1. No sleep, all stress
Stressful days and a bad night’s sleep go together like too-tight yoga pants and camel toe—and both can tank your workouts. “When someone is struggling with their energy in the middle of a workout, the first thing to do is look at what her life has been like over the last few weeks,” says Hamilton. Have you been sleeping well and getting regular me time?
It’s important to remember that working out also stresses your body—and all stress is cumulative. So if your job, lack of sleep, and relationship are all taking a toll on you, your workout is going to make your body cry “uncle.”
Hamilton suggests adding a column for notes to your fitness tracker. In it, jot down how you feel during each workout, your stress level, and how much sleep you got the night before. If you’re regularly seeing little sleep, lots of stress, and miserable workouts, there you go.
2. Allergies and asthma
Allergies and asthma (exercise-induced or otherwise) can make getting air a struggle. And guess what: Your body isn’t doing squat without oxygen, says Hamilton. Every cell in your organs and muscles requires air to survive and do its thing.
If you experience coughing, wheezing, a tight chest, or shortness of breath during or immediately after cooling down, definitely talk to your doc. You might have exercise-induced asthma or bronchoconstriction, in which the airways in your lungs narrow in response to strenuous exercise. And if you know or suspect you have allergies or asthma, talk to your doctor about ways to open up your airways in the gym.
3. A drop in pH
When you’re in beast mode, hitting “a wall” is a completely natural biological process. Here’s how it works: As your body converts carbs into fuel during high-intensity exercise, the byproducts are little hydrogen ions, Hamilton says. The longer and harder you keep pushing it, the more they can build up in your system.
As a result, your body’s pH levels drop and become more acidic. (It’s worth mentioning that some people used to blame lactic acid for this, but lactate can actually help fuel your workout.) As your body becomes acidic, everything slows down. The enzymes that supply your muscles with energy all become less efficient, she explains.
That’s when you feel like you’re running through peanut butter. Luckily, the more fit you get, the better your body slays those hydrogen ions. So keep at it!
4. Too much beast mode
If you feel dead after every single workout, sooner or later it’s going to catch up to you. “If you ramp up your workouts too fast or don’t give yourself enough recovery time, you’ll feel like crap early on in a workout,” says Hamilton.
And when that happens, you need to slow your roll. Give yourself at least 2 full recovery days per week, as well as a couple of “lighter” workouts. A good rule to follow: Don’t do more than two intense workouts in a row.
This condition means your blood has too few oxygen-carrying red blood cells, which limits the amount of oxygen your body’s cells receive, Hamilton says. When your cells don’t have enough oxygen, they can’t function at their best. Having too-low iron levels, which can happen in women who cut out iron-rich meat and animal products or have heavy periods, most often causes anemia.
Other signs of anemia include insomnia, dizziness, leg cramps, pale skin, and easy bruising. Sound familiar? Talk to your doc ASAP and get tested.
The smallest dip in your fluid levels makes your blood thick and mucky, so it’s harder for your heart to pump and get where it needs to go, says Hamilton. Meanwhile, if you’re sweating buckets, you’re sweating out more than water. You’re also losing electrolytes that are vital to your muscle cells’ ability to talk to each other and power your workouts.
To make sure you’re adequately hydrated during your workouts, strip down in the locker room and weigh yourself before and after each sweat session. If you’ve lost more than 2% of your body weight (if you weigh 140 pounds, that’s 2.8 pounds), you need to drink more fluid, she says.
7. Thyroid issues
OK, so low thyroid function can zap your energy at any time, but if you’re often fatigued during your workouts and aren’t finding any other cause, it’s worth talking to your doctor about possible thyroid issues, says Hamilton. Hypothyroidism, in which the little butterfly-shaped gland in your neck doesn’t churn out enough thyroid hormone, can cause extremely low energy levels as well as weight gain, depression, and muscle pain.
And while it’s extremely common—one out of eight women will deal with some sort of thyroid problem in her lifetime—about 60% of sufferers don’t realize their thyroid is to blame for their symptoms, according to the American Thyroid Association.
8. Not enough carbs
This is a big one in women who are working out in an effort to lose weight, says Hamilton. While you need to burn more calories than you’re taking in to lose fat, you also need to consume enough calories (especially from carbs) to fuel your workouts and actually burn calories in the gym.
So if you find yourself struggling through workouts and just happen to be dieting, try bumping up your calorie and carb intake (seriously, avoid any extremely low-carb ketogenic diets). Most women need 1,200 to 1,400 calories per day to have healthy energy levels, she says.
9. Your glycogen is 000
Unless you have an existing issue with your blood sugar—or you’re on one of those low-carb diets—a dip in energy likely isn’t due to low blood sugar levels. But it could be due to low glycogen levels, says Hamilton.
Glycogen is your body’s form of stored carbs, and it hangs out in your muscles and liver. The glycogen in your muscles is your body’s preferred source of energy. However, once you run through all of that glycogen, say, during a workout that lasts an hour or more, your body turns to the glycogen in your liver to fuel your workout. Unfortunately, that takes time and isn’t all that efficient.
“It’s like running to the supermarket rather than to your kitchen’s pantry for food,” Hamilton explains. The only way to get more glycogen in your muscles is to nosh on some simple carbs. Sports drinks and energy bars are great for providing an instant boost, she says.