7 Reasons You're More Tired Than Usual During Your Workouts

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A tough workout should wear you out in a a good way. Sudden exhaustion could mean something else is going on.
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You stroll into the gym in full-on beast mode. Fast forward a few minutes into your workout, and you're already wiped. Sound familiar? Everyone has off days, but if you notice your energy is consistently zapped during workouts, it could be the symptom of something more.


Here, a medical expert explains why you might feel more tired after a workout than usual, so you can get to the root of your fatigue and get back to kicking butt. And if you're chronically exhausted, talk to your doctor before adopting any of these suggestions.

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1. You're Not Getting Enough Sleep

If you're sucking wind during workouts, the culprit might simply be lack of sleep. More than one-third of American adults aren't getting the prescribed minimum seven hours of shut-eye per night, according to the Centers for Disease Control and Prevention (CDC).


Not a total shocker: Stress is often to blame. Around half of Americans report lying awake at night worrying, per a 2017 ‌Stress in America‌ survey from the American Psychological Association.

"When we don't get adequate sleep, our bodies release more cortisol and adrenaline — stress hormones to keep us going," says Cynthia Li, MD, a board-certified internist.


Exercise — especially intense workouts like HIIT — can further raise cortisol levels, she says. Over time, "this can create a sustained high stress state in the body, which dampens the body's capacity to repair itself."

What you can do:‌ Try and add a little calm to your life before hopping into bed. One April 2015 JAMA Internal Medicine study found mindfulness meditation enhanced sleep quality for people with disrupted sleep patterns. An increase in sleep quality is critical for all, but especially those who don't have as much time as they'd like between the sheets. Other healthy sleep tips include keeping a consistent sleep schedule (yes, even on weekends), leaving your phone outside the bedroom and making sure your room is cool, dark and quiet.


2. You Could Have a Thyroid Condition

Another common cause of drained energy is a thyroid problem. More than 12 percent of Americans develop a thyroid condition during their lives, and up to 60 percent don't even know they have a health issue, according to the American Thyroid Association.


"The thyroid hormones play a primary role in regulating metabolism, the process by which the body converts food into usable energy for our cells," Dr. Li says. If thyroid hormone levels are too low, the body produces less energy than it needs. If they're too high, you might feel an initial upswing in energy, but over time you can experience muscle breakdown and inflammation.


What you can do:‌ Dr. Li recommends getting plenty of minerals in your diet including zinc, selenium and iron, as well as enough iodine, which you can get from sea vegetables, eggs, fish and table salt. Also, build in time for relaxation. Adequate sleep, meditation and spending time in nature can reduce stress and support healthy thyroid function, Dr. Li says.

3. You're Dehydrated

Dehydration can contribute to workout fatigue, too. That's because when you're parched, your heart has to work harder, according to the CDC. Not getting enough fluids reduces total blood volume, which places demands on your ticker, Dr. Li says; it needs to beat faster and stronger for the same amount of nutrients and oxygen to get to your muscles.


Plus, you release water through sweat during exercise, which means you're also losing important electrolytes like sodium and potassium. Both of these are vital to your body's healthy functioning.

What you can do:‌ As a general rule of thumb, drink enough water so your urine is light yellow, Dr. Li says. If it's dark, your body is concentrating urine to retain more fluids. And don't forget you also get water from hydrating foods like cucumbers and watermelon.


4. You Skimp on Carbs

If you're following a low-carb diet, there's a good chance you're not getting enough carbs to power through your workouts. "The human body's primary energy source during exercise is glucose, a simple sugar derived from carbohydrates," Dr. Li says.


Even though your body can use protein and fat for energy, neither is as readily available as carbohydrates. That means if you're on a carb-restricted eating plan like the ketogenic diet, you may run out of fuel during a more intensive sweat session, Dr. Li says.


What you can do:‌ You may need to up your carb intake (or overall calorie intake, if you're not getting enough). A healthy low-carb diet should still leave room for fruits, non-starchy veggies like leafy greens and legumes like beans and lentils.

You can also try switching up your exercise routine. Lower-impact workouts that require less intensity may make you less tired with fewer carbs stored away, Dr. Li says.

5. You Don't Give Your Body Time to Recover

If you've been known to skip rest days, sooner or later it'll catch up to you. Muscle fatigue is a serious sign your body is stressed out. "Exercise generates oxidative stress," says Dr. Li, explaining this happens at the cellular level and can damage tissues. If you push too hard, you risk injuring yourself.

Not only does overtraining exhaust your body, but it can also hurt your mental health. In fact, overtraining has been linked to a depressed mood, according to a March 2012 review in Sports Health.

What you can do:‌ Slow down. "Enough time for recovery between workouts can allow the body to come back into balance and repair," Dr. Li says. Give yourself at least two days a week to recharge. If you're too antsy to sit still, do light active recovery exercises like yoga or a leisurely stroll in the park.

6. You Might Be Deficient in Iron

Do you have heavy periods? Have you cut out meat and animal products from your diet? If so, your fatigue could be due to an iron deficiency. "With low iron concentrations — either from blood loss or insufficient intake from one's diet — less oxygen is delivered to the body, leading to less efficient output of energy by the muscles and brain," Dr. Li says. In other words, when your cells don't have enough oxygen, they can't function at their best.


What you can do:‌ Eat foods rich in iron. There are two types of iron found in what you eat, Dr. Li explains. Heme iron, found in animal products, is readily absorbed and used by our bodies. Non-heme iron, found in plants, isn't as easy to absorb.

7. Your Medications Could Be to Blame

Taking certain meds may also make you feel pooped, according to Dr. Li. Beta-blockers — which lower blood pressure — keep your heart from increasing beyond a certain heart rate. "So, during exercise, you may feel fatigued when not enough blood is pumped to the brain or muscles," she says.

Then there are statins, a class of drugs prescribed for high cholesterol. "One of its well-documented side-effects is blocking the production of coenzyme Q10, a nutrient necessary for energy production by the body," according to Dr. Li. That said, some people report experiencing muscle cramps or fatigue while taking this drug. Add exercising to that equation, and you're likely to feel even more wiped.

What you can do:‌ Talk to your doctor about the side effects of your medication. If fatigue is possible, they may be able to suggest an alternative. (Never stop talking a medication you've been prescribed without first discussing it with your doctor.)

Working out with a certified personal trainer who's knowledgeable about health conditions and can appropriately modify exercises may be helpful, too, Dr. Li says.




Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.

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