Expert Tips for Exercising Safely & Comfortably in the Heat

There are plenty of things to appreciate about exercising outdoors in the summer—no snow or ice, no frozen fingers, no bundling up in bulky layers—but sweltering heat isn’t usually one of them. On those days when walking out of your house is comparable to walking straight into an oven, it can be difficult to get motivated to take part in activities that boost your body temperature even higher. When you don't take the necessary precautions for exercising in the heat, you can set yourself up for dangerous health issues, ranging from dehydration to heat stroke.

Jason Karp, Ph.D., owner of Run-Fit and creator of REVO₂LUTION RUNNING™, has trained extensively in the heat and studied its effects. As your body temperature increases, Karp explains, so does your sweat rate. The more you sweat, the more water you lose, which can then cause dehydration. This becomes a vicious cycle, as dehydration then causes the body temperature to increase even more, which in turn leads to even more sweating, and so on.

Not only is this cycle uncomfortable, it can also cause your performance to suffer and can increase the risk of heat-related illness, Karp says. "Exercise performance declines with only a 2 to 3 percent loss of body weight due to fluid loss," he notes. What's more, the heart has to work harder in hot weather, as the heart rate rises anywhere from three to eight beats per minute for every 1 percent of body weight loss from dehydration.

Hot and humid days present an even greater challenge, Karp says. "When it’s humid, the air is already saturated with water, limiting the amount of sweat evaporating from your skin," he explains. "As a result, the ability to dissipate heat is minimized, and the core body temperature rises rapidly [and can] lead to hyperthermia. In extreme cases, hyperthermia can lead to heat exhaustion and heat stroke."

Karp explains the difference: Heat exhaustion, the most common heat illness, is an inability to continue exercising in the heat due to water depletion or salt depletion. Heat stroke, which is a medical emergency, occurs when the body temperature rises to a level that causes damage to the body’s tissues, greater than 103-104 degrees Fahrenheit.

Tips for Exercising Safely and Comfortably in the Heat

Hydrate before, during and after.

If you wait until you're soaked in sweat and desert-level thirsty, it may be too late to save your workout. Karp says it's important to start warm-weather workouts fully hydrated, which can delay dehydration during exercise, maintain exercise performance and decrease the risk for heat-related illnesses. He instructs his clients to drink fluids before they exercise and then continue to drink during workouts longer than one hour.

How do you know if you're hydrated? Karp says the best indicator is urine color. "The lighter the urine color, the better the level of hydration," he says. "It should look like lemonade rather than apple juice."

While water is essential for hydration, strength and conditioning coach Brandon Mentore also recommends having an electrolyte-containing beverage on hand for extended exercise sessions lasting 90 minutes or longer. "As you sweat more, the loss of fluids also means the loss of vital electrolytes, such as sodium, chloride and potassium," he says. "A drink that contains an electrolyte base will help you thermoregulate better, because you'll be replenishing the resources that are directly involved in regulating that process."

Give your body time to acclimatize.

If you're new to exercising in the heat, take it slow and don't expect peak performance. Karp says it takes anywhere from three to six days for the cardiovascular system to adapt to the effects of a hot, humid environment, and two weeks for full acclimatization.

"While exercising in the heat will always present stress, acclimatization has a moderate prophylactic effect, minimizing the stress and reducing the risk of heat-related illnesses," he says.

According to Mentore, as a very general rule of thumb, if the level of sweat remains the same during the course of an activity, you've acclimated. "Some people sweat more and more profusely, and in more and more locations on their body," he explains. "If you sweat on your forehead and it pretty much stays there without an increase in intensity or body locations, that's a pretty good sign of acclimation."

Become an early bird.

If you're exercising outdoors in the summer, Karp says the best time is in the morning, when the temperature is lower. "Not only is it cooler and thus safer to exercise in the morning than in the evening, you may also get a better workout," he notes. "Research has shown that endurance exercise capacity in the heat is significantly greater in the morning than in the evening."

Dress the part.

If you have no choice but to exercise during one of the hotter parts of the day, Karp recommends wearing loose-fitting, moisture-wicking, light-colored clothes that reflect the sunlight. 

Don't be afraid of the heat.

It can be tempting to avoid the heat in favor of an air-conditioned gym, but running coach Kyle Kranz encourages his clients to embrace warm-weather workouts as a training tool. "When the body is subjected to high temperatures before or after exercise, certain adaptations take place over time—increased sweat rate, decreased sweat electrolytes, increased blood plasma volume, decreased perceived exertion in the heat and more," he explains. All of these changes, Kranz says, ultimately increase performance and strength.

Hot temperatures and humid conditions don’t have to cause a workout meltdown. By staying hydrated, wearing the right clothes, being patient with your body and scheduling your sessions appropriately, you’ll be able to beat the heat and stay active all summer long.