Are Hot Workouts Safe?

Squeezing any physical activity into a hectic schedule is a great idea, but does a hot, humid environment make a difference? Turning up the heat isn't exactly a new idea—in fact, Bikram Choudhury decided to start practicing yoga in higher temps about three decades ago. Since then, the practice has expanded to more than 600 Bikram studios in the US alone. For the 90-minute class, an instructor runs through 26 postures in intense heat: 105 degrees and 40 percent humidity.

But in the past few years, hot workouts have gone from a niche experience for devoted yogis, to include a wide variety of barre, strength training, and cycling classes. So before you attempt to maintain a solid dumbbell grip with sweaty palms or start slip-n-sliding down a wet yoga mat, here's what you need to know.

What Happens When You Heat Up

Mimi Benz, founder of The Sweat Shoppe, an indoor cycling studio in North Hollywood, offers "warm" spin classes. Unlike Bikram, the temp in these classes never rises above 82 degrees. The difference, Benz says, is that training in these temps carries a relatively low risk compared to environments above 90 degrees.

As the body's internal temperature rises, the heart beats about 10 beats faster per minute with every one centigrade increase.¹ Higher than 90 degrees—the heart beats even more rapidly. "Your heart has to work harder for blood to pump to the working muscles," says Santiago Lorenzo, M.D., a former Olympian and researcher who studies physiological changes in hot and cold weather. To regulate body temperature, the body sweats more in high heat, and consequently loses nutrients and minerals.²

The Pros & Cons of Heating Up

Studies have shown that there may be some negatives to cranking up the thermostat. Elevated temps may make heat-sensitive medical conditions worse, and increase risk for heat injury, which can range from mild cramps to a life-threatening heat stroke. Heat exhaustion—which includes symptoms such as nausea, vomiting, headache, dizziness, weakness, and fainting—is more likely to occur as core temperature rises, says Robynn Europe, a Greatist expert.

People with high blood pressure should take caution before heading into the heat, and in general, pregnant women should not participate in hot workouts.³

While heat adds a level of risk, it may also offer some benefits (though the research is limited)."Sweating promotes detoxification and elimination through the skin, which is the body's largest eliminating organ," Benz says. In fact one study found that sweat actually helped to eliminate trace amounts of lead, arsenic, and mercury from the body.⁴ However, other experts believe the main function of sweating is simply to cool down and that extra sweat may impair natural detox function by the liver and kidneys.

You may also notice many classes are heated via infrared lamps. Though the research is unclear, manufacturers and hot workout devotees claim infrared heating detoxifies the body faster and removes more toxins and less water through sweat than hot air or gas heating (like the kind you likely have in your home).

And in one study, elite cyclists who hit a chilled space after acclimating to a 104-degree lab showed improvements in performance by 4 to 8 percent.⁵ Lorenzo, who was involved with the study, believes working out in high heat can be safe because of peoples' ability to adapt to elevated temperatures.⁶ But he cautions exercisers to stay hydrated and listen to their body. If the heat becomes unbearable, Lorenzo suggests slowing the pace, cooling down, and stretching.

Know Before You Go

Since the aforementioned study examined only elite athletes, researchers can't promise the same adaptation ability for recreational exercisers. So what if you’re interested in trying a new hot yoga or hot cycling class?

“Definitely eat something,” says Sarah Levey, co-founder of Y7 Yoga, a hot yoga studio. “You’re going to sweat a lot of nutrients and water, so have something with sugar or electrolytes beforehand.”

She also says to wear lightweight clothing—and not necessarily shorts, if you think you might end up slipping too much on your mat. Drink 17 to 20 ounces of water beforehand, and bring water and a towel to your class.

A loss of 2 percent of your total body weight or more can be a sign of dehydration (that's three pounds for a 150-pound person). If you tend to get dizzy in heat or dehydrated quickly, check with your doc before trying that first hot session. Paying attention to your body and knowing your own limits is also important.

“Take breaks when you need them,” Levey says. “You don’t have to feel pressured to go along with everyone else.”

Originally published July 2012. Updated July 2015.

Works Cited

1. The relationship between body temperature, heart rate and respiratory rate in children. Davies P, Maconochie I. Emergency medicine journal : EMJ, 2009, Nov.;26(9):1472-0213.
2. Sweat mineral-element responses during 7 h of exercise-heat stress. Montain SJ, Cheuvront SN, Lukaski HC. International journal of sport nutrition and exercise metabolism, 2008, Mar.;17(6):1526-484X.
3. Hot yoga and pregnancy: fitness and hyperthermia. Chan J, Natekar A, Koren G. Canadian family physician Médecin de famille canadien, 2014, Sep.;60(1):1715-5258.
4. Arsenic, cadmium, lead, and mercury in sweat: a systematic review. Sears ME, Kerr KJ, Bray RI. Journal of environmental and public health, 2012, Feb.;2012():1687-9813.
5. Heat acclimation improves exercise performance. Lorenzo S, Halliwill JR, Sawka MN. Journal of applied physiology (Bethesda, Md. : 1985), 2010, Aug.;109(4):1522-1601.
6. Effects of endurance training and heat acclimation on psychological strain in exercising men wearing protective clothing. Aoyagi Y, McLellan TM, Shephard RJ. Ergonomics, 1998, Apr.;41(3):0014-0139.

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