Most people are under the impression that cardio is your best friend if you’re trying to lose weight and burn fat. But if you’re trying to gain mass and strength, you must forget cardio.

So, you’ve probably heard things like “cardio will burn muscle” or “you can’t gain muscle if all you do is cardio.” While there is some truth to these statements, cardio isn’t the devil.

Cardio can chew through your muscle, but if you’re trying to gain weight and put on mass, it’s all about timing your cardio and incorporating it properly into a sound training program.

When performed correctly—and at the right time—cardio can be an excellent complementary exercise to a solid strength training program to boost cardiovascular health and increase fat loss. So, let’s look beyond the catabolic reputation of cardio and dive into the research.

Does Cardio Burn Muscle?

When people suggest that cardio burns muscle, they’re referring to the fact that prolonged cardiovascular activity produces a catabolic environment whereby the contractile proteins that comprise your muscles are broken down.

And while that’s partially correct, cardio will burn muscle tissue if you’re doing everything else wrong diet and lifestyle-wise.

If you’re following a well-programming training protocol and eating to support muscle growth, cardio isn’t likely to hurt your gains. Cardio can actually improve your health, with benefits for your risk of heart disease, cancer, and other chronic diseases 1, 2.

A healthy cardiovascular system and cardio also make it easier to prevent fat accumulation and can even improve your athletic performance.

Simply put, cardio might hamper your ability to gain muscle and strength if you make certain mistakes, which we’ll discuss in a minute.

However, if you focus on implementing cardio at the correct times and doing the right activities, you can do it without losing muscle.

Here’s an overview of the top five reasons why people think cardio burns muscle:

  1. They’re not lifting weights
  2. Cardio is part of a crash diet
  3. Excessive steady-state cardio
  4. Too much cardio
  5. Doing cardio at the wrong time

5 Mistakes You’re Making That Can Make You Lose Muscle

While cardio isn’t bad, you could make certain mistakes that might interfere with your ability to gain muscle. Let’s take a look.

1. You’re not lifting weights

If you’re a cardio bunny who isn’t picking up the weight (or isn’t picking them up often enough), cardio probably isn’t to blame for muscle loss—lack of lifting is.

People are under the impression that low-intensity steady-state cardio like running will lead to severe muscle loss and result in a rather scrawny appearance. And if you lift and avoid cardio or do very little, you’ll end up like a bodybuilder. Both of these notions are false.

The big thing here is that if you’re not lifting weights and stimulating your muscles to grow, or at least maintain, they’re not going to. The result? Muscle loss.

So, if you’re an endurance athlete eating and lifting in a way that supports muscle growth, you’re not going to lose muscle. You don’t want to pick cardio at the expense of weightlifting.

2. Cardio is part of a crash diet

For anyone constantly doing cardio, the end goal is likely weight and fat loss. While cardio exercise can be great for both, excessive cardio doesn’t favor muscle maintenance, especially if your diet isn’t on point.

Want proof? A 2015 study published in the Scandinavian Journal of Medicine & Science in Sports had fifteen overweight men follow a diet supplying just 10% of their daily caloric needs for four days.

All these men were also to exercise for nine hours per day—eight hours (20 miles) of walking followed by 45 minutes of arm cranking 3.

Can you guess the results? The men might have lost a ton of body fat, almost five pounds in four days, but they also lost nearly a pound of muscle.

This example is extreme, of course, but many people follow a more moderate version of this plan and fail to understand why they’re losing muscle. For example, people will cut calories by 25-50% and increase cardio for weeks to lose weight.

And while yes, they will lose weight, they quickly become “skinny fat,” and cardio takes the blame. Extreme calorie restriction, which causes muscle loss even in the absence of exercise, and lack of protein will result in muscle loss, not just cardio 4.

Reckless calorie restriction and crash diets are to blame for muscle loss—not cardio.

3. Excessive steady-state cardio

Excessive cardio, especially running, is not ideal for gaining or maintaining muscle mass. Running is hard on the body and appears to cause more muscle damage than other types of cardio. It impairs muscle gain in two ways 5:

  1. Increases muscle protein breakdown before and after running, making it more challenging to build new muscle tissue
  2. It causes more fatigue than other forms of exercise, which can interfere with your ability to effectively strength

Here’s an example. A study published in 1980 looked at an individual’s ability to a combination of strength and endurance training compared to adaptations elicited by either strength or endurance training separately 6. Participants were divided into three groups:

  1. Strength group that exercised 30-40 minutes per day for five days a week
  2. Endurance group that exercised 40 minutes per day for six days a week
  3. Strength and endurance group performed the same daily exercise regimens as the strength- and endurance-only groups

Results showed that people who did strength training and cardio gained almost the same muscle as those who only did strength workouts, suggesting that cardio doesn’t burn muscle, but too much can interfere with your gains.

Generally, don’t exceed 2-3 hours of running per week.

4. Too much cardio, period

As with everything else, cardio is about moderation. Even if you’re doing everything else right—eating, sleep, recovery—too much total cardio can still hamper your gains.

Your body has a finite capacity to recover per week, and if you’re lifting five times a week, adding the same amount of cardio will throw a wrench in your recovery abilities.

But more cardio doesn’t necessarily equate to a harder time building muscle. Studies show that assuming you’re following a proper diet and strength training program, you can gain muscle as effectively with a few hours of cardio as you can without it 7.

Doing more won’t chew through muscle, but it will impair your body’s ability to synthesize new muscle tissue.

5. Doing cardio at the wrong time

Lastly, doing cardio at the wrong time can also cause you to lose muscle—we don’t want to combine cardio and strength training in the same workout.

For example, many people will hop on the treadmill before lifting or interweave strength exercises with high-intensity cardio (ex., CrossFit).

Although it may not seem terrible, it’s not ideal. Performing cardio immediately before a lift makes it harder to perform your lifts at maximum capacity and harder to stimulate muscle growth 7.

And doing cardio immediately after a lift can also interfere with muscle growth by dampening the anabolic signals from weight training 8.

The mechanisms behind why this is are beyond the scope of what we’re covering, but the point is that ideally, you want to keep them separate.

Studies show that as long as you keep cardio workouts short and low-intensity, it won’t impair muscle building 9, 10.

Three Tips To Protect Muscle Gains

So, how do you incorporate cardio into your training program and avoid muscle loss? Follow these tips!

1. Don’t forget to lift

As we’ve said, cardio isn’t the devil—you must know how to time it right. If you’re planning to add cardio to your training program, don’t compromise your lifts for it.

Work it into a well-designed program that balances out strength training with 1-2 days of cardio to enhance cardiovascular health, burn fat, and improve overall performance.

2. Consume enough protein

Triggering muscle damage is necessary to stimulate muscle growth, but protein is required for repair.

If you’re not consuming enough protein, your muscles don’t have the substrates needed to repair tissue, which means it will pull amino acids from elsewhere (i.e., existing muscle tissue).

Ensure you’re meeting your protein requirements daily, especially if you want to gain muscle.

3. Supplement

Protect your hard-earned gains with supplements! While protein, carbs, and fats are essential for muscle growth, compounds like HMB and ForsLean® in Burn Lab Pro® can help to preserve lean muscle mass while accelerating fat burn and enhancing overall performance.

And for times when you need an energy boost to get you through cardio or weight sessions, Pre Lab Pro® comes to the rescue.

It’s the ultimate pre-workout formula with natural ingredients designed to increase work capacity, enhance focus and drive, and accelerate post-workout muscle recovery.


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