For some people, sweating through an intensely hot workout class can border on a spiritual experience. For others, a toasty studio simply offers some relief from frigid winter weather.
Not all heated workouts are equally hot: Bikram yoga classes are typically 105 degrees with 40 percent humidity, while other heated classes can range from a cozy 80 degrees to a scorching 125. And while hot yoga is perhaps the most familiar heated workout, hot Pilates and hot high-intensity interval training classes are also popular.
Those who swear by these workouts claim that turning up the temperature can increase your flexibility, enhance your heart health or even help you sweat out supposed toxins.
Here’s what exercising in the heat really can — and can’t — do for you.
Heat may improve your flexibility.
Some small studies suggest that applying heat directly to your muscles, such as with a heating pad, can increase your flexibility and range of motion. Stretching in a heated room may have similar effects, though there is limited research in this area.
Your blood vessels expand in the heat, allowing them to deliver more oxygen and blood to your muscles and tendons. This may help loosen your muscles and make you more flexible, said Kelsey Bourbeau, an exercise physiologist at the University of Northern Iowa.
Hot workouts get your heart pumping.
Even if you’re not working out, just being in a hot environment, such as a hot tub or a sauna, speeds up your blood flow. Both heat and exercise make your cardiovascular system work harder, Ms. Bourbeau said. Those stressors trigger changes that can improve your health, such as strengthening your heart and lowering your blood pressure.
But in one study — which was funded by a nonprofit dedicated to promoting yoga’s health benefits — adults who did either hot yoga or cooler yoga three times per week for 12 weeks saw similar improvements to their vascular health, suggesting that exercising at either temperature was equally beneficial.
Since you’ll also sweat more than usual during heated exercise, the workout may feel more intense as your body fights to cool itself down. Your heart rate will also probably be higher than usual, but that doesn’t necessarily mean that your body used more energy during the workout, said Stacy Hunter, an exercise physiologist at Texas State University.
Some research suggests that when endurance athletes like runners and cyclists consistently train in the heat, their bodies start to adjust to the higher temperatures by sweating more and lowering their heart rates. They also produce more hemoglobin, a protein that helps shuttle oxygen to the muscles, which can help improve their speed in both hot and temperate environments.
Sweating more won’t flush out toxins.
Some hot workout enthusiasts claim that extra sweat can ferry toxins out of the body. This is a “popular but misleading belief,” Ms. Bourbeau said. Your liver, kidneys and spleen process any toxic chemicals you’ve been exposed to, and while the increase in blood flow during exercise could theoretically help speed the process along, the amount of toxins found in your sweat is negligible.
You should take extra precautions to stay safe.
Before you show up to a heated workout class, check exactly how hot the class will be, said Erin McNeely, a primary care physician at Corewell Health in Grand Rapids, Mich.
The hotter it gets, the more fluids and electrolytes you’ll lose. You should pay attention to how you feel in any class, but Dr. McNeely noted that temperatures above 100 degrees warrant extra caution. (One study on Bikram yoga found that some participants’ core temperatures reached 102 to 104 degrees during the class, which can raise the risk of heat illness.)
If you’re taking a hot yoga class and feel more flexible than usual, be careful not to overstretch, Dr. McNeely added. Pushing yourself too far can lead to muscle strains. A little bit of tension in the muscle during a stretch can be normal, but if you feel pain or discomfort, “that’s your body telling you to back away from the pose,” she said.
Make sure to show up to any heated exercise class well hydrated and keep drinking throughout the workout. If you feel dizzy or nauseated, if you sweat excessively or if your skin feels hot to the touch, you should take a break and step into a cooler area.
“Those are all red flags for heat illness,” Ms. Bourbeau said.
And if you’re new to heated workouts, be patient with yourself. “Don’t go in there thinking you’re going to necessarily do every single pose that they offer,” Dr. McNeely said — or even that you’ll perform at your usual level at first.
Give yourself time to adapt, and embrace the sweat.
Emma Yasinski is a freelance science journalist whose work has appeared in National Geographic, Undark and more.