Concurrent Training: Can Cardio Build Muscle?

Many gym-goers focus almost exclusively on cardiovascular exercise or resistance training. We’ve all witnessed the five-o-clock rush where not a single cardio machine is vacant. Pretty lame, right? Now you have to wait for 30 minutes until someone finishes their leisurely bike ride or stroll on the treadmill...or do you? 

Not at all. In fact, this is a blessing in disguise since there’s an even better form of exercise waiting for you in the resistance training area; ya know, that intimidating "other" part of the gym with all the meatheads. (It's okay, they're usually pretty friendly and nonjudgmental.)

But don’t worry if you’ve been doing predominantly cardio for exercise until this point. There is merit to both cardio and resistance training, also known as concurrent training, for getting in shape and improving athletic performance. 

People think they need to commit to either being a hardcore bodybuilder or an ultra-marathon runner, but new research suggests that's actually not optimal no matter where you fall on the fitness spectrum.

Here are the basics of why concurrent training is essential for muscle building, fat loss, and overall health.

Benefits of Concurrent Training

It’s common knowledge that cardio is useful for burning fat and keeping the heart healthy, but what about cardio for muscle building? Can cardio actually build muscle? 

In short: Yes it can, but there are some finer points to discuss before you hop on the step mill in hopes of spurring muscle growth...

Quite a few studies show that cardio can build muscle and increase mitochondrial biogenesis when done in conjunction with resistance training (1, 2). 

Hence, concurrent training is thought to be one of the best ways to improve body composition. A large part of this appears to be due to the changes in mitochondrial health in response to concurrent training. 

So, what makes mitochondria so important?

At their most basic, mitochondria are bean-shaped organelles inside of cells that serve as “energy processing centers.”  For example, through cellular/aerobic respiration, mitochondria use molecular oxygen, electrons (from NADH) and pyruvate (from glucose) to create adenosine triphosphate (ATP) - the “energetic currency” of cells. 

Aerobic respiration yields 34 molecules of ATP per each pyruvate molecule. That’s a pretty sizable return on investment, wouldn’t you say? It’s necessary considering that we spend the vast majority of our lives depending on this metabolic pathway for energy. 

But what happens when cells are deprived of oxygen, they need to adapt and divert metabolism to anaerobic respiration - the pathway that produces energy in the absence of oxygen. 

In contrast to aerobic respiration, anaerobic respiration does not occur within mitochondria. Instead, it takes place within the cytosol (cellular fluid). 

A key difference is that anaerobic respiration only yields 2 ATP per pyruvate, making it much less efficient than aerobic respiration. 

However, for getting lean and burning body fat, metabolic inefficiency is precisely what you want! 

Energy Homeostasis and Fat Metabolism

Surviving is your body’s main priority. To do so, the amount of energy the body expends is constantly in flux to account for changes in energy input (i.e. how much food you consume). 

This is why “crash” diets are not smart approaches for getting lean. Your body isn’t easily fooled. 

If you drastically reduce calorie intake and starve yourself, the body senses this and adapts by lowering basal metabolic rate (BMR). In other words, you burn fewer calories throughout the day to compensate for the drop in calorie consumption. Doing excessive amounts of low-intensity, long-duration cardio has the same effect (3). 

As counterintuitive as it seems, if your goal is to get lean (and stay lean), it is not favorable to have an “efficient” metabolism. 

Quite the opposite, actually. If your metabolism is efficient, you’ll have a tough time losing much weight at all.  

As an analogy, let’s say you have a car that only travels 15 miles per gallon of gas. Compared to a vehicle that gets 30 miles per gallon, your car is much less fuel-efficient. Now, let’s apply this to the human body, which is fueled by nutrients/calories instead of gas. Would you rather have your body get “more miles per nutrient/calorie” or fewer? 

When your metabolism is less efficient, you burn more fuel (read: calories) to go the same distance as someone who has a more efficient metabolism. 

Therefore, the less efficient your metabolism is, the higher your basal metabolic rate (i.e. calorie burn) will be throughout the day. 

This is why making your body metabolically inefficient is a great thing for getting lean and staying lean while you focus on building muscle. Plus, you’ll get to eat more without putting on body fat! 

Sounds pretty awesome, right? But how do we make our metabolism less efficient? In a few words: Concurrent training.

Concurrent Training for Burning Fat and Building Muscle

Research consistently demonstrates that a combination of both cardiovascular and resistance training - known as “concurrent training” - is ideal for health, longevity, and increasing metabolic rate (4). 

Cardio/endurance training is generally an aerobic (oxygen-dependent) activity since it involves lower intensity exercise carried out for a longer duration, whereas intense resistance training  (e.g. heavy weight lifting) relies predominantly on anaerobic (oxygen-deprived) metabolism. 

Recall from earlier that aerobic respiration is a very efficient type of metabolism. Intuitively, doing only aerobic exercise isn’t going to help your body become a calorie-burning machine. Your body is already great at aerobic respiration; it’s like second nature. 

This is where intense short-duration forms of anaerobic exercise, such as high-intensity interval training (HIIT) and heavy weight training, play a pivotal role in increasing metabolic rate. Anaerobic exercise forces cells to rely on oxygen-deprived metabolism for energy (which, if you remember from earlier, is a very inefficient process). 

By performing intense, anaerobic exercise regularly, your body increases the number of mitochondria (via mitochondrial biogenesis) to compensate for the increased energy demands at rest (5). 

In layman’s terms, anaerobic exercise holds the key to making your body burn more calories throughout the day, even while you’re laying on the couch watching Netflix. In general, the more mitochondria you have, the higher your metabolic rate. 

However, this is not to say that aerobic exercise (cardio) should be avoided at all costs since it can actually enhance the benefits of anaerobic exercise. 

People often question if cardio builds muscle? Surprisingly, cardio can build muscle...

Mitochondrial Biogenesis & the Role of Concurrent Training

The right types of exercise are arguably the best ways to make your body metabolically inefficient and promote mitochondrial health. When we say “promote mitochondrial health,” we mean boosting the rate at which mitochondria consume substrates (such as pyruvate) to produce ATP and increasing mitochondrial density in cells. (For simplicity, just think of it as an “increase in metabolism.”)

Concurrent training (i.e.lifting in combination with cardio) is arguably the best way of approaching your workouts, and science is continuing to uncover why that is. Recent research shows that a family of transcriptional coactivators - known as the peroxisome proliferator-activated receptor-gamma (PPARγ) coactivator (PGC-1) family - are the “master regulators” of mitochondrial biogenesis (6). 

The PGC-1 family of proteins function as discriminate coactivators, meaning they interact directly with specific steroid hormone receptors and promote transcription - the first step of gene expression. These proteins appear to play major roles in our response to exercise (especially endurance training and cardio). 

New findings suggest that one of these proteins -  PGC-1α4 - actually stimulates skeletal muscle hypertrophy by controlling the myostatin and IGF-1 systems (7, 8). 

In fact, a study in athletes found that PGC-1α4 increased by about 150% after resistance training (9). 

But there’s a catch…

Both PGC-1α4 and another protein - PGC-1α1 - increased significantly more in skeletal muscle tissue after the athletes performed a concurrent training routine of weightlifting followed by cycling. 

In layman’s terms, there’s an “endurance” protein ( PGC-1α1) stimulated primarily by aerobic exercise that acts synergistically with the “resistance training” protein ( PGC-1α4) to facilitate even greater muscle growth. 

The “endurance” protein also regulates many other physiological adaptations to exercise, notably mitochondrial biogenesis, fiber-type switching, and protection against muscle catabolism (10). However, it does not increase anabolism in skeletal muscle mass on its own.

Given these novel findings, the case for concurrent training and doing cardio even while trying to build muscle only gains credence. 

Is Concurrent Training the Best Workout Style?

All in all, the metabolic, muscle-building, and fat-burning benefits of concurrent training are more pronounced than if you were to do just cardio or just resistance training. Neglecting either aerobic or anaerobic exercise modalities is only going to limit your potential.

Therefore, the most effective workout style for getting leaner, stronger, more muscular, and living longer is a combination of resistance training and cardio. 

There seems to be a misapprehension as of late that you should only lift weights and keep cardio to a minimum since the latter is merely a means of “burning calories,” but that’s simply not the case. Don’t be lazy; even if your primary goal is to pack on mountains of muscle, you should still be doing some cardio. 

And obviously, you should be focusing on hard and heavy resistance training (with modest amounts of cardio) even when your main goal is to cut body fat; doing hours of cardio and barely lifting is not the answer to getting shredded. 

But how much cardio is too much? Check out our Guide to Cardio to figure out how much cardio you should do.