Why Do My Legs Feel Heavy When I Run? – 3 Unusual Reasons To Avoid

For you to enjoy running, you need to be able to feel light on your feet. Such lightness is what gives runners that high and inspires them to go on. One of the challenges you may face is when your legs feel like bricks.

If this is your current situation, you may ask: Why do my legs feel heavy when I run? What can I do about it? These questions will be answered in this article.


Reasons For Heavy Legs When Running

Here are different reasons why your legs may feel heavy when you run. For simplicity, we'll categorize these into three mainly, your lifestyle, your health, and your technique.

#1. Your Lifestyle

Sitting Work

Being overweight is one of the top possibilities leading to you experiencing heavy legs when running. If your job requires sitting for extended periods of time, you are especially at risk. According to statistics, on average, Americans sit 11 hours per day. Such lifestyles cause up to 20% deaths of people 35 and older.

Aside from causing weight gain, having a sitting job also restricts blood circulation in the legs. Varicose veins may result which may trigger a heavy feeling when you run.

Other lifestyle changes such as recent pregnancy can also contribute to weight gain. When you are overweight, there is a lot of stress put on your feet and legs which may result in a pounding feeling when running.

#2. Your Health

Green vegetable smoothie. Woman living healthy lifestyle drinkin

Another reason for experiencing heavy legs when running is a vitamin deficiency. For example, lack of vitamin B1 or Thiamine may result in muscle cramps and a tingling sensation in your legs. The family of B vitamins is vital in converting food into fuel. If you are vitamin B deficient, your body loses its ability to repair itself after a workout. This, in turn, affects your energy levels leaving you feeling tired when you run.

Another vitamin deficiency that can cause heavy legs is iron deficiency. Hemoglobin is an iron-containing protein that transports oxygen to your muscles when you run. When you have an iron deficiency, you have fewer red blood cells and lower hemoglobin levels. Because of this, your muscles will have less oxygen, a condition that can result in the heaviness of the legs.

Additional Health Triggers

Dehydration is another issue that can trigger a tired feeling in your legs. When you lack water, you also lack electrolytes which help your muscles function properly. Since your body is made up of up to 70% water, dehydration can affect your running performance drastically. Sweating can reduce water levels in your body to up to 90% so keeping hydrated is a very big help.

Being dehydrated causes the body to choose to cool you down instead of fueling your muscles. This leaves your body feeling weak and legs heavy.

Lack of oxygen is another trigger that can cause your muscles to feel weak and even result in what are known as “side stitches”. Since running requires high amounts of energy, your lungs need to work overtime to produce a constant supply of oxygen to keep up with this need.

#3. Your Technique

Your Running Form

If you have the habit of neglecting warming up before you run, this may be another cause of the heaviness you experience. Warming up boosts the circulation of blood in your entire body preparing it for your workout. Failure to perform a quality warm up causes low blood circulation and reduces the chances of your getting cramps.

Another technique related issue is running with the wrong form. Running with the wrong form is one of the common mistakes that leads to injuries and lower performance. Always keep the right form with your body straight, hands relaxed and knee in line.

Having bad posture can also be another reason for your bad running technique. If you don’t maintain good posture, you put extra stress on your shoulders when you swing your arms when running.

This in turn affects your overall running posture which can strain your legs and make them feel heavy. Other side effectives of bad posture include having shoulder pain.

How To Prevent Heavy Legs When Running

Prevention of heavy legs when running lies in addressing the three main causes aforementioned. Here are some tips to help you do this:

  • Walk at least 30 minutes if you have a sitting job,  a day and in between sitting hours to help your blood circulate.
  • Keep track of your diet. To reach your peak performance, make sure you eat foods that contain iron, B vitamins, and magnesium. These are vital for your running health.
  • ​Keep hydrated. Always take water with you when you run to feed your muscles and avoid dehydration.
  • Warm up well. This enhances blood flow and prevents serious injuries.
  • Adjust your form. As you run, be conscious of your form and adjust it accordingly.


Having heavy legs when you run is not a major problem. It can be caused by vitamin deficiencies, lifestyle issues such as being overweight and improper technique. If you identify the possible cause of your heavy legs and address it, you will be able to achieve the highest performance possible.

Did you enjoy our article? Have you experienced heavy legs when you run? What did you do? We’d love to hear your thoughts in the comments below. Feel free to share this with others too.​