Why Do My Legs Feel Heavy When Running? + What To Do About It

Our running coach explains the various causes of heavy legs.

As a running coach, one of the most common complaints or concerns that I get from athletes who are looking to start training is that their legs feel heavy while running. 

Interestingly, while beginners often complain of having heavy legs or tired legs when they first start training, it’s also common to see experienced long-distance runners dealing with feelings of heaviness in the legs or noting that a relatively easy run feels like it’s causing tired legs.

Generally, the top causes of heavy legs when running include overtraining or increasing your training volume too quickly, poor nutrition, not getting enough sleep, and a lack of strength in your leg muscles, which causes muscle fatigue from running workouts.

In this guide, we will discuss common causes of heavy or tired legs when running, and what to do if your legs feel heavy when running.

A runner with his hands on his needs as his legs are heavy from running.

Why Do My Legs Feel Heavy When Running?

Let’s delve into the most common causes of heavy legs:

#1: Muscle Fatigue

Beginners often complain that their legs feel heavy while running simply because they are experiencing muscle fatigue.

Long-distance running requires repetitively lifting your legs, using your quads, glutes, hamstrings, and calves to support your body weight when you land, and then propelling your body off of the ground at push-off using these same lower body muscles.

If you increase your training volume, running speed, or workout intensity or start doing a lot of hill training or trail running, you may experience tired legs or a general feeling of heavy legs while running.

It is important to build up gradually and incorporate strength training exercises to build muscle and increase strength in your glutes, hip flexors, quads, calves, abductors, adductors, hamstrings, and core muscles.

Strength training exercises such as squats, lunges, step-ups, calf raises, split squats, hip thrusts, glute bridges, and side steps are a great starting place to build up strength to hopefully prevent muscle fatigue and reduce your risk of injury from running.

A tired runner with their hands on their knees.

#2: Overtraining

For experienced runners and those who have suddenly taken on a more aggressive training plan, overtraining is generally the most common reason that the legs feel heavy while running.

Overtraining causes muscle fatigue because your body is not getting adequate recovery between workouts.

This can result in central fatigue and changes in glutathione, glycogen, and hormones required for optimal athletic performance and recovery.1Kreher, J. B., & Schwartz, J. B. (2012). Overtraining Syndrome. Sports Health: A Multidisciplinary Approach4(2), 128–138. https://doi.org/10.1177/1941738111434406

‌Note that overtraining can occur if you are doing too much volume or mileage and/or too much intensity and speed work relative to the number of rest days or how much recovery you are taking.

It is also common to see runners experience signs of overtraining if they are running their easy runs or recovery runs too hard.

Moreover, overtraining syndrome occurs in the context of your overall life.

If you are not getting enough sleep, fueling properly, particularly in terms of getting enough carbs in your post-run meal or snack and enough calories overall, and/or experiencing external stress or added physical activity outside running, you increase your risk of overtraining.

A nutritionist putting together a diet plan.

#3: Nutritional Issues

A poor diet or nutritional deficiencies can absolutely cause a feeling of tired legs while running or poor recovery after workouts.

It is important to not only take in enough calories to support your training, but also get enough carbohydrates, protein, and micronutrients such as iron and B vitamins.

Consider working with a registered dietitian or nutritionist if you think your fueling strategy is not supporting your training or that you might be at risk of iron-deficiency anemia.

You should be trying to follow a balanced diet that provides enough carbs, especially before and after your running workouts to fuel your muscles and replenish glycogen stores.

Carbohydrates are a key source of energy not only for your actual running workouts but also for supporting your overall energy needs and recovering from all of the training that you do.2Ludwig, D. S., Hu, F. B., Tappy, L., & Brand-Miller, J. (2018). Dietary carbohydrates: role of quality and quantity in chronic disease. BMJ361, k2340. https://doi.org/10.1136/bmj.k2340

‌Good sources of carbohydrates for distance runners include whole grains, legumes, sweet potatoes, and other starchy veggies, fruits, and vegetables.

The standard recommendation to refuel glycogen storage after long workouts is to consume 0.6–1.0 grams of carbohydrates per kilogram of weight within 30 minutes and again every 2 hours for the next 4–6 hours.3Jentjens, R. L. P. G., van Loon, L. J. C., Mann, C. H., Wagenmakers, A. J. M., & Jeukendrup, A. E. (2001). Addition of protein and amino acids to carbohydrates does not enhance postexercise muscle glycogen synthesis. Journal of Applied Physiology91(2), 839–846. https://doi.org/10.1152/jappl.2001.91.2.839

‌Moreover, in the overall diet, the recommendations for the carbohydrate needs of runners and endurance athletes suggest the following:4Burke, L. M., Cox, G. R., Cummings, N. K., & Desbrow, B. (2001). Guidelines for Daily Carbohydrate Intake. Sports Medicine31(4), 267–299. https://doi.org/10.2165/00007256-200131040-00003

  • 5-7 grams of carbohydrates per kilogram of body weight per day for runners training at a “moderate“ level, which is considered less than one hour of running most days per week at a moderate or low intensity.
  • 7 to 10 grams of carbs per kilogram of body weight per day for runners who are training at a moderate to high level—considered to be 1 to 3 hours of moderate- to high-intensity exercise per day
  • 10 to 12 or more grams of carbohydrates per kilogram per day for runners who are training at a very intense level such as 4 to 5 hours of moderate to high-intensity running per day.

The American College of Sports Medicine recommends that endurance athletes consume at least 1.2–2.0 grams of protein per kilogram of body weight per day.5ACSM Certification Blog and Articles. (n.d.). ACSM_CMS. https://www.acsm.org/all-blog-posts/certification-blog/acsm-certified-blog/2021/01/25/nutrient-ratios-for-strength-training

‌You can estimate your caloric needs based on your total daily energy expenditure (TDEE) here.

A test tube and the words "iron deficient anemia"

#4: Low Iron Levels

Iron deficiency anemia or low iron levels are common causes of heavy legs or tired legs while running.

Iron is important for runners because it is part of the hemoglobin molecule in red blood cells.

Hemoglobin is a protein that carries the oxygen in your blood. 

Iron is also part of the myoglobin molecule, which is a protein found in muscles that plays the crucial role of extracting oxygen from the hemoglobin molecules once it is delivered to the muscle.

Iron deficiency limits the ability of the body to transport oxygen to your muscles when you’re running and to use the oxygen. 

Finally, iron also assists in the energy-generating pathways in your muscles that convert carbohydrates and fats into ATP, or usable cellular energy.

One study that looked at the iron and hemoglobin status in 113 recreational and competitive runners found that 56% of the runners (63 in total) had systemic iron deficiency.6Hunding, A., Jordal, R., & Paulev, P. E. (1981). Runner’s anemia and iron deficiency. Acta Medica Scandinavica209(4), 315–318. https://doi.org/10.1111/j.0954-6820.1981.tb11598.x

Consider getting your iron levels checked and incorporate iron-rich foods into your diet such as red meat, liver and organ meats, dark meat poultry, spinach, iron-fortified cereals, and lentils.

A person yawning.

#5: Lack of Sleep

It should come as no surprise that not getting enough sleep per night can compromise your recovery and certainly make you feel tired, sluggish, and like you are dragging heavy legs while running.7Mougin, F., Simon-Rigaud, M. L., Davenne, D., Renaud, A., Garnier, A., Kantelip, J. P., & Magnin, P. (1991). Effects of sleep disturbances on subsequent physical performance. European Journal of Applied Physiology and Occupational Physiology63(2), 77–82. https://doi.org/10.1007/bf00235173

According to the American Academy of Sleep Medicine and Sleep Research Society, adults need at least 7-9 hours of sleep per night. The needs of athletes are usually somewhat higher.8Watson, N. F., Badr, M. S., Belenky, G., Bliwise, D. L., Buxton, O. M., Buysse, D., Dinges, D. F., Gangwisch, J., Grandner, M. A., Kushida, C., Malhotra, R. K., Martin, J. L., Patel, S. R., Quan, S., & Tasali, E. (2015). Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep38(6), 843–844. https://doi.org/10.5665/sleep.4716

#6: Dehydration 

Dehydration can lead to overall fatigue, and it can cause heavy legs while running because stroke volume decreases, which decreases blood flow.

Your muscles need adequate blood flow to receive oxygen to support energy production and muscle contractions for running.

Hydrating before, during, and after running and working on your hydration throughout the day is the best way to prevent dehydration fatigue.

You may also need electrolytes in your hydration beverages, particularly if you are sweating a lot, doing a long run, or running first thing in the morning on an empty stomach.

A workout plan in a notebook.

#7: Not Following a Proper Training Plan

If you are not following a training plan, you might not be taking an adequate number of rest days, which can put you at risk for overtraining.

Or, you might be following a training plan that is too advanced or aggressive for your current fitness level.

You also want to make sure you warm up and cool down before and after your workouts.

A warm up with easy running and dynamic stretches can increase circulation and range of motion.

A cool down can potentially decrease post-run muscle soreness, which can then potentially cause your legs to feel tight and tired at the start of the next run.

#8: Certain Health Conditions 

Aside from iron deficiency anemia, certain health conditions can potentially cause heaviness in the legs while running for poor post-run recovery.

For example, any medical condition or medication that compromises circulation or blood flow, particularly if you have venous insufficiency, can compromise energy production in the leg muscles because they simply aren’t receiving adequate blood flow.

Talk with your doctor if you have venous insufficiency or other health conditions that might be causing heavy legs running.

Running shoes.

#9: Wearing the Wrong Running Shoes

Runners tend to blame running shoes for various pains and problems with running, and while running shoes aren’t always to blame, it is possible that wearing the wrong shoes can cause heaviness in the legs while running

If your running shoes are too big or too clunky, such as if you are wearing maximalist running shoes, or your running shoes are compromising your ability to use proper running form, it will decrease your running economy.

This will make running harder, making you feel like you are dragging your legs.

#10: Poor Running Form

Wrong shoes or right shoes aside, poor running form decreases running economy.

This means that you will be working harder and increasing your heart rate without maximizing the efficiency of your running speed and energy production from a metabolic standpoint.

For example, if you are shuffling or dragging your feet instead of lifting your legs through the swing phase and using a full range of motion, you will be wasting energy and impeding your running performance.

Similarly, if you are overstriding, your running economy decreases, and the risk of injury increases because you are applying a braking force towards your forward momentum and increasing impact stresses on your lower body.9Barnes, K. R., & Kilding, A. E. (2014). Strategies to Improve Running Economy. Sports Medicine45(1), 37–56. https://doi.org/10.1007/s40279-014-0246-y

Two people doing squats.

How Can I Prevent Heavy Legs When Running?

Now that we’ve given you the main causes to answer your question, why do my legs feel heavy when I run, let’s get to the solutions to prevent heavy legs.

As a summary, here are some of the top ways to prevent tired legs while running:

  • Strength training with exercises such as squats, lunges, and step-ups to build muscle.
  • Taking adequate rest days to prevent muscle fatigue and overtraining, decrease the risk of injury, and to facilitate recovery.
  • Improving your hydration strategy and ensuring you are getting enough electrolytes.
  • Working with a nutritionist to fix your diet.
  • Improve your hydration and take in electrolytes if necessary.
  • Improving post-run fueling with enough carbs to replenish glycogen stores.
  • Following a training plan that is appropriate for your fitness level and uses a gradual build up in volume and intensity.
  • Doing a warm up and cool down.
  • Getting enough sleep, aiming for a minimum of 7-9 hours of sleep per night.
  • Getting a running gait analysis to ensure you are using proper running form.

Consider checking out some of our free training plans to find a training plan that meets your needs.


Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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