8 February 2019


by Jacob Schepis 0

The fitness community has an unhealthy obsession with cardio. For better or worse, whenever cardio is discussed, debate inherently ensues. HIIT or LISS, fasted or fed, the great divide between proponents of different protocols continues, and this article is here to cut through the BS, put forward the science, give practical recommendations and educate you so that…

The fitness community has an unhealthy obsession with cardio. For better or worse, whenever cardio is discussed, debate inherently ensues. HIIT or LISS, fasted or fed, the great divide between proponents of different protocols continues, and this article is here to cut through the BS, put forward the science, give practical recommendations and educate you so that you can make your own informed opinion and decisions about cardio. 

Energy expenditure 101.

The first topic we must discuss before delving into the nuances of cardio is energy expenditure. There are a number of different components that contribute to our Total Dailey Energy Expenditure (TDEE).
    • Basal Metabolic Rate


    • Resting Metabolic Rate


    • Physical Activity (Non Exercise Activity Thermogenesis & Exercise Activity Thermogenesis )


  • Thermic Effect of Feeding.

Some definitions…

Basal Metabolic Rate (BMR):

BMR is the rate of energy expenditure fasted, rested and supine conditions in thermoneutral environment. he rate at which your body uses energy when you are resting in order to keep vital functions going such as breathing. The rate at which your body uses energy to breath and stay warm, noting else.

Resting Metabolic Rate (RMR):

RMR is the rate of energy expenditure when at rest but not basal, which is basically our daily functions and this represents the largest fraction of our the daily energy expenditure in sedentary populations.

It is important to note that the primary determinant of energy expenditure at rest is Body Size, with smaller individuals burning less calories when compared to larger individuals. Especially when considering small females with more body fat and less muscle mass than larger males. The differences in body size are usually expressed in terms of body surface area BSA.

RMR & BMR combined contribute to approximately 60 to 75% of TDEE.

A few tidbits on RMR are that it increases significantly when females are pregnant, because they’re growing a human and can also triple in extremely cold climates due to an increase in thermoregulation. So if you’re serious about getting lean, keep your aircon pumping day and night – kidding.

Physical Activity Thermogenesis:

For obvious reasons, physical activity thermogenesis can vary largely. If you are really active, you’ll have a higher proportion of daily energy expenditure from PAT. If you’re a lazy sod and rely on machines as most do in the 21st century, you’ll have a smaller calorie burn per day from PAT.

The rough percentage of PAT is dependant on an individuals habitual exercise routine, job and lifestyle factors but ranges between 15-30% and can change from day to day. For example, you may burn more calories on days you walk to work and the weekends when you don’t work, your PAT will drop. Thus, you can start to see why TDEE is a very dynamic, ball park number and is not static.

Now, this is where it gets interesting.

The assumption people make when adding in 1 hour of cardio per day is that they are somehow contributing an additional hour to their day. This assumption is false, as the calories burned during cardio must deduct the calories that would have otherwise been burned at rest or doing whatever else you may have been doing.

This Energy Expenditure from cardio can be expressed as the following equation:

Total (gross) – Resting energy expenditure (REE) = Net energy cost of the activity per se.

Therefore, if you burned say 300 calories in 60 minutes of walking (5 calories per minute), and you would have otherwise burned 180 calories (3 calories per minute) just moping around the office, then the net difference is only 120 calories.

Not a whole lot right?

If we were to compartmentalise our daily activity into the following areas, it can be evident why there is such a large variation in PAT:

  • Sleeping
  • Sitting
  • Standing
  • Walking
  • Recreational Activity

Where do you spend most of your time during a 24-hour period?

Not engaging in recreational activity, that requires you to move a hell of a lot!

*** A quick side not before we get into fat loss fundamentals that can help explain weight gain over time is to think about the ageing process. As as we get older, there is a large shift in our daily activities.

 Fat Loss Explained:

Fat loss (adipose tissue) is a result of an energy imbalance that forces the body to rely on stored energy aka fat. The energy imbalance we are interested in creating is a calorie deficit – less calories consumed than the body burns per day.
This deficit can be created by either:
    1. Reduced food intake.


    1. Increased energy expenditure; or


  1. Both.
Nutrition key for fat loss and cardio can simply supplement a well structured diet to assist our pursuit of a leaner physique. This is especially true for individuals with a smaller TDEE who cannot eat a lot of food when dieting.
Don’t fall into the trap of thinking that cardio is inherently ‘fat burning’…
Cardio such as walking briskly on a treadmill is simply movement.
Movement at a faster rate than you would otherwise move if you were walking at a slower pace, standing, sitting or in bed asleep.
Therefore, cardio is not some mystical fat burning activity like people think it is. It is simply a tool to increase daily energy expenditure and the calories you burn whilst doing cardio don’t necessarily equate to a whole lot either, and we’ll explain why.

How many calories does cardio really burn?

Hopefully this article has highlighted that we are in a constant state of calorie expenditure. Whether we are lying in bed or on the treadmill, we are continuously expending energy at different rates, burning different amounts of calories. Movement has a cost to the body, and that cost is paid in the form of calories.

How many calories you burn at rest is very difficult to measure, unless you’re in an exercise science lab. Therefore, we can draw some conclusions from what the research has shown and at best draw inferences from the data.


Calorie expenditure has been shown to be dependant upon three things:

1. Body size
2. intensity; and
3. duration,
Bigger people, who weigh more (with more muscle mass), will burn more calories than smaller people. They have to do more mechanical work to perform the same tasks, simple.
The intensity you exercise also determines how many calories you burn, with higher intensity activity burning greater calories per unit of time. However the drawback here is that higher intensities cannot be performed for long durations.
The third and final actor in determining energy expenditure is duration. As mentioned, intensity closely correlates with duration, and thus the longer we exercise or move, the more calories we burn over time.
Calories burned at rest:
For example, you may burn between 3-5 calories per minute just being awake and performing normal daily tasks.
Calories burned during exercise:
Here is an estimate of how many calories we burn at different intensities. Remember, the accuracy of these numbers will be effected by individual differences such as body mass, mechanical efficiency and a number of other things.
Low Intensity (Brisk Walk): 5-6 calories per minute.
Moderate intensity: (Jogging) 7-8 calories per minute.
High intensity: (Sprinting) 9-10 calories per minute.
Not as many as what you thought right?
What you must not forget is that you are burning calories whether you do cardio or not. When you step on a treadmill, you just start burning slightly more calories than you were previously. Thus, the net difference from not doing any ‘cardio’ is only an additional ~3 calories burned per minute equating over the span of 30 minutes. This means instead of burning 90 calories over the course of 30 minutes standing around talking smack with your friends, you are burning 150 (an additional 90 calories). This isn’t a hell of a lot, and is grossly less than what people typical think they are burning when walking on the treadmill.

Problems with tracking calories burned with cardio

The equations machines like treadmills, elliptical and bikes use to monitor calorie expenditure are for the most part, extremely inaccurate. Diet should be the primary means by which you create a calorie deficit. As not to sound like a broken record, cardio is a tool to further that deficit and relying on burning calories through cardio to improve your physique is a dangerous game.
Her are some potential problems with tracking calorie expenditure:
– Non Exercise Activity Thermogenesis can go down in response to cardio;
– It is less predictable than reducing calorie intake – slumping over the treadmill, recumbent bike watching porn etc; and
– More difficult to monitor due to individual variations.
So whilst it is great to increase physical activity to assist in weight management, a fat loss phase should not be addressed with exercise alone.

How to choose a modality.

For successful cardio implementation for fat loss and body composition we need to think about 4 key things when selecting a type of cardio to perform.
1. Enjoyment
At a fundamental level, you must enjoy what you’re doing so that you will continue to do it consistently. Fat loss is a function of creation a consistent calorie deficit over time. Therefore, if you hate the cardio that you’re performing, it won’t last.
Find what you enjoy and stick to it, simple.
Enough on that…
2. Consistent tracking.
One of the important things to consider when you’re serious about fat loss is how well you can track your cardio. For example, if your ‘cardio’ is playing a weekly basketball match, and one week you are on the bench for 15 minutes, the following you play a full game etc then this can be an issue for tracking your energy expenditure over time.
What gets tracked gets measured, and to give a more accurate indication of when and why you’re fat loss may by stalling, constant  tracking of your cardio is key.
We recommend using the same modality and monitoring intensity, heart rate, calorie expenditure and duration.
The choices are endless…
    • Brisk Walk


    • HIIT


    • Cycling


    • Elliptical


    • Swimming


    • Jogging


    • Sprinting


    • Skipping


  • Barbell Complexes

The list goes on…

The key is to pick something you don’t hate and can track with some form of consistency.

3. Orthopaedic profile:

Not all individuals are structurally or functionally the same. As a result, some people have better mobility, stability, joint structure, lactate threshold, motor control and strength. Thus, some individuals are suited better to higher intensity exercise than others. For those who may not be as ‘primed’ to perform such exercise, lower intensity modalities are a more advisable choice.

It is important to understand that sprinting is a skill, and if you’re someone who is looking to lose fat exclusively with no goals of being a competitive track & field athlete, the risk and recovery costs of sprinting may outweigh any benefit it may afford in terms of calorie expenditure.

4. Muscle damage & Soreness

The higher the intensity, the greater the muscle damage and impact this has on your recovery processes. We also know that anything that has an eccentric component to it increases muscle soreness. Therefore, we must consider a modality that causes the least soreness if we want to maximise our ability to lift heavy things. As more soreness will mean you won’t be able to perform at your best in the gym.

For example, sprinting has an eccentric component (deceleration) whereas swimming has no deceleration and actually burns more calories due to the horizontal drag and potential requirement of buoyancy. More calories burned, less soreness, it’s a winner right?

Well, only if you like it.

If not, it’s back to the drawing board.


The way you challenge your body is the way it will adapt.

The chronic physiological adaptations that occur in response to exercise are highly specific to the type of exercise performed and the variables within that program – Volume, Frequency, Intensity.

Because the 2 types of exercise (strength training & aerobic exercise) are located at the opposite extremes of a muscular power continuum, the design of a program must be highly specific with regard to the exercise to be undertaken, as well as the intensity, duration, and frequency, in order to attain optimal results.

Strength exercise programs involve picking up weights, and putting them down. I hope you’re all familiar with this. Aerobic exercise involves exercise performed for longer durations (e.g., 10-40 minutes) with large muscle activity involving hundreds of consecutive repetitions that challenge the delivery of oxygen to the active muscles.

Very different physiological process to perform and recover from, resulting in a completey different adaptation to each.

You get what you train for, and unless you want to look like a skinned rabbit when getting lean, preservation of lean mass is your goal during an extended fat loss phase. Therefore, your priority in terms of a specific exercise is NOT cardio, for the aforementioned reasons.


Don’t forget that for bodybuilding and physique development the two outcomes we are interested in are: muscle gain and fat loss. Resistance training is therefore the primary focus for muscle gain and retention whilst cardio is a tool to further create an energy deficit aiding fat loss.

Accomodation & Adaptation.

When the body is challenged with a physical task such as cardio, the body responds through a series of integrated changes in function of its physiologic systems.

Movement requires activation and control of the musculoskeletal system; the cardiovascular and respiratory systems provide the ability to sustain this movement over extended periods which is what occurs when we perform aerobic exercise.

When the body performs cardio several times a week or more frequently, each of these physiologic systems undergoes specific adaptations that increase the body’s efficiency and capacity to perform the tasks involved. As the body adapts, it becomes more efficient at performing the movement and thus overtime, less calories are burned.

What this means for you is that over time, more and more cardio is required to have the same caloric burn. Thus there is a point of diminishing returns.

Progressive overload

An extremely important exercise principle is progressive overload.

We know that the body adapts to exercise, and therefore to continually improve we must increase the difficulty of the training stimulus to ensure we positively adapt. Progressive overload can come in many forms – intensity, volume, duration, workout density, range of motion etc. However in the context of cardio, we are looking at intensity and duration.

Once fat loss stalls, we know that we have reached calorie maintenance. This means that if we wish to further our deficit we must overload our training or diet by;

a) Increasing energy expenditure (Progressively Overload Cardio)

b) Decreasing energy intake (Reduce Calorie Intake); or

c) Both of the above.

When it comes time to make a decision whether to cut calories or increase cardio, some important considerations are:

1. Body Size & Current Calorie Intake 

Body Size & Calorie Intake are closely related as we know now. Hence, the first thing to consider when trying to further a deficit is how large a person is and how many calories they are eating.

When calorie intake is high, you have more room to move.

For larger individuals with more muscle mass, they get to eat more. Hence it is common for males and larger females to get lean with minimal to no cardio.  In these circumstances reducing calorie intake will be a far better choice as it is more reliable and less time consuming for an individual with an abundance of food.

On the flip side, smaller females typically have a much lower BMR/RMR and must eat less to create the same deficit when  compared to larger individuals. Thus it is common for smaller individuals to perform more cardio in a fat loss phase.

It is common sense to increase activity aka cardio when someone is consuming very little calories. The burden of reducing food intake will far outweigh the potential burden an additional 20-30 minutes of activity per day will place on their lifestyle and enjoyment of diet and exercise.

We can look at this in a practical sense and compare a male who weighs 80kg eating 2500 calories  to a small female who weighs 55kg eating 1300 calories to create the same 20% calorie deficit.

Which calorie intake do you think would be easier to follow?

It should be obvious that with almost double the calories, a male has far more room to move when it comes to reducing food intake in comparison to the small female.

2. Current Cardio Protocols

The second consideration is how much cardio the individual is performing currently.

If someone is doing a hell of a lot of cardio, additional cardio may not be a wise idea, and looking at calorie intake will be a more advisable choice. On the flip side, if someone isn’t doing any cardio and their fat loss stalls, we can look to add some additional activity to their TDEE to further the deficit.

Being aware of these considerations is critical in decision making when fat loss stalls.


Low Intensity Steady State cardio is as the name suggest, low intensity activity performed over longer durations with no fluctuations in intensity or effort such as brisk walking.

Conversely, High Intensity Interval Training is performing an all-out, exhaustive physical effort for a short time followed by a short, sometimes active, recovery.

Many have compared the two to see who is the victor when it comes to fat loss, however unfortunately the answer is neither.

We must first stop comparing them. At a basic level, LISS is burning calories at a low intensity and HIIT is energy expenditure at a higher rate using completely different metabolic pathway.

I’ve even read that HIIT will make your dreams come true and help you ‘torch’ fat. There have been three claimed benefits for HIIT’s superiority:

  1. Lean Muscle Retention/Gain.
  2. Greater Energy Expenditure Due To Excess Post Exercise Oxygen Consumption (EPOC).
  3. Time Efficiency.

Claim 1: Muscle Growth/ Retention

To address the first claim that HIIT is superior to LISS due to it’s muscle building/retention benefits may be true in two scenarios – if somebody is a novice lifter (therefore adding in extra high intensity exercise is increase lower body volume), and if somebody doesn’t train their legs and have now introduced some lower body training, increasing the volume they perform.

Claim 2: EPOC

As for the second claim that EPOC is some mystical fat burning mechanism that is only afforded when we perform HIIT, lets look first look at what EPOC is. EPOC is known by fitness enthusiasts as the ‘afterburn’ which boost your body’s metabolism for up to 48 hours after a high intensity workout. Essentially, the body is starved of oxygen when performing high intensity activity for short durations as this type of exercise is anaerobic (without oxygen).

The body is an extremely adaptive, dynamic and compensatory organism and whilst it is starved from oxygen during the training bout, it will endeavour to replace this oxygen after the workout has been completed which results in a small spike in calorie burn aka metabolism.

However, what people fail to realise is that duration is an important factor in terms of energy expenditure, and HIIT cannot be performed for long durations. So whilst the ‘afterburner’ may be real, over a 24 hour period the total calorie expenditure what drives fat loss, and whilst more calories may be burned after a HIIT session due to EPOC, you can burn the same amount of calories during a LISS session. Whether you burn calories during or after a workout isn’t of importance, it is the net energy balance that needs to be considered.

Claim 3:Time Efficiency

Whilst short intervals at high intensities may be a time efficient means to exercise and increase energy expenditure, they come at a cost. High intensity activity has a high recovery cost, and as such will carryover into your resistance sessions. Not only could this potentially impact your training performance resulting in loss of lean body mass, but it means you can’t perform HIIT as frequently as LISS.

When we look at LISS, it certainly does take longer (almost double the time) to burn the same amount of calories as HIIT. However, with low intensity exercise comes a low recovery cost as it is simply movement at a slightly faster rate than sitting or standing. As such, it can be performed more frequently and for longer durations.

The questions really becomes – where do you want to invest your time?

As we get deeper and deeper into the intricacies of cardio, I would like to again draw your attention back to what we discussed at the beginning of the article. Cardio is simply burning calories, and if you don’t have time to burn calories, tighten up your diet and reduce your food intake.

But Jacob, which one should I do?

Consider the following when determining which modality you choose:

  • Sustainable – are you going to perform it consistently over time?
  • Enjoyable – do you like it?

Remember, you are a weight lifter not a runner. Therefore, the ratio and time spent performing cardio:resistance training should represent your primary training goal – cardio is the tool for energy expenditure.

The key is to find the right tool to fit your situation and ensure you don’t burn out or negatively impact your resistance training. Remember, the goal is to do as little cardio as possible to see progress in your fat loss, otherwise known as the Minimum Effective Dose.

Final Comments on HIIT:

  • HIIT recovery cost of HIIT means that it cannot be performed 5-6 times per week at the requisite intensity due to negative impact on weight training.
  • Most individuals orthopaedic, cardiac, and even psychological make up doesn’t suit HIIT.
  • Most HIIT modalities (sprinting) if not performed correctly may increase the risk of injury.
  • Inter-individual lactate thresholds will influence tolerance to HIIT.
  • HIIT and LISS combined, cycled or rotated can work well.

Fasted Vs Non Fasted

As the name suggests, fasted cardio simply means performing your exercise in the fasted state before you’ve eaten a meal. Conversely, cardio that is not fasted is performed in the fed state otherwise known as post prandial state.

The premise for ‘fasted cardio’ being superior for fat loss than cardio in the fed state is that:

  1. Blood glucose levels are lowest after fasting, influencing insulin levels.
  2. Insulin is low when fasted, increases fat oxidation.
  3. Low intensity activity (over longer durations ~45-60 minutes) utilises fatty acids as an energy substrate.
  4. More fatty acids used as substrate = greater fat loss.

This is what is known as ‘substrate utilisation’ and is the premise for the proposition that cardio performed first thing in the morning fasted, at a low intensity for 45-60 minutes is inherently ‘fat burning’…

Substrate utilisation explained:

Substrate utilisation is  the energy source used to fuel exercise.

Low Intensity: When people walk at low intensity after fasting, the energy needed is provided mostly by oxidation of plasma fatty acids.

Moderate Intensity: As exercise intensity increases (eg, to moderate running), plasma fatty acid turnover does not increase and the additional energy is obtained by utilization of muscle glycogen, blood glucose, and intramuscular triglyceride.

High Intensity: High intensity exercise is fueled by increases in muscle glycogen utilization with some additional increase in blood glucose oxidation.

Long Duration Exercise: Muscle glycogen and blood glucose contribute equally to carbohydrate energy production over 2-3 h of moderate-intensity exercise; fatigue develops when these substrates are depleted.

Is it that simple?

The problem with taken a mechanism such as insulin and acute substrate utilisation and looking at it in isolation is that it neglects to consider the big picture and how the body responds as a whole – the body is dynamic and an extremely adaptive organism and responds to everything we do by accomodating in some way shape or form.

In theory, low glycogen and insulin levels cause the body to shift energy utilization away from carbohydrates, thereby allowing greater mobilization of stored fat for fuel. Studies that looked at this in the short term (during the exercise bout) support this.

However, evidence does not support this hypothesis when looking at substrate utilisation and energy expenditure over chronic periods and taking into consideration the big picture. For example, a recent study by Brad Schoenfeld, Alan Aragon & James Kreiger that compared FED vs FASTED cardio found that when variables were controlled, all participants of the study lost fat. However, the fat was not lost as a result of being fasted or fed when performing their cardio.

This confirms the first and second laws of thermodynamics – energy balance. Shifting the balance of energy in favour of energy expenditure is the primary driver of fat loss. The rest is just ‘fluff’.

What people often fail to consider are the potential benefits with having a meal before performing cardio. More energy can result in greater performance and calorie expenditure. Whilst this may not be the case for everyone as there is large inter-individual variance in response to diet and training, but its a matter of trial and error.

Wrap Up:

  1. Fat loss is a function of energy balance being in favour of energy expenditure > energy intake.
  2. Cardio is a tool to increase energy expenditure.
  3. Resistance training is the primary driver of muscle gain/retention during a fat loss phase.
  4. Creating a calorie deficit through diet is more accurate than cardio induced deficits.
  5. Choosing a cardio modality should be based on orthopaedic profile, preference, time availability, tracking ability.
  6. HIIT has a high recovery cost when compared to LISS, which may negatively impact body composition long term.
  7. Wether your perform cardio FED or FASTED is a matter of preference.


Coach Jacob.

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