Does Running Make Your Legs Look Bigger?

Does Running Make Your Legs Look Bigger?

Running is a pastime that many people use for enjoyment, exercise, and even as a way to bond with others. For some, the idea that running can make your legs look bigger is a good thing, and for others, not so much. So, does running make your legs look bigger?

Running can build muscle in the legs thus making them bigger, stronger and more muscular. Running can also help make your legs leaner, giving them a thinner appearance as you replace fat with muscle. It primarily depends on the type of running. Sprinters will build a larger muscle, while long distance runners may develop leaner muscle.

If you’re looking to learn about what types of running, as well as external factors may cause your legs to look bigger, then stick with us! You aren’t alone in your questions, and we are here to help you learn why running might make your legs look bigger.

What Muscles are Used During Running?

When you’re running, you use multiple different muscles in your legs such as your quadriceps, hamstrings, glutes, and calves. Additionally, your hip flexors and the muscles in your core region will be worked.

The constant use of all these muscles helps them build strength and, quite often, with strength comes an increase in size.

Not only is running a good way to help tone your core, but it can also lead to toned legs and thighs.

The size of the legs is something that may shift and evolve as your muscles become more toned and resilient.

Why Are My Legs Getting Bigger from Running?

You may have heard the term ‘runner’s legs’ before. While this is something that many athletes proudly boast, not everyone is as keen on having muscular legs.

Knowing the reasons that your legs are getting bigger from running is a good way not only to understand your own physiology, but also to understand what it is about working out that effects your body in ways that lead to the building of muscle.

Your legs are getting bigger from running because you are building more muscle. Overall, you are burning calories and losing body fat, which is being replaced with muscle. 

It is important to understand that there are many types of exercise, including running, and that different styles of running may impact your body (and legs) in different ways.

So, how do these different types of running change your legs, and what exactly are they?

Types of Running Comparison

As we dive into comparing a couple different styles of running, it is important to note that different speeds and types of running use different targeted muscles, which produce different results.

We’ll begin by talking about sprinting and its impacts.

1. Fast-Twitch Muscles Used in Sprinting

So, you may be asking yourself, ‘what on earth is a fast-twitch muscle?’

Fast-Twitch is a type of muscle fiber that is used in sprinting. It is stronger than its counterpart muscle type, but also tires much faster.

Think about a time when you’ve sprinted versus when you’ve been on an even-paced, moderately fast run. Your legs will feel fatigued in quite a different way, thanks to the use of those fast-twitch muscles.

The use of fast-twitch muscles most often leads to the more muscular, bulging appearance of a sprinter. So, if you sprint more than you run long-distance, you may notice your legs begin to bulk up more quickly.

2. Slow-Twitch Muscles Used in Running

Now, let’s dive into slow-twitch muscles. 

A slow-twitch muscle is not as strong as the former, but their access to oxygen supplies is greater which means they have more endurance to run for longer.

Slow-twitch muscles used by runners that opt for distance over speed tend to be much thinner and leaner, while still strong and muscular.

Have you ever been jogging or briskly running and could last an hour, whilst barely making it on your 10-minute intensive sprint? That would be why, the muscles used had quite a different set of strengths and worked for what they were intended to- short and fast, or long and steadily paced.

Muscle TypeSpeedProsCons
Fast-TwitchFast; SprintingStrongTire easily
Slow-TwitchPaced; RunningDurableLess strength

To recap: 

If you’re a sprinter, you will be using more fast-twitch muscles. Fast twitch muscle are larger in size, thus growing the quads larger and more muscular.  Sprinting puts a higher demand on the quads, which may make them appear bigger.

If you’re a long-distance runner, you will be using more slow twitch muscles. Long distance runners can, like the name says, go long distances! The slow twitch muscles are smaller in size, thus producing that leaner look of the legs. Long distance running puts a higher demand on the hamstrings as opposed to the high demand sprinting puts on the quads.

Does Genetics Play a Factor?

Aside from what we now know about the different types of running and their impact on the type and size of muscles, there are still other factors at hand to consider.

Genetics certainly play a factor in whether your legs appear larger from running. Genetics are a huge part of how we work and what changes in our bodies. Especially when it comes to fitness, muscles, strength-building, and performance, genetics are crucial.

Because of the way that our bodies are built to perform in different ways, sometimes people can do the exact same exercise and see different results over time.

If you are somebody that just cannot seem to bulk up no matter how often you do those intensive sprints, or you see that your legs appear to be getting larger even though you’re an avid distance runner, genetics might be the culprit.

On the other hand, there are a few other potential causes to your muscle composition that we should touch on.

How Does My Diet Play a Role?

One of the other major players in the way that muscles adapt and grow as you work them is your diet.

If you consume less carbohydrates, your body will begin to use your stored fat instead of the easily accessible carbs while you are working out. This will lead to a leaner appearance over time.

If you are someone looking to bulk up, eating lots of foods that are high in protein such as eggs, meat, nuts and seeds, beans, cheese, and other foods such as oil will help you to bulk up your muscles as opposed to cutting them down.

Similar to carbs, if you are consuming lots of sugary, processed foods, you might see in the long run that those things are being used as fuel before any additional stores of fat on your body.

Additionally, if you consume excessive amounts of alcohol, you might not see the positive impacts of something like running as much. Why is this, exactly?

Like with carbs, sugars, and other things that your body has easy access to as fuel, working out after consuming alcohol will see you sweating out all the bad stuff (which is great), but you’ll also be a bit slower to see that toning of the muscles.

Additional Factors


Have you ever heard that the amount of sleep you get can affect your body in more ways than just added tiredness?

It’s true, your metabolism is lower when you are deprived of sleep, as well as other processes in your body being off balance.

It is so important to exercise on a healthy amount of sleep, in order to keep yourself safe and healthy.

Intensity of Running

Another thing that can add to the way that your muscles grow when running is the intensity of running, which is set apart from the style itself. Things like running at a steep incline will ensure that you are automatically running at a pace that is slower than you would run on a completely level surface.

So, running at an incline will lead to leaner muscles, because this type of running will also end up engaging the slow-twitch muscles, by nature.

Be sure to consult a certified personal trainer, exercise physiologist and/or registered dietitian prior to start your training program. These professionals are experts in the field can assist you in reaching your goals for weight loss, muscle building or for overall health.

Final Thoughts

Genetics, age, and activity level can play a role in the way your muscles grow, or lack thereof, from running. As we know, everyone is built as a unique individual. Just because one long distance runner may not have long, lean legs, doesn’t mean they aren’t a physically fit, long-distance runner! Same goes for a sprinter.

Ultimately, a combination of all of the above factors is what will determine how big (or not) your legs will look like as a result of running.

The combination of running style, genetics, diet, and sleep all create this internal balance that can be seen externally in your muscle composition.

Happy running!

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Choosing Nutrition Team

Here at Choosing Nutrition, our goal is to help people with making smarter food choices. Whether you're wondering about vegan, keto, paleo, or other diets, we'll help you determine which options fit your nutritional lifestyle. Our staff is composed of registered dieticians, nutritionists, and health-conscious individuals.

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