Illustration of a bodybuilder doing cardio after lifting weights.

Does Cardio Kill Muscle Gains?

Cardio can kill muscle gains. We’ve known this for many decades. It’s common knowledge among lifters and has been proven in peer-reviewed studies. Most recently, a study found that cardio cut muscle growth in half. We’ll go over the nuance of that study in a moment.

However, if you’re clever, you can use cardio to improve your muscle growth. This is fairly well-documented, too. We’ll go over some interesting research. I’ll also point out that in our twelve years of helping skinny guys bulk up, the guys who get the best results are the ones in good shape overall.

So, let’s talk about how to do cardio in a way that enhances instead of destroying your muscle gains.

A skinny guy bulking up and becoming muscular, illustrated by Shane Duquette.

How to Combine Lifting & Cardio

Resistance training and cardio both stimulate different sorts of adaptations. Lifting helps build muscle, makes you stronger, and toughens your bones and tendons. Your cardiovascular health will improve a little, too, but not very much.

Cardio does the opposite. It helps build more blood vessels, improves lung capacity, and buffs up your heart. You’ll gain a little muscle and strength, but not much, especially when compared to lifting weights.

Study graph showing that doing cardio right after lifting weights reduces muscle growth by over 50%.

Here’s the problem: if you do cardio right after lifting weights (or vice versa), the muscle-building and cardiovascular adaptations interfere with one another, reducing muscle growth by over 50% (study).

All hope is not lost. You can adapt in both ways at once. You just need to stagger the stimulus. You need to separate your cardio and your lifting sessions by at least 6 hours, and ideally by a full day (study).

The Benefits of Getting In Shape

When you do cardio, you build more blood vessels, improve blood flow, and improve nutrient delivery all through your body, including to your muscles. When you get into good cardiovascular shape, you’ll be better at lifting weights, you’ll regain your strength faster between sets, and you’ll recover more quickly between workouts. All of this is great for building muscle.

In a study by Thomas and colleagues, they found that doing cardio improved capillarization in the muscles being worked, potentially improving future muscle growth there (study). It’s still too early to know the full implications, but since the side effects of cardio are healthy, you may as well take advantage of the possible muscle-building benefits.

Before and after photo showing a skinny-fat guy bulking and then cutting.

Frequently Asked Questions

What If You Need to Lift & Do Cardio in the Same Workout?

The best way to improve your health is to do resistance training and cardio. If you don’t have time to separate them, it’s okay to do them together. You’ll build muscle more slowly, but you’ll still make progress toward both goals. Perhaps more importantly, you can still do a fantastic job of improving your health.

If you have to lift and do cardio in the same workout, and if your main goal is to build muscle, then a study by Eddens and colleagues suggests that it’s better to lift first and do cardio second (study). That way, your best effort is going towards your main goal.

Is It Okay to Do Cardio to Warm Up or Cool Down?

You can hop on a treadmill or stationary bike to warm up or cool down. That’s totally fine. If the cardio is energizing or relaxing, it’s not challenging enough to interfere with muscle growth (study, study). Just keep it relatively easy and brief. If your main goal for that workout is to stimulate muscle growth, save your best energy for lifting weights.

Should Skinny Guys Avoid Cardio?

I’m a naturally skinny guy. This fear haunted me for many years. The worry is that cardio burns calories, making it more difficult to get into a calorie surplus. That’s true, but cardio doesn’t burn that many calories. Plus, it can speed up digestion and increase appetite, both of which make it easier to eat enough calories.

If you’re just starting to lift, it’s better to focus on one new habit at a time. Once that habit hardens, feel free to add some cardio. When you do, ease into it. Start small and work your way up.

If you already do cardio and you’re considering adding lifting into your routine, you may want to cut back on the cardio, but only if it interferes with your lifting. If you can manage both, more power to you. That’s the dream.

What Type of Cardio Pairs Best With Weight Training?

All types of cardio can pair well with lifting, provided you keep your workouts separated and don’t overdo it. High-Intensity Interval Training is a good choice (study, study), but it’s already somewhat similar to lifting. You work your muscles hard, rest, and then do it again.

I’m of the opinion that steady-state cardio pairs better with lifting. It’s more distinct from lifting, giving you a more well-rounded fitness routine. I think going on brisk walks makes for the best place to start. When that becomes easy, you could up the ante by swapping out 2–3 of those walks for 20-minute jogs or bike rides.

Does Running Make You Lose Muscle?

Running won’t make you lose muscle. In fact, running helps to preserve muscle when you’re in a calorie deficit (study, study). It’s not nearly as good as lifting weights, but it helps quite a lot. Even if you’re doing your cardio and lifting in the same workout, the interference effect won’t cause muscle loss, it just slows growth. You’ll still make progress, just more slowly.

Summary

If you do your cardio and resistance training as part of the same workout, it can cut your rate of muscle growth in half. It won’t kill your gains, but it can certainly maim them. However, if you separate your cardio from weight training by at least 6 hours, the interference effect seems to disappear. Even better if you do your cardio and lifting on separate days.

As you get into better shape, your cardiovascular fitness will increase, improving your lifting performance, recovery, and muscle growth. Just make sure not to do too much at once. If your cardio is beating you up so much that you’re showing up to your muscle-building workouts feeling fatigued, that can interfere with your workout and, thus, your results. If you’re new to cardio, ease into it.

If you want a deeper dive into how and why to combine cardio with your lifting routine, I wrote a full article on Outlift.

Photo showing the Bony to Beastly Bulking Program for Skinny and Skinny-Fat Guys

Alright, that’s it for now. If you want to know the ins and outs of bulking up, we have a free newsletterIf you want a full muscle-building program, including a 5-month workout routine, a bulking diet guide, a gain-easy recipe book, and online coaching, check out our Bony to Beastly Bulking Program. Or, if you want a customizable intermediate bulking program, check out our Outlift Program.

Shane Duquette is the founder of Outlift, Bony to Beastly, and Bony to Bombshell, each with millions of readers. He's gained seventy pounds and has over a decade of experience helping more than ten thousand naturally thin people build muscle. He also has a degree in design, but those are inversely correlated with muscle growth.

Marco Walker-Ng is the founder and strength coach of Outlift, Bony to Beastly, and Bony to Bombshell. He's a certified trainer (PTS) and nutrition coach (PN) with a Bachelor's degree in Health Sciences (BHSc) from the University of Ottawa. He has over 15 years of experience helping people gain muscle and strength, with clients including college, professional, and Olympic athletes.

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