When bodybuilding if you want to lose fat, you must do cardio, correct? At least, that’s what most fat loss experts and personal trainers preach.
But did you know that cardio can actually prevent you from getting lean? And that cardio can blunt your ability to pack on new muscle?
In this evidence-based article, you’ll discover why cardio can have such detrimental effects. In addition, you’ll find out what you should do instead if you bodybuilding or want to shape a shredded figure.
Let’s dive in!
Do You Have to Do Cardio to Lose Fat While Bodybuilding?
The answer is no and here is why.
Franco Columbu 2x Mr.Olympia: “We didn’t do any cardio when bodybuilding back in the day. Bodybuilding with 30 second rest between sets is cardio!”
That’s because fat loss is all about energy balance. To lose fat, you must consume fewer calories than you burn. In other words, you must be in a calorie deficit.
It doesn’t matter, however, whether you achieve that energy deficit by eating less or by doing cardio − given the same energy balance, you’ll lose the same amount of weight and fat.
So, you’ll get identical results whether you burn eight hundred calories each week through cardio or you just reduce your calorie intake by that number.
(And no, it doesn’t matter whether you do that cardio in a fasted state or bodybuilding exercise in the ‘fat burning zone’ − you’ll get the same outcome.)
Now, you may argue that even though cardio doesn’t have any unique fat- loss benefits, it still helps you get lean because it causes you to burn calories.
While that seems to make sense, that’s not how it works in real life. That’s because there are three reasons why adding cardio to your bodybuilding workout plan isn’t the most effective way to enhance fat loss.
The first one is that…
Reason #1: Cardio Tends to Reduce Overall Activity Levels
Owing to a concept called constrained energy expenditure, adding cardio to a bodybuilding exercise plan often doesn’t reduce total daily calorie expenditure.
Constrained energy expenditure refers to the fact that after people do (aerobic) exercise, they unconsciously tend to reduce their overall energy expenditure, in particular their non-exercise physical activity (NEAT).
In simpler terms, if someone burns calories through cardio, they’ll automatically become less active throughout the rest of the day.
For instance, after a cardio session they may slouch around in their chair instead of sitting in an active and upright position.
They may keep their hands and feet still, instead of fidgeting and bouncing their feet around, as they otherwise might. Or they may drive to work instead of walking or cycling.
You may have experienced this yourself as well. After a physical day, cardio or heavy bodybuilding workout, it may require too much energy to go to the kitchen to grab a glass of water, even though you’re thirsty.
But if you weren’t active that day, you wouldn’t have a problem dragging yourself out of the couch in the quest for a glass of water.
Owing to such (unconscious) adaptations, total calorie expenditure doesn’t tend to increase much, if at all, when people add cardio to their bodybuilding workout program. That’s why cardio isn’t effective for losing fat.
One meta-analysis on overweight and obese subjects, for instance, concluded that “aerobic exercise is not an effective weight loss therapy in these patients.”
And another meta-analysis, which mostly examined cardio, found that adding cardio to a diet plan didn’t enhance weight loss results (11kg vs. 10.7 kg of weight loss).
But that’s not all.
Adaptations in activity levels aside, there’s another reason cardio isn’t ideal for fat loss. I’m referring to the fact that…
Reason #2: Cardio Doesn’t Burn That Many Calories
In fact, you’ll burn about the same number of calories during resistance training as you do during cardio, as found by a 2015 study from the University of Colorado.
The scientists compared how many calories recreationally active men would burn during thirty minutes in the following scenarios:
- Steady-state cardio: This routine consisted of doing steady-state cardio at 70% of maximum heart rate
- Strength training/bodybuilding: This routine was a full-body resistance-training workout during which each exercise was done for three sets of ten reps
- HIIT training: This high-intensity interval training routine consisted of intervals of twenty seconds at maximum effort, followed by forty seconds of rest.
As you can see in the graph below, energy expenditure did not significantly differ between the resistance training and cardio sessions.
In other words, from a calorie-burning perspective, bodybuilding and resistance training is just as effective for fat loss as cardio.
However, hitting the weights also has two additional benefits over cardio.
First, bodybuilding and resistance training enhances your muscle mass. Second, research shows that we tend not to suffer constrained energy expenditure after we hit the iron.
Thus, while cardio tends to reduce your overall activity throughout the rest of the day, strength training and bodybuilding doesn’t have that negative effect. That’s why lifting weights is better for fat loss than cardio is.
So, to summarise what we have covered so far:
Cardio isn’t ideal for fat loss because most people automatically compensate for the calories they burn during cardio by moving less throughout the rest of the day.
Instead, it would be better to do resistance training because it optimizes muscle mass, burns just as many calories, and doesn’t cause a reduction in total energy expenditure.
Now, what we haven’t covered yet is the main downside of cardio − one that’s a lot more worrisome than the fact that cardio isn’t ideal for fat loss, namely…
Reason #3: Cardio Hurts Muscle Growth
That’s what a 2012 meta-analysis published in the Strength and Conditioning Journal found.
The researchers looked at how adding cardio to a resistance training plan would influence hypertrophy, and they found that it lowered muscle growth effect size by almost 50%.
That’s right! All those hours of grinding away on the treadmill may do more harm than good for your muscle mass and bodybuilding goals. (There’s a reason most long-distance runners look like walking sticks.)
But why does cardio hurt muscle growth?
The primary reason is the influence cardio has on the pathways mTOR and AMPK.
I won’t bore you to death with how these pathways work, but the key takeaway is that the mTOR enzyme stimulates muscle growth while AMPK decreases it.
That’s why you want to have elevated concentrations of mTOR. But low levels of AMPK in your muscles, something lifting weights and bodybuilding helps you accomplish.
The problem, though, is that cardio triggers the exact opposite. It reduces muscle growth by increasing AMPK while reducing mTOR.
What’s more, overdoing cardio also creates excessive levels of fatigue, which can further reduce muscle growth by impairing gym performance. That’s why you should avoid cardio if you want to optimize muscle growth.
Now, some people will argue that I’m overstating the interference effect of cardio. They’ll cite studies such as this one or this one to show that doing cardio doesn’t hurt but actually causes muscle growth.
But what they fail to mention is that these studies are done on poorly trained or untrained individuals, which alters the situation.
Because the truth is, if someone has been a couch potato for the last few years or decades, any training stimulus is enough to trigger muscle adaptations − even cardio.
After untrained folks do a few weeks of cardio, however, the training ceases to remain a sufficient stimulus and won’t enhance muscle growth further, but will actually impair it.
So, the bottom line is that you should avoid cardio if you want to maximize muscle growth, instead focus on proper bodybuilding. That said, even though cardio is not needed or is even counterproductive in almost all scenarios…
There is One Exception When Cardio Can Be Beneficial
By now, it may seem that all the data is anti-cardio for bodybuilding and those who want to lose fat and build muscle. However, besides cardio’s health benefits, there is one other scenario in which adding it to your workout plan can be helpful.
That’s when you want to lose fat but cannot reduce your calorie intake further − something that can happen to physique athletes when they prepare for a show.
For instance, let’s say you’re going on stage in eight weeks from now and you’re already relatively lean. However, to optimize your chances of winning, you’ll have to drop an additional five percent of body fat percentage, which means you’ll have to reduce your calorie intake further.
Now, the problem is that since you’ve already been dieting for months, you may not be able to set your calorie intake any lower.
Further reducing your calorie intake may make it impossible to consume enough protein and hit your daily micronutrient needs. (This is often a problem for those who prep for a bodybuilding or a physique contest.)
Plus, you already hit the gym six days per week, and you can’t add extra volume on top of that because that would put you at risk of overtraining.
What should you do then?
Your only solution would be to add cardio to your workout program. Sure, that’s not ideal from a muscle-maintaining perspective. But you’ll have no other options left.
That’s why cardio can be beneficial for physique competitors. But in 99% of the other scenarios it’s better to avoid cardio and focus on getting lean by eating less and doing enough strength training instead.
You might also like: 17 Powerful Tips To Boost Muscle Growth [Backed By Science]
Do All Forms of Cardio Hurt Muscle Growth?
The answer is no. Very low-intensity activities such as walking and low-pace cycling don’t interfere with muscle growth because they’re not intensive enough to trigger much of an adaptation response.
All forms of cardio done at a moderate to high intensity, however, interfere with muscle growth. And the higher the intensity of the cardio, the stronger the interference.
Also, it’s important to note that the extent of the cardio you do has a huge impact on how it will influence your gains. To be more specific, the more cardio you do, the more it will interfere with muscle growth.
Here’s What to Do If You Want to Do Cardio
It is clear that cardio doesn’t help but can actually hurt progress in most scenarios. That’s why, for 99% of lifters and bodybuilders, it’s best to cut all moderate- to high-intensity cardio from their workout plan.
(Low-intensity cardio such as walking and low-paced cycling are fine.)
If, however, you still want to do cardio, what follows are five tips you can use to minimize the downsides cardio can have on your gains.
1. Avoid cardio forms that have much of an eccentric phase
Don’t perform cardio movements that have much of an eccentric phase, such as running.
That’s because the most muscle damage occurs during the eccentric part of a movement. (In this case, that’s the phase when your foot hits the ground and you absorb your body weight.)
Instead, perform cardio that does not have much of an eccentric component, like cycling on an exercise bike or on an Air Bike.
Both of these movements produce less muscle damage, which helps you recover faster from your cardio sessions. As a result, the cardio will have less of a negative impact on your lifting performance and bodybuilding.
2. Schedule your cardio as far away from your strength-training workouts as possible
Let’s say you want to do a cardio session on the exercise bike. Since that movement primarily trains your leg muscles, it’s not wise to do that training on your leg days.
That’s because doing cardio before you lift weights increases fatigue and reduces strength performance while doing cardio after your resistance training hurts muscle growth by interfering with AMPK and mTOR.
Instead, do the cardio on a rest day, ideally at least twenty-four hours away from your resistance-training workout. That way, the cardio will have less of a negative impact on your lifting performance.
3. Keep the intensity of your cardio session low
The higher the intensity of the cardio, the stronger the interference effect. That’s why you want to keep the intensity of your cardio sessions low.
A good guideline to hold onto is that you should still be able to breathe comfortably through your nose. If you cannot do that, the intensity is too high and the session will interfere with muscle growth.
An excellent form of cardio is slow-paced cycling. Other good options are walking, stepping on the Stairmaster, or using an Air Bike.
4. Don’t do more cardio than necessary
The more cardio you do, the more it’ll interfere with your strength and muscle gains. That’s why it’s best to limit the amount of cardio you do. Ideally to no more than twenty minutes per session.
If you have to do more cardio − forty minutes in total, for instance − then it’s better to split up the total volume into smaller sessions. That will minimize the negative impact of cardio.
The Bottom Line on Cardio for Fat Loss and Muscle Growth
At the end of the day, fat loss comes down to one thing: energy balance.
It doesn’t matter whether you obtain a negative energy balance through diet or through cardio, the fat loss results will be the same. That’s why you don’t have to do cardio to lose fat.
I don’t recommend cardio for fat loss since such sessions automatically causes most people to become less active throughout the rest of the day, causing them burning the same number of calories as they otherwise would.
But that’s not all.
A bigger problem with cardio is that it impairs muscle growth, which it does by increasing AMPK while lowering mTOR. That’s why, if you want to maximize muscle growth, it’s best to cut cardio from your bodybuilding exercise plan.
Instead, focus on optimizing your diet and maintaining a proper bodybuilding exercise routine. That’ll bear more fruit when it comes to shaping an eye-catching figure.
Do you have anything else to share about cardio? Or do you have any questions you’d like to have answered? Let us know by leaving a comment below.
Certified Personal Trainer and Fitness Writer
Stefan de Kort is a certified personal trainer and fitness writer from the Netherlands. He focuses on creating science-based content, and always strives to present both sides of an argument. Alongside studying physical therapy at the Han University of Applied Sciences in Nijmegen, the Netherlands, Stefan has been ghostwriting for over seven years. Content he has produced for his clients has been published in publications like Men’s Fitness, Inside Fitness, Women’s Health, IRON MAN, and others. Besides, he has written four Amazon best-sellers for his clients. When Stefan is not writing and separating scientific facts from marketing mumbo-jumbo, he’s either giving personal training, working out, or exploring exotic countries.