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Does Cardio Kill Gains?

It’s the big question. And the answer is commonly misexplained. Does cardio kill gains?

Cardio has an array of benefits and comes highly recommended by both doctors and fitness trainers. Yet, it causes a process where our body breaks down energy stores. And you want to gain muscle.

It can get a bit nuanced. That’s why I took a closer look. I gathered the research to answer this question once and for all. Let’s get moving!

Man flexing arm

Source: Sarah Althea (Flickr)

Does Cardio Make You Lose Muscle?

Overdoing it with cardio will bring your gym gains to a dead halt. However, the right amount of cardio and in the right order can increase your gains.

You’ll also reap the benefits that cardio has to offer, including:

  • Improved cardiovascular health
  • Improved respiratory health
  • Increased recovery abilities
  • Optimal body composition
  • Decreased risk of diabetes

Here’s the thing:

Heavy lifting creates small tears in the muscles. After your workout, your body repairs these damaged muscle fibers which cause growth (hypertrophy). And muscle growth requires energy.

Many fear cardio because it burns energy. For men, it also decreases testosterone levels which is associated with higher body fat % and less muscle. But, does this mean you shouldn’t do it?

If done right, cardio can increase the efficiency of your body’s systems. It can even help you break through those frustrating plateaus.

People running on treadmills at gym

Don’t be afraid to jump on one of these things from time to time. Source: Giovanni Chigogne (Flickr)

But, how?

Cardio is great for endurance. It’s also excellent for promoting muscle recovery. As your heart health and circulation improve, your body becomes more efficient at providing the oxygen and nutrients to the muscles that need it.

What does this mean?

It means your body is better at maintaining your energy levels and clearing lactic acid from the muscles. Lactic acid builds up when we don’t have enough oxygen available and. It leads to muscle fatigue.

If the body becomes more efficient at clearing lactic acid, you can lift longer and heavier. In turn, your lifting sessions are more productive and you make gains faster.

Cartoon of weightlifter

Your muscles start building up lactic acid when they don’t have enough air. Source: Work it & Lactic Acid (Flickr)

How To Do Cardio Without Burning Muscle

There are 3 main aspects to consider. The amount, intensity, and order are significant. Let me explain.

The Amount Matters

Various studies showed that doing cardio less than 3 days a week for no more than 20-50 minutes a session had little to no impact on bodybuilding gains.

More than that decreases your total force generation capacity, meaning you lack the energy you need to sustain the time under tension to drive muscle growth.

Another study analyzed 4 different groups over a 6-week duration. Each group was given a different training program.

First group was strictly strengthening exercises. Second group did cardio once a week, with 3 strengthening days. Third group did cardio and strengthening during every workout. Fourth group did nothing.

Researchers found that the first and second group had the most bodybuilding gains. Translation: stick to 3 30-minute cardio sessions (or less) per week to avoid losing muscle.

The Order & Intensity Matters

Weightlifters like to give it their all. When I’m strength training, I want to lift the most I can to achieve optimal gains.

For cardio, you want to dial it back. Stay between 60-85% of your max heart rate. Try low-intensity cardio such as cycling, swimming, or rowing. You’ll get the best results and won’t wear yourself out.

If your ultimate goal is to gain muscle and get bigger, avoid doing cardio before you lift. The YouTube video below explains this more in-depth.

It talks about energy-stores and how we use them, and whether you should lift or do cardio first.



Q: What is the best time to do cardio without losing muscle?

A: For optimal gym gains, perform your cardio sessions on your rest days. If this isn’t possible, try to perform your cardio sessions as far apart from your lifting sessions as you can.

You can always lift in the morning, then do cardio at night.

Q: What kind of cardio should I be doing?

A: It depends on your goal. If you’re are looking to strengthen and build the upper body, lower body cardio is best. Try out cycling or running.

If you’re looking to strengthen and build the legs, upper body cardio is best. Air bikes are a great form of cardio that won’t kill your gains.

Q: What’s the maximum amount of cardio I can do without losing muscle?

A: From research, it seems that any more than 3 50-minute sessions could cause you to lose your bodybuilding gains.

Q: Is there such thing as cardio hypertrophy?

A: Not really. Yet, there’s a thing called cardiac hypertrophy which is the enlargement of the heart muscle. Cardio activity works this muscle, building your endurance and increasing the size of your heart.

A strong heart increases the efficiency of your lifting sessions. However, an overly large heart can have adverse effects, such as a heart attack or stroke. There’s always a fine line.

This is another potential reason to keep your cardio to a minimum if your goal is to build muscle.

Woman riding air bike

Air bikes are great for HIIT training which can help you build muscle while doing cardio. Source: The Alpha Project (Flickr)


Final Thoughts

Essentially, if you eat enough, don’t overdo it, and train properly, cardio won’t kill your gains. In fact, it could enhance them.

Educating yourself on how the body’s systems work and the science behind it can help you make informed decisions regarding your training regime.

If something doesn’t feel right, you feel pain, or overly tired, your body is trying to tell you something. Listen to it. Take full rest days when you need it.

When it comes to bodybuilding gains, what has worked for you? What hasn’t? Let us know in the comments below!


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