Can Running Increase Muscle Mass? What Endurance Runners Need to Know

Running is often framed as “pure cardio,” while muscle mass is usually associated with lifting weights. That leads to a common question among endurance athletes:

Can running increase muscle mass, or does it only improve endurance?

The short answer is: yes, running can increase muscle mass in certain conditions — but it depends heavily on how you run, how much you run, and how you support your training. For long-distance and high-output runners, the goal usually isn’t bodybuilding-style size, but strong, durable muscle that supports performance over long efforts.

This guide breaks down what actually happens to your muscles when you run, when running can support muscle growth, when it can work against it, and how endurance runners can train intelligently without sacrificing strength.

Does Running Build Muscle or Just Endurance?

Running primarily trains the cardiovascular system, but it also places repeated mechanical load on the muscles of the lower body. Running can stimulate muscle growth, particularly in the calves, quadriceps, and hamstrings, especially when the running involves higher intensity or incline. 

For example, look at many experienced ultra-runners who regularly train on hills or technical terrain. Their calves and quads often show noticeable development—not because they’re chasing size, but because years of repetitive load, climbing, and long descents demand durable, well-adapted muscle.

However, long-duration, steady-state running mainly improves endurance and muscular efficiency rather than significantly increasing muscle size. This is why many endurance runners maintain lean muscle mass rather than visibly gaining it.

So when people ask, does running build muscle, the honest answer is:

Running can help build or maintain muscle, but it is not the most efficient way to maximize muscle mass on its own.

Muscle Mass, Strength, and Endurance: What’s the Difference?

Understanding the difference between these concepts is critical for endurance athletes.

Muscle Mass

Muscle mass refers to the size of your muscle fibers. Increasing muscle mass (hypertrophy) happens when muscle protein synthesis exceeds muscle protein breakdown over time.

Strength

Strength is the ability to produce force. You can become stronger without adding significant muscle mass, especially through neural adaptations and efficient movement patterns.

Endurance

Endurance refers to the ability of muscles to sustain repeated contractions over long periods. For runners, endurance is often more important than raw size.

Endurance training has been shown to promote muscular adaptations that improve fatigue resistance and efficiency, rather than large increases in muscle fiber size.

For a broader look at how these adaptations affect the entire system—not just muscle—read what running does for your body.

How Running Affects Your Muscles

Muscles Most Involved in Running

Running primarily loads the glutes, quadriceps, hamstrings, calves, and stabilizing muscles of the hips and core. Each stride creates both concentric force (pushing off) and eccentric force (absorbing impact).

Repeated running loads lead to structural and metabolic adaptations in skeletal muscle that improve endurance capacity rather than maximal muscle growth.

Why New Runners See More Muscle Change

Beginners often experience greater muscle gains from running than experienced runners. This happens because new stimuli create stronger adaptation responses. As training age increases, muscle growth from running alone may become limited.

There is also a phenomenon known as muscle plateau. This is where if you are an athlete that has been working hard for a long time, you begin to see a point of diminishing returns on your muscle gains. Not to worry though, it doesn’t mean you’re getting old, it just means you’re in great shape.

When Running Can Increase Muscle Mass

Running is more likely to increase muscle mass when it includes higher mechanical load and intensity.

Sprinting and High-Intensity Intervals

Short, high-intensity running efforts recruit a greater proportion of fast-twitch muscle fibers, which have a higher potential for muscle growth. Sprint intervals, track repeats, and short hill sprints place greater tension on the muscles than easy jogging.

Hill Running

Uphill running increases force production in the glutes and quadriceps. Hill training can act as a form of resistance training for runners, particularly when efforts are short and powerful.

Moderate Volume With Adequate Recovery

When overall running volume is moderate and recovery is sufficient, muscle protein synthesis can remain elevated, allowing muscle maintenance or small gains.

When Running Makes Muscle Gains Harder

For endurance runners, this section is critical. Evidence from endurance sport research shows that low energy availability can impair muscle maintenance and recovery in endurance athletes, especially during high-volume training.

High Mileage in a Calorie Deficit

Multiple studies show that chronic energy deficiency increases muscle protein breakdown. Long-distance running without sufficient caloric intake can lead to muscle loss over time.

I’ve made this mistake myself. In 2018, while training for the Tahoe 200, I assumed running more and losing weight by eating less would make me faster. I’d eat a salad for lunch and head out for 20-mile runs. The result wasn’t performance, I was tired all the time, and generally felt depressed – it was constant fatigue, poor mood, and stalled progress. I was overtraining in a severe calorie deficit. Over time, I actually lost muscle and gained weight, a clear example of how high mileage without sufficient fuel can backfire.

High mileage doesn’t just challenge muscle gain — it also raises the cost of mistakes. If intensity and volume climb too fast, injury risk rises, and injury is one of the fastest ways to lose strength and consistency. For practical basics, see this guide on preventing running injuries.

Excessive Steady-State Running

Large volumes of low-intensity running improve endurance but provide minimal stimulus for hypertrophy. Without strength training or intensity variation, muscle size is unlikely to increase.

Signs Muscle Mass May Be Declining

Declining power output, slower recovery, persistent fatigue, and reduced strength in hills or sprints can all signal inadequate support for muscle maintenance.

This structure supports performance without excessive fatigue.

Periodize Your Training

During base phases, strength work can be emphasized more heavily. During peak mileage or race preparation, strength volume can be reduced to maintenance levels. Supporting muscle isn’t just about training load—mobility and tissue care matter too, which is why many follow a consistent stretch routine for runners alongside strength work.

Running Workouts That Support Muscle Development

Certain running workouts are better suited to supporting muscle mass.

Hill Sprint Sessions

Short uphill sprints with full recovery encourage power development and muscle recruitment without excessive endurance fatigue.

Short Interval Workouts

Intervals such as 200–400 meters at high effort increase mechanical tension and neuromuscular activation.

Strides

Short accelerations at the end of easy runs help maintain muscle recruitment patterns without adding much stress.

These running workouts for speed and endurance support muscle function while still fitting into long-distance training.

If you want a deeper breakdown of how to structure these sessions within a full week, see our guide on running workouts to build endurance and strength.

Nutrition Basics for Runners Who Want to Preserve Muscle

Research consistently shows that muscle maintenance requires adequate energy and protein intake. Endurance athletes need sufficient carbohydrates to fuel training and support muscle repair and adaptation alongside high training loads.

This does not require extreme diets. It requires consistency, sufficient total calories, and alignment with training load.

Hydration also plays a role in muscle performance and recovery. Dehydration negatively affects strength, coordination, and endurance, increasing overall stress on the body.

Can Long-Distance and Ultra Runners Increase Muscle Mass?

For athletes running high weekly mileage, large increases in muscle mass are unlikely and often counterproductive. Recent reviews suggest that while long-distance training limits large increases in muscle size, endurance athletes can maintain functional muscle with appropriate training and recovery strategies.

The goal for endurance athletes is not size, but durability, force production, and resistance to fatigue.

With proper training structure, nutrition, and recovery, long-distance runners can stay strong without sacrificing endurance. 

FAQs: Can Running Increase Muscle Mass?