My legs—and lungs—are burning as I pedal. The cycling interval’s only 10 seconds long, but it sure feels like the clock is moving in slow motion. Coach Mauricio Andrade stands in front of me, offering support that’s motivating but firm. There’s not a chance he’ll let me slow down or slack off.

When he finally calls time and I ease up my cadence, I glance around to the view of snow-capped peaks. That, and the thin air, have momentarily transported me to a place like Leadville, Colorado or Cusco, Peru, at an altitude of about 10,000 feet.

But once I’m mercifully finished with my two rounds of 10 high-intensity intervals, I’ll step outside, inhale deeply, and get back in my car to drive to my apartment on the North Side of Chicago. That mountain view? It’s a wall-sized decal.

I’m working out this morning in the altitude chamber at Well-Fit Performance, a training hub for many of the city’s triathletes and other endurance athletes. In addition to endless pools, strength- and functional-training equipment, and a full complement of treadmills and bike trainers, Well-Fit has now installed one of the few altitude chambers in the country, and the first in the region. 

The facility’s expensive compressors essentially suck the oxygen out of the air, simulating some of what I’d experience if I hiked to Machu Picchu or ran the Leadville 100-miler. There are two other women near me, doing their own workouts on top-of-the-line Woodway treadmills; when I catch my breath enough to chat with them afterward, I learn they’re training for a trek in Kathmandu.

If I visit the room regularly—twice a week for four to eight weeks—I just might see my race times come down and my fitness level reach new heights, Well-Fit’s owner and head coach Sharone Aharon tells me. “There’s such enormous benefit to training at altitude, at high intensity,” he says. “If I say one sentence about it, you train less and you gain more.”

RELATED: 10 Simple Ways to Actually Enjoy Running

Why athletes train at altitude

For decades, elite endurance athletes have headed to the mountains for altitude training. Because there’s less oxygen in the air to begin with—and less atmospheric pressure pushing it into athletes’ veins—their bodies respond by boosting the production of red blood cells. The effect is temporary, so they have to time it right. But when they then head back down to sea level for competition, these adaptations deliver hard-working muscles an augmented supply of oxygen to power each contraction.

The problem is that sweating in thinner air isn’t just harder for us mere mortals, it’s also more challenging for the likes of marathon champions like Shalane Flanagan. You just can’t pedal as hard or run as fast at higher elevation. So athletes have to find other ways to push their bodies to the limit, says Andrew Subudhi, PhD, professor and chair of the department of biology at the University of Colorado Colorado Springs, who’s studied the effects extensively…

Post Malone isn't the only person who loves face tattoos. Celebrities like Lena Dunham, Minka Kelly, and even Mandy Moore have jumped on the face-tat bandwagon with the recent trend of microblading (to make your eyebrows appear fuller). And now there's a new beauty tat fad called dark circle camouflage—aka tattooing the dark circles under your eyes to make the skin lighter.

Professional tattoo artist Rodolpho Torres has gained over 2 million Instagram followers in part for his "eye camouflage" work of covering up dark circles via tattoo. He also uses this tattooing method to "camouflage" stretch marks on the legs and chest. (Side note: We love our tiger stripes and so does Padma Lakshmi.)

RELATED: A Celebrity Makeup Artist’s Steps for Covering Up Dark Under Eye Circles

While Torres has more than 10 years of tattooing experience, derms say you shouldn't trust anyone with such fragile skin if they aren't a doctor. "No nonmedical personnel should be touching that area of your eyes—especially with a sharp instrument," says Lance Brown, M.D., a leading dermatologist in New York City and the Hamptons. "Under the eye, you need to be very cautious—you can cause an infection around the eyelid, or a sty or cyst could grow around the hair follicles," says Dr. Brown.

RELATED: My Perfectly Microbladed Eyebrows Are Ruining My Life Right Now

It is common for tattoo scarring to occur if the artist is inexperienced or presses too deeply with the needle. Apply these potential mishaps to the skin beneath your eyes and it's a recipe for serious concern. Scarring on the lower eyelids, in particular, can create a contraction in the skin that pulls the lower eyelid down, causing ectropion, a condition where the lid pulls or sags away from the eye. "Ectropion can lead to tear duct issues, cysts, and more," says Dr. Brown.

For the record, traditional tattoos are largely safe (and can even boost your health according to the American Journal of Human Biology) but it's probably not worth taking the risk when it comes to the sensitive skin under the eyes—especially considering the new report from the FDA that they've seen an alarming rise of infections and adverse reactions to tattoos as a result of moldy ink. (One woman recently experienced a life-threatening infection after her microblading appointment went south.)

RELATED: I Tried Kim Kardashian’s Trick for Making Dark Under Eye Circles Disappear

RELATED: Hyperrealistic Nipple Tattoos Are Changing the Game for Breast Cancer Survivors

If vanity wins out over your health concerns, consider this: While tattooing your circles may save you from having to pack on the concealer (I mean, we can't deny that the before-and-afters look pretty impressive) since it doesn't address the underlying cause of dark circles, it's likely just a temporary band-aid solution…

The low-carb, high-fat ketogenic diet continues to be the trendiest weight-loss plan around. Maybe that's because following keto is relatively simple: by cutting way back on your carbohydrate intake while eating lots of fat and a moderate amount of protein, your body goes into a state of ketosis, burning fat instead of carbs for energy. 

Stories of keto diet weight-loss success are all over social media. Yet the plan isn't without some side effects, especially when it comes to the way it can affect your workout. Here are four must-knows if you’re an athlete or regular exerciser who’s gone keto—or is thinking of trying it. 

RELATED: Your Ultimate Keto Diet Grocery List

You might feel weak during the first few weeks

Transitioning from burning carbs to burning fat takes about two weeks, so at the diet’s start, your system is not in ketosis yet. “That means that your body is still using stored glucose for fuel rather than ketones," says Jim White RDN, ACSM exercise physiologist, and owner of Jim White Fitness and Nutrition Studios in Virginia. "But because your carbohydrate intake is restricted, the amount of stored glucose (or energy) is limited, which can cause you to feel weak and fatigued.”

Some people experience symptoms such as brain fog, headaches, chills, and a sore throat during this transition. These symptoms are collectively referred to as “the keto flu," explains Dave Asprey, founder and CEO of performance nutrition company Bulletproof. It's not really the flu, of course. But symptoms like these will make you feel like a flu sufferer and “will negatively affect your ability to tackle a workout,” says Asprey.

The "keto poops" could interrupt your workout

Yep, this is a real thing. It's also known as keto diarrhea, and it can strike in the middle of a gym session. Keto poops are a common side effect of the high-fat diet. “This is likely due to the gallbladder—the organ that produces bile to help break down all the fat in the keto diet—feeling overwhelmed or overworked,” says Josh Axe, a natural medicine physician and author of the upcoming book Keto Diet.

Feeling an urgent need to go number two during yoga or CrossFit isn't too much of an issue; you can just hightail it to the gym restroom or locker room and then resume your workout. But when you’re on an outdoor run, well, that could be a problem. If you’re a casual runner, just pick a shorter route or one with known bathroom stops. And consider adjusting your meal schedule, so any poop problems happen before or after you lace up your running shoes.

RELATED: Keto vs. Atkins: Which Is the Better Low-Carb Diet?

You'll need to hydrate a lot more often

Dehydration is another common side side effect of keto. “Ketosis causes you to lose electrolytes because it increases urine output," says Axe…