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What Causes Extreme Fatigue After Running?

author image Henry Halse
Henry Halse is a Philadelphia-based personal trainer, speaker, and writer. He's trained a wide variety of people, from couch potatoes to professional athletes, and helped them realize their own strength, determination and self-confidence. Henry has also written for various fitness and lifestyle publications, including Women’s Health, AskMen and Prevention.
What Causes Extreme Fatigue After Running?
Sometimes fatigue is due to overtraining. Photo Credit Wavebreakmedia Ltd/Wavebreak Media/Getty Images

Not every run ends in a triumphant arm raise and a new personal best time. Sometimes you feel like you can barely make it through a few miles. It's hard to gauge how tired you are when you're focused on putting one foot after the other, but you'll feel the effects of the run when you're done.

Pushing too hard, not fueling properly and not resting enough can lead to extreme fatigue with serious symptoms.

Too Much of a Good Thing

Exercise helps many aspects of your life. It can help you live longer, feel happier and look the way you want to. It's incredibly beneficial but can also be dangerous if you go overboard. Too much exercise breaks down your body, instead of building it up.

Running is a very popular form of exercise. You don't need much equipment. Just put on some running shoes, weather-appropriate running clothes, grab a water bottle and head out the door. It's so accessible that it's easy to do it all the time, which can feed into a running obsession if you're not careful.

Read More: Aching Legs After I Exercise

Extreme fatigue from running can happen in just one run. Many marathon runners experience extreme fatigue and can be seen stumbling as they cross the finish line. Extreme fatigue can also be something that builds up over time and hinders training.


One of the most extreme forms of fatigue from exercise is rhabdomyolysis. It happens when your muscles break down so much that your kidneys can't handle it. Your muscles are made out of protein and, if they're under a lot of stress, get damaged and the protein breaks down. It then seeps into your bloodstream. This extra protein in your blood can become toxic very quickly, so your kidneys have to filter it out.

Working out normally will make some of your muscle break down. Rhabdomyolysis only comes from extreme runs, like a marathon. Even then, it's only likely to happen if you're dehydrated and overheated. If it does happen, however, the symptoms are concerning. You'll have tender muscles, dark-colored urine and possibly a fever. On top of that, you might feel dizzy or nauseous.

You'll have to go to a doctor or hospital to have a proper diagnosis and treatment. The most important thing to look at if you have rhabdomyolysis is the health of your kidneys, because it can damage them.

Athletes often push themselves too hard, too often.
Athletes often push themselves too hard, too often. Photo Credit Orlando florin Rosu/Hemera/Getty Images

Overreaching and Overtraining

Rhabdomyolysis is an extreme reaction to an intense run, but your fatigue doesn't necessarily come from one run. It can come from pushing your boundaries one too many times.

Overreaching is the first thing you'll notice if you're running too much. It can happen with just a couple of weeks of intense training. If you take time off and focus on recovery you can be back to normal in a couple of weeks, ready to train again.

Read More: What Causes Extreme Fatigue?

If you ignore signs of overreaching and keep pushing you'll become overtrained. The difference between the two is that the signs of overtraining can last for months. The symptoms of both are depression, constant fatigue, getting sick more often and getting injured more often. On top of that, your performance will go downhill and you'll feel fatigued during and after every run.

Part of the equation is that you might not be eating enough. If you don't have enough calories, especially carbohydrates and protein, to recover, your body will get weaker. The same thing can happen if you don't have enough vitamins and minerals in your diet. Try using a calorie calculator like MyPlate to see how much you should be eating every day.

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