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What Causes Feeling Heavy Legs While Running

Why do our legs feel heavy sometimes when running? We can get ready for our run and feel fine, but once we start running we might feel our legs not normal but heavy and weak. And after several days of heavy legs, we might wonder what might affect these heavy legs. There are different causes of heavy legs while running. To figure out what affects our legs can help us fix these issues.

1. Poor Running Form

There are many reasons good running form is important. It improves our efficiency to help us run faster, better and prevents us from injuries.

The other important reason to keep good running form is to prevent us from too much fatigue too quickly. If our body is not using energy efficiently, it not only makes us run slower, but it also will make us feel more tired too quickly.

Not a good running form can cause heavy legs and more fatigue while running.

  • Over-striding- While running, our landing forward foot should be directly under our body (knee), we can’t pick up our leg up and reach out too far ahead. For a good stride, we should bend our knee slightly, take a shorter stride, and keep the leg closer to the ground. Focus on getting a higher running cadence.

  • Swinging our arms too much- Some people think they need to push their bodies forward mostly with the arms, but the real goal is just to keep us stable and balanced. Our legs, hips, and the slight forward bend of our torso is enough to propel us. We should focus on keeping our arms at the right angles, and keep them in line with our shoulders.

  • Not running using our core and hips- We shouldn’t start pushing with our quads, unless it’s a steep uphill. We should start our leg movement from the hips and use the hips and core to power the leg movement. Supporting our body and running form using and activating our core muscles will support a good stabilized running form and stronger run.

2. Weight Training

Strength training with weights is a good benefit for runners. We need that core and leg strength to keep our body running properly, especially when running uphill and downhill.

Many people think the core is just the abdominal muscles. But the true core is all the muscles that support our spine and hold it upright: the hips, glutes, pelvic floor, our diaphragm (big muscle for respiration) located in the centre of the abdomen, this muscle is connected to all the main core muscles, and also the rectus abdominus and obliques.

Keeping these muscles strong is essential for a good running form and our health in general.

Strength Training Recommendations

  • Do some heavy leg workouts- weighted squats, lunges.

  • To perform some upper body weight training sessions weekly, is also very helpful for runners, to support a better and stronger running form.

  • DOMS is very common after lower leg workouts, and it’s common to feel a bit sore 1-2 days after our leg strength workout.

  • If you combine a speed session (like hill sessions or farklets) with weight training, then strongly consider having a rest day the following day.

  • A good recommendation is to perform a light recovery run 1 or 2 days after a leg strengthening workout.

If you’re in the off-season and keeping in shape for training season, that’s when you want to focus on building up those core and leg muscles.

3. Overtraining

If we feel and love to push our limits and train too hard or too much distance, that will affect our overall muscles, and our legs will feel heavy.

It can be exciting to see ourself achieving new goals and watching our body transform. But overdoing it, and overtraining often causes heavy legs while running.

Minor running injuries fall under this category as well.

If we feel any strains, sprains, or leg fractures, it’s important to rest and allow them heal.

4. Not Enough Carbs and Iron

These are the two food-fuel deficiencies that often cause heavy legs.


Complex carbohydrates are especially important during long-distance runs. When running a shorter distance, our body starts by converting fat into energy, unless we perform fast speed short distances.

But the energy stores there quickly run out, and the body then turns to carbohydrates for more endurance. If our body doesn’t have enough carbs, the body then isn’t able to keep up the necessary levels of oxygen to convert to energy, and that causes fatigue, and heavy legs.


Iron is another important part of the energy-making process during running. Iron helps our blood pump oxygen into the muscles, which then convert it to energy.

For long-distance runners, the body tends to get more depleted of iron, or if you’re a woman on your cycle and are losing more than usual amounts of blood, you will be more depleted of iron. It is important to eat iron-rich healthy foods and take natural supplements but no more dosage than 18-36mg/day.

Here are some iron-rich foods you can eat to avoid the low levels:

  • Red meat- We usually recommend lean meats like chicken, but red meats can get you some good iron quickly.

  • Beans and Legumes- Red meat is high in iron, but is not the best for the environment or vegan runners, so if you want to get extra iron while eating vegan foods, beans and legumes (lentils, chickpeas, peas, soybeans, and beans) are a great source, and have good carbohydrates and protein too.

5. Dehydration

Runners should know that hydration is important during a run, water and electrolytes are essential during a long run because it replaces all the fluids we lose in the process. When we sweat, we need water to carry important nutrients through our body to help with the energy process.

Since 50-60% of our body is made up of water, we might feel fatigued and have trouble with heavy legs when we are dehydrated.

6. Sleep Deprivation

Before we started running long distances, most runners probably had no issues functioning on very few hours of sleep. According to some research, 1 in 3 people don’t get enough sleep.

While our bodies do adapt to our current lifestyle, such as the ‘built-in alarm clock,’ that helps us wake up naturally when we’ve been getting up at the same time for many days, there’s a limit to how much we should force your body to adapt. Especially when it comes to running.

Sufficient sleep enhances our running performance, while lack of sleep causes drowsiness, lack of mental stamina, and heavy legs.

7. Poor Blood Circulation

When we get heavy legs while running, the cause is often due to a lack of energy production in our body.

Determining the cause for our heavy legs is ultimately a matter of finding out where our body is missing the fuel it needs to produce energy.

High-intensity exercises can affect our blood circulation.

While we run, our blood pumps oxygen into the muscles to convert into energy. Over time (during a long-distance run), the heart and lungs have a hard time getting enough blood to those muscles to meet the high demand. When not enough blood circulates into those muscles, there is not enough oxygen to convert into energy.

This means over-exerting ourself and are trying to run longer distances than our body can handle. In this case, we need to work on cross-training and strength training, so that our muscles have the capacity to convert the necessary amount of oxygen.

With Heavy Legs, Listen to Your Body, Good Running Form, Strength Training, Hydration, Nutrition, Good Sleep, Good Recovery, Then Feel Better and Enjoy Nice Runs!


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