Does Cardio Kill Your Muscle Gains?

Cardio exercise has a lot of health and performance benefits, and it can also be a useful tool for losing weight.

But what if your goal is to build muscle?

Is it something you should be doing? How much should you do? And most importantly, will doing cardio kill your gains?

Let’s answer all of these questions right now.

2 Ways Cardio Can Kill Your Gains

First, the bad news.

Cardio definitely has the potential to be bad for muscle growth.

That doesn’t mean it will be bad, or that it will kill your gains. It just means that the potential is there for cardio to negatively affect your muscle building progress.

The good news, however, is that it’s pretty easy to prevent this from happening.

In order to do that, you need to first understand the two main problems that cardio can create.

1. It Can Burn The Calories Needed For Building Muscle

In case you didn’t know, you can’t build muscle out of nothing. There needs to be some source of additional energy available for muscle growth to occur.

This “additional energy” can come two different ways:

  • External Sources
    This would be a caloric surplus, where you eat more calories than you burn to provide the additional energy needed to support the muscle building process.
  • Internal Sources
    This would be your stored body fat being converted into the additional energy needed to support the muscle building process.

Now, where this gets tricky is the fact that not everyone is going to be capable of using internal sources for this purpose (at least, not to the meaningful degree we’d all like to).

And in cases like those, external sources (a caloric surplus) will indeed be a requirement to gain the muscle you want to gain.

So what does cardio have to do with this, you ask? It’s pretty simple…

Building muscle requires more calories. Cardio burns calories.

Can you see the direct conflict here?

You need to eat additional calories in order to build muscle, and cardio can potentially burn off those calories.

Therein lies the first way that cardio can kill your gains: by wiping out the calories your body needed to use for building new muscle.

Here’s an example.

Let’s say that you’ve figured out that your calorie maintenance level (the amount of calories your body needs per day to maintain your current weight) is 2000 calories.

Again, this is just a random example.

And let’s say that as part of your effective muscle building diet, you’re going to eat 2200 calories a day to create a daily caloric surplus of 200 calories.

So far, so good.

But what if you then add in cardio exercise 3, 4, or 5 days a week? Or maybe even 6 or 7 days a week?

And what if it’s an amount of cardio that burns off those 200 additional calories, which puts you right back at your 2000 maintenance level (or potentially even below maintenance, in a deficit).

In this scenario, you’ll no longer be in a surplus, and your muscle building gains will suffer as a result.

Additional details here: How Many Calories A Day To Build Muscle

2. By Interfering With Recovery And Progress

Whether we like it or not, and whether we’re too stubborn to accept it, the reality is that there is only so much exercise our bodies can handle before it starts to interfere with our ability to recover.

This is why all effective weight training programs are designed with sufficient recovery in mind.

The volume, frequency, intensity, split and schedule, exercise selection, deloadseverything. It’s all set up in a way that optimizes recovery.

Now add cardio into this equation.

Cardio represents additional exercise, and additional exercise requires additional recovery.

Not just in terms of the body parts being used the most (typically the legs with most forms of cardio), but the central nervous system (CNS)… which affects everything.

Weight Training + Cardio = More To Recover From

As you can imagine, adding any other form of exercise on top of your weight training workouts (which are already putting a tremendous amount of stress on your body) increases the potential for cutting into the recovery process.

And therein lies the second way cardio can kill your muscle gains.

Now, exactly how much of an impact cardio will have on recovery would depend on the exact frequency, duration, and intensity of the activity being done.

For example, 3 cardio workouts per week will have less of an impact than 5-7 workouts.

30 minutes of cardio will have less of an impact than 60 minutes.

A low intensity activity – like brisk walking – would have little to no impact compared to a more moderate intensity activity… such as jogging.

And neither would have nearly as much of an impact as something with a high intensity – like HIIT – which can almost be like adding an extra weight training session in terms of the stress it places on your body and how recovery-intensive it is.

Endurance Doesn’t Play Well With Muscle And Strength

In addition to recovery, cardio can also hinder muscle gains thanks to something called the interference effect.

Research shows that the adaptations needed for your body to improve at endurance-based exercise like cardio interferes with the adaptations needed for your body to improve at strength-based exercise like weight training.

This doesn’t mean you can never have both cardio and weight training in your program, or never have endurance goals and strength/muscle building goals at the same time.

It just means that these goals conflict with each other, so trying to simultaneously improve at both probably isn’t going to work very well, and doing too much cardio can slow muscle gains to some extent.

How To Easily Prevent These Issues

So now you know the two most common ways that cardio can be bad for muscle growth or potentially kill your progress altogether.

The next obvious question is, how do you prevent it from happening?

It’s quite easy.

1. Eat More

To prevent cardio from burning the calories needed to support the muscle building process, you simply need to eat additional calories to compensate for the calories being burned during cardio.

This way, your intended surplus remains intact and your muscle gains aren’t negatively affected.

For example, if your maintenance level is 2000 and you’re eating 2200 calories a day to create a small surplus (again, this is just a random example), and you then burn 300 extra calories during cardio today, you’d eat an extra 300 calories (2500 total in this example) to make up for it.

Simple enough, right?

There are, however, two important things you need to be aware of:

  1. The number you get from your smart watch, workout app, calculator, or cardio equipment you’re using for how many calories you’re supposedly burning during cardio is often overestimated. And if you end up eating more calories than you needed to (e.g. it says you burned 500 but you really only burned 300), your surplus would be too big and excess body fat would be gained. So, always be sure to closely monitor real-world changes (body weight, measurements, etc.) so you’ll know if something is off and an adjustment needs to be made.
  2. If you’re someone who already struggles to eat enough to create a surplus (details here: Why Can’t I Gain Weight?), adding in a bunch of cardio will only worsen that problem. In this case, a more realistic option might be to cut back on cardio rather than trying to out-eat it.

2. Do Less

To prevent cardio from causing any issues with recovery or progress, you need to keep it to a frequency, duration, and intensity that isn’t problematic for you.

Exactly how much cardio is “problematic” in this context will vary from person to person based on individual recovery capabilities.

But, in general, the best way to approach cardio when muscle growth is the goal is to do the least amount necessary to get the benefits you’re doing it to get.

Whether you have endurance or performances goals, or you’re doing it for overall health, start out doing the least amount needed, at the lowest intensity needed, and then monitor how things go.

If everything feels good, your weight training progress is going well, and you’re building muscle at a solid rate, awesome.

Feel free to stick with this amount or experiment with gradually adding in a little more if it’s needed.

If things continue to go well, great.

But if that’s not the case, or it eventually becomes problematic over time, you need to make sure you adjust accordingly by cutting back on cardio in some way (doing it less often, or for shorter durations, or at a lower intensity).

If you don’t adjust, you run the risk of letting cardio kill your gains.

To learn more about the best way to balance cardio and weight training when building muscle is your goal, check out my specific recommendations in chapter 14 of Superior Muscle Growth.

It’s all covered in there.

What’s Next?

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ABOUT THE AUTHOR
About Jay
Jay is the science-based writer and researcher behind everything you've seen here. He has 15+ years of experience helping thousands of men and women lose fat, gain muscle, and build their "goal body." His work has been featured by the likes of Time, The Huffington Post, CNET, Business Week and more, referenced in studies, used in textbooks, quoted in publications, and adapted by coaches, trainers, and diet professionals at every level.