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, carry more oxygen in our blood, 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 at the same time causes us to adapt in two complementary but 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 muscle-building advantages to doing cardio.

Things get even more confusing if you’re a naturally thin “ectomorph” or “hardgainer.” 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—brisk walking, rucking, jogging, cycling, rowing, aerobics, and so on.

Cardio is an important part of a healthy exercise routine. The benefits are robust 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 reduces the risk of heart disease.
  • It improves mood and reduces anxiety.
  • It makes people look and feel more youthful.
  • It improves sleep.
  • It increases energy levels.

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

Should Skinny Guys Do Cardio While Building Muscle?

Skinny guys should do cardio. Lifting and cardio provoke completely different adaptations, each of which is important. For example, a meta-analysis by Momma and colleagues found that weight training reduced all-cause mortality by 15%. When cardio was added in, all-cause mortality dropped by 40% (reference). By doing both, we can add the better part of a decade to our lifespans.

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’re ready to take a break from overeating.

In the meantime, going on a 20-minute walk every day can be a great form of cardio, especially if you’re new to it. That’s what I did during my first two bulks while gaining my first 40 pounds of muscle.

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. Their cardiovascular fitness wasn’t the limiting factor, so it isn’t perfectly ideal, but it’s quite a lot better than nothing. If you’re out of shape, lifting can improve your fitness, at least during your first few months.

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 20-minute daily walk 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 a truly Hellish amount of calories. I burned over 1,000 calories running 10 kilometres this morning. And unfortunately, our appetites don’t always increase by a proportionate amount (study, study). If you burn 1,000 calories while jogging, you might only want to eat back 700 of those 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. It all depends on how intense your cardio is and how much of it you’re doing.

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 Gain?

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 general health, do 150+ minutes of cardio and 2+ hypertrophy training workouts per week. If you’re new to cardio, you can start by going on a brisk 20-minute walk every morning. That won’t be enough forever, but it’s more than enough for now.

If you’re bulking 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 showing the Bony to Beastly Bulking Program

If you want us to walk you through the entire bulking process, check out our Bony to Beastly (men’s) program or Bony to Bombshell (women’s) programThey include a 5-month customizable workout routine, a full bulking diet plan, a bulking recipe book, a deep dive into lifestyle and fitness, and coaching from us.

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.