6 Things You Never Knew About Muscles—But Totally Should

When we think about muscles, our minds quickly go to abs, quads, biceps, and triceps—but of course we have hundreds more. "Muscles make up roughly 30 percent of a woman's body mass," says Naresh C. Rao, DO, a sports medicine physician in New York City. The more muscle you have, the more calories you burn. And some good news: Despite what you may have heard, it's not inevitable that your muscles will wither as you age. There are simple ways to outsmart the clock and keep your metabolism cranked. Check out the three must-do workout moves, the nutrients you need to grow muscle tissue, and more tips that will help you get stronger all over.

It's a cruel reality of weight loss: When people drop pounds, their metabolism often takes a dive. Fat cells make leptin, a chemical that tells your brain you're full. When leptin levels dip (which can happen if you're on a diet), your body slows its metabolism to conserve energy. But you can boost your burn by pumping iron. A 2015 study found that people who did resistance training for nine months had a roughly 5 percent increase in their resting metabolic rate.

RELATED: The Best Strength Exercises for Weight Loss

Getting more protein is key as well, says Caroline Apovian, MD, director of the Nutrition and Weight Management Center at Boston Medical Center. While the recommended dietary allowance is 0.8 grams per kilogram (0.36 grams per pound) of body weight per day, "my research shows that to prevent muscle loss while losing weight, you need to almost double that," she says.

You already know to eat plenty of protein-rich foods to build muscle. But that's not all you need: There are crucial nutrients in produce as well. A study from Sweden found that nitrate, a natural compound in fruits and veggies, helped people use less oxygen while exercising, making muscles more efficient. Another study, from Tufts University, followed people age 65 and older for three years and indicated that those with a higher intake of potassium—found in foods like spinach, broccoli, kale, cantaloupe, and bananas—maintained more muscle than the folks who ate half as much of the mineral.

Estrogen appears to be related to muscle strength, which means that as your estrogen level declines, your muscles may get weaker. One thing that might help: a vitamin D supplement. A 2015 study published in the journal Osteoporosis International found that postmenopausal women who took 1,000 IU of D3 per day for nine months had a 25 percent increase in their muscle strength; the women taking a placebo had a 7 percent drop in muscle mass. But popping a pill isn't enough to fight the decline, stresses JoAnn Pinkerton, MD, executive director of the North American Menopause Society and professor of obstetrics and gynecology at the University of Virginia Health System. "Strength training is also needed," she says—ideally, you should do two or three workouts a week.

It's good to push yourself at the gym. But there is a risk in pushing too hard: Rhabdomyolysis (rhabdo for short), a condition that can result from overexertion, causes muscle cells to break down and leak proteins into the bloodstream. If it's not caught early, it can lead to kidney damage, even death. Though rare, the condition is known as "Uncle Rhabdo" in certain CrossFit circles.

RELATED: What to Know About Rhabdomyolysis, the Potentially Fatal Condition Caused by Extreme Exercise

"I had a patient who got rhabdo after doing 70 pull-ups on her first day in a class," says Rao. "Her biceps were so swollen, she looked like Popeye." To stay safe, keep yourself well hydrated and always listen to your body, he says. If you develop severe muscle pain or weakness or have cola-colored urine, head to the ER.

After a gym session, you may be tempted to pop an over-the-counter anti-inflammatory to ward off soreness. But post-workout inflammation might be a good thing: Researchers from Brigham Young University found that after exercise, pro-inflammatory T cells infiltrate damaged muscle fibers, possibly to help repair the tissue; after a repeat round of exercise, inflammation increases.

"One of our theories is that this inflammation is a healthy process your body uses to heal muscles," says senior author Robert Hyldahl, PhD, assistant professor of exercise sciences. What's more, "inflammation and postexercise soreness didn't actually seem to be linked." In fact, folks experienced less soreness after their second round of exercise, when inflammation was higher. Try easing aches with ice or moist heat instead of meds.

During certain stages of sleep, you can't move a muscle—literally. "When you enter a REM cycle, two neurotransmitters switch off brain cells that allow your muscles to be active," explains Nitun Verma, MD, a sleep medicine physician at Crossover Health in Northern California. If you wake up in the middle of a REM cycle, you may be unable to speak or move, and that can be frightening. Luckily, adds Dr. Verma, sleep paralysis is not dangerous and lasts only a few minutes at most.