Guide: How Aerobic Exercise Builds Muscle Size

Aerobic exercise can lead to an increase in muscle size.

Aerobic exercise has been proven to improve your overall health and lower the risk of disease. But something you may not acknowledge is that it can also strengthen your muscle size and strength. Here’s how aerobic exercise builds your muscle size

However, before we proceed further, it is good to know that not all endurance exercises are created equal.

Different aerobic activities are better suited for different goals. So, if you’re looking to grow muscle size, you’ll want to choose the proper cardio workout.

What is aerobic exercise?

It is a form of physical activity that improves or maintains physical fitness and overall health. It increases the heart and respiratory rates to enhance oxygen transport to the muscles.

It encompasses physical activities that increase the body’s need for oxygen. Some endurance exercises are walking, jogging, hiking, bike riding, running, swimming, and other similar activities.

What research says about building muscle with aerobic exercise?

In one study, researchers looked at such exercises and whether it makes muscles shrink. The result? It does not shrink muscle.

In fact, it can lead to larger muscles in some men and women. For example, one study showed that a man who did such exercise 4 days a week for forty-five minutes per workout grew his muscles.

However, it’s not as easy as said. You cannot build muscle with such exercise if you do it only in your leisure time. It needs to be of higher intensity to grow the strength.

The various study concludes that the participants who gained the muscles with aerobic training have a higher intensity on their exercise.

When younger and older men complete cardio for 45 minutes, around four times a week at 80% of their max heart rate, they can significantly increase their legs’ size. The men’s journal says this.

Aerobic exercise repairs your muscles.

It helps to promote recovery and repair of the muscles after you’ve done weight training. This is an excellent exercise for improving endurance, especially when it comes to your cardiovascular system.

When you’re doing cardio exercises, you’re not only increasing your heart rate but you’re also changing the composition of your muscular fiber. This means you’re building your endurance.

According to the American Council on Exercise, aerobic workouts increase endurance by changing muscle fiber composition.

Cardio activities such as running and cycling cause muscles to burn more fat for fuel, which in turn causes fibers to become more efficient at extracting oxygen from the blood.

It can help you tone your muscles and build strength and endurance. For example, suppose you’re trying to tone your arms.

In that case, you should do weight training with cardio exercises like running or jumping rope.

What happens when you exercise aerobically?

When you exercise aerobically, you’re essentially converting some of your fast-twitch muscle fibers into the slow-twitch fiber.

You’re taking fast-twitch muscle fibers that rely on energy from ATP, and you’re turning them into slow-twitch muscle fibers that rely on energy from fat.

Why do you need to do aerobic exercise?

Working out a few times a week is excellent for overall fitness. However, it’s essential to break up those workouts with days of rest to give your body a chance to repair and recover.

Cardio activity is excellent for encouraging blood flow and circulation to muscles and joints. Cardio training boosts endurance by increasing the number of mitochondria in your muscles.

During such exercise, muscle fibers are broken down and rebuilt. This is what causes muscle fatigue.

It alters muscle fiber composition, making them stronger and more efficient to contract with greater force for more extended periods.

Top 3 aerobic exercises.

Swimming: It is one of the most beneficial endurance exercises out there. It’s low-impact on the joints, and it burns calories at a fast pace. It’s also a full-body workout, and people of all ages and fitness levels can go swimming.

Running: It is indeed one of the most popular aerobic exercises because it’s free, low-impact, easy to do, and convenient.

Running also helps in muscle growth. However, the intensity and duration of your runs play a significant role.

Outdoor cycling: If you cycle regularly — especially at high intensity — you will be rewarded with lower body fat levels. You’ll also be speeding up your metabolism and gaining muscle.

Walking: Walking is another endurance exercise that is easy to do and doesn’t require anything expensive. If done regularly, walking can help you in minor muscle development.


It is undoubtedly possible that endurance exercise will help you to grow muscle. However, here’s something you should be aware of.

All the muscles you have gained through it may plateau after a few periods if you are not doing resistance exercise.

Also, you need to be aware of the catabolic effect.

In certain circumstances, long aerobic activity periods create a catabolic effect interfering with intensity, power gains, and muscle by causing the body to burn more calories for energy.

Things to remember

  • High-intensity endurance exercise usually helps build muscle size, mainly in untrained people rather than trained individuals.
  • It increases endurance by changing muscle fibers’ composition.
  • When you do cardio activity for a longer time, it may interfere with muscle size.
  • Instead of just doing endurance exercise, it is good to engage in aerobic and non-aerobic exercises to improve muscle growth.


For the longest time, many people thought you needed to do strength training exercises to fabricate muscle size.

But aerobic exercise is also a great way to grow muscle size. If you want to lose weight, build muscle, or feel better, such activity is one of the most important things you can do.

Many people think that this kind of exercise is boring and monotonous, but it’s not. Cardio can help you lose weight, build muscle, and improve your endurance.

I hope this article has debunked the myth that only strengthened training can build muscle and has given you a new insight into aerobic exercise.