The Sweat Report

The inside story on why you sweat so much during an indoor cycling class.

Among the best-known facts about indoor cycling is that it’s a serious sweat-fest. Most people emerge from a 45- or 60-minute class absolutely drenched. If you’ve ever wondered why you sweat so much more during an indoor cycling class than if you were to cycle at a brisk pace outdoors, even in hot or muggy weather, you are in good company. It’s a worthy question—and the reason isn’t only because you’re working hard.

Sweat is part of your body’s built-in cooling mechanism. Millions of sweat glands on the surface of your skin secrete fluids that contain electrolytes, primarily sodium and chloride but also potassium, magnesium, and calcium to a lesser extent.  This fluid loss can reduce blood volume, increasing the risk of dehydration if those fluids aren’t replaced with adequate hydration. To replenish lost fluids and maintain your proper core body temperature, you need to drink—a lot!—as in 45 ounces before, during, and after a 45-minute cycling class. That may sound extreme but not when you consider that you can lose 1 to 2 liters of water (34 to 68 ounces) per hour during high-intensity exercise (such as indoor cycling), according to exercise scientist Len Kravitz, Ph.D., of the University of New Mexico.

What Affects Your Sweat Rate

Several factors conspire to make you sweat like mad in an indoor cycling class.

For one thing, you don’t have the benefit of wind and fresh air swirling around your body to cool you off, as you would when riding outside. As Kravitz explains, “Convection is the process of losing heat through the movement of air or water molecules across the skin. The amount of heat loss from convection is dependent upon the airflow.” Warm, humid temperatures in a cycle studio, especially when airflow and ventilation are poor, can overwhelm your body’s cooling system, causing you to feel fatigued and forcing your heart and lungs to work harder.

Another factor involves the close proximity of your fellow cyclists: When you have dozens of warm bodies working hard in an enclosed space, the studio can get super hot, sometimes even steamy, during the class, which can make your body follow suit.  

In addition to your hydration status and the humidity and temperature of the exercise environment, genetic factors, your body weight, how hard you’re working, and your overall fitness level also influence the rate at which you sweat. Believe it or not, fitter people often sweat sooner and more because their bodies are more efficient at regulating their core temperature, according to the American College of Sports Medicine (ACSM). As Julieann Hansen, an ACSM-certified personal trainer, certified Spin® instructor, and certified group fitness instructor, explains, “When you start sweating earlier, the body cools down faster, which releases extra body heat and allows you to work out harder for longer.”

How to Stay Cool While Cycling

The type of clothing you’re wearing also can affect your sweat rate.

Remember: It’s best to wear lightweight, moisture-wicking fabrics for indoor cycling and to keep a towel handy to wipe off your face and hands. (Wearing a bandana or headband can help absorb some of the sweat.) Take frequent sips of water or a sports drink that contains electrolytes (consider diluting it with water to minimize unnecessary sugar and calories) throughout the session. (And don’t forget to wipe down your bike with a disinfecting cloth after the ride; it’s simple courtesy and etiquette.)

But if there doesn’t seem to be proper air circulation in the cycle studio, speak up! Research from Spain found that when cyclists pedaled for 60 minutes in a setting without adequate airflow, rehydration alone didn’t cool off their bodies sufficiently. This isn’t just a matter of comfort; it’s a safety concern, too. So talk to your instructor or the club’s manager about the ventilation issue if it’s a problem. If the built-in air-conditioning system isn’t doing the job, bringing in additional fans may help.

Continue Reading