The 5 Biggest Myths About Cardio and Muscle Building – Totally Busted | Learn: Your Fitness Business Resource

The 5 Biggest Myths About Cardio and Muscle Building – Totally Busted

Tyler Spraul is the director of UX and the head trainer for He has his Bachelor of Science degree in pre-medicine and is an NSCA-certified strength and conditioning specialist. He is a former All-American soccer player and still coaches soccer today. In his free time, he enjoys reading, learning, and living the dad life. He has been featured in Shape, Healthline, HuffPost, Women's...

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UPDATED: Jun 30, 2021

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  • Cardio is an important part of your overall health; it improves your heart health, helps burn calories and fat, strengthens your respiratory system, improves oxygen levels in your tissues and so on.
  • Research has shown that fasted cardio has two really serious downsides.
  • High-intensity interval cardio is the best cardio out there.

Bodybuilders seem to find and hang onto a lot of misinformation about the relationship between cardio and building muscle and about best practices for cardio itself.

Cardio is an important part of your overall health; it improves your heart health, helps burn calories and fat, strengthens your respiratory system, improves oxygen levels in your tissues and so on.

It’s also an important part of your bodybuilding program, as long as you’re doing it properly and for the right reasons, rather than buying into old (and since disproven) science and whatever the guy across the street says.

Here are the five biggest myths about cardio and muscle building – along with the science-based truth.

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Myth #1: Low-Intensity Cardio Burns the Most Fat

This myth is not only wrong; it also wastes a ton of time in the gym for people who believe it.

The people who subscribe to this myth spend hours doing low-intensity cardio on the elliptical or the treadmill because their only focus is the calories they’re burning during that training.

Instead, they should be focused on high-intensity interval cardio that will burn calories all day long.

Let’s put this in really simplistic (and random) mathematical terms: Would you rather spend an hour on the treadmill and burn 400 calories or would you rather spend 20 minutes doing HIIT and burn an additional 700 calories over the next 24 hours?

It’s like the difference between putting $400 in a jar under your bed or investing it in something that will turn it into $700.

Myth #2: Fasted Cardio Burns More Fat

To its credit, the pseudo-science behind this myth sounds logical. But it’s still wrong and it’s been fairly well-proven wrong.

The theory is that if you do your cardio first thing in the morning, without eating first, your body will be forced to rely on fat stores to do the work since you haven’t given it any fuel.

That really does seem to make sense, but it doesn’t actually work that way.

Research has shown that fasted cardio has two really serious downsides: first, it can result in muscle catabolism (the body tears down muscle tissue and uses that as fuel) and it limits the after-burn effect, which is the raised metabolic rate (for up to 48 hours) that results from a good workout.

There is also research that says eating first thing actually speeds our metabolism on its own and that we may burn more calories (and fat) by working out after we’ve eaten.

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Myth #3: Cardio Is for Fat Loss and Weight Training Is for Building Muscle

That sounds right as long as you don’t look into it too much. This was the thinking for years, but it got debunked way back in the 80s. The fastest and most permanent way to lose body fat is to build lean muscle mass and revamp your nutrition.

So often, people say, “I’m going to do cardio to lose fat first, then I’ll start doing weights in the gym to reshape what I have left.”

Losing a significant amount of weight by doing cardio takes hours and hours of cardio every week for many weeks. Also, the more cardio you do, the better at it you get, and the fewer calories you burn doing it because your body has adapted to the work.

So, all you can do is do more sessions per week with more time per session or more intensity per session until you adapt to that level. It’s a hamster wheel.

The more lean muscle you have on your body, the more calories you burn all day long. Every pound of muscle you add increases your metabolism and you burn more calories whether you’re working out or not.

You don’t have to keep working out more often or for longer sessions and your fat loss isn’t limited to your workout sessions, either.

Myth #4: Cardio Before Weight Training

We wouldn’t call this a myth so much as a misguidance. If you’re doing cardio and weight training in the same session, you have to decide which one to do first.

Many beginners and even some more experienced athletes aren’t sure whether it’s best to do cardio first or to hit the weights first and then do cardio.

The answer is that you need to do your weight training first.

This, of course, is if you’re doing them back-to-back. If you expend too much of your energy store doing cardio, you’re:

  1. Not going to have enough left to handle a really effective weight training session and
  2. You may even get into an issue with your body going into muscle tissue for amino acids because your cardio used up all your glycogen stores. (See myth #2 again)

Myth #5: High-Intensity Cardio Intervals Are Only for Advanced Athletes

This would be true if intensity wasn’t such an individual matter. High-intensity intervals for a more experienced and fit athlete might mean sprinting like a madman for 30 seconds and jogging for two minutes, repeating for a total of maybe 20-30 minutes.

For a less experienced or less fit person, jogging might be the high-intensity part, with walking being the moderate work portion of the workout.

As they become more fit, they can decrease the time devoted to walking and increase the time devoted to jogging and then start sprinting and jogging.

In any event, the less-fit person will get the same benefits as the person doing the sprinting, because the high intensity is what your body thinks is intense.

High-intensity interval cardio is hands down the best cardio out there.

You get more done in half (or less) the time you would with steady-state, moderate or low-intensity cardio. You burn far more calories over the following 48 hours than you would after steady-state cardio. It has no downside, including being too difficult for a beginner.

All you need to do, if you’re not in a fairly fit condition, is to be sure that your high/moderate work is tailored to your fitness level, not someone else’s.

You may see it as being “less than” what someone else is doing, but your body will just see it as hard and will respond by burning fat, increasing metabolism, and improving your cardio function.

Frequently Asked Questions (FAQ)

How many days a week should I work out?

A minimum of three days a week is recommended.

Can I work out twice in one day?

You can, however, it important that you do not overtrain and injure yourself. If you plan on tackling two-a-days, it is imperative that you program rest days into your routine.

Can I exercise if I am sore?

If you are mildy sore, it is okay to exercise. However, if your muscles are very sore, either take a rest day or train the unaffected body parts.

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