Does Running Cause Muscle Loss

Does Running Cause Muscle Loss or Is That Just a Fitness Myth?

Introduction

Running's super popular for good reason: it's simple, cheap, and great for your heart, mind, and body. But some people, especially in the weightlifting world, think running is bad news. They say it kills gains or makes you lose muscle. You hear this a lot in gyms and online, which makes people wonder if they should even bother running.

So, does running really make you lose muscle? It's not a simple yes or no. It depends on how you train, what you eat, how you recover, and what you're trying to achieve. Running itself isn't bad for muscle, but how you do it matters. If you know how your muscles react to endurance training, you can stop worrying and make smart choices.

This article will talk about where the muscle loss idea comes from, how running affects your muscles so runners can keep or even build muscle while still enjoying a good run.

What is muscle loss, really?

Before we get into whether running causes muscle loss, let's talk about what that even means. Muscle loss, or muscle atrophy, is when your muscles get weaker and smaller over time. This can happen if you're not active enough, not eating right, sick, getting older, or not eating enough calories.

Muscle loss doesn't happen overnight. It's not like after a few runs, your muscles are gone. It happens slowly when your body doesn't get the signals or stuff it needs to keep muscle. Lifting weights, eating enough protein, and getting enough calories tell your body to keep the muscle. If you don't do those things, muscle breakdown can happen faster than muscle building.

A lot of people mistake temporary muscle fatigue or just muscles not feeling as full for real muscle loss. After a long run, your muscles might feel smaller because you've used up their energy stores and lost water. But that's not muscle loss; it's just temporary and goes away with rest and food.

Why Does Running Have a Bad Reputation?

The idea that running makes you lose muscle didn't just come from nowhere. It's based on what people see and misunderstand. Long-distance runners are usually skinny with not much muscle compared to weightlifters. So people think running must destroy muscle.

Another reason is that your body adapts to what you do. Running trains your muscles to be good at repeating the same movement for a long time, not at using a lot of force. So, over time, your muscles might become lighter and better at resisting fatigue instead of getting bigger.

Also, endurance athletes sometimes train super hard while trying to stay very light to run faster. If they don't eat enough calories, this can cause muscle loss. But it's not just the running; it's the combination of too much training and not enough food.

image credit: FREEPIK

How Running Changes Your Body

Running is aerobic exercise, which means it mainly works your heart and your lower body muscles. When you run, your muscles contract repeatedly at a moderate level for a long time. This makes your body adapt by improving oxygen delivery, increasing the number of mitochondria in your cells, and boosting your endurance.

These changes aren't the same as what happens when you lift weights, which focuses on high-force contractions that make muscles grow. Running doesn't provide the same tension as lifting weights, so it doesn't make your muscles get much bigger. But that doesn't mean it breaks them down.

For most people, running just keeps their existing muscle while improving endurance. Muscle loss only becomes a problem if you run a lot, don't recover well, or don't eat enough calories and protein.

Calories and Energy Balance

One of the biggest things that affects muscle loss is energy balance. If you burn more calories than you eat, your body has to get energy from somewhere. If you're in a calorie deficit for too long, your body might break down both fat and muscle for energy.

Running can burn a lot of calories, especially if you do it often or for a long time. If you don't eat more to make up for those calories, you might end up in a calorie deficit. Over time, this can lead to muscle loss.

That's why some runners lose muscle while others don't. It's not the running itself, but whether you're eating enough for how much you're doing. If runners eat enough to fuel their activity, they're much less likely to lose muscle.

Protein Intake and Muscle

Protein is super important for keeping and fixing muscles. Your muscles are always breaking down and rebuilding, and protein provides the stuff they need to do that. If you don't get enough protein, muscle breakdown can happen faster than muscle building.

Runners who don't eat enough protein might be more likely to lose muscle, especially if they run a lot or at a high level. This risk gets even higher if they don't eat protein evenly throughout the day or skip it after runs.

Getting enough protein helps your muscles repair after running and keeps your muscle during hard training. For most active people, eating protein regularly throughout the day is enough to keep muscle, even if they run regularly.

How Much You Run and How Hard Matters?

Not all running is the same. Short, easy runs are different from training for a marathon. If you just run a few times a week at a moderate distance, you probably won't lose muscle from running alone.

But training hard for endurance races like marathons puts a lot more stress on your body. If you increase how much you're training without recovering well and eating right, muscle loss can become more likely. This is especially true if you're training for a long time at a low level.

How hard you run also matters. Sprints and hill running use more force than jogging. These types of running can actually help you keep and build muscle, especially in your legs.

Endurance Runners vs. Strength Athletes

Endurance runners and strength athletes often look different, but that's because they have different goals. Endurance athletes train to be fast and efficient, not to get big muscles. Their bodies adapt to that.

Strength athletes, on the other hand, train to get as big and strong as possible. They lift heavy weights with fewer reps and rest longer between sets. This tells their bodies to build muscle.

So, if endurance runners look lean, it doesn't mean running made them lose muscle. It just means they're not training to build it. If runners lift weights and eat enough, they can keep or even build muscle while still running.

Can Running and Weightlifting Work Together?

People often think running and weightlifting are opposites, but they don't have to be. A lot of athletes do both. If you do it right, running can improve your heart health while weightlifting keeps your muscle.

The key is to manage how much you're doing, how hard you're working, and how well you're recovering. If you do too much endurance training too close to hard weightlifting workouts, it can mess with muscle growth. But if you schedule things well and get enough rest, you can minimize that.

For example, you can separate long runs and heavy weightlifting sessions by several hours or do them on different days. This helps your body do both instead of having to choose one.

The Cardio Kills Gains Myth

Cardio kills gains is a common saying in the fitness world. While too much cardio and not enough food can make it harder to build muscle, moderate cardio doesn't automatically make you lose muscle.

Cardio can actually help you build muscle indirectly by improving blood flow, recovery, and overall health. A healthy heart and good oxygen delivery help you train harder and recover better from weightlifting workouts.

The problem is when you do extreme amounts of cardio or when you stop weightlifting entirely to do cardio. In those cases, muscle growth might slow down or stop, but that's not the same as losing muscle.

How Hormones Affect Muscle

Hormones play a big role in keeping muscle. Exercise affects hormones like cortisol, testosterone, and growth hormone, which all affect muscle tissue.

Long endurance exercise can temporarily increase cortisol, which is linked to stress and muscle breakdown. But this is normal and doesn't last long if you're eating well. If you recover and eat enough, cortisol levels go back to normal and don't cause long-term muscle loss.

Weightlifting and eating enough calories help keep your hormones in a state that supports muscle. Running alone doesn't automatically create a hormonal state that makes you lose muscle.

Age, Growth, and Running

For kids and teens, muscle development is affected by growth, hormones, and how active they are. Running during these years doesn't stop healthy muscle development. In fact, regular exercise helps with bone health, coordination, and fitness habits for the future.

Problems only happen if training becomes too much or if they don't eat enough to support their growth and activity. Balanced exercise and enough food are important for healthy growth, whether they're running or not.

Things People Mistake for Muscle Loss

A lot of runners think they're losing muscle when they're just experiencing temporary changes. If their muscles aren't as pumped, if they lose water weight, or if they're tired, their muscles might look smaller.

Another common thing is losing fat along with weight. As you lose body fat, your muscles might look less full, even if you still have the same amount of muscle. People often think this means they're losing muscle.

Real muscle loss is best seen through long-term decreases in strength, muscle size, and how well you perform, not short-term changes after endurance exercise.

How to Run Without Losing Muscle

You can totally run without losing muscle if you do it right. The most important things are eating enough, training smart, and recovering well. Eating enough calories helps prevent your body from breaking down muscle for energy.

Lifting weights two to three times a week tells your body to keep the muscle. You don't have to do crazy bodybuilding routines; basic strength exercises are enough.

Rest and sleep are also important. Muscles repair and rebuild during recovery, not during exercise. If you don't get enough rest, you're more likely to lose muscle, no matter what kind of training you're doing.

When Muscle Loss Can Happen

Muscle loss from running usually happens in extreme or poorly managed situations. Running very high mileage with low calories, not much protein, and little weightlifting can create an environment where muscle breakdown happens faster than muscle repair.

This is more common among competitive endurance athletes who care more about weight and performance than muscle mass. Even then, muscle loss is often a choice they're making, not something that can't be avoided.

For the average runner, these conditions are unlikely unless they're really messing up their training and diet.

Think Differently About Running

Instead of asking if running causes muscle loss, it's better to ask how running fits into your fitness goals. Running is a tool, not a threat. How it affects you depends on how, how often, and why you use it.

If you combine running with good nutrition and balanced training, it can support your long-term health, athletic ability, and mental well-being. It doesn't automatically shrink your muscles or undo your strength gains.

If you understand this, you can stop being afraid of fitness myths and start making smart, sustainable habits.

Conclusion: Does Running Cause Muscle Loss

So, does running cause muscle loss, or is that just a myth? For most people, it's mostly a myth. Running doesn't inherently cause muscle loss. Muscle loss happens when you're not managing your training, nutrition, and recovery well over time.

Running can work with strong, healthy muscles if you support it with enough food, weightlifting, and rest. Instead of avoiding running out of fear, it's better to learn how to fit it into a balanced lifestyle.

In the end, fitness isn't about choosing between cardio and strength. It's about using the right tools in the right way to support your health, performance, and long-term wellness.