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Strength training

How does running build muscle?

February 15, 2022 | By Jonathan Thompson
Runner on a trail
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One memory from my high school health class has stuck with me throughout my fitness career. The teacher confidently stood before the class and claimed that running destroys muscle. And I've heard this sentiment repeated from a variety of sources since. Science and the experience of countless athletes, however, disagree. So what's actually going on here? Does running build muscle?

Muscle-building basics

Before focusing on how running impacts your muscular system, it's important to talk about how muscle-building works in a general sense. When your muscles are challenged by a workout or some other stimulus, they undergo a minor trauma. In response, your brain unleashes a series of reactions designed to make your muscles bigger, stronger, faster, and better suited to handle that type of activity should it happen again. Collectively, this response is known as muscle protein synthesis (MPS). Like any building project, though, this adaptation requires the proper materials. For muscles, that means protein.

At the same time, however, various factors can cause your body to remove protein from your muscles. This is known as muscle protein breakdown (MPB). Building muscle, then, is a bit of a balancing act between these two forces. As long as synthesis occurs at a higher rate than breakdown, muscle shall result. The trick, though, is that both muscle protein synthesis and breakdown occur at different rates with different forms of exercise.

Does running build muscle?

The next logical question, then, is whether running builds muscle or not. How does our beloved sport interact with this synthesis / breakdown system? Well, it depends on what kind of running we're talking about.

A study in the International Journal of Exercise Science found that high-intensity interval training (HIIT) focused on sprints caused an impressive 11% increase in muscle growth in just 10 weeks. This growth was primarily in the quadriceps, but all of the muscles in the legs can be challenged and, therefore, grow from these workouts.

Another study, published in the Journal of Physical Therapy Science, focused on endurance runners after they clocked 10, 21, or 42 kilometres. For these athletes, markers of muscle protein breakdown increased and stayed elevated for up to three days after the workout. Interestingly, the level of MPB was directly linked to the distance the athletes ran, with longer distances leading to higher levels of these markers.

So, does running build muscle? Sometimes. Short-distance, high-intensity workouts encourage muscle growth; while long-distance endurance runs tend to have the opposite effect. A simple example of a HIIT workout to encourage muscle growth would look like this:

  • Warm up for five minutes
  • Sprint for 30 seconds
  • Walk for 60 seconds
  • Repeat the sprint / walk pattern eight times
  • Cool down for five minutes

The diet factor

There's another athletic axiom that's stuck with me over the years — this one because it's true: "Muscles are built in the kitchen." Remember, your muscles are built by protein synthesis. In order to synthesize that protein, the nutrient has to be present in your body. Adequate protein intake, equal to about 1.41–2.00 grams of protein per kilogram of body weight each day, has been shown to encourage muscle growth in athletes.

It's also important, however, to make sure your body has enough carbs and fats to fuel your workouts. Without them, your body will start breaking down protein for fuel. And we don't want that.

To answer the primary question that started this discussion, then: Yes, running does build muscle. Or at least, it can. Short-duration, high-intensity workouts will cause growth in the muscles of your legs, as long as your body has the raw materials it needs to build that muscle.

Our writer's advice is intended for informational or general educational purposes only. We always encourage you to speak with your physician or healthcare provider before making any adjustments to your running, nutrition, or fitness routines.

Written By
Jonathan Thompson

Fitness Nerd

Jonathan with a dog in the snow

My interest in fitness started young, primarily as the survival strategy of a scrawny asthmatic. After receiving my certifications as a personal trainer and nutritionist, I started writing fitness articles. At this point, running is a non-negotiable part of my life.