lower proportion of energy from fat, but the total calories is way higher.

And this can lead to more fat being burned in total.

Excess post-exercise oxygen consumption

An additional factor that might sway things in favor of HITT is the concept of excess post-exercise oxygen consumption (EPOC). 

EPOC refers to the calories you burn after your workout has finished, as your body works hard to bring things such as your heart rate and temperature ‘back to normal’.

While HIIT doesn’t burn a great deal of fat during exercise, it’s benefit might lie in it’s ability to burn fat after your session has finished.

So working at higher intensities increases the amount of calories you burn after exercise, not just during.

And whilst LISS has only a minimal after burn (20 or so minutes), HITT can elevate your fat burning for over 10 hours [3].

The Winner – LISS or HIIT?

If you’re short on time, injury free and wanting to really maximize your results then HIIT is your winner.

Not only does it boost fat loss but it also improves your fitness and conditioning too. It’s a time-efficient strategy to stimulate adaptations that lead to a better physique.


Sometimes it’s nice to just go out for a gentle jog, see the sights and enjoy the sun on your face.

LISS is a stress-free, easier variety of cardio that might take up more of your time, but is perfect during intense stregnth training phases where you want to relax but still be active.

Do You Even Cardio?

You might be wondering if you even need to include cardio in your fat burning program?

Couldn’t a calorie deficit and some strength training work just as well?

Sort of.

Too much LISS cardio can reduce your strength and force output and can even have a negative effect on your muscles.

You don’t actually need to put cardio in your shred. You can burn excess fat by hitting a calorie deficit and including plenty of strength training in your program.

But cardio is still the best way to burn calories in the short term.

You want to reduce your body fat quickly?

Then cardio is the way to do it. Yes you might be a little weaker, but it’s worth it to get that ultra low body fat.

And when you include it in your session plan you’ll see improvements fast.

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  1. Romijn, JA et al. Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. Am J Physiol. 1993; 265(3 Pt 1): E380-91
  2. Carey, DG et al. Quantifying differences in the fat burning zone and the aerobic zone: implications for training. J Str Cond Res. 2009; 23(7): 2090-2095
  3. Børsheim, E et al. Effect of Exercise Intensity, Duration and Mode on Post-Exercise Oxygen Consumption. Sports Med. 2003; 33(14): 1037-1060