Illustration of a skinny "ectomorph" doing cardio while bulking up.

Should You Do Cardio While Bulking? Yes, Sort Of

Cardio causes a different type of adaptation from hypertrophy training. Cardio causes us to build more blood vessels, gain additional mitochondria in our cells, and strengthen our hearts. Hypertrophy training stimulates muscle growth, makes us stronger, and makes our bones and tendons tougher.

Here’s the issue. Doing both hypertrophy training and cardio causes us to adapt in two separate, competing ways. This is called the interference effect. That’s what people say, anyway. Is it true?

On the other hand, if cardio makes you fitter, maybe you’ll be able to handle tougher hypertrophy training workouts. If it improves blood flow to your muscles, maybe you’ll have improved performance and better recovery. There could be advantages to doing cardio.

Things get even more confusing if you’re a naturally thin “ectomorph.” The more cardio you do, the more calories you’ll burn and the more calories you’ll need to eat. If you’re already struggling to eat enough calories to gain weight, that can be a problem.

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

The Many Benefits of Cardio

Cardio stands for cardiorespiratory training, where the goal is to elevate our heart rate in order to improve our cardiovascular fitness. It’s a catch-all term for activities designed to strengthen our hearts and lungs—jogging, rowing, biking, aerobics, and so on.

Cardio is an important part of a healthy exercise routine. The benefits are real and plentiful, whether you’re skinny or not (study):

  • Cardio burns calories and helps people lose weight.
  • It makes our hearts bigger and more efficient.
  • It increases our lung capacity.
  • It helps to reduce our risk of heart disease.
  • It improves mood and reduces anxiety.
  • It can improve sleep.
  • It makes people look and feel more youthful.

But as healthy as cardio is, it won’t help us get bigger, stronger, or more robust. For that, we need hypertrophy training. You probably already know that. So let’s assume you’re considering doing cardio in addition to hypertrophy training.

Should Skinny Guys Do Cardio While Building Muscle?

Skinny guys should do cardio. Lifting and cardio provoke completely different adaptations, both of which are important, so we should do both. That applies to everyone, including us naturally skinny guys.

But you don’t need to improve every aspect of your lifestyle all at once. If you’re new to exercise and your main goal is to build muscle, you could start by spending a few months bulking up, focusing on gaining 20–30 pounds of muscle.

You could focus on cardio after bulking. When you finish your bulk, you can ease back on lifting and start listening to your appetite again. You don’t need a calorie surplus to improve your cardiovascular health, so that might be a great goal to fight for when you aren’t bulking.

You could also compromise. You could prioritize weight training but spend a little energy doing easy forms of cardio, such as going on brisk walks. Even just going on a couple of 20-minute walks every day can be a great form of cardio, especially if you’re new to it.

Lifting Can Count as Cardio (Sort Of)

A 2014 study published in the Journal of Exercise Science (study) evaluated a bodybuilding workout by cardio standards. They measured the heart rate of sixteen people while doing a typical bulking workout. They were doing bench presses, lat pulldowns, bicep curls, leg presses, and so on. They did three sets of ten reps for each exercise.

The researchers found that the participants had the ideal heart rate for improving cardiovascular fitness for about half of the time they were weight training.

Illustration of a guy doing chin-ups to build bigger lats.

How to Lift for Cardiovascular Health

If you wanted even greater cardiovascular benefits, you could structure your bulking workouts to keep your heart rate higher for longer. One way to do that is to be strict with your rest times. You can take that even further by doing supersets.

To build muscle properly, it helps to give your muscles enough rest between sets. However, while one muscle rests, you can train a different muscle group. For example, you can do a set of squats, rest a minute, then do a set of chin-ups, rest another minute, and then return to your squats. That’s a superset.

To be clear, even dense workouts are still designed for muscle growth, not for improving cardio. Bulking workouts won’t ever rival a dedicated cardio routine. But it’s a step in the right direction. Add a couple of daily walks to that, and you can get quite a few steps in the right direction.

Can Cardio Make it Harder to Gain Weight?

Doing cardio while bulking can make it harder to gain weight. Cardio burns quite a lot of calories, and our appetites don’t always increase by a proportionate amount (study, study). So if we burn 500 calories while jogging, we might only want to eat an extra 300 calories.

It’s not quite as bad as it sounds. Going on walks can speed up and smooth out digestion. If you’re feeling sluggish after a big meal, you can often walk it off. In that sense, bulking and cardio fit together quite well.

Does Cardio Interfere With Muscle Growth?

Technically speaking, yes, cardio could kill your gains. Even if you can manage to eat enough calories to gain weight, you’ll run into something called the interference effect. The muscle-building stimulus will compete with the cardiovascular stimulus.

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

If you do your cardio and hypertrophy training as part of the same workout, the interference effect can cut your rate of muscle growth in half (study). However, there’s a simple solution. All you need to do is separate your cardio and lifting sessions by at least 6 hours, and ideally by a full day (study).

Does Cardio Improve Muscle Growth?

There’s something else to consider, too. One of the benefits of cardio is improved blood flow to your muscles. This improved blood flow supports muscle growth. So it could be that as you improve your cardiovascular fitness, you’ll have an easier time building muscle (study).

Furthermore, the extra activity that you’re doing will improve your general fitness, speeding up your recovery between workouts. Because you’ll be generally fitter, you’ll be in better shape to bulk up.

To get these benefits, you don’t need to do cardio while bulking. You could bulk, then do cardio. Or do cardio, then bulk. You could also incorporate high-rep sets into your workout routine.

The cardiovascular adaptations are muscle-specific. If you want to improve blood flow to your biceps, you wouldn’t go jogging, you’d do rowing… or high-rep sets of bicep curls. Doing sets of 20–40 reps should be heavy enough to stimulate muscle growth while also being light enough to improve blood flow.

Does Cardio Ward Off Fat?

Doing cardio could conceivably make your gains leaner. There’s an idea called energy flux (G-Flux). Ryan Andrews, RD, and John Berardi, Ph.D., are famous for writing about it over on Precision Nutrition. We’ve written about it in our article for skinny-fat guys, too.

Illustration of a man running to lose fat.

The idea is that the more calories you burn, the more calories you’ll need to eat, and so the more nutrients you’ll be able to get into your system. That means more vitamins, minerals, antioxidants, probiotics, fibre, and phytonutrients. And since your overall food volume is higher, you won’t need to worry as much about making every calorie count.


For our general health, we should aim for at least 150 minutes of cardio and two resistance training workouts every week. If you’re new to cardio, an easy way to start is to walk. Go on a 20-minute walk every morning. Maybe go on another walk in the afternoon.

If doing cardio seems overwhelming right now, it’s okay to save it for when you finish bulking. Your weight training workouts will provoke some beneficial cardiovascular adaptations anyway.

If you’re lifting and doing cardio, make sure to prioritize your priority. If your main goal is to stimulate muscle growth, invest your best energy into training for muscle growth. Do your cardio on your rest days, and keep it easy enough that it helps you feel energized the next day, not tired.

Illustration of a man going from skinny to muscular from doing cardio

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.