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

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.

A good workout should wear you out. But why are you suddenly exhausted? (Image: dima_sidelnikov/iStock/GettyImages)

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

1. Surprise, Surprise: 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 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. Up to 45 percent of Americans report lying awake at night worrying, as per a 2017 ​_Stress in America_​ survey by 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 and author of the upcoming book, ​_Brave New Medicine: A Doctor's Unconventional Path to Healing Her Autoimmune Illness._​

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 zen to your life before hopping into bed. One April 2015 study published in ​_JAMA Internal Medicine_​ found that 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.

2. You Could Have a Thyroid Condition

Another common issue that drains your energy? Thyroid problems. One in eight women will develop a thyroid condition during her lifetime, and upward of 60 percent of those with thyroid disease 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," says Dr. Li. If thyroid hormone levels are too low, the body produces less energy than it needs. If they're too high, then 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 consuming 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 promote healthy thyroid function, says Dr. Li.

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, says Dr. Li; 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 that your urine is light yellow, says Dr. Li. If it's dark, your body is concentrating urine to retain more fluids. Also, sipping on salty fluids like broth can help the body hold onto water, too.

4. You Skimp on Carbs

Listen up, because this is a big one. If you're trying to shed some pounds and you're following a low-carb diet, there's a good chance that you're not consuming enough carbs to power through your workouts. "The human body's primary energy source during exercise is glucose, a simple sugar derived from carbohydrates," says Dr. Li.

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, says Li.

What you can do:​ Bump up your carb intake. But if you're sticking to a strict keto regimen, be cautious: Just one serving of carbohydrates can damage blood vessels while on a high-fat, low-carb diet, according to a March 2019 study in ​_Nutrients_​.

To be safe, switch up your exercise routine instead. Try lower-impact workouts that require less intensity, suggests Dr. Li.

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

When you hit the gym and skip rest days, sooner or later it'll catch up to you. Muscle fatigue is a serious sign that 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're likely to seriously injure 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 published in ​_Sports Health_​.

What you can do:​ Slow your roll. "Enough time for recovery between workouts can allow the body to come back into balance and repair," says Dr. Li. So, give yourself at least two days a week to recharge. If you're too antsy to sit still, do light active recovery exercises. Think: 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," says Dr. Li. 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, says Dr. Li, who explains there are two types of iron found in what you eat. First, heme iron, found in oysters, beef, turkey and chicken. This doesn't require processing, so it's readily absorbed and used by our bodies.

The second form is non-heme iron. It's plentiful in dark leafy greens, broccoli, lentils, beans, beets, fish and poultry — but isn't as easy to absorb. To help your body soak up all that good iron, make sure you get enough vitamin C.

Another easy way to get more iron in your diet: Cook with a cast iron skillet, says Dr. Li. If your diet is loaded with iron and you're still exhausted, talk to a medical professional.

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:​ Read the labels on your medication. If fatigue is listed as a side effect, your doctor may be able to suggest alternatives. (Do not stop talking a medication you've been prescribed without first discussing it with your doctor. ) Working out with a professional trainer who's knowledgeable about health conditions and can appropriately modify exercises may be helpful, too, says Dr. Li.

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