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Does Running Make Your Legs Bigger? It Depends

Are you looking for a way to make your legs bigger? Maybe you’re looking to make sure your legs don’t get bigger? Most people think that running is solely a cardiovascular activity, but it also has some great benefits for your lower body as well. When you run, you are working all of the muscles in your legs, from your calves to your glutes. So, does running make your legs bigger? Let’s find out.

Running can help to make your legs bigger and more toned. In addition, running can help to improve your bone density, which can also lead to stronger and healthier legs overall. Running works several major muscles in your legs including your hamstrings, quadriceps, calves, and others.

So if you are looking for a way to make your legs bigger, consider adding some running to your workout routine. But not all running is created equal in terms of adding size to your legs. Some types of running may reduce your leg size. We will break down which types of running affect leg musculature the most, and what types of drills to do to help. You may be surprised by how quickly you see results.

Does Running Make Your Legs Bigger? The Effects of Different Types of Running on Muscles

does running make your legs bigger

Running can certainly make your legs bigger, but the type of running you do makes a big difference. If you are looking to add some size to your legs, sprinting, or similar explosive training, is going to be much more effective than long-distance running.

Let’s look at the two extremes of running – sprinting vs long-distance running – and break down the muscle-building benefits of both. Here is a quick chart to help visualize the data.

Source: nasm.org

Long-Distance Running (Think Marathons)

Long-distance running can lead to smaller legs because it breaks down muscle tissue and doesn’t build it back up as effectively. The body does its best to adapt to its circumstances and environment. In the case of long-distance running, the body is more efficient with smaller, slower twitch muscles. Therefore it will adapt over time to actively fight against gaining muscle. Training for a marathon actually reduces a runners ability to jump high due to this phenomenon.

In addition, running long distances burns so many calories that there likely isn’t a lot of energy left over to build muscle and pack on size.

Sprinting (Think 100M Dash)

Sprinting, on the other hand, helps to build muscle tissue and can lead to bigger legs. If you want to add some sprinting to your workout routine, try incorporating some hill sprints. Hill sprints are a great way to build leg muscle because they force your muscles to work harder than they would on level ground. You can also try incorporating some resistance training into your sprint work like running with a weight vest.

The additional resistance for short bursts will force your body to adapt and attempt to add muscles to aid in force production in the future.

What Types of Muscle Fibers Are Used In Running? Fast vs Slow Twitch

There are two main types of muscle fibers in the body: fast twitch and slow twitch. Most people’s muscles are split close to 50/50 with each type, however certain exceptions exist. Fast-twitch muscles are more explosive and look more impressive, while slow-twitch are meant for endurance and are fatigue resistant.

leg muscles used in running

Let’s take a look at each type of muscle group and whether it’s a fast twitch or slow twitch as well as how to train it to help maximize leg size.

Fast Twitch vs Slow Twitch

When training with explosive movements or more for power, the body adapts by increasing the size of the fast-twitch muscle fibers in the muscle. At the same time, the slow-twitch fibers start to atrophy. The rate of increase in the fast-twitch fibers outpaces the atrophy in the slow-twitch fibers resulting in an overall larger muscle.

This is true for all of the main muscle groups in the legs including the hamstrings, quadriceps, calves, glutes, and a multitude of smaller muscles that all work together to make sure we run efficiently.

The opposite is true as well – when a marathon runner trains they develop their slow-twitch muscle fibers from long runs. The body has to make a decision – get bigger or develop its ability to resist fatigue. When the body is forced to run for long distances, it prioritizes fatigue resistance. This causes the body to signal the slow-twitch muscle fibers to step up their game.

When this happens, the fast-twitch fibers start to atrophy. In this case, the fast-twitch fibers atrophy faster than the slow-twitch fibers grow. This results in an overall smaller muscle.

marathon runner

How Does Running Make Your Legs Skinnier?

Running for longer distances will have a slimming effect on your legs. Sustained Low Impact Steady State (LISS) workouts will tend to slim the legs by forcing the body to focus on the slow-twitch muscle fibers and ignore the fast-twitch. Over time, this will result in an overall slimmer appearance for the muscle.

If your goal is the ultimate in slim, slender legs, then focus on running long distances and doing a lot of low impact steady-state cardio. If you want to beef up those bad boys, focus on lifting weights, sprinting, or other plyometric work that requires short bursts of high force production.

Whatever you choose to do, make sure you have a good training plan and implement any training safely and under the advice of someone you trust. Exercise is very rewarding, but when done incorrectly, it can cause issues. This is especially true if you have a specific goal in mind. When looking to modify your body shape, for example by having skinnier legs, it’s important to truly understand the impact of all facets of your life: sleep, nutrition, training, stress, etc.


Does running make your legs bigger? Yes, it can. It can also make them smaller. As with many things in life, it all depends on how you execute your plan and how well you understand the physiological aspects of muscle growth.

While it doesn’t take a Ph.D. in exercise science to wade through this material, having a basic understanding of it does help when pursuing long-term goals. Running is a great exercise and can do many wonderful things. It can make skinny legs, or make beefy tree trunk-like legs, but just not at the same time.

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About the author

Jasper loves to write about fitness, running, and anything else that gets him moving outdoors. He's an avid hiker, backpacker, and climber who loves to stay fit so he can make sure he's healthy enough to enjoy his favorite hobbies. He also spends time writing about his true passions in life.