H.I.I.T. vs Cardio

HIIT or cardio training, what is worth the time and effort?

Firstly, it is important to define HIIT, and more importantly the work/rest ratios. The work/rest ratio in your workout determines which energy system is being targeted, and therefore the different results you will gain. For the purpose of this post, HIIT will be defined as what is becoming popular in gyms and outdoor circuit groups. This style of training is typically, 30-45 seconds of work with either the same amount of rest or sometimes less. When work/rest is equal, this is commonly referred to as 1:1, and when work is more than rest, this is known as negative rest. An example would be 2:1, commonly used in Tabata training.


“Cardio” will be defined as working submaximally, i.e. maintaining a heart rate of 50-75% of your maximum heart rate (MHR).  


HIIT training uses the anaerobic lactic system, with short rest periods. The table below shows that it’s not quite as simple as breaking each activity down to aerobic (with oxygen) or anaerobic (without oxygen).

*table sourced from https://www.brianmac.co.uk/energy.htm.

You don’t need to understand this entire table to understand the difference between HIIT and typical cardio training.  

What is important to understand, is these energy systems never work in isolation. They are always working together, some are just able to contribute more and for longer periods of time. Nothing is ever 100% Anaerobic ATP and 0% Aerobic or visa versa. The percentage of contribution from the energy systems may get close to 100% and 0% but will never reach it.

Another key to understanding, is all these energy systems are trying to do one thing, make Adenosine Triphosphate (ATP). ATP is what our cells always use for energy. The different energy systems are different pathways the body has to make ATP. So, ATP is always the source of energy, but the speed and efficiency of its production are dependent on the energy system.

Using the table above, you can see that the first 1-4 seconds of maximal effort is fueled primarily by ATP (energy that is already loaded and ready to be used instantly). However, this stuff is in short supply, CP (creatine phosphate) is used to quickly make more ATP and extend our ability to restore ATP at a fast rate, to around 10secs.

Any maximal effort over 10 seconds to about 45 seconds needs to use muscle glycogen (stored energy) to form more ATP. This process is slower and is why human explosiveness (think 100-meter sprint) starts to decline after 10secs. However, all is not lost! As long as lactic acid (the waste product) is not present, our ability to work at a near maximal output is not too bad. Think 200 meter and 400-meter sprinters, they can hum along at a near top speed until they reach their lactic acid threshold!


Things start to hurt at the lactic acid threshold.


You know when you’ve hit it, your legs burn, you feel like you’re dragging a sack of weight behind you, this is where you want to give up! This typically happens around the 120-second mark. However, this is completely dependent on fitness levels, and pushing this threshold further and further out, is essentially how you become fitter.

Aerobic or “cardio” training is anything before the lactic threshold. Aerobic energy pathways can also take over after the lactic threshold is reached and the athlete has had to slow down (in order to take in more oxygen). Aerobic energy pathways use muscle glycogen or fat stores to fuel ATP. Muscle glycogen is a fairly effective fuel source, but once fat is being used, intensity and output drops considerably. As this process of ATP creation is the slowest. This is commonly referred to as ‘hitting the wall”. A well-conditioned athlete can feel the moment their body switches to fat as fuel, as performance can drop, if not conditioned to it.

Interestingly, one can condition their body to be more effective with using fat, which can be more than efficient with the proper adaptations. Article here.    

 HIIT can mean purgatory …


HITT training doesn’t want you fully recovered, it is training what the author of this ebook refers to as a ‘purgatory zone’. Meaning, training in the 75-89 % max heart rate zone. He argues that the best training adaptations are found in the extremes and that messing around in the purgatory zone too much is not ideal and has nothing much to offer. In summary, it negatively affects your speed and power gains.  






World renowned sports and athletic coach Charlie Francis has famously said. “Train fast or slow, nothing in between”.


Charlie’s athletes train > or = 90% max speed/intensity 35% of the time and < or = 75% max speed/intensity 65% of the time. They never train in the 75-90% zone.

Of course, not everyone is wanting to be super fast or powerful, so this quote must be taken with a grain of salt (it was from a coach of high-performance athletes). Nevertheless, it is interesting.


HIIT training has recently been popularized while cardio (aerobic) is now largely ridiculed as being ineffective.

While HIIT is definitely effective and offers a gut busting workout in under 20 minutes. It has many benefits, including an increase in human growth hormone. Study here. However, many benefits have been largely overblown and exaggerated to demonize other methods of training. Often HIIT is an easy sell for personal trainers and gyms. It’s hard to argue you haven’t had a good workout when half the class has passed out and the other half can barely muster the strength to drive home. We are conditioned to think the more hurt the better, we all know the common sayings ‘no pain no gain’ or “pain is weakness leaving the body” etc.


While there is a time and place for these workouts, and depending on your goals, HIIT might be a perfect fit. However, they are not great all the time and are not suited for everyone. One over the top HIIT workout might be enough to put an unfit person off fitness training for good.


The problem with HIIT is not that it’s bad, it’s that it claims to do things that are either not true, or exaggerated.

Cue table of common misconceptions of HIIT and cardio.

HIIT increases VO2 more than Cardio. Some studies have shown this to be marginally true. While others, like this study, have shown there is no difference. The important thing to note here is that VO2 increased, which is good. This is only disappointing if you wanted a clear winner, there doesn’t seem to be, and it shouldn’t annoy you so much.
HIIT burns more fat during exercise. This study and especially this study, show this is not true. In trained athletes, the highest rate of fat oxidation is a 75% of VO2max, and in untrained people, this happens way earlier at 65% VO2max.  These percentages are at moderate to hard aerobic training rates.
HIIT burns more fat after exercise.  Post-exercise oxygen consumption (EPOC) This made intuitive sense to the fitness industry and was quickly adopted as true, especially when marketing new HIIT workout classes.

However, a study found that although it’s true HIIT training raises EPOC, it is a marginal increase when put into context. EPOC= Excess post-exercise oxygen consumption. 

It was found that aerobic cardio training has a 7% EPOC, meaning an extra 7% of calories burned during a cardio workout will be burned after the training session. HIIT training was found to have a 13% EPOC. At first glance, that looks impressive, as its nearly double!

The claim to fame of HIIT falls apart when the total calories burned after activity and EPOC are added together. HIIT workouts are short and sharp (they have to be), usually 20mins. A typical HIIT workout of 20mins will burn about 300 calories. Adding the 13% EPOC, it comes to a total of 340. Compare that to a typical aerobic session of 60mins, burning around 640 calories, add the EPOC and the total is 685.

If you dropped the cardio session to the same time frame of the HITT (20mins) then total calories burned will be the same(ish).

This article summed this all up well.

HIIT is more sports specific. To be precise here, one must ask which sport? For argument’s sake, let’s take team game sports like soccer, rugby, hockey etc. It has been argued, that HIIT training is the more specific training method for these sports.

This is not true, take soccer for example. This study and this study show that soccer players run anywhere from 10-13 km per match, only 1.5 to 2.5km are performed at “high intensity.” So 70-80 % of a soccer game is low intensity running, relying on aerobic energy pathways. You would assume then, that aerobic training is more specific for most, if not all team sports.

HIIT makes you explosive and fast. Well… it depends. If you’re doing a Tabata style HIIT workout, you aren’t having enough rest to be getting faster.

Remember earlier in this post, I spoke about training in a “purgatory zone”. If you want to be fast or explosive, you need to train fast and explosively, so you need adequate rest to do so.  The basic rule of specificity right there

You can get a good workout quicker with HITT. True, but only to a certain extent. You may burn more calories in comparison to cardio when comparing time spent working out. However, HIIT is tough work, it’s a stressor. Stressors are needed, but too much stress, and you go backward. If you do HIIT properly and you’re in decent physical shape, you can’t do more than 3 sessions a week. This is because you don’t want your autonomic nervous system to be in constant fight or flight mode. If you’re really unfit, a HIIT workout may not only leave you injured but may hinder you from working out for days/weeks on end. Just like with most things, your “dose” of HITT must be carefully individualised. Group sessions usually don’t do a good job of accounting for the individual.


So does this mean that cardio is better?


To say one is better than the other is over simplistic, and plays into the fallacy that you have to choose a favorite. This mindset of choosing a team, team HITT or team cardio, is the wrong way to approach fitness, or for that matter, life. The questions to ask yourself are; What are your goals? Where is your fitness level currently at? How much effort are you willing to put in?


The key to HIIT is the work/rest ratio. It doesn’t always have to be with minimal rest and completed with self-destruction in mind. Sure, kicking your own arse is valuable and can have benefits, but there is only so much you can take before you start going backward. The key to kicking your arse is to see and reap the rewards, not just kicking it, for the sake of the kicking.


The thing is, cardio, HIIT, intervals, weight training, yoga etc, they are all methods, tools to get you somewhere. Claiming one is the answer and the only answer is a bit naive, to say the least. They all have their pros and cons, the trick is using the pros of one to balance the cons of another. 

HIIT and Cardio are commonly used as weight management tools, most trying to lose fat. As far as using fat as a fuel it steady state Cardio is the winner. However, the all-important piece to the puzzle of fat loss is nutrition and calories.

Click the picture below to learn the basics and misconceptions about calories.