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.


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.


We’ve Created A Quiz To Help You Determine Your Body Type!

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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 Lean Legs Program 1 which is designed to help you get lean legs without the bulkiness :)

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

The resistance training has FULL-LENGTH videos that you can follow from warm up to cool down.

To find out more about my Lean Legs Program, CLICK HERE!

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

Love Rachael xx

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.

51 Responses

  1. Hey, i am running before reading your blog and i wasnt running & walking on treadmill which was always flat surface. but recently i was doing interval running and i got lateral knee pain i decided to rest myself for 3-4 days. ı have read that to decrease stress on my knee i should run on %1 incline. Can i do that or will it increase my thighs size?

    1. Hey lovely! When it comes to running, I recommend that you opt for steady state running and make sure that you do it on a flat surface. If your goal is to slim down your legs, I would encourage power walking 5-6x a week. :)

    1. Hey lovely! Walking on an incline will put a lot of pressure on your quads which may result to unwanted bulkiness. It would be best if you always power walk on a flat surface. :)

  2. Hi, i am 23 year old and i believe i have endomorph body type. I have been struggling to reduce the size of my calf, they make me feel so insecure which is why i dnt wear skirts and skinny jeans. I have tried running without inclined mode, squats and most of the exercises but i have not succeeded to reduce the size of my calf muscles it just makes me leg look so manly and only gets bigger and bigger. Its definitely not the genes, i do not know what is the reason behind. Please if you could give me some tips on it. Thank you.

    1. Hi lovely,
      Calves are a bit tricky because genetics is a big factor. I often get these questions so I wrote a very detailed blog post about it.

      I think you’re going to find it very helpful :)

      And if your calves got bigger from training or you’ve gained weight, I’m happy to tell you that my Lean Legs Program could help you with that :)

      You can find out more about it here. :)

  3. Hello! I am a 15 year old girl who likes to run on the treadmill, and I noticed that my legs are getting bigger. I want to lose weight, so should I give up running?

    1. Hey lovely,

      Thanks for reaching out!

      Since you are still very young it is best to stay focused on simply staying physically active.
      However, don’t include diets until you’re fully developed and exit the teenage phase of your life because it can seriously damage your metabolism and lead to gut issues that will make it difficult for you to slim down in the future.

      Make sure that the treadmill doesn’t have an incline installed – that you’re using the one with a 0% incline option.

      When you work out, there is an increase in blood that is being pumped into your system and the muscles becomes temporarily engorged which will make them appear bigger than normal but again, this is only temporary. Keep this in mind in case you’re already using a 0% incline treadmill.

      You can also practice walking on a treadmill instead of running.

      Hope this helped!


  4. Hello, so I am 31 years old female, From reading your article my body type is definitely an ectomorphs I find it very difficult to gain muscles will probably never get bulky legs which I love, but I also noticed I loose muscles quicker than gain muscles from any little cardio that I’ve done, i have been doing cardio like spinning, stair masters, gym classes, alone with my weightlifting. My eating pretty clean I have discipline, I don’t really run so I was thinking about adding some sprinting in my routine to see if I can get some sorts of bulking in my legs

    1. Hey lovely,

      You may also include some HIIT and resistance trainings to your routine in order to get more definition. :)


  5. Hi, so i am 13 years Old Girl, and i have Seem to notice that my legs are big. There is some fat in MY thights but not that much so i am scared that if i try to do cardio or running they just get bigget:(
    I relly want to slim Down the muscle in MY thight but i just startes growning so i dont know if i sjould do a deficit or what
    Please help me i relly need it

    1. Hi lovely,

      Thank you for reaching out! :)

      ​Since you are 13 years old, your body is still going through a lot of transformations so ​if you want to lose weight, it’s best you talk to your parents so they can get you an appointment with a specialist. A nutritionist can advise you on your nutrition and workouts so that you can achieve the results you wish in a healthy way that suits your age.

      Wishing you the best of luck! xx

  6. Hiii
    I have been running at a low intensity after reading why you need cardio for lean legs and it has worked out great! I have 100% noticed my legs slimming down( I’m a mesomorph btw)! The advice has been great however I’m worried that if I stop running/walking my legs will go back to being quite muscly! How shall I keep my legs lean forever?

    1. Hi lovely,

      Running and power walking are great cardio activities you can continue to do for your entire life! If you don’t feel like running all the time, strive to accumulate 10,000 steps in a day for at least 5 times a week. Also, staying lean also means you need to eat healthily and be careful not to over-eat.

      I hope this helps! xx


  7. Hi, I’m an mesomorph, I have an overall fit body, my abdomen is flat, and I guess I don’t have too much fat, but my legs and arms are very bulky! Someone told me once that this is just naturally how my body is, and that I can’t change it with exercise, because I don’t have much fat, instead I have bulky muscle… Is this true? And if not, is there a way to get the thin muscle that runners have. I haven’t started running regularly, because I’m scared it will bulk me up more. But I really want to get rid of my thick muscles! I’m 15 btw, and I’ve tried going on a calorie deficit, and it didn’t go well, I got very weak :/
    Thanks :))

    1. Hi lovely,
      Thank you for reaching out! :)
      ​Since you are 15 years old, your body is still going through a lot of transformations so ​if you want to lose weight and slim down your body, it’s best you talk to your parents so they can get you an appointment with a specialist. A nutritionist can advise you on your nutrition and workouts so that you can achieve the results you wish in a healthy way that suits your age.
      Wishing you the best of luck! xx

  8. 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?

    1. 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

    1. 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

  9. 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?

    1. 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

  10. 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?

    1. 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 <3

  11. 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

    1. 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

  12. 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.

    1. 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.


  13. 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?

  14. 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.

    1. 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


    2. 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.

  15. Hi,

    Last year, I began running 1-2 miles during the week. I would do as much as I could almost 6-7 days a weeks. When I started this, I noticed I was losing weight quite rapidly, and the size of my hips and legs decreased. I have a mesomorph body type.

    I took a break for a couple of months, and I am now back in training. I run the same amount for the most part, but since I am training for a physical exam, I am training particularly in fast runs. I have also been doing sit-ups and push-ups. After about a month of running, I didn’t notice that much of a difference in my stomach or my legs. Recently, I feel as though my thighs are much bigger and touch when I walk. I’ve never had that problem, but now I do. I feel like my stomach has lost some weight and looks more toned.

    Why is this happening? Last year when I was running, I was strictly running. Now, I incorporate as much as I can in my workouts, but feel like I am gaining more than what I’m used to. I’m also VERY hungry. I crave a sandwich after my runs.

    Am I doing something wrong? Thank you for your help!!


    1. Hi lovely,

      We’d love to help as much as we can :) that’s why we have created our Lean Legs Program and our Lean Legs Training Club.

      The program in the eBook is an 8 week workout and nutrition plan designed to help you get lean and toned without bulking. It will help you slim down your legs, but will also help you slim and tone your upper body and core too (the workouts are full body). It also includes a full meal plan, a separate recipe eBook and demonstration videos.

      You can find out more about the Lean Legs program here:

      For more helpful info please have a read of these blog posts:

      Love, Lean Legs Club support Xx

  16. Hi Rachael. I have been doing yoga for the past 6-8 months and I am really proud of how flexible I am. However, over the last few months I have gained a lot more muscle on the legs.
    I read some where online that long distance and walking can help slim your legs but it has not been working out

    1. Hi lovely,
      Your diet is just as important as your workout routine, both play a big role in slimming down your legs.
      Rachael would love to help you as much as she can :) that’s why she has created her Lean Legs program and Lean Legs Training Club.
      The program in the eBook is an 8 week workout and nutrition plan designed to help you get lean and toned without bulking. It will help you slim down your legs, but will also help you slim and tone your upper body and core too (the workouts are full body). It also includes a full meal plan, a separate recipe eBook and demonstration videos.

      You can check out the Lean Legs program here

      Love, Lean Legs Club support

  17. Hi Rachael! I’m a short endomorph. About 3 weeks ago, I started doing barre exercises (which are mostly floor, no squats or lunges or jumps) and then a 30 minute walk right after on 0 incline, 3.8 – 4.0 mph.

    At night I’ve been walking another 45 minutes, again 0 incline, 3.8 – 4.0 mph.

    My legs are getting muscular and I see the definition but also a bit bulky. Will this lean out over time as I just started a new workout program? Or should I cut down in the amount i’m walking?

    1. Hi lovely,

      Rachael would love to help you with any questions you have and give personalized nutrition advice, that’s why she created the Lean Legs Club where she can help you achieve your fitness goals faster :) If you’d like to join find more useful info and join us here

      For more useful info, check out this post

      Lean legs Club support

  18. I run a 5k every day as well as 2 days including strength training. I am an endomorph. and my legs are not toning much. I also eat a nutritious and controlled diet. Any suggestions?

    1. Hi lovely,

      I know that reaching your fitness goals is hard! And that you probably have lots of questions about how to get that lean and toned body.

      I would love to help :) So that’s why I have created my eBook and the Lean Legs Club, where I’m available to answer ALL of your questions.

      If you’re interested in joining, I’d be happy to answer all your questions. Here is the link.

      Love Rachael xx

  19. But if we do your program, is there a chance for us to build more muscle than we want or it will be okay because we do a lot of walking and resistance training?

    1. Hi Sandy! It depends a bit on your body type. If you do my program and follow is correctly, it should be OK. Unless you are a short endomorph – then I would recommend avoiding the running xx

  20. Hi Rachael!
    I have run track for the past 6 years, and my leg muscles have built up significantly from all the running. I’ve read your article on losing muscle, but should I just be walking and eating low carb and low protein to reduce it? Also, I feel like all of my muscle is just turning to fat and my legs are not getting any skinnier. Is there anything I should be doing differently? Thank you and I love your blog so much!

    1. Hi Katie, thank you! :) Yes I would suggest walking and a good diet as you mentioned. Muscle doesn’t turn to fat so please don’t worry about that. You can also add in some light circuits like the workouts on my blog. Also please know that reducing muscle takes time, especially after 6 years of track. When I bulked up my legs, it took 6-12 months to get them back to slim. Keep on doing what you’re doing, be consistent and give it time! xx

  21. Hi Rachael,

    I’m looking at getting your Ebook too and but not too sure what body type is mine. I’m about 54kg and 159cm. I’m a size small on the top but M to L on the bottom. Pear shape obviously! I was on Kayla Itsine program and done it for 6 weeks and realise I got bulky which isnt what i want. I want to still lose weight and tone up that elephant legs! Could you kindly advise which one should i go for?

    1. Hi Eve! I’m sorry to hear that happened to you. I think you sound most like the mesomorph body type. However if you do buy the eBook, please send me an email and we can chat about it more and I will help you pick the best one :) xx

  22. Hello,

    I am a mesomorph and I do the elliptical every day for 30-45 minutes with no resistance. I try to keep my heart rate in the fat burning zone but not going crazy. Could this make my legs bulkier? I do not like running as much as I like the elliptical :(

    1. Hi Natalia, if your legs are bulky then yes this could be a cause. The elliptical does use your quad muscles so will build them a little, but not as much as lifting weights and doing squats, lunges, etc. You don’t necessarily need to run to slim down your legs – walking is actually better! xx

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