You might be surprised when you find out what the causes of extreme fatigue following exercise is.

“Mostly fatigue comes from deconditioning, dehydration, uncontrolled hypertension and psychological as the most common reasons,” says Dr. Cynthia Thaik, MD, cardiologist and author of “Your Vibrant Heart,” which can be can be purchased at 

As a fitness expert, I was surprised when I came upon the question of “What causes extreme fatigue after strenuous exercise?” in a health forum.

By definition, strenuous exercise will cause extreme fatigue!

That’s why it’s called strenuous, or very intense, or high intensity.

So if you’re doing sprints up a hill and wondering why, at the top, you must lean over, hands on knees, and are unable to speak for 30 seconds because you’re panting so heavily, this is normal. You just ran up a hill.

The same breathlessness or extreme fatigue will result if you run up multiple flights of stairs fast enough, do nonstop squat jumps for 30 seconds or pedal a stationary bike as fast as you can at medium tension for 30 seconds.

What’s strenuous or very intense is relative, too. To the deconditioned person, simply trotting, rather than running, up flights of stairs will exhaust them.

Brisk walking, rather than jogging or sprinting, up an incline will exhaust them.

As a personal trainer, I’ve had very deconditioned clients who allowed their mental state to contribute quite a bit to the fatigue following a level of exercise that to fitter individuals, would have qualified as a warm-up to them.

When is extreme fatigue after exercise something to be concerned about?

When you begin noticing that your warm-ups are beginning to feel like the actual workout—and this decline has occurred over a rather short period.

People will report that they’re “getting old.” This age-related decline in the fitness enthusiast is very, very gradual, over the years.

They can no longer run a mile in six minutes. It now takes seven, but this decline was very gradual.

However, a rapid decline is worrisome. Uncharacteristic fatigue from exercise that used to be a warm-up, or from activity that not too long ago hardly got your breathing rate up, is something to take strong notice of.

Dr. Thaik says, “Less common would be actual cardiac issues such as cardiomyopathy, heart failure, hypertensive heart disease, hypertrophic cardiomyopathy or lung conditions.”

There are also many non-cardiac causes of uncharacteristic fatigue following exercise levels that you used to handle pretty well.

Some that you’d never think of include celiac disease, low thyroid (hypothyroidism), overactive thyroid (hyperthyroidism), sleep apnea, side effects of medications, depression, anemia, chronic fatigue syndrome and diabetes.

An obvious consideration to many health conscious people would be cancer.

The most serious possible explanations should be investigated promptly.

dr. thaik

Dr. Thaik’s clinical interests include congestive heart failure and women’s heart disease, and is affiliated with the American Heart Association.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.  


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