Does Cardio Burn Muscle? No, If You Avoid These 3 Mistakes.

I love strength training and I always have. Give me a barbell, some weights, a couple of dumbbells, and a few bands, and I’ll be one happy fellow.

But, I recognize that people also enjoy doing cardio. As someone who used to run for a time, I remember the allure.

In that line of thinking, I’ve gotten this question a few times before, “Does cardio burn muscle mass?”

So, if you’re interested in lifting weights and doing cardio, read on. We’ll go over absolutely everything you need to know about combining the two.

Does Cardio Burn Muscle?

Well, cardio can lead to muscle loss, but a better way to phrase it would be, “Does cardio impair muscle gain?”

The question of, “Does cardio burn muscle mass?” sounds logical, but it implies that aerobic exercise alone is the problem. In reality, cardio alone is rarely the problem, but how the trainee chooses to approach their overall training and nutrition.

To give you some context, we’ll briefly go over a 2012 meta-analysis of 21 studies (1). In it, researchers concluded that combining cardio and weight training improperly can result in up to:

• 31 percent lower muscle growth rates
• 18 percent lower strength gain rates

Researchers conclude, “Our results indicate that interference effects of endurance training are a factor of the modality, frequency, and duration of the endurance training selected.”

In other words, how aerobic exercise impacts our strength training depends on the type of cardio we do, how often we do it, and how long each session is. This makes a lot of sense when you think about it. It’s one thing to cycle for an hour per week, and it’s a whole other thing to run for 40 minutes five days each week.

For most people under normal circumstances, cardio won’t necessarily lead to muscle loss, so long as the person eats enough calories and protein (2). But, this doesn’t mean it can’t interfere with future strength and muscle gains. Let’s review further.

Cardio’s Effects on Muscle Growth And Strength Gain

The meta-analysis we saw above seems pretty cut-and-dried, right? Do cardio and expect to slow down muscle growth by a third and significantly slow down strength gains. But is this the whole story?

On the one hand, we have the interference effect. Aerobic exercise is inherently different from weight training, and the metabolic processes it stimulates aren’t necessarily good for muscle growth. Trying to improve in both is like chasing two rabbits running in opposite directions. If you try to catch both, you won’t get anywhere. But you can still grab one and let the other get away temporarily.

On the other hand, we can also argue in favor of aerobic exercise and its positive effects on our weight training results. Most notably, we need some basic endurance to go through our weight training. If you find yourself stopping sets because you’re getting winded, you’re leaving gains on the table.

For example, a few years ago, I decided to do some high-repetition squatting after months of heavy training. So, I loaded less weight on the bar and thought I would do four sets of 15 to 20 repetitions. By the time I got past ten repetitions, I could barely keep going, and not because my legs were too tired. I simply didn’t get enough air.

This is because lifting weights is more aerobic than most people realize, especially when doing full-body exercises like squats and deadlifts (3). Whether you like it or not, you need some endurance to train effectively.

Besides having essential endurance to do individual sets, we also need decent conditioning to recover sufficiently between sets and workouts. For example, if it takes you several minutes to bring your heart rate down after an average set, you have two options:

• Spend nearly two hours per workout to do your sets in a relatively recovered state
• Try to rest for the recommended periods, but risk getting too tired and unable to do enough repetitions (4)

Research shows that good endurance allows us to recover better between individual sets and workouts (5). So, while many people avoid cardio for fear of losing their hard-earned gains, not doing any cardio is also not an option. Instead, we should consider how we can include some cardio into our training without negatively impacting muscle growth.

In case you’re getting a bit confused, don’t worry. We won’t dive any deeper into the topic. If you’re looking for additional material on the relationship between aerobic capacity and recovery, I strongly recommend this.

Do We Even Need Cardio For Fat Loss?

Ah, cardio and fat loss. Walk into any gym at the start of spring, and you’ll see dozens of people on cardio equipment, running, cycling, and climbing. Ask any of them about their goals, and most would probably say, “I’m trying to lose weight and get in shape for the summer.”

It’s clear that cardio is the go-to choice for many people looking to shed some fat. But how good is it for that goal? Not very, I’d say.

We know that weight loss comes down to creating and sustaining a calorie deficit - consuming fewer calories than you burn (6). The most obvious way to achieve this is to eat less. But many people also love to do tons of cardio to lose more weight. The problem is, cardio isn’t your best option, and there are three reasons why:

• Cardio makes you tired and pulls away resources your body would otherwise use for muscle recovery and growth.
• Some research shows that cardio can increase hunger for some people, leading to compensatory eating (7). In other words, you might burn 500 calories, but overeat later and cancel that benefit out.
• On its own, cardio doesn’t burn that many calories, and you can’t hope to out-exercise a bad diet. You still need to focus on your calorie intake more than anything.

Fat loss training is about causing enough stimulus to retain your strength and muscle mass without piling on too much fatigue. This is because eating less compromises your recovery, so doing lots of work increases the risk of overtraining and makes you more likely to lose muscle.

The good news is that most people won’t need to do a single minute of cardio to get decently lean. It’s only when folks try to step on a bodybuilding stage that cardio becomes beneficial and even necessary.

Still, this isn’t to say that you shouldn’t do any cardio. Just as I recommend some cardio while gaining muscle, I also advise people to do aerobic exercise when losing fat. But this mostly has to do with the positive effects of cardio on our aerobic capacity and performance, not because of the great calorie burn. We’ll go over specific recommendations below.

But What About High-Intensity Interval Training (HIIT)?

High-intensity interval training has become quite popular in recent years. HIIT takes less time, burns many calories, has a small EPOC effect, and might even add a bit of muscle to your frame.

But many people fail to remember something important: HIIT is incredibly demanding. Sure, you might only do it for twenty minutes, but the effort is tremendous. You stress your entire body a lot more, and you need time to recover from that work later.

I remember doing an interval running session after taking a break from HIIT for six months or so. I went to the local track, did fifteen minutes worth of intervals, and went home. It then took me over five days to overcome the incredible soreness in my lower body. My adductors and glutes were fried, and I had to miss a squat session because of that.

Depending on the effort you put into a HIIT session, it could almost be comparable to a weight session. For instance, if you do three weight sessions and two HIIT workouts, you’re essentially doing five sessions per week. It mostly comes down to asking yourself, “Is my recovery good enough for me to train five days per week?”

Plus, we also need to consider how a HIIT session might impact your subsequent weight training. For instance, say that you follow a typical upper/lower split like this one:

So, you decide to add a HIIT session:

How would your second upper and lower workouts turn out after that? In other words, would the juice be worth the squeeze?

How to Do Cardio If Your Goals Are Muscle Growth, Fat Loss, And Strength Gains

Given that most of my readers primary care about strength training and physique development, I’ve listed the three crucial things you need to pay attention to if you want to do cardio:

1. Be Mindful of The Type

Your first consideration for mixing cardio and weight training should be for the form you choose. There are plenty of ways to get aerobic, so you should consider which one has the smallest impact on your recovery and lifting performance.

For instance, many people choose running because, let’s face it, running is one of the most popular cardio options. Ironically, running is also one of the worse choices because of its toll on your body. Most notably, research suggests that running hinders lower body strength gains significantly (1). This makes sense, given that your leg muscles work the most, so it’s only natural for your performance to drop and strength to stagnate.

High-intensity interval training is another form of cardio to be extremely careful with. It takes a significant toll on your recovery, and doing too much of it can lead to poor weight training performance and stagnation. As I shared above, I had to miss a squat session after interval running before, which is not exactly ideal for strength and muscle gains.

Low-impact choices like cycling on a stationary bike seem best (1). The reason is, they still tax your aerobic system considerably and deliver many of the benefits you would expect. But unlike more demanding modalities, these don’t fatigue you as much and don’t stop you from lifting weights well.

Other good examples to consider include:

• Elliptical machine
• Incline walking on a treadmill

2. Be Mindful of The Duration

Besides choosing the right form of cardio, you should also make sure to keep the amount moderate. Even less impactful options like stationary bike cycling can lead to muscle and strength loss if you do too much.

The problem is, many people overdo cardio because they feel it’s vital for effective fat loss. But, as we discussed above, you don’t need the caloric burn from cardio to lose fat. Instead, you need to focus on lifting weights, getting enough protein, and maintaining a calorie deficit (2, 6). Some cardio can be beneficial, but you don’t need several hours’ worth of it to get lean.

Here is what I recommend:

Start with a couple of 20-minute low-intensity sessions per week, do that for a few weeks, and monitor your recovery. Take note of:

• How you’re feeling
• How you’re performing at the gym
• If you’re experiencing more soreness
• If cardio-related aches are preventing you from lifting weights

You can gradually bump it to an hour of cardio per week. I don’t see a need to do more than that, especially given that you’re already lifting weights. Plus, if you tend to move around a lot during the day, you might not even need that much.

3. Be Mindful of The Timing

The final thing you need to be careful about is the timing of your cardio sessions. This alone can have a significant impact on your weight training.

Many people find it convenient to do their cardio when they go to the gym for a lifting session. Since you’re already there, you might as well cross it off your list, right? Well, it’s not that simple. Research suggests that doing as little as twenty minutes of cardio before lifting weights can lower your training performance.

In one study, subjects had to perform 20 minutes of treadmill running at four different speeds (8). Ten minutes later, they had to do five resistance exercises (high pull, squat, bench press, deadlift, and push press) for three sets of 6 to 10 reps with 70 to 80 percent of their 1RM. Subjects also got to rest for three minutes between sets.

Researchers found that subjects who did aerobic exercise before lifting got between 9.1 and 18.6 percent fewer repetitions. Their squat performance took the largest hit, which seems logical, given that your legs get tired on the treadmill.

So, what does this mean? Well, let’s say that you can typically do 27 repetitions across three squat sets with a given weight. If you do cardio before that, you can drop to as few as 22 total repetitions. And that’s just your performance on a single exercise. What if you plan on doing four, five, even six movements?

If you must do cardio around your weight training, make sure to do it after. That way, you can get the most out of your lifting performance and do some aerobic exercise before going home. It’s not ideal, but it’s better.

In any case, it would be better to do your cardio or rest days, if possible (9). This will put enough time between your cardio and resistance training, hopefully minimizing the interference effect.

If you can’t do cardio on rest days, make sure to space the two sessions out by at least six hours (10). For example, do your cardio in the morning, and lift weights in the evening.

Does Cardio Burn Muscle: To Summarize

So, does cardio burn muscle? It likely doesn’t under normal circumstances. But this doesn’t mean it can’t interfere with future muscle and strength gains.

So, here is a quick summary:

1. Be careful what type of cardio you do.

HIIT is more demanding, and activities like running can prolong recovery. It’s better to go for less impactful options like stationary bike cycling, using an elliptical, and incline walking on a treadmill.

2. Be careful how much cardio you do.

Even less impactful activities can interfere if you do too much of them. As a rule of thumb, I don’t recommend doing over an hour of cardio per week, regardless if your goal is fat loss or muscle gain.

3. Be careful when you do cardio.

Ideally, you should do your cardio on days when you don’t lift. This will give you more time to recover and hopefully minimize the interference effect. If that’s not possible, try to space out your cardio and lifting by at least six hours - for example, cardio in the morning and lifting in the evening. And if even that isn’t possible, do your cardio once you’re finished with the weights.

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