Why Do My Legs Feel Heavy When Running?

Nothing is worse than starting to pound the pavement and feeling like your feet are laced up with bricks instead of sneakers. With each step, you find yourself wondering why your legs feel so heavy during your run. If this sounds familiar, rest assured—there are many common causes for that dreaded dead-leg feeling, and many of them have easy fixes.

heavy legs when running
Illustration by Emily Roberts, Verywell

Intense Strength Training

Strength training is a smart addition to round out any runner’s weekly routine. It helps maintain muscle mass, can make you a faster runner (as you can propel your stride easier), and provides balance in your exercise routine. However, too many strength training sessions, or very intense lower-body sessions, can cause your legs to feel heavy on subsequent runs.

If your primary fitness goal is related to running—like training for your first half marathon or qualifying for Boston—you’ll want to adjust your strength training in line with a periodized running training plan. In other words, modify the volume and intensity of your strength workouts based on the part of the training season you’re in.

  • Off-season: During this time, you can focus more on strength training. This will help you build muscle mass that will power your runs later in the year. You may have some occasional off-season runs where your legs feel heavy, but that’s OK since you won’t have any upcoming races to worry about.
  • In-season: During your peak training for road races, cut down to one to two strength sessions a week. Research shows this amount of training during the season can maintain the strength built during the off season.

Skipping Post-Run Stretches

That post-run stretching and foam rolling is for more than post-run relaxation. It can also decrease muscle stiffness and pain. 

If you’ve been skipping stretches, try to give yourself 10 minutes at the end of your runs to focus on a few static leg stretches. This will leave your legs feeling limber and lighter on your next run. Try to stretch all the different parts of your body involved in running—quadriceps, hamstrings, glutes, hips, and back.

Overtraining

If you seem to be experiencing heavy legs frequently, it may be a sign that you are overtraining. Overtraining means you are putting too much physical stress on your body. It can be caused by high overall volume in your training plan, mileage that progresses too rapidly, large jumps in long-run mileage, and/or trying to do too much too soon after an injury or break

Aside from heavy legs, other signs of overtraining include:

  • Decreased performance
  • Fatigue and tiredness
  • Mental fatigue (runs feel harder than they used to)
  • Headaches
  • Irritability
  • Increased rate of injuries
  • Illness (increased frequency of colds)

If you’re experiencing these symptoms, it’s worthwhile to first check in with a physician to make sure there are no other underlying medical issues. If these symptoms are in fact due to overtraining, try taking a few days of rest followed by a few weeks of reduced training volume. Overtraining can be serious, so don't try to power through it—get the rest your body needs.

Wearing the Wrong Shoes

As silly as it sounds, the wrong shoes can make your legs feel heavy, too. You want running shoes that are lightweight, while still meeting any support requirements.

For example, stability shoes for overpronation tend to weigh more, as structurally they’re a bit thicker and provide more support. But there is still a wide range of stability shoes on the market. Try on several options and jog a few test laps around the store to make sure they don’t feel too heavy.

On the flip side, sometimes having a shoe that’s too light and not supportive enough can cause problems too. If you’re not getting enough support in your shoe, your body may be experiencing more stress when the foot hits the pavement. This can cause accelerated fatigue in the muscles.

This can also happen with shoes that are worn out and old. Be sure to replace your running shoes every 300 to 500 miles.

Poor Running Form

If you consistently run with poor form, it puts extra stress on your body and can cause tired, heavy legs. Two of the biggest metrics related to form to pay attention to are:

  • Ground contact time: The amount of time your foot stays on the ground with each stride
  • Vertical oscillation: How high in the air you bounce with each step

For proper running form, you want to keep both of these low. Staying on the ground too long acts as a brake, slowing you down and requiring more effort every time you push off. Too much bouncing wastes energy and creates more force (stress) on your legs when you land.

New runners, in particular, may struggle with these; especially with ground contact time. Weaker hip and core strength combined with a slower pace typically means that the foot stays on the ground for longer periods of time. Instead, you want quick steps to propel you forward, without much bouncing upwards.

While wearable devices are helpful for measuring these metrics, you don’t necessarily need one to improve your form. Simply think “quick steps” while you’re running, focusing on pushing off as soon as your foot touches the ground. This easy change can reduce stress on the legs—not to mention improving pace over time.

Weight Gain

There’s no such thing as one type of runner’s body—anyone can run at any weight. But if you’ve personally just started to experience a heavy legs sensation, hop on the scale and see if there have been any fluctuations in your weight. Even an extra 5 or 10 pounds compared to the last training season can cause your legs to feel sluggish.

If you have gained a few extra pounds that you want to lose, try implementing these changes.

  • Focus on hunger and satiety cues: Eat when hungry and stop when satisfied. Avoid distractions like watching television while eating.
  • Track your food for a few days: See if there are any less-than-healthy habits you can pinpoint. For example, do you tend to reach for the cookies during that mid-afternoon energy lull? Do you have a few too many calorie-dense cocktails at happy hour? See what small changes you can make.
  • Practice good portion control: Try using smaller plates, or measuring out foods to see if you're serving yourself the amount you see on the label.
  • Avoid using your runs as justification for less-healthy foods: It's fine to include some indulgences in your diet, but practice the 80/20 rule—80% nutritious choices and 20% flexibility for treats.

Low-Carbohydrate Diet

Have you started a new low-carb diet? Or maybe you’ve just been busy at work and haven’t had time for lunch recently? Either way, a lack of carbohydrates can lead to that heavy-legs feeling.

When you’re running, your body is always using a mixture of carbohydrates and fat for the energy your muscles need. Those carbohydrates are stored in your muscles in a form called glycogen. 

If you dramatically cut down on your carbohydrate intake at meals, your body can’t store as much glycogen in your muscles. This affects energy production on your run and can cause the dreaded "dead legs."

Occasional depleted runs can actually be beneficial for competitive athletes, as they teach the body how to run in a sub-optimal state. However, if you do these too often, training can feel tough and performance might be compromised.

For most runners, a well-balanced meal plan that includes healthy sources of carbohydrates is the optimal choice. Try mixing in more fruits, vegetables, whole grains, and/or dairy products in your meals and snacks and see if that improves your runs.

If you would like to stick with a lower-carbohydrate meal plan, some athletes find success with a ketogenic style of eating. This enables the body to use more fat for fuel on a run and may help with body composition goals, though it has not been shown to improve performance. Note that it may take a few months of adaptation before that heavy legs sensation goes away on this type of meal plan.

Iron Deficiency

Iron is a component of hemoglobin, a part of your red blood cells that helps carry oxygen to working muscles. If you suffer from iron deficiency, your body has a more difficult time supplying that oxygen to your muscles on a run. You'd likely experience overall fatigue and tiredness when this happens, but some people may also perceive it as a heavy leg feeling.

Most athletes get enough iron in their diet through an overall balanced eating plan. However, there are two groups of athletes who may find it more challenging to meet their iron needs.

  • Vegetarian and vegan athletes: It’s certainly not impossible to meet iron needs on these diets; it simply requires a bit of planning. Include a variety of iron-rich plant-based foods, and eat them with a good source of vitamin C, as this helps with iron absorption.
  • Female runners: Since they lose iron each month during their period, female runners may be at greater risk of iron deficiency—especially if they experience heavy menstrual bleeding.

If you are experiencing heavy legs during running along with overall fatigue, check with your doctor. A quick blood screening may be able to identify if you’re suffering from iron deficiency anemia, and then your doctor can make recommendations for treatment. This can be as simple as adding new iron-rich foods to your diet or taking a daily iron supplement until levels reach normal.

Dehydration

Most people associate dehydration with muscle cramps, but dehydration can also cause general fatigue during a run. Similar to iron deficiency, people may perceive this fatigue as heavy legs.

Hydration is critical during long runs. When you lose fluid through sweat and you don’t drink enough to help offset this, your blood volume can actually become thicker. Your body has to work harder to pump this blood. You might feel like your legs are more tired than usual or the run just feels harder.

To prevent dehydration on a run, follow these tips:

  • Drink fluid according to thirst: If you find yourself not tuning into your body’s thirst signals, though, try setting a reminder on your watch that tells you to drink every so often.
  • Wear a hydration belt or pack: Add this to your gear list so that you have fluid to drink as desired, especially on long runs.
  • Chose the right beverage: If you’re exercising for less than an hour, plain water will meet your needs. If you’re exercising for more than an hour, choose a drink that also has electrolytes (namely sodium).
  • Adjust hydration along with the weather: Your body may need more fluid for runs in hot, humid weather.

Poor Circulation

Poor circulation, most notably from a condition called chronic venous insufficiency, can also cause heavy legs. In normal physiology, veins carry blood from the lower extremities back to the heart. Contractions in the legs during movement help this process work against gravity. There are also little valves in the veins that prevent blood from flowing back down.

In chronic venous insufficiency, though, those valves don’t function correctly. Blood can drip back down into the legs and pool there. This causes swollen, heavy legs.

Experts estimate that 40% of people have chronic venous insufficiency. It sounds scary, but the good news is that regular exercise helps prevent the condition. As a runner, it’s more common that your heavy legs are related to one of the other causes.

That said, it can still occur in those who run regularly, especially if you have other risk factors, such as:

  • History of blood clots
  • Long periods of sitting or standing at work
  • Smoking
  • Pregnancy
  • Older age
  • Obesity

Your doctor will be able to assess if the heavy leg feeling is due to chronic venous insufficiency. If it is, treatment will be prescribed based on your symptoms, overall health, and the severity of the condition. Treatment may include compression gear, medications, weight loss, nonsurgical procedures, or (less commonly) surgical procedures.

Lack of Sleep

While you might be able to power through your day on just a few hours of sleep, you’re probably not doing your body any favors. That lack of sleep can manifest itself as tired, weary legs during training and racing.

Most athletes need seven to nine hours of sleep each night. There are individual variations, though—some outliers may only need six hours, while others may need 10 for optimal functioning.

If you think sleep might be a cause of your heavy legs while running, try incorporating these tips in your routine:

  • Make sleep a priority, just like you do for training and good nutrition.
  • Power down the TV, computer, and phone screens at least a half-hour before bedtime.
  • Avoid alcohol and caffeine close to bedtime.
  • Schedule morning workouts: These may help you sleep better compared to evening workouts.
  • Try naps: If you absolutely can’t get at least seven hours of sleep at night, short afternoon naps may help training feel easier and improve performance.

A Word From Verywell

Most runners will find relief by implementing the tips related to these eleven concerns. There's a small chance that heavy legs during running are unrelated to these, though, and instead stem from another medical condition. If you've ruled out the issues above and are still experiencing problems, be sure to see your doctor to address your concerns.

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