Why Are My Legs Getting Bigger From Running?

legs getting bigger from running

I get a lot of complaints from women who have found their legs getting bigger from running, which isn’t the desired results for most of us. So let me explain why this is happening.


Running uses your glutes, quadriceps, hamstring and calves constantly, meaning that your leg muscles are working and this will cause them to develop and get bigger in size.

Any form of exercise that engages your muscles will cause them to grow in size. However, some exercises cause more muscle growth than others.

Running will not build as much muscle as weightlifting, sprinting and high-intensity interval training.


We all know that sprinters have very muscular physiques, especially compared to distance runners. Sprinting engages your muscles more and focuses on muscular power. Therefore, sprinting will build more muscle than just steady state running.

Doing a lot of sprint training and plyometric type exercises will develop a more muscular look, but will also help you get lean. If you don’t mind this look, then this is probably a great style of workout for you. If not, it might be best to avoid these style of workouts.

When I was training for a triathlon, I used fast past interval runs (not a full on sprint) to help me develop my cardio fitness quicker. It definitely did this, but what I found was that it actually helped me lean out my legs quicker too.

If you still want to include some cardio interval training, have a read of this blog post which explains how to do the fast past runs.

why are my legs getting bigger from running


Your ability to get bulky muscle from running depends on your body type. If you don’t know your body type, click here to find out.

Ectomorphs find it very difficult to gain muscle and will probably never get bulky even if they do lots of weight lifting. Mesomorphs build muscle easily but can also lose muscle and fat quickly too. Some mesomorphs may get bulky legs whereas others might not.

And finally, endomorphs probably already have naturally muscular legs so find it easy to bulk up.

Running does burn a lot of calories and will help you lose weight all over your body. It may help you lose weight in your legs too. But at the end of the day, it will still build muscle in your legs. I have mentioned this before, but if you are a shorter endomorph build, I would avoid running as it can make your legs bigger.


There are 2 basic types of muscle fibers. Slow twitch fibers are those used for longer endurance style workouts; and fast twitch fibers are those used for short bursts of energy such as sprinting, HIIT and plyometric workouts.

Everyone has different amounts of these fibers, and the amount and type you have will determine whether or not your legs get bigger from running. Someone with lots of fast twitch fibers might have muscular legs, even though they don’t do any type of weight lifting or sprinting. They may even build muscle just from walking.

On the other end of the scale, someone with lots of slow twitch fibers might do lots of sprinting and HIIT and find it difficult to gain muscle.

As you can see, genetics play a huge factor in whether or not your legs will get bigger from running. Some people will run all their life and their legs will stay slim and toned, while others will get bigger legs from running after just a month or so.

You need to adjust your running (and exercise program) to suit your body type and your goals.

legs getting bigger from running
Both women are long-distance runners. The difference is their genetics


Running on an incline will also use your muscles more (especially your quads and glutes) and will build them. This is due to the pushdown and jumps motion. If you want a leaner look, always try to run on a flat surface.

Another factor that might cause your legs to get bigger from running is your exercise experience. If you haven’t done much exercise and have very little muscle in your legs, then you start running, you are going to build muscle and this is going to be a significant difference.

But if you already exercise and have muscle in your legs, the change caused by running might not appear as significant. What is considered significantly bigger depends on your preference.

Another thing to keep in mind is that your legs can also swell after a run. This is short-term and the swelling will reduce. So try not to judge your progress based on what your legs look like immediately after a run.


The takeaway points from this are:

  • Running builds muscle in your legs, but doesn’t build as much as sprinting, HIIT and weightlifting;
  • Your body type and muscle fibers (i.e. genetics) will determine whether your legs will get significantly bigger from running. But “significantly bigger” is determined by YOU and what you think is too big;
  • You need to adjust your running (and exercise program) to suit your body type and your goals; and
  • Run on a flat surface and at a steady pace to avoid building more muscle from running.


If running has made your legs bulkier and you would like to lean them out, I should also mention my 3 Steps to Lean Legs Program which is designed to help you get lean legs without the bulkiness :)

There are 3 different versions fo my program, one for each body type. Each version combines the right type of cardio and resistance training for one particular body type so you can be sure you’re going to get the best possible results. 

And of course, since you cannot train and be on a crappy diet, I included a complete 8-week meal plan in my program.

Also, the resistance training part of my program now has FULL-LENGTH videos that you can follow from warm up to cool down.

To find out more about my 3 Steps to Lean Legs Program click the link below:


To find out more about my FULL-LENGTH VIDEOS, follow this link: 


And as always, if you have any questions, please feel free to ask! 

Love Rachael xx

Picture of Rachael

Rachael is an Australian born certified personal trainer and nutritionist who holds a Bachelor degree in Science.

After struggling for years to find an exercise and diet program that is tailored to women striving for lean and toned body with no bulk she designed her Lean Legs Program. This program is tailored to each body type and focused on helping women get toned but feminine bodies, without getting bulky.

Her mission is to empower women and help them stay in shape in a healthy and balanced way.

35 comments on “Why Are My Legs Getting Bigger From Running?”

    Izzy says:

    I’m happy with my body but my legs are a little bit bigger than I’d like. In the past I have noticed running bulks up my legs. Should I stick to walking? If not how many runs and how far is best?

      Tijana - Lean Legs Support says:

      Hi lovely,

      If you noticed your legs, you better switch to just walking, e.g. a 20-minute run is a 40-minute walk. Try to walk 10,000 steps at least 5 times a week for optimal results <3


    Lisa says:

    If I diet the same time I run (I do sprinting for track & field) will my legs still get more bulky?

      Tijana - Lean Legs Support says:

      Hi lovely,

      While healthy diet matters (and eating at a slight calorie deficit (200-300 calories less than you spend) if you wish to lose weight in a healthy manner), as mentioned in this blog post, you will develop a more muscular look with sprinting. The nutrition can’t cancel out the effect the sprinting has on your legs so your legs would look lean but with prominent muscles.

      Hope this helps! xx


    Odette says:

    So I’ve been running since summer 2016 and i remember how fit i used to be after the summer. The problem is that i have periods where i am very physically active and periods where exams make time tight. I used to be really confident with running because i love how it makes me so fit. I feel that jogging is the best exercise for me because my main problem is fat. I have a lot of fat on different parts of my body and jogging just is the best and fun way to get rid of it. My problem in this time is of course my legs. They have just gotten bigger and bigger from running and i dont know what to do! Jogging is like my therapy so i want to continue to do it, but at the same time im worried about my legs that just keep growing.. I run maybe like 2-3 times in a week in like 40 minutes. And i also have a chill day after each jogging day. Furthermore i also avoid running in uphill and downhill but on flat ground. What can i do about this? How can i keep running without getting large calves?

      Tijana - Lean Legs Support says:

      Hi lovely,

      Thank you for reaching out! :)

      Since you love running so much but you notice it bulking your legs, I suggest you try to run less often. So, instead of 2-3 times a week, try to make it first 1-2 and if you don’t see any improvement, although it may sound harsh to you, reduce it to once a week. It may be that the mental benefit of running can be substituted by power walking (not jogging) – so you can go power walking more often (5-6 times a week for 45-60 minutes each time) and run 1-2 times a week for 20 minutes. Combine it, observe your legs, listen to your body and mind but in general, your legs would most likely benefit more from power walking than running.

      I hope this helps! xx


    lucy says:

    I’ve recently started running. I am an endomorph. I’ve been running about 2.5 miles on my treadmill at a speed of 5.5 . and noticed my legs especially my calves getting so big! Which is not what I want at all :(
    I’m trying to slim my legs down.
    What should I do?! Should I start walking instead? if so what treadmill speed do you recommend for the walking?

      Tijana - Lean Legs Support says:

      Hi lovely!

      Yes, unfortunately, many endomorphs experience that problem :( But don’t worry hun, you can reduce the bulk, so definitely switch to walking and try to aim at 3.7 – 4.3 mph and make sure there is no incline. If you have more questions, you can also write to [email protected] <3


    Valerie says:

    Hey chick I’m Endomorph body type I have started jogging rather than running . Will this make my legs bigger?? The people at the gym tell me jogging is less stress on the legs than running so I want tone but not mass

      Tijana - Lean Legs Support says:

      Hi lovely,

      Rachael prefers either running or walking instead of jogging and here’s why:

      When you are jogging slowly, the action of your legs means that it is the same as running (which builds muscle). The action of walking actually really helps to get rid of fat on your legs, not running or jogging. So slow jogging for 45 minutes means you will build muscle, without really getting rid of the excess fat that walking will. So you’re probably better off better walking.

      When you are running faster, your body is burning lots of calories and you’re pushing yourself so your fitness is increasing, which is great. But jogging slowly isn’t really that challenging, and you’ll burn less calories. It may even bulk up your legs because you are overdoing the running. You’re not getting the full benefits of running if you’re just slowly jogging.

      So it’s more effective to either run faster or just walk. Slow jogging is still better than nothing though so you can do it – it’s up to you. But from her experience, it’s as effective as the other two.

      If you have any other questions, feel free to ask! xx


    Frustrated says:

    Not only have my legs gotten bigger, but so has my butt, and with continued running, I am not going down on the scale at all. I gained about 20 lbs from running this year! I’m done with this. I finally lost weight when I started modifying diet, but my huge legs remain!! There’s so much muscle built on them. At this point I’m going to do walking instead.

      Diana - Lean Legs Support says:

      Hi lovely,
      It sounds like you were probably eating at a calorie surplus which is why your weight has increased so much. If you find that running makes your legs bulky, power walking is the best substitute. Also, make sure you’re eating less calories than you burn. :)
      For more helpful tips on how to calculate your ideal calorie intake please have a read of this blog post.


    Jolie says:

    Hi, I was happy with my legs…then decided to try walking to get them a little more leaner. Yesterday, I walked 10km, but today they are even bigger! Is this just after-day swelling since I’m not used to walking that much?

    Natalya says:

    The first picture is the wrong comparison for showing the difference between sprinter and marathon runner. As you can see between those women is a huge age difference. The right one is at least 25 years older from the left one. Maybe back then she had muscles like the girl from the left.

      Diana - Lean Legs Support says:

      Hi lovely,
      You have a point, this could’ve been true. You can find another sprinter VS marathon runner image here. These athletes are about the same age. However, the pic was only posted as an example to show the effects that different types of cardio can have on your body. You can find more similar images using Google search! xx


      Lance says:

      Not so. The women on the right is of similar age but her East African heritage makes her look older. That tends to be the case with East African heritage.

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