7 myths about cardio

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If you want to lower your body fat percentage, you can hardly avoid doing cardio. But this form of training is surrounded by many half-truths and whole lies. Time to definitively refer these to the land of cardiofables. The seven biggest cardio myths debunked.


Is Cardio Necessary to Lose Weight? No. For fat loss, you can in principle suffice with a calorie-restricted diet. If you had to choose between diet or cardio, diet would be superior to cardio xx ] .

Whether you also do cardio in addition to dieting is primarily a matter of personal preference. If you like food and if you find it difficult to stick to a diet, there is of course nothing wrong with achieving the desired energy deficit partly or completely through cardio. In this way you more or less continue to eat your normal amounts, while at the bottom there is still an energy shortage.


The body can draw on two energy stores: carbohydrates (glucose and glycogen) and fat. And yes, there is such a thing as a fat burning zone, or actually aerobic training zone. It is between 65 and 75 percent of your maximum heart rate. And it is true that you burn a relatively large amount of fat in that zone. About 50 to 60 percent of the energy you use exercising at this relatively low intensity is provided by fat. This is because more oxygen is available when exercising at a low intensity. And to use fat as an energy source, more oxygen is needed than with carbohydrates.

Now it is nice and nice if you burn a relatively large amount of fat during that cardio session, but at other times of the day your body will use a relatively large amount of carbohydrates as an energy source. For the total picture, your energy consumption over 24 hours, it doesn’t matter xviii ] .

If you train at a higher intensity, your body also burns more calories after training. Although this so-called afterburn effect is not as great as is often assumed, as we will see later.

Remember: fat burning is not the same as fat loss. For fat loss, it doesn’t matter which energy source you use at what time. Whether you lose fat depends on your energy balance throughout the day (calories in, calories out). You only lose fat if there is an energy deficit, or a negative energy balance.

Of course there is nothing wrong with training in the fat burning zone. It’s fine if you can’t or don’t want to train more intensively.


It’s traditionally something bodybuilders do: fasted cardio, usually (early) in the morning, before breakfast. The idea behind this is that, deprived of food, the body must use body fat as an energy source. Sounds logical, doesn’t it?

Well, it is true that you will burn body fat faster on an empty stomach. But that’s just a snapshot. See point 1: whether you actually lose fat depends on your energy balance over a longer period of time, basically over your entire day. It must be negative. A recent meta-study confirms that it makes no difference to fat loss whether you do your cardio on an empty or full stomach xvii ] .

For (natural) bodybuilders, there may even be a disadvantage to fasted cardio, namely that there is a greater chance of the breakdown of muscle tissue than with ‘fed’ cardio. This is because the levels of the ‘stress hormone’ cortisol are highest in the early morning. As a result, your morning cardio session may release even more of the muscle-depleting cortisol than cardio at other times of the day ii ] . In addition, you cannot train very intensively on an empty stomach. Certainly doing High Intensity Interval Training (HIIT) then becomes a difficult story.

Fasted cardio may offer other benefits. For example, you could ‘teach’ your body to use fat as fuel more efficiently. However, more research is needed on this and other purported benefits.


Another myth: an effort should last at least half an hour before you start burning fat. We have already seen that the body can draw on two energy stores: carbohydrates and fat. People who are very overweight naturally have a large stock of fat. But no matter what your body composition is, your body will always burn as much glycogen stores as possible first. As these run out, more and more fat stores are used. How quickly that happens also depends on the intensity at which you train (see point 1). If you work for more than about 20 minutes, you will burn more fat. After an hour of training, fat is almost exclusively used as fuel for your energy. Then the fat burning is optimal. When you look at it that way, the myth doesn’t seem like a myth.

But again we refer to point 1: weight loss is about creating a calorie deficit. And that deficit is the result of your calorie intake and burn seen over the entire day (or possibly over a longer period of time). Let’s say you do cardio for half an hour in the morning (not fasted cardio). You will probably burn mainly carbohydrates and not fat. But you also use up the necessary energy for the rest of the day, even when you rest. Once your carbohydrate stock has been used up, your body still switches to burning fat. And the opposite is also true: if you eat so much during the rest of the day that you end up with a calorie surplus, you don’t lose fat, but you gain fat. Despite that half hour of cardio.


You’ve probably read about the afterburn effect. Official name: EPOC (Excess Post-exercise Oxygen Consumption). This is the increased energy expenditure in your body that occurs after a certain effort (eg cardio or strength training): ‘increased’ compared to your normal energy consumption at rest (the basal metabolic rate).

Your body uses more energy after exercise because it has to perform a variety of tasks to recover, including replenishing oxygen, ATP and creatine stores, removing lactic acid and repairing muscle tissue. These processes require oxygen, so oxygen consumption increases and that costs energy. As a result, you burn extra calories.

But how big is that afterburn effect? Research shows that EPOC can last as long as 10 to 72 hours iii ] . The exact duration and magnitude of the effect is, logically, dependent on several factors iv ] : type of exercise (cardio or strength training), duration and intensity of the training, age, gender, training experience and so on. To give some sort of general guideline, we looked at some studies of EPOC v ] [ vi ] [ vii ]. From this you can conclude that the amount of extra energy burned during EPOC is about 5-20% of the amount you burned during the exercise itself. In the Norwegian study, 80 minutes of moderate-intensity cycling resulted in an average EPOC of 150 calories. The participants had thus burned an ‘extra’ 150 calories. That’s a nice bonus, but with 80 minutes (!) of effort it’s not that much.

In short, the afterburn effect does exist, but don’t stare at it blindly. You burn by far the largest number of calories (> 80%) during the effort. And that effort has to be quite long and/or intensive if you want to create an afterburn that matters.


High Intensity Interval Training (HIIT) is a much acclaimed form of training, because you burn a lot of calories in a short time. If you’re short on time and don’t shy away from a tough, intense workout, HIIT is for you.

However, a meta-analysis of scientific studies shows that HITT is no better for body composition than low-intensity steady state (LISS). The other way around also not xxi ] . Because HIIT and LISS are very similar physiologically, they also result in similar interference with strength training.

What form of cardio you do is mainly a matter of preference. But if we must give some advice, during a long cut, do LISS, the form of cardio that bodybuilders traditionally do (such as brisk walking, jogging, cycling and swimming).

The big advantage of LISS is that you can keep the intensity low enough not to cause ‘competition’ with your strength training. This is much more difficult with HIIT due to the high intensity. Doing a lot of HIIT during a calorie deficit (cut) can even be at the expense of strength gain and lean muscle mass.

And what about the afterburn? With HIIT it is slightly larger than LISS, but we already saw that the afterburn is only a small amount of calories, even if you do HIIT.

And the release of testosterone and growth hormone? It is indeed greater with HIIT, but it only compensates for the higher release during HIIT of the ‘stress hormone’, cortisol.

HIIT is especially a useful tool to burn a lot of calories in a short time and improve your cardiovascular fitness. If you’re cutting, do HIIT in moderation, no more than a 20-minute session, say, three times a week.


Many bodybuilders see cardio as a necessary evil or something to avoid altogether. Cardio kills gains, it sounds.

Indeed, if you do excessive cardio with a long-term energy deficit, your body will sooner or later withdraw proteins from your muscle tissues to get energy. But if you eat enough protein and you limit your cardio in terms of duration and frequency, it usually won’t hurt your gains, including muscle maintenance during the cut. Especially not when you’re walking. You can even do that indefinitely, so to speak.

In addition, cardio could hinder the recovery of your strength training and therefore also hinder muscle growth. This is because cardio is a different type of training, which is why people also speak of competitor training. But that too is only the case if you do excessive cardio. Recent research shows that you can safely do HIIT a few times a week, without hindering muscle growth ixx ] .

As long as your sleep and nutrition are in order, for optimal recovery, you can safely combine strength training with other sports. See top footballers taking off their shirts after the game. Despite doing many other types of training besides strength training, almost all of them have muscular torsos. Or read the book “The Hybrid Athlete”. In it, Alex Viada describes how he was able to simultaneously excel in powerlifting and running.


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